Marjoram extract prevents ischemia reperfusion-induced myocardial damage and exerts anti-contractile effects in aorta segments of male wistar rats.

ETHNOPHARMACOLOGICAL RELEVANCE: Marjoram (Origanum majorana L.) is an herb traditionally used as a medicine in different countries, as Morocco and Iran, because of its beneficial cardiovascular effects. Some studies suggest that these effects are due, at least in part, to the presence of phenolic compounds such as rosmarinic acid (RA) and luteolin. AIM OF THE STUDY: To analyze the possible cardiprotective effects of a marjoram extract (ME) reducing myocardial damage after coronary ischemia-reperfusion (IR) and its possible antihypertensive effects reducing the response of aorta segments to the vasoconstrictors noradrenaline (NA) and endothelin-1 (ET-1). MATERIALS AND METHODS: Male Wistar rats (300g) were used. After sacrifice, the heart was immediately removed and mounted in a perfusion system (Langendorff). The aorta was carefully dissected and cut in 2 mm segments to perform vascular reactivity experiments. RESULTS: In the heart, ME perfusion after IR reduced heart rate and prevented IR-induced decrease of cardiac contractility, possibly through vasodilation of coronary arteries and through the upregulation of antioxidant markers in the myocardium that led to reduced apoptosis of cardiomyocytes. In the aorta, ME decreased the vasoconstrictor response to NA and ET-1 and exerted a potent anti-inflammatory and antioxidant effect. Neither RA nor 6-hydroxi-luteolin-O-glucoside, major compounds of this ME, were effective in improving cardiac contractility after IR or attenuating vasoconstriction to NA and ET-1 in aorta segments. CONCLUSION: In conclusion, ME reduces the myocardial damage induced by IR and the contractile response to vasoconstrictors in the aorta. Thus, it may be useful for the treatment of cardiovascular diseases such as myocardial infarction and hypertension.

Caloric restriction attenuates aging-induced cardiac insulin resistance in male Wistar rats through activation of PI3K/Akt pathway.

BACKGROUND AND AIM: Caloric restriction (CR) improves insulin sensitivity and is one of the dietetic strategies most commonly used to enlarge life and to prevent aging-induced cardiovascular alterations. The aim of this study was to analyze the possible beneficial effects of caloric restriction (CR) preventing the aging-induced insulin resistance in the heart of male Wistar rats. METHODS AND RESULTS: Three experimental groups were used: 3 months old rats (3m), 24 months old rats (24m) and 24 months old rats subjected to 20% CR during their three last months of life (24m-CR). After sacrifice hearts were mounted in a perfusion system (Langendorff) and heart function in basal conditions and in response to accumulative doses of insulin (10-9-10-7 M), in the presence or absence of Wortmannin (10-6 M), was recorded. CR did not attenuate the aging-induced decrease in coronary artery vasodilation in response to insulin administration, but it prevented the aging-induced downregulation of cardiac contractility (dp/dt) through activation of the PI3K/Akt intracellular pathway. Insulin stimulated in a greater extent the PI3K/Akt pathway vs the activation of the MAPK pathway and increased the protein expression of IR, GLUT-4 and eNOS in the hearts of 3m and 24m-CR rats, but not in the hearts of 24m rats. Furthermore, CR prevented the aging induced increase in endothelin-1 protein expression in myocardial tissue. CONCLUSION: In conclusion CR partially improves cardiac insulin sensitivity and prevents the aging induced decrease in myocardial contractility in response to insulin administration through activation of PI3K/Akt pathway.

Study of insulin vascular sensitivity in aortic rings and endothelial cells from aged rats subjected to caloric restriction: Role of perivascular adipose tissue.

The prevalence of metabolic syndrome is dramatically increasing among elderly population. Metabolic syndrome in aged individuals is associated with hyperinsulinemia and insulin resistance both in metabolic tissues and in the cardiovascular system, with this fact being associated with the cardiometabolic alterations associated to this condition. Caloric restriction (CR) improves insulin sensitivity and is one of the dietetic strategies most commonly used to enlarge life and to prevent aging induced cardiovascular alterations. The aim of this study was to analyze the possible beneficial effects of CR in aging-induced vascular insulin resistance both in aortic rings and in primary culture of endothelial cells. In addition, the inflammatory profile of perivascular adipose tissue (PVAT) and its possible role in the impairment of vascular insulin sensitivity associated with aging was also assessed. Three experimental groups of male Wistar rats were used: 3 (3m), 24 (24m) fed ad libitum and 24months old rats subjected to 20% CR during their three last months of life (24m-CR). Aorta rings surrounded or not by PVAT were mounted in an organ bath and precontracted with phenylephrine (10-7.5M). Changes in isometric tension were recorded in response to cumulative insulin concentrations (10-8-10-5.5M) in the presence or absence of L-NAME (10-4M). Aortic rings and primary aortic endothelial cells were incubated in presence/absence of insulin (10-7M) and the activation of the PI3K/Akt and MAPK pathways as well as nitrite and nitrates concentrations and the mRNA levels of eNOS, insulin receptor, and GLUT-4 were assessed. CR prevented the aging-induced decrease in the vasodilator response to insulin and the aging-induced increase in the vasoconstrictor response to high insulin concentrations. Changes between 24m and 24m-CR aorta rings were abolished in the presence of L-NAME. CR induced-improvement in insulin vascular sensitivity was related with activation of the PI3K/Akt both in aortic rings and in aortic endothelial cells in response to insulin. CR attenuated the overexpression of iNOS, TNF-α and IL-1ß in the PVAT of aged rats although aortic rings surrounded by PVAT from 24m rats showed and increased vasorelaxation in response to insulin compared to aortic rings from 3m and 24m-CR rats. In conclusion, a moderate protocol of CR improves insulin vascular sensitivity and prevents the aging induced overexpression of pro-inflammatory cytokines in PVAT.

Effects of early overnutrition on the renal response to Ang II and expression of RAAS components in rat renal tissue.

BACKGROUND AND AIMS: The aim of this study was to analyze the effects of early overnutrition (EON) on the expression of the renin angiotensin aldosterone system (RAAS) components in renal cortex, renal arteries and renal perivascular adipose tissue (PVAT), as well as the vascular response of renal arteries to Angiotensin II (Ang II). METHODS AND RESULTS: On birth day litters were adjusted to twelve (L12-control) or three (L3-overfed) pups per mother. Half of the animals were sacrificed at weaning (21 days old) and the other half at 5 months of age. Ang II-induced vasoconstriction of renal artery segments increased in young overfed rats and decreased in adult overfed rats. EON decreased the gene expression of angiotensinogen (Agt), Ang II receptors AT1 and AT2 and eNOS in renal arteries of young rats, while it increased the mRNA levels of AT-2 and ET-1 in adult rats. In renal PVAT EON up-regulated the gene expression of COX-2 and TNF-α in young rats and the mRNA levels of renin receptor both in young and in adult rats. On the contrary, Ang II receptors mRNA levels were downregulated at both ages. Renal cortex of overfed rats showed increased gene expression of Agt in adult rats and of AT1 in young rats. However the mRNA levels of AT1 were decreased in the renal cortex of overfed adult rats. CONCLUSION: EON is associated with alterations in the vascular response of renal arteries to Ang II and changes in the gene expression of RAAS components in renal tissue.

Peritumoral adipose tissue as a source of inflammatory and angiogenic factors in colorectal cancer.

PURPOSE: Obesity is a risk factor for the development of human colorectal cancer (CC). The aim of this work is to report the inflammatory and angiogenic scenario in lean (BMI < 25 kg/m2) and obese (BMI > 30 kg/m2) patients with and without CC and to assess the role of peritumoral adipose tissue in CC-induced inflammation. MATERIAL AND METHODS: Patients were divided in four experimental groups: obese patients with CC (OB-CC), lean patients with CC (LEAN-CC), obese patients without CC (OB), and lean patients without CC (LEAN). RESULTS: Plasma levels of pro-inflammatory cytokines (interleukin (IL)-6, IL-4, IL-8) and granulocyte-macrophage colony-stimulating factor (GM-CSF) were increased in OB-CC patients. Peritumoral adipose tissue (TF) explants and cultured mature adipocytes secreted higher amounts of nitrites and nitrates than did control and non-tumoral (NTF) adipose tissue both alone and in response to lipopolysaccharide (LPS). Nitrite and nitrate secretion was also increased in TF explants from OB-CC patients compared with that from LEAN-CC patients. Gene expression of adiponectin, tumor necrosis factor alpha (TNF-α), insulin-like growth factor type I (IGF-I), cyclooxygenase-2 (COX-2), and peroxisome proliferator-activated receptor γ (PPAR-γ) was increased in TF explants from CC patients. LPS increased the gene expression of IL-6, IL-10, TNF-α, vascular endothelial growth factor (VEGF), and COX-2 in OB and in TF explants from OB-CC patients. COX-2 and PPAR-γ inhibition further increased LPS-induced release of nitrites and nitrates in TF explants and adipocytes from OB-CC patients. CONCLUSIONS: In conclusion, OB-CC patients have increased plasma levels of pro-inflammatory and angiogenic factors. TF from OB-CC patients shows an increased secretion of inflammatory markers compared with both TF from LEAN-CC and non-tumoral adipose tissue (AT) through a COX-2- and PPAR-γ-independent mechanism.

Liberación de óxido nítrico en arterias tumorales de pacientes con cáncer colorrectal / Nitric oxide release on tumour arteires form patients with colorectal cancer

INTRODUCCIÓN. El óxido nítrico es un factor liberado por el endotelio vascular que participa en los procesos de formación de tumores porque es capaz de estimular la proliferación celular, fomentar la angiogénesis y regular el flujo sanguíneo tumoral. Además, la dilatación de los vasos sanguíneos tumorales provocada por el NO puede aumentar la eficacia de los tratamientos oncológicos ya que facilita el acceso al tumor de los fármacos antineoplásicos e incrementa la oxigenación de la masa tumoral potenciando los efectos beneficiosos de la radioterapia. MATERIAL Y MÉTODO. Para estudiar si la liberación de NO está alterada en las arterias tumorales, se obtuvieron de 19 pacientes intervenidos quirúrgicamente por cáncer de colon y recto, arterias mesentéricas irrigando el tumor y arterias mesentéricas de una región alejada del tumor, y asimismo se obtuvieron arterias mesentéricas de pacientes intervenidos de diverticulitis (n=4) o enfermedad inflamatoria intestinal (n=3). Los segmentos vasculares se montaron en un sistema de registro de la tensión isométrica y se realizaron curvas de concentraciónrespuesta a la bradikinina, con las arterias previamente contraídas con U46619 en presencia de placebo, del inhibidor de óxido nítrico cintaza L-NAME y del inhibidor de la ciclooxigenasa meclofenamato. RESULTADOS. La relajación a la bradikinina fue similar en los tres grupos de arterias y esta vasodilatación era disminuida en presencia de L-NAME y no se modificaba con meclofenamato. CONCLUSIÓN. La liberación de NO está preservada en las arterias humanas que irrigan los tumores de colon y recto (AU)

INTRODUCTION. Nitric oxide is an endothelium-derived relaxing factor involved in tumour growth because it could regulate celular proliferation, tumour angiogenesis and tumor blood flow. So this relaxation of tumour arteries could enhance medical effects of oncological therapy because facilitates the delivery of anticancer drugs to tumor cells and stimulates oxygenation of tumor tissue increasing the response to radiotherapy. MATERIAL AND METHOD. To study whether release of nitric oxide is altered in tumooir arteries, mesenteric arteries suppying blood flow to colorectal tumor, mesenteric arteries far from said tumor were obtained from 19 patients undergoing colectomy and mesenteric arteries were also obtained from surgical patients with diveticulitis (n=4) or inflammatory bowel disease (n=3). Arteries were prepared for isometric tension recording in an organ bath and were precontrated with U46619. The relaxation produced by bradykinin was recorded in each of these arteries with and without the nitric oxide sinthase inhibitor L-NAME and cyclooxygenase inhibitor meclofenamate. RESULTS. Bradykinin produced a dose-dependent relaxation that was similar in all the three types of artery. This relaxation was reduced with L-NAME and was not modified with meclofenamate. CONCLUSION. Nitric oxide release is preservered in human arteries supplying blood flow to colorectal tumors (AU)

[Effect of endothelin-1 on tumor arteries in patients with colorectal cancer]. / Efecto de la endotelina-1 sobre las arterias tumorales de pacientes con neoplasia colorrectal.

Endothelin-1 is an endothelium-derived vasoconstrictor peptide whose plasma levels are increased in patients with colorectal cancer, and which may be involved in tumor blood flow regulation. To study whether response to this peptide is altered in tumor arteries, mesenteric arteries supplying blood flow to colorectal tumors, and mesenteric arteries far from said tumors were obtained from 13 patients undergoing colectomy; mesenteric arteries were also obtained from patients with diverticulitis (n = 4) or inflammatory bowel disease (n = 3). Arteries were prepared for isometric tension recording in an organ bath, and in this preparation it was found that endothelin-1 induced contraction in all three types of arteries, but that sensitivity to this peptide was greater in arteries supplying blood flow to the tumor than in arteries far from the tumor or arteries from patients without cancer. These results suggest that endothelin-1 may regulate blood flow to colorectal tumors by inducing a greater contraction in tumor-supplying arteries than in non-tumor arteries.

Efecto de la endotelina-1 sobre las arterias tumorales de pacientes con neoplasia colorrectal / No disponible

La endotelina-1 es un péptido vasoconstrictor producido por elendotelio vascular, cuyos niveles plasmáticos están aumentadosen los pacientes con cáncer colorrectal y que puede participar enla regulación del flujo sanguíneo tumoral. Para estudiar si la respuestaa este péptido está alterada en las arterias tumorales, seobtuvieron, de 13 pacientes intervenidos quirúrgicamente porcáncer colorrectal, arterias mesentéricas irrigando el tumor y arteriasmesentéricas de una región alejada del tumor, y asimismo seobtuvieron arterias mesentéricas de pacientes intervenidos por diverticulitis(n = 4) o enfermedad inflamatoria intestinal (n = 3). Lasarterias mesentéricas se montaron en una preparación para el registrode la contracción isométrica en un baño de órganos, encontrándoseque la endotelina-1 producía contracción en los tres tiposde arterias, pero la sensibilidad a este péptido fue mayor enlas arterias irrigando el tumor que en las arterias alejadas del tumoro en las arterias de pacientes sin patología tumoral. Estos resultadosindican que la endotelina-1 puede regular el flujo sanguíneoen los tumores colorrectales, produciendo una mayorvasoconstricción en las arterias que irrigan el tumor que en las arteriasno tumorales

Endothelin-1 is an endothelium-derived vasoconstrictor peptidewhose plasma levels are increased in patients with colorectal cancer,and which may be involved in tumor blood flow regulation.To study whether response to this peptide is altered in tumor arteries,mesenteric arteries supplying blood flow to colorectal tumors,and mesenteric arteries far from said tumors were obtainedfrom 13 patients undergoing colectomy; mesenteric arteries werealso obtained from patients with diverticulitis (n = 4) or inflammatorybowel disease (n = 3). Arteries were prepared for isometrictension recording in an organ bath, and in this preparation it wasfound that endothelin-1 induced contraction in all three types ofarteries, but that sensitivity to this peptide was greater in arteriessupplying blood flow to the tumor than in arteries far from the tumoror arteries from patients without cancer. These results suggestthat endothelin-1 may regulate blood flow to colorectal tumorsby inducing a greater contraction in tumor-supplying arteriesthan in non-tumor arteries

Coronary reactive hyperaemia and arterial pressure in anaesthetized goats.

To study the effects of arterial pressure on coronary reactive hyperaemia, left circumflex coronary artery flow was measured, and reactive hyperaemia was determined after 5, 10 or 20 s of occlusion of this artery in anaesthetized goats during normotension, hypertension and hypotension. During hypertension induced by aortic constriction (mean arterial pressure, MAP = 140 +/- 6 mmHg) coronary vascular resistance (CVR), reactive hyperaemia (ratio of peak in hyperaemic flow to control flow and ratio of repayment to debt) and the decrease in CVR during the peak in hyperaemic flow were comparable to those during normotension. During hypertension induced by noradrenaline (MAP = 144 +/- 6 mmHg) CVR was 16% lower (P < 0.05), reactive hyperaemia was reduced by 14-25% (P < 0.05) and the decrease in CVR during the peak in hyperaemic flow was lower than the values of these parameters during normotension. During hypotension induced by constriction of the caudal vena cava (MAP = 40 +/- 4 mmHg) CVR was 22% lower (P < 0.05), reactive hyperaemia was reduced by 25-65% (P < 0.05) and the decrease in CVR during the peak in hyperaemic flow was less compared to the values of these parameters during normotension. During hypotension induced by isoprenaline (MAP = 45 +/- 4 mmHg) CVR was 59% lower, reactive hyperaemia was reduced by 55-100% (P < 0.01) and the decrease in CVR during the peak in hyperaemic flow was less compared to the values of these parameters during normotension. Arterial pressure is a main determinant of coronary reactive hyperaemia after brief periods of ischaemia, and the relationship between arterial pressure and reactive hyperaemia may depend in part on changes in CVR after variations in arterial pressure. These changes in CVR may be related to the action on coronary vessels of myocardial factors and vascular myogenic mechanisms.

Diabetes abolishes the gender difference in vasopressin-mediated potentiation of sympathetic vasoconstriction.

Electrical field stimulation (4 Hz, 0.2 ms pulse duration, at a supramaximal voltage of 70 V, for 1 s) of isolated rat tail artery segments produced contraction which was lower in female than in male rats, and was reduced by streptozotocin-induced diabetes in both genders. This contraction was potentiated by vasopressin (10(-12)-10(-10) M) more in normoglycemic male than in normoglycemic female rats, and this effect of vasopressin was increased by the cyclooxigenase inhibitor meclofenamate (10(-5) M) in female control rats, but not in diabetic female, or control and diabetic male rats, and it was not modified by the nitric oxide synthase inhibitor N(omega)-nitro-L-arginine methyl ester (L-NAME, 10(-4) M). Endothelin-1 (10(-10)-3 x 10(-9) M) also potentiated the contraction to electrical stimulation. This potentiation was similar in all experimental groups, and it was not modified by meclofenamate or L-NAME. These results suggest that the potentiating effect of vasopressin, but not that of endothelin-1, on the sympathetic vasoconstriction, is lower in females than in males, probably by an increased release of vasodilating prostanoids, and this release may be reduced by diabetes in females.

Adrenergic vasoconstrictor activity in the cerebral circulation after inhibition of nitric oxide synthesis in conscious goats.

The interaction between nitric oxide (NO) and adrenergic activity in the cerebral circulation was studied using conscious goats, where blood flow to one brain hemisphere (cerebral blood flow) was electromagnetically measured, and the effects of phentolamine and hexamethonium on cerebrovascular resistance were evaluated before (control) and after inhibition of NO synthesis with NW-nitro-L-arginine methyl ester (L-NAME). L-NAME (12 goats, 40 mg kg(-1) administered i.v.) reduced cerebral blood flow from 62 +/- 3 to 44 +/- 2 ml min(-1), increased mean systemic arterial pressure from 100 +/- 3 to 126 +/- 4 mm Hg, decreased heart rate from 79 +/- 5 to 50 +/- 4 beats min(-1) and increased cerebrovascular resistance from 1.63 +/- 0.08 to 2.91 +/- 0.016 mm Hg ml(-1)min(-1) (all P < 0.01). These hemodynamic variables normalized 48-72 h after L-NAME administration. Phentolamine (six goats, 1 mg), injected into the cerebral circulation. increased cerebral blood flow without changing systenic arterial pressure, but its cerebrovascular effects were augmented for about 24 h after L-NAME. The decrements in cerebrovascular resistance induced by phentolamine, in mm Hg ml(-1) min(-1), were: under control, 0.42 +/- 0.05; immediately after L-NAME, 1.38 +/- 0.09 (P < 0.01 compared with control); by about 24 h after L-NAME, 0.71 +/- 0.09 (P < 0.05 compared with control); and by about 48 h after L-NAME, 0.40 +/- 0.07 (P > 0.05 compared with control). Hexamethonium (six goats, 0.5-1 mg kg(-1) min(-1) i.v.) decreased mean systemic arterial pressure to about 75 mm Hg and caused tachycardia similarly before and after L-NAME, but the decrements in cerebrovascular resistance were augmented for about 24 h after L-NAME. The decrements in cerebrovascular resistance induced by hexamethonium, in mm Hg ml(-1).min(-1), were: under control. 0.61 +/- 0.09, immediately after L-NAME, 1.33 +/- 0.16 (P < 0.01 compared with control); by about 24 h after L-NAME, 1.18 +/- 0.10 (P < 0.01 compared with control): and by about 48 h after L-NAME, 0.99 +/- 0.10 (P > 0.05 compared with control). Therefore, these results suggest that adrenergic vasoconstrictor tone in cerebral vasculature may be augmented after inhibition of NO synthesis, and that this increment may contribute to the reduction of cerebral blood flow after inhibition of NO formation.

Cerebral vasoconstriction produced by vasopressin in conscious goats: role of vasopressin V(1) and V(2) receptors and nitric oxide.

To examine the role of vasopressin V(1) and V(2) receptors, nitric oxide and prostanoids in the cerebrovascular effects of arginine vasopressin, cerebral blood flow was electromagnetically measured in awake goats. In 16 animals, vasopressin (0.03 - 1 microg), injected into the cerebral circulation, caused increments of resting cerebrovascular resistance which ranged from 18% (0.03 microg, P<0.01) to 79% (1 microg, P<0.01). Desmopressin (0.03 - 1 microg, four goats) did not affect significantly cerebrovascular resistance. The cerebrovascular resistance increases by vasopressin were reduced significantly by the antagonist for vasopressin V(1) receptors d(CH(2))(5)Tyr(Me)-AVP in a rate depending way (five (six goats) and 15 (four goats) microg min(-1)), and by the mixed antagonist for vasopressin V(1) and V(2) receptors desGly-d(CH(2))(5)-D-Tyr(Et)Val-AVP (5 microg min(-1), four goats), and they were not significantly affected by the antagonist for vasopressin V(2) receptors d(CH(2))(5), D-Ile(2), Ile(4)-AVP (5 microg min(-1), four goats). The inhibitor of nitric oxide synthesis N(w)-nitro-L-arginine methyl ester (L-NAME, 47 mg kg(-1) i.v., five goats) augmented cerebrovascular resistance by 130% (P<0.01), and for 24 h after this treatment the cerebrovascular effects of vasopressin were potentiated. The inhibitor of cyclo-oxygenase meclofenamate (6 mg kg(-1) i.v., five goats) did not modify significantly resting haemodynamic variables measured or the cerebrovascular effects of vasopressin. Therefore, the vasopressin-induced cerebral vasoconstriction may be mediated by vasopressin V(1) receptors, without involvement of vasopressin V(2) receptors, and may be modulated by nitric oxide but not by prostanoids.

Effect of neuropeptide Y on the sympathetic contraction of the rabbit central ear artery during cooling.

In order to analyse the effect of neuropeptide Y (NPY) on the cutaneous vascular response to sympathetic nerve stimulation during cooling, the isometric response of isolated 2-mm segments of the rabbit central ear (cutaneous) artery was recorded at 37 degrees C and during cooling (30 degrees C). Electrical field stimulation (4-16 Hz) at 37 degrees C produced a frequency-dependent contraction, which was reduced during cooling (45% for 16 Hz) and potentiated by NPY (10(-8), 3x10(-8) and 10(-7) M), this potentiation being greater at 30 degrees C than at 37 degrees C. The NPY-induced potentiation of the contraction elicited by electrical field stimulation (8 Hz) was abolished by an antagonist of Y1 subtype NPY receptors, BIBP3226 (10(-6) M), at 37 degrees C and 30 degrees C, reduced by phentolamine (10(-6) M) at 30 degrees C but not at 37 degrees C, was not modified by the purinoceptor antagonist PPADS (3x10(-5) M) and was reduced by application of both phentolamine and PPADS at both temperatures. Both NiCl2 (10(-3) M) and verapamil (10(-5) M) abolished the potentiating effect of NPY at 37 degrees C and reduced it at 30 degrees C. Neither application of an inhibitor of nitric oxide synthesis, L-Nomega-nitro-arginine (L-NOARG, 10(-4) M), nor endothelium removal modified the potentiating effect of NPY at 37 degrees C or 30 degrees C. NPY (10(-8), 3x10(-8) and 10(-7) M) potentiated in a concentration-dependent way the arterial contraction in response to exogenous noradrenaline (10(-8)-10(-4) M) at 30 degrees C but not at 37 degrees C, and it increased the response to ATP (10(-4)-10(-2) M) at both temperatures. Therefore, in cutaneous (ear) arteries: (1) NPY potentiates the sympathetic response at 37 degrees C and at 30 degrees C, (2) this potentiating effect of NPY was more marked at 30 degrees C than at 37 degrees C, probably because of greater potentiation of the alpha-adrenoceptor response during cooling, and (3) the potentiating effect of NPY at both temperatures is mediated by NPY receptors of the Y1 subtype, is dependent of Ca2+ channels and is independent of the release of endothelial nitric oxide.

Impaired potentiation by endothelin-1 and vasopressin of sympathetic contraction in tail artery from hypertensive rats.

OBJECTIVE: To analyse the effects of endothelin-1 and vasopressin on the sympathetic vasoconstriction during hypertension. METHODS: Electrical field stimulation (4 Hz) was applied to isolated, 2 mm segments of the tail artery from spontaneously hypertensive (SHR) and normotensive Wistar-Kyoto (WKY) rats prepared for isometric tension recording. RESULTS: The contraction to electrical stimulation was potentiated by endothelin-1 (10(-10)-10(-8) M) in arteries from WKY but not from SHR, and by vasopressin (10(-12)-10(-10) M) more markedly in arteries from WKY than from SHR. The potentiation by endothelin-1 was reduced more markedly by the antagonist of endothelin ETA receptors BQ-123 (10(-5) M) than by the endothelin ETB receptor antagonist BQ-788 (10(-5) M). The potentiation by vasopressin was reduced by the antagonist of vasopressin V1 receptors d(CH2)5Tyr(Me)AVP (10(-7) M), but not by the vasopressin V2 receptor antagonist d(CH2)5D-Ile2, Ile4AVP (10(-7) M). The blocker of L-type calcium channels verapamil (10(-5) M) reduced the potentiation by both endothelin-1 and vasopressin in arteries from WKY rats, and increased the potentiation by vasopressin in arteries from SHR. Noradrenaline (10(-8)-10(-4) M) contraction was not modified by endothelin-1 (3 x 10(-9) M) or vasopressin (3 x 10(-11) M), and contraction to endothelin-1 (10(-9)-10(-7) M) and vasopressin (10(-10)-10(-7) M) was lower in arteries from SHR than from WKY rats. CONCLUSIONS: (1) The potentiation by endothelin-1 and vasopressin of the sympathetic vasoconstriction, probably due to increased release of noradrenaline, is impaired during hypertension, and (2) this potentiation is mediated mainly by endothelin ETA receptors, and by vasopressin V1 receptors, in both WKY and SHR, and for both peptides it is mediated by L-type calcium channels in arteries from normotensive but not in those from hypertensive animals.

Role of nitric oxide in vascular tone and in reactivity to isoproterenol and adenosine in the goat coronary circulation.

The present study examined the role of nitric oxide in coronary vascular tone and in the coronary vasodilatation in response to beta-adrenoceptor stimulation and adenosine. In anesthetized goats, the effects of intracoronary and i.v. administration of the inhibitor of nitric oxide synthesis, N(w)-nitro-L-arginine methyl ester (L-NAME), and those of isoproterenol, adenosine and acetylcholine on coronary blood flow, measured electromagnetically in the left circumflex coronary artery, were recorded. Intracoronary infusion of L-NAME (30-40 microg kg(-1) min(-1), four goats) reduced resting coronary blood flow by 14+/-3% (P<0.05) without changing arterial pressure and heart rate. L-NAME (40 mg kg(-1), eight goats) i.v. reduced resting coronary blood flow by 19+/-4% (P<0.05), increased mean systemic arterial pressure by 22+/-3% (P<0.01) and decreased heart rate by 10+/-2% (P<0.05). These effects of L-NAME were partially, but significantly reversed by L-arginine (six goats). Isoproterenol (10-100 ng, eight goats), adenosine (0.3-10 microg, seven goats) and acetylcholine (3-100 ng, five goats), injected intracoronarily, increased coronary conductance in a dose-dependent way and, under control conditions, these increases for isoproterenol, ranged from 32+/-5% to 82+/-12%; for adenosine, 6+/-2% to 174+/-22%; and for acetylcholine, 39+/-5% to 145+/-15%. During i.v. L-NAME the increases in coronary conductance induced by isoproterenol and acetylcholine were significantly reduced by about 50 and 60% (P<0.05), respectively, whereas those induced by adenosine were significantly increased further (about 30-100%, P<0. 05). During L-NAME plus L-arginine, the effects of isoproterenol, acetylcholine and adenosine on coronary conductance were not significantly different from those under control conditions. Therefore, it is suggested that in the coronary circulation: (a) nitric oxide may produce a basal vasodilator tone under normal conditions; (b) nitric oxide may be an intermediate in the vasodilatation due to beta-adrenoceptor stimulation and acetylcholine, and (c) the vasodilatation due to adenosine is potentiated during reduction of nitric oxide production.

Insulin effects on the sympathetic contraction of rabbit ear arteries.

Electrical field stimulation (4 Hz, 0.2 ms, 70 V supramaximal voltage, 10 s duration) produced contraction of perfused rabbit central ear arteries, and this contraction was reduced by incubation with insulin (0.6--200 mU/ml). This inhibitory effect of insulin was not significantly modified by removing the endothelium, or by treatment with N(W)-nitro-L-arginine (L-NA, 10(-4) M), meclofenamate (10(-5) M), ouabain (10(-6) M), or cocaine (10(-5) M). Insulin (200 mU/ml) did not modify the vascular contraction due to exogenous norepinephrine (10(-8)--10(-4) M) nor the relaxation due to acetylcholine (10(-8)--10(-4) M). This suggests that insulin may reduce vascular contraction by sympathetic stimulation, and this effect is not dependent on endothelial nitric oxide, prostanoids, or Na(+)--K(+) pump activation.

Basal inhibitory action of endogenous endothelin on the sympathetic contraction in the isolated rat tail artery.

In order to test whether endogenous endothelin modulates the sympathetic vasoconstriction, arterial segments, 2 mm long, from rat tail artery were mounted in organ baths for isometric tension recording. Electrical field stimulation (2-8 Hz, 0.2 ms, 70 V during 1 s) produced frequency-dependent arterial contraction (maximal contraction 770+/-49 mg) that was nearly abolished (over 95% reduction) by tetrodotoxin (10(-6) M) or phentolamine (10(-6) M). This contraction was increased by pretreatment with the antagonist of endothelin ET(B) receptors N-(N-(N-(2, 6-dimethyl-1-piperidinyl)carbonyl)-4-methyl-L-leucyl)-1-(methoxycarbo nyl)-D-tryptophyl)D-norleucine (BQ-788, 10(-7)-3x10(-6) M), and was not modified either by the antagonist of endothelin ET(A) receptors cyclo(D-alpha-aspartyl-L-prolyl-D-valyl-L-leucyl-D-tryptophyl) (BQ-123, 10(-7)-3x10(-6) M) or the agonist of endothelin ET(B) receptors endothelin-1 (8-21), N-Suc-(Glu(9), Ala(11,15)) (IRL-1620, 10(-8)-10(-7) M). The potentiating effect of BQ-788 was not modified in arterial segments without endothelium or pretreated with the inhibitor of nitric oxide synthesis N(W)-nitro-L-arginine (L-NA, 10(-4) M) or with the inhibitor of endothelin converting enzyme N-(alpha-rhamnopyranosyloxy-hydroxyphosphinyl)-leu-trp (phosphoramidon, 10(-4) M). Exogenous noradrenaline (10(-9)-10(-4) M) produced concentration-dependent arterial contractions that were not modified by BQ-788 (3x10(-6) M), BQ-123 (3x10(-6) M) or IRL-1620 (10(-7) M). Therefore, an inhibitory action of endogenous endothelin on sympathetic vasoconstriction may be present under basal conditions. This inhibition could be produced by endothelin through activation of prejunctional endothelin ET(B) receptors, which may inhibit noradrenaline release from perivascular sympathetic nerves.

Effects of vasopressin on the sympathetic contraction of rabbit ear artery during cooling.

In order to analyse the effects of arginine-vasopressin on the vascular contraction to sympathetic nerve stimulation during cooling, the isometric response of isolated, 2-mm segments of the rabbit central ear (cutaneous) artery to electrical field stimulation (1-8 Hz) was recorded at 37 and 30 degrees C. Electrical stimulation (37 degrees C) produced frequency-dependent arterial contraction, which was reduced at 30 degrees C and potentiated by vasopressin (10 pM, 100 pM and 1 nM). This potentiation was greater at 30 than at 37 degrees C and was abolished at both temperatures by the antagonist of vasopressin V1 receptors d(CH2)5 Tyr(Me)AVP (100 nM). Desmopressin (1 microM) did not affect the response to electrical stimulation. At 37 degrees C, the vasopressin-induced potentiation was abolished by the purinoceptor antagonist PPADS (30 microM), increased by phentolamine (1 microM) or prazosin (1 microM) and not modified by yohimbine (1 microM), whilst at 30 degrees C, the potentiation was reduced by phentolamine, yohimbine or PPADS, and was not modified by prazosin. The Ca2+-channel blockers, verapamil (10 microM) and NiCl2 (1 mM), abolished the potentiating effects of vasopressin at 37 degrees C whilst verapamil reduced and NiCl2 abolished this potentiation at 30 degrees C. The inhibitor of nitric oxide synthesis, L-NOARG (100 microM), or endothelium removal did not modify the potentiation by vasopressin at 37 and 30 degrees C. Vasopressin also increased the arterial contraction to the alpha2-adrenoceptor agonist BHT-920 (10 microM) and to ATP (2 mM) at 30 and 37 degrees C, but it did not modify the contraction to noradrenaline (1 microM) at either temperature. These results suggest that in cutaneous (ear) arteries, vasopressin potentiaties sympathetic vasoconstriction to a greater extent at 30 than at 37 degrees C by activating vasopressin V1 receptors and Ca2+ channels at both temperatures. At 37 degrees C, the potentiation appears related to activation of the purinoceptor component and, at 30 degrees C, to activation of both purinoceptor and alpha2-adrenoceptor components of the sympathetic response.

Role of nitric oxide in the cerebral circulation during hypotension after hemorrhage, ganglionic blockade and diazoxide in awake goats.

The role of nitric oxide in cerebrovascular response to hypotension was analyzed by evaluating the changes in cerebrovascular resistance after inhibition of nitric oxide synthesis with Nw-nitro-L-arginine methyl ester (L-NAME) during three types of hypotension in conscious goats. Blood flow to one brain hemisphere was electromagnetically measured, hypotension was induced by controlled bleeding, and by i.v. administration of hexametonium (ganglionic blocker) or of diazoxide (vasodilator drug), and L-NAME was injected by i.v. route (35 mg kg-1). Under control conditions (13 goats), L-NAME increased arterial pressure from 98 +/- 3 to 123 +/- 4 mmHg and decreased cerebral blood flow from 65 +/- 3 to 40 +/- 3 ml min-1 (all P < 0.001); cerebrovascular resistance increased from 1.52 +/- 0.04 to 3.09 +/- 0.013 mmHg ml-1 min-1 (P < 0.01) (delta = 1.59 +/- 0.12 mmHg ml-1 min-1). After bleeding (five goats), mean arterial pressure decreased to 60 +/- 4 mmHg and cerebral blood flow decreased to 37 +/- 4 ml min-1 (all P < 0.01); cerebrovascular resistance did not change (1.56 +/- 0.14 vs. 1.54 +/- 0.12 mmHg ml-1 min-1, P > 0.05). During this hypotension, L-NAME increased arterial pressure to reach the normotensive values an did not affect the hypotensive values for cerebral blood flow; cerebrovascular resistance increased from the hypotensive values to 2.91 +/- 0.19 mmHg ml-1 min-1 (P < 0.01) (delta = 1.37 +/- 0.16 mmHg ml-1 min-1), and this increment is comparable to that under control conditions (P > 0.05). Ganglionic blockade (six goats) decreased arterial pressure to 67 +/- 2 mmHg) and did not affect significantly cerebral blood flow; cerebrovascular resistance decreased from 1.71 +/- 0.11 to 1.05 +/- 0.09 mmHg ml-1 min-1 (P < 0.01). During this hypotension, L-NAME increased arterial pressure to 103 +/- 6 mmHg (P < 0.001), and did not affect cerebral blood flow; cerebrovascular resistance increased from the hypotensive values to 1.68 +/- 0.18 mmHg ml-1 min-1 (P < 0.01) (delta = 0.63 +/- 0.10 mmHg ml-1 min-1), and this increment was lower than under control conditions (P < 0.01). Diazoxide (six goats) decreased arterial pressure to 69 +/- 5 mmHg (P < 0.01) without changing cerebral blood flow; cerebrovascular resistance decreased from 1.89 +/- 0.11 to 1.16 +/- 0.14 mmHg ml-1 min-1 (P < 0.01). During this hypotension, L-NAME increased arterial pressure to 87 +/- 6 mmHg (P < 0.05) and did not affect the hypotensive values for cerebral blood flow (P > 0.05); cerebrovascular resistance increased from the hypotensive values to 1.53 +/- 0.13 mmHg ml-1 min-1 (P < 0.05) (delta = 0.36 +/- 0.06 mmHg-1 ml-1 min-1), and this increment was lower than under control conditions (P < 0.01). Therefore, the role of nitric oxide in cerebrovascular response to hypotension may differ in each type of hypotension, as this role during hemorrhagic hypotension may not change and during hypotension by ganglionic blockade or diazoxide may decrease. These differences may be related to changes in nitric oxide release as stimuli on the endothelium (shear stress and sympathetic activity) may vary in each type of hypotension.

Adrenergic reactivity after inhibition of nitric oxide synthesis in the cerebral circulation of awake goats.

The interaction between nitric oxide (NO) and adrenergic reactivity in the cerebral circulation was studied using in vivo and in vitro preparations. Blood flow to one brain hemisphere (cerebral blood flow) was electromagnetically measured in conscious goats, and the effects of norepinephrine, tyramine and cervical sympathetic nerve stimulation were recorded before (control) and after inhibition of NO formation with Nw-nitro-l-arginine methyl ester (l-NAME). The responses to norepinephrine, tyramine and electrical field stimulation were also recorded in segments, 4 mm in length, from the goat's middle cerebral artery under control conditions and after l-NAME. In vivo, l-NAME (10 goats, 47 mg kg-1 administered i.v.) reduced resting cerebral blood flow by 37+/-2%, increased mean systemic arterial pressure by 24+/-3%, reduced heart rate by 35+/-2%, and decreased cerebrovascular conductance by 52+/-2% (all P<0.01). Norepinephrine (0.3-9 microgram), tyramine (50-500 microgram), and supramaximal electrical sympathetic cervical nerve stimulation (1. 5-6 Hz) decreased cerebrovascular conductance, and these decreases were significantly higher after l-NAME than under control conditions, remaining higher for about 48 h after this treatment. Norepinephrine (10-8-10-3 M), tyramine (10-6-10-3 M) and electrical field stimulation (1.5-6 Hz) contracted isolated cerebral arteries, and the maximal contraction, but not the sensitivity, was significantly higher in the arteries treated than in non-treated with l-NAME (10-4 M). Therefore, the reactivity of cerebral vasculature to exogenous and endogenous norepinephrine may be increased after inhibition of NO synthesis. This increase might be related, at least in part, to changes at postjunctional level in the adrenergic innervation of the vessel wall, and it might contribute to the observed decreases in resting cerebral blood flow after inhibition of NO synthesis.