Metformin prevents vascular prostanoid release alterations induced by a high-fat diet in rats.

Perivascular adipose tissue dysfunction induced by high-fat feeding leads to alterations in the modulation of inflammation, contractile activity of the vascular smooth muscle and endothelial function, all risk factors in the development of hypertension. Metformin, an activator of AMP-activated protein kinase (AMPK), is currently the first-line drug treatment for type 2 diabetes (T2DM) and metabolic syndrome. Besides its glucose-lowering effect, there is an interest in actions of this drug with potential relevance in cardiovascular diseases. The high-fat (HF) diet is an experimental model that resembles human metabolic syndrome. We have previously reported an altered pattern of prostanoid release in mesenteric vessels in this model. The aim of this study was to analyse the effects of metformin on mesenteric vascular bed prostanoid release, adiposity index and its relation to blood pressure in Sprague-Dawley rats fed a HF diet for 8 and 12 weeks. Eight groups were used: control (C8, C1), HF diet (HF8, HF12, 50% w/w bovine fat), metformin-treated (CMf8, CMf12, 500 mg/kg/day) and metformin-treated HF diet (HFMf8, HFMf12, both treatments). HF diet increased mesenteric vascular bed adiposity index (%, HF8: 1.7±0.1 vs C8: 0.9±0.04 and HF12: 1.8±0.1 vs C12: 0.8±0.1, P<.001); systolic blood pressure (SBP, mm Hg, HF8: 145±6 vs C8: 118±4, P<.01 and HF12: 151±1 vs C12: 121±3, P<.001). We found a positive correlation between these two parameters. Moreover HF diet increased the release of vasoconstrictor prostanoids such as thromboxane (TX) B2 (ng PR/mg of tissue, HF8: 117±6 vs C8: 66±2 and HF12: 123±6 vs C12: 62±5, P<.001) and prostaglandin (PG) F2α (ng/mg, HF8: 153±9 vs C8: 88±3 and HF12: 160±11 vs C12: 83±5, P<.001). We also found that this increase in the release of vasoconstrictor prostanoids positively correlates with the elevation of SBP. In addition, HF diet increases the release of PGE2 and decreases the prostacyclin (PGI2 )/TXA2 release ratio at 8 and 12 weeks of treatment compared to control groups. In the HFMf group, metformin treatment prevented all these increases in mesenteric vascular bed adiposity index (%, HFMf8: 1.3±0.2 vs HF8 and HFMf12: 1.3±0.1 vs HF12, P<.05); SBP (mm Hg, HFMf8: 127±2 vs HF8 and HFMf12: 132±1 vs HF12, P<.001); TXB2 release (ng PR/mg of tissue, HFMf8: 65±12 vs HF8, P<.05 and HFMf12: 53±3 vs HF12, P<.001) and PGF2 α (ng PR/mg of tissue, HFMf8: 99±13 vs HF8, P<.01 and HFMf12: 77±8 vs HF12, P<.001). Meanwhile metformin prevented the increment in PGE2 release only at 12 weeks. On the other hand, metformin improved the PGI2 /TXA2 ratio in both periods studied. In conclusion, metformin could exert beneficial effects on adipose tissue and the vascular system by improving endothelial dysfunction induced by an imbalance of vasoactive substances in mesenteric perivascular adipose tissue in this model.

A high-fat plus fructose diet produces a vascular prostanoid alterations in the rat.

In the rat, a high-fat (HF) plus fructose (F) diet produces cardiovascular and metabolic alterations that resemble human metabolic syndrome. Prostanoids (PR), cyclo-oxygenase-derived arachidonic acid metabolites, have vasoactive properties and mediate inflammation. The aim of this study was to analyse the effect of a HF+F diet on blood pressure (BP), metabolic parameters and mesenteric vascular bed PR production in male Sprague-Dawley rats. Four groups were studied over 9 weeks (n = 6 each): control (C), standard diet (SD) and tap water to drink; F+SD and 10% w/v F solution to drink; HF 50% (w/w) bovine fat added to SD and tap water; and HFF, both treatments. PR were determined by HPLC. Blood pressure was elevated in all experimental groups. Triglyceridaemia, insulinaemia and HOMA-IR were increased in the F and HF groups. HF+F animals showed elevated glycaemia, insulinaemia, HOMA-IR and triglyceridaemia. F decreased the vasodilator prostanoids PGI2 and PGE2 in the mesenteric vascular bed. Body weight was not significantly altered. In HFF, production of PGE2 , PGF2 alpha and TXB2 was elevated. The increased BP in HF and HFF could be partly attributed to the imbalance in vascular PR production towards vasoconstrictors. On the other hand, this dietary modification could induce inflammation, which would explain the elevation of PGE2 . In the F group, hypertension could be related to decreased vasodilator PRs. The simultaneous administration of HF and F in the rat produces deleterious effects greater than observed when treatments are applied separately.

Sodium molybdate prevents hypertension and vascular prostanoid imbalance in fructose-overloaded rats.

(1) Fructose (F) overload produces elevated blood pressure (BP), hyperglycaemia, hypertriglyceridemia and insulin resistance, resembling human metabolic syndrome. Previously, we found altered vascular prostanoid (PR) production in this model. (2) Sodium molybdate (Mo), as well as sodium tungstate, causes insulin-like effects and normalizes plasma glucose levels in streptozotocin-treated diabetic rats. We studied the effects of Mo on BP, metabolic parameters and release of PR from the mesenteric vascular bed (MVB) in F-overloaded rats. (3) Four groups of male Sprague-Dawley rats were analysed: Control, tap water to drink; F, F solution 10% W/V to drink; CMo, Mo 100 mg kg day(-1) and FMo, both treatments. After 9 weeks, the animals were killed and MVBs removed and the released PRs measured. (4) F increased BP, glycemia, triglyceridemia and insulinemia. Mo treatment prevented the increases in BP and glycemia, but did not modify triglyceridemia or insulinemia. In addition, Mo decreased BP in controls. (5) Prostaglandins (PG) F2 alpha and E2, PG 6-ketoF1 alpha and thromboxane (TX) B2 , as well as inactive metabolites of prostacyclin (PGI2 ) and TXA2 were detected. F decreased the production of vasodilator PRs PGI2 and PGE2 in MVB. Mo prevented these alterations and increased PGE2 in controls. Vasoconstrict or PRs PGF2 alpha and TXA2 release was not modified. (6) Mo treatment, beyond its known lowering effect on glycemia, prevents the reduction in the vascular release of vasodilator PR observed in this model. This could be one of the mechanisms by which Mo avoids the increase in BP caused by F overload in the rat.

Metformin reduces vascular production of vasoconstrictor prostanoids in fructose overloaded rats.

Metformin is a hypoglycaemic drug currently used to increase insulin sensitivity in the treatment of type 2 diabetes and metabolic syndrome. Its main mechanism of action is through activation of AMP-activated protein kinase, an enzyme that regulates cellular and whole organ metabolism. The fructose-overloaded rat is an experimental model with features that resemble human metabolic syndrome. We have previously reported alterations in vascular prostanoids (PR) in this model. The aim of this study was to analyse the effects of metformin treatment on blood pressure, metabolic parameters and PR production in aorta and mesenteric vascular bed (MVB) from fructose-overloaded animals. Four groups of male Sprague-Dawley rats were used: control, fructose overloaded (10% w/v fructose), metformin treated (50 mg kg(-1) day(-1) ) and fructose-overloaded treated with metformin. Rats with fructose overload had significantly elevated systolic blood pressure, glycaemia, triglyceridaemia, cholesterolaemia and insulinaemia compared with controls. Except for insulinaemia, metformin limited all these increases in fructose-overloaded animals. Fructose overload reduced prostacyclin levels in aorta and MVB, but prostaglandin E(2) levels were only reduced in MVB. Metformin treatment reduced the levels of the vasoconstrictor prostaglandins, PGF(2) α and thromboxane, in both vascular preparations from fructose-overloaded rats. PGF(2) α levels were significantly reduced by metformin in controls. In conclusion, one of the mechanisms by which metformin reduced blood pressure in this model is by decreasing vasoconstrictor prostaglandin production.

Lipopolysaccharide (LPS) induction of nitric oxide synthase-2 and cyclooxygenase-2 is impaired in fructose overloaded rats.

AIMS: Fructose (F) overload in rats induces metabolic dysfunctions that resemble the human metabolic syndrome. In this paper, we aimed to investigate the response of F overload rats to lipopolysaccharide (LPS) challenge in terms of nitric oxide (NO) production and prostanoids (PR) release. MAIN METHODS: NO blood steady-state concentration was monitored through the detection of nitrosyl-hemoglobin complexes (NO-Hb) by electronic spin resonance. Production of 6-keto PGF(1)α, PGE(2), PGF(2)α and TXB(2) was measured in aorta and mesenteric beds by HPLC. Western blot analysis was used to examine the changes in the expression levels of NOS-2 and COX-2 in aorta. KEY FINDINGS: Our results showed that increases in NO circulating steady-state concentration and PR production by aorta and mesenteric beds 6h after LPS administration were significantly attenuated in F overload rats with respect to control animals. Oxidative stress parameters were equally affected in the presence or absence of the F treatment. Aorta protein levels of NOS-2 and COX-2, two enzymes inducible by LPS, were significantly lower in F overload rats with respect to control rats at the end of the treatment (-39% and -61% for NOS-2 and COX-2 respectively). SIGNIFICANCE: These results suggest that the metabolic alterations established by 15 weeks of F overload should affect the response to LPS challenge due to an attenuation in the induction of NOS-2 and COX-2. This effect would be one of the components contributing to abnormalities in the course of the inflammatory response in other conditions associated to insulin resistance, such as diabetes.

Time course of vascular prostanoid production in the fructose-hypertensive rat.

1 There is a relationship between hypertension, insulin resistance and an altered plasmatic lipid profile known as 'metabolic syndrome'. Fructose (F) overload induces in the rat a mild hypertension associated with metabolic alterations such as hyperglycemia, hypertriglyceridemia and insulin resistance, resembling such syndrome. 2 Prostanoids (PR), metabolites of arachidonic acid, include vasoactive substances synthesized and released by the vessel wall. An altered pattern of PR release has been previously found in mesenteric vessels of experimental diabetic rats. 3 This study analyzed the effects of F-overload during different periods (4, 9, 15 and 22 weeks) on PR release in aorta (A) and mesenteric vascular beds (MVB). Animals received tap water (control) or F solution (10% w/v) to drink. 4 Rats with F overload showed significantly higher systolic blood pressure, glycemia and triglyceridemia than controls; but no differences in this parameters were found among periods of treatment either in controls or experimental animals. 5 In A, prostacyclin was decreased at 9, 15 and 22 weeks of treatment when compared to 4 weeks and controls. In MVB, prostacyclin showed different patterns of release in the studied periods of F overload. Prostaglandin (PG) E(2) diminish in MVB at the same extent in all periods. No changes were observed in A. The vasoconstrictor thromboxane was elevated in the MVB at 9 weeks. PGF(2)alpha, also a vasoconstrictor, remains unchanged. 6 In conclusion, F overload provokes in the rat a decrease in the vascular production of vasodilator PR and, in one of the studied periods, an increase in the release of the vasoconstrictor thromboxane, leading to a negative imbalance in the prostacylin/thromboxane ratio. This could be involved in the blood pressure alterations found in this experimental model of metabolic syndrome.

Pioglitazone and losartan modify hemodynamic and metabolic parameters and vascular prostanoids in fructose-overloaded rats.

This study analyzes the effects of losartan (AT1 blocker) and pioglitazone (insulin sensitizer), alone and in combination, in the fructose-overloaded rat, a model of metabolic syndrome. All treatments (nine weeks) reduced blood pressure and triglyceridemia and also restored the diminished release of vasodilator prostaglandins (prostacyclin in aorta and mesenteric vascular bed and prostaglandin E(2) in the latter). Pioglitazone, alone and in combination with losartan, reduced the release of the vasoconstrictor thromboxane in controls and fructose rats in both vascular preparations. In conclusion, although combination therapy and single treatments exerted similar effects, there may still be some advantage to the combined treatment.

Noradrenaline and angiotensin II modify vascular prostanoid release in fructose-fed hypertensive rats.

1 A fructose-enriched diet induces hypertension, metabolic alterations and insulin resistance in rats, resembling human metabolic syndrome. Previously, we found that prostanoid production was altered in fructose-fed rats. 2 This study analysed the effects of incubation with noradrenaline (NA) and angiotensin II (Ang II) on prostanoid release in mesenteric vascular beds from control and fructose-fed rats. Animals which received fructose solution (10% w/v) for 22 weeks showed higher systolic blood pressure and triglyceridaemia. 3 In controls, NA increased 6-keto-prostaglandin (PG) F(1)alpha (prostacyclin metabolite) and thromboxane (TX) production. Ang II increased only TX release. In fructose-fed animals, NA increased 6-keto-PG F(1)alpha and TX. PGF(2)alpha (vasoconstrictor) was also elevated. Ang II also increased PGF(2)alpha and PGE(2) levels. 4 In conclusion, in fructose rats Ang II in vitro stimulates a vasoconstrictor prostanoid not stimulated in controls. This could be related to the observed in vivo blood pressure increase. In fructose-fed animals, NA and Ang II also augment vasodilator prostanoids, suggesting a compensatory mechanism because of long-term hypertension.

Enzymatic activities in brains of diabetic rats treated with vanadyl sulphate and sodium tungstate.

The hypothesis of the present study was that diabetes mellitus might affect brain metabolism. Streptozotocin (STZ)-induced diabetic rats, treated with vanadyl sulphate (V) and sodium tungstate (T) were employed to observe the aspartate aminotransferase (AST), alanine aminotransferase (ALT) and creatine kinase (CK) activities in brain homogenates. Significant increases in AST, ALT and CK activities were found in diabetic brain homogenates against controls, suggesting increments of transamination in brain and/or increases in cell membrane permeability to these enzymes. The increase in brain CK possibly expresses alterations in energy production. The decrease in CK activity caused by V and T treatment in diabetic rats suggests that both agents tend to normalize energy consumption. It is also possible that V and T-induced hypoglycemic effects cause metabolic alterations in brain.

Long-term streptozotocin-induced diabetes alters prostanoid production in rat aorta and mesenteric bed.

Vascular disease is a major cause of mortality and morbidity in chronic diabetes mellitus. Prostanoids, metabolites of arachidonic acid, include vasoactive substances produced and released from the vascular wall. Alterations in prostanoid production have been reported in the vasculature of diabetic humans and experimental animals. The aim of the present work was to study the influence of three different periods of long-term streptozotocin-induced diabetes, 30, 120 and 180 days in the production of prostanoids in the thoracic aorta and in the mesenteric vascular bed of the rat. The prostanoids released to the incubation medium by the tissues were extracted and measured by reversed-phase HPLC. In the diabetic groups, body weight was reduced and glycaemia was increased when compared with the corresponding non-diabetic controls. In the aorta, 30 days of diabetes did not modify the prostanoid release pattern, meanwhile 120 and 180 days of incubation decreased prostacyclin (PGI(2)) production. In the mesenteric bed, at 30 days the release of the vasodilators PGI(2) and prostaglandin (PGE(2)) and the vasoconstrictor thromboxane (TXA(2)) was reduced. At 120 days the vasodilators were reduced and at 180 days such reduction was joined by an increase of the release of vasoconstrictor metabolites. Thirty days of diabetes did not modify the PGI(2)/TXA(2) ratio in the aorta or mesenteric bed. On the other hand, 120 and 180 days of diabetes reduced significantly the ratio when compared with the corresponding controls. In conclusion, the mesenteric bed, a resistance vascular bed, seems to be more sensitive than the aorta, a conductance vessel, to the effects of diabetes on prostanoid production. The observed effects contribute to a displacement of the balance of prostanoid release in favour of the vasoconstrictor metabolites, a phenomenon that could be related to the vascular complications of diabetes mellitus.

Oral treatment and in vitro incubation with fructose modify vascular prostanoid production in the rat.

1.-- In the rat, a fructose-enriched diet induces hyperglycaemia, hypertriglyceridaemia, insulin resistance and hypertension; a model which resembles the human metabolic syndrome. 2.-- Prostanoids, metabolites of arachidonic acid, include vasoactive substances synthesized and released from the vascular wall that have been implicated in the increase of peripheral resistance, one of the mechanisms involved in the fructose-induced hypertension. 3.-- The aim of the present study was to: (i) analyse the effects of the in vitro incubation with fructose on the production and release of prostanoids in rat thoracic aorta and in rat mesenteric bed and (ii) compare the effects of incubation with those of the in vivo acute and chronic treatment of rats with fructose and with the combination of both in vivo and in vitro procedures. 4.-- Blood pressure, glycaemia and triglyceridaemia were significantly elevated in both 4- and 22-week fructose-treated groups. Meanwhile, body and heart weight as well as insulinaemia were similar between experimental animals and controls. 5.-- In aortae, 4 weeks of Fructose treatment did not modify the prostanoid pattern release, but in vitro incubation decreased prostacyclin (PGI(2)) production. However, after 22 weeks, fructose treatment and incubation exerted the same effect. 6.-- In mesenteric bed, after 4 weeks, the incubation and the combination of both procedures reduced the release of the vasodilators PGI(2) and PGE(2), while fructose treatment only diminished the PGE(2) release. On the contrary, the production of the vasoconstrictor thromboxane A(2) (TXA(2)) was enhanced by incubation and both the procedures. After 22 weeks, fructose treatment increased PGI(2) release, while it was reduced by incubation. The combination of both did not modify this peripheral resistance when compared with controls. Finally, incubation of tissues from treated rats increased the release of the vasoconstrictors, PGF(2alpha) and TXA(2). 7.-- In conclusion, the mesenteric bed, a resistance vascular bed, seems to be more sensitive than the aorta, a conductance vessel, to the effects of fructose on prostanoid production. This difference could be related to a more relevant role of resistance vessels in the regulation of peripheral resistance and consequently of blood pressure. The observed effects should contribute to a shift in the balance of the release of prostanoid in favour of vasoconstrictor metabolites. This phenomenon could be related to an increase in the peripheral resistance and the mild hypertension observed in the fructose-treated rats.

Fructose overload modifies vascular morphology and prostaglandin production in rats.

1. A fructose (Fru)-enriched diet induces a mild increase in blood pressure associated with hyperglycaemia, hypertriglyceridaemia, and insulin resistance, resembling the human 'syndrome X', being an useful model to study hypertension and type 2 diabetes. 2. A sustained elevation of blood pressure is associated with cardiovascular structural modifications such as left ventricular hypertrophy and increased wall thickness:lumen diameter ratio in blood vessels. 3. Prostanoids (PR), metabolites of arachidonic acid through the cyclooxygenase pathway, include vasoactive substances synthesized and released by the vessel walls. 4. The aim of the present study was to analyse, in Fru-treated rats: (i) the morphology of mesenteric vessels and; (ii) the PR production in aorta and mesenteric vessels, in order to assess whether these parameters are related with the haemodynamic alterations observed in this experimental model. 5. Blood pressure, glycaemia and triglyceridaemia, were significantly elevated in both (4 and 22 weeks) Fru-treated groups. Meanwhile body and heart weight as well as insulinaemia were similar between experimental animals and controls. 6. The mesenteric vessels of Fru-treated rats (22 weeks) showed an increased thickness and area of the media when compared with the controls; meanwhile, the lumen diameter was similar in both groups. 7. The Fru treatment for 4 weeks did not modify PR production in aorta, whereas in the mesenteric bed it diminished prostaglandin (PG) E(2) release significantly compared with the controls. However, in the group treated for 22 weeks, Fru reduced PGI(2) production in the aorta, as assessed by 6-keto-PGF(1)alpha measurements. Meanwhile, in the mesenteric bed, the chronic Fru treatment decreased PGE(2) release but, rather surprisingly, increased the output of PGI(2) when compared with its corresponding controls. 8. In conclusion, the present study shows the existence of an alteration in the morphology of mesenteric vessels in Fru-treated rats, which could be related to an increase in peripheral resistance and the consequent mild hypertension observed in this model. However, a diminished release of vasodilator PRs, such as PGE(2) in mesenteric vessels at 4 and 22 weeks and PGI(2) in aorta at 22 weeks could further impair the vessel response. The increase in PGI(2) observed in the chronic group in mesenteric vessels could be attributed to a compensatory mechanism.

Opposite effects of endogenous nitric oxide and prostaglandin F2 alpha in the rat mesenteric bed.

1. The relationship between the effects of endogenous nitric oxide (NO) and prostanoids on the noradrenaline (NA)-induced contractions and the mechanisms involved were investigated in the rat perfused mesenteric bed, using NG-nitro-L-arginine methyl ester (l-NAME), a NO synthase inhibitor and sodium nitroprusside (SNP), a NO donor. 2. The constrictor responses to NA were reduced to 50% by the cyclooxygenase inhibitor 10 microm indomethacin as well as by 1 microM SNP. When indomethacin and SNP were perfused simultaneously the contractions were further reduced. 3. The NA-induced contractions were increased by the addition of 400 microM L-NAME and the addition of either indomethacin or SNP abolished such increases. The simultaneous perfusion of both agents further reduced the contractions. 4. Removal of the endothelium increased NA-induced contractions to a similar extent as L-NAME and this increase was abolished by indomethacin as well as by SNP. 5. The perfusion of 10 microM NA augmented the release of prostaglandin (PG) F2 alpha by the mesenteric bed without modifications in any other prostanoid. In the presence of L-NAME, this effect was further increased. However, SNP abolished the NA-induced stimulation of PGF2 alpha release. 6. In de-endothelialized preparations NA also stimulated PGF2 alpha production as observed in intact preparations. This effect was more marked in the presence of L-NAME; in contrast, SNP abolished the stimulation. 7. In conclusion, the present results suggest an opposite action between NO and PGF2 alpha on the NA-induced contractions in the rat mesenteric bed.

Defibrotide modulates prostaglandin production in the rat mesenteric vascular bed.

Defibrotide 1 microM, a polydeoxyribonucleotide extracted from mammalian organs, reduced the contractile responses to noradrenaline (NA) in the rat isolated and perfused mesenteric vascular bed, in intact as well as in de-endothelialized preparations. Defibrotide was without effect on the acetylcholine-induced relaxations of U-46619-precontracted mesenteric vascular beds. Moreover, defibrotide increased 6-keto prostaglandin (PG) F(2alpha) (stable metabolite of prostacyclin) release sixfold in the presence, but not in the absence of the endothelium, with no modification on the release of other prostanoids. Defibrotide also inhibited the NA-induced increase in PGF(2alpha) release, in both intact and de-endothelialized mesenteric vascular beds. In conclusion, the present results show that defibrotide modulates PG production in the mesenteric bed and that the observed inhibition of the contractile responses should be due to the impairment of the NA-induced increase in PGF(2alpha) release.

Bradykinin and electrical stimulation increase prostaglandin production in the rat vas deferens.

The epididymal portion of the rat vas deferens produced prostaglandins (PG) E(2), F(2alpha)and 6-keto F(1alpha). Electrical stimulation (ES, 0.1 Hz, 1 ms) increased such production by 100%, and similar results were obtained in the presence of 1.0 microM bradykinin (Bk). When both stimuli were applied simultaneously, the increases in PG production were 1100% for PGE(2), 800% for PGF(2alpha)and 400% for PG6-keto F(1alpha). Prazosin abolished the effect of ES on PG production. A selective Bk B(2)-receptor antagonist abolished the increase in PG production induced by Bk, both in non-stimulated and in ES tissues. Bk (1.0 microM) elicited contractile responses in non-stimulated as well as in ES tissues, responses that were not modified in the presence of 10 microM indomethacin. In conclusion, the effects of Bk on prostaglandin production appears to depend on the activation of B(2) receptors, while the increase in prostaglandin release induced by ES, and the effects observed with both stimuli simultaneously, should be mediated by the release of noradrenaline and the subsequent activation of alpha(1) adrenoceptors.

Prostanoid release and constrictor responses to noradrenaline in the rat mesenteric vascular bed in non-insulin-dependent diabetes mellitus.

1. The administration of streptozotocin (STZ) to 2-day old rats induced a non-insulin-dependent diabetes mellitus (NIDDM)-like state, with mild hyperglycaemia and no alterations in body weight at the adult age. 2. In the isolated and perfused mesenteric vascular bed of NIDDM animals, the constrictor responses to either noradrenaline (NA) or potassium chloride (KCl) were not modified as compared with age-matched non-diabetic controls. 3. The reduction in NA contractions induced by the cyclooxygenase inhibitor, 10 microM indomethacin in the control group was absent in the NIDDM rats. 4. The increase in the NA-induced contractions caused by endothelium removal was suppressed by indomethacin in the controls but not in the NIDDM group. 5. The prostanoid release from the mesenteric vascular beds of NIDDM rats was markedly reduced as compared with non-diabetic controls. Noradrenaline increased production of the constrictor prostaglandin (PG) F2alpha in control but not in NIDDM rats. 6. In summary, these results show that in STZ-induced NIDDM rats, there is an impairment of the prostanoid production, as well as a suppression of the role of prostanoids in the contractile effects of NA in the mesenteric vascular bed. These alterations are more severe than those previously observed in a model of insulin-dependent diabetes mellitus (IDDM), in which hyperglycaemia and reduction of body weight were more marked. The conclusion is that, in these models of diabetes and in the preparation studied, vascular alterations and modifications of glycaemia and body weight are not closely related.

Effects of eicosanoids and nitric oxide on the noradrenaline-induced contractions in the rat mesenteric bed.

1. The effects of the inhibition of the metabolism of arachidonic acid (AA) on the constrictor responses to noradrenaline (NA) were studied in the rat perfused mesenteric bed. The inhibitor of all the pathways of AA metabolism, 10 microM eicosatetraynoic acid (ETYA), reduced the constrictor responses to all the concentrations of NA assayed. 2. The constrictor responses to NA were also reduced by the cyclooxygenase (COX) inhibitor, indomethacin (10 microM), as well as by the lipoxygenase inhibitor, nordihidroguaiaretic acid (1 microM; NDGA), whereas they were unmodified by the cytochrome P450 monooxigenase inhibitors, clotrimazole (10 microM), metyrapone (10 microM) and proadifen (10 microM). 3. The reduction in NA contractility induced by indomethacin was reverted with a decreasing order of potency by the thromboxane A2 analogue, U-46619 > prostaglandin (PG) E2 > PGF2alpha. The exposure of the mesenteric bed to NA increased the production of PGF2alpha, whereas it did not modify the production of the remaining AA metabolites. 4. The increase in the NA-induced contractions caused by endothelium removal, as well as by the inhibition of nitric oxide synthase (NOs) with NG-nitro-L-arginine methyl ester (400 microM; L-NAME), was suppressed by indomethacin but not by NDGA. These observations suggest that the lipoxygenase-derived metabolites are formed in the endothelium, whereas the COX-derived metabolites are formed in the vascular smooth muscle. 5. The TP receptor antagonist, SQ29548, did not modify the NA-induced contractions, either in the presence or in the absence of the endothelium. 6. Contractions elicited by KCI (60-100 mM) were unmodified by the AA metabolism inhibitors, ETYA, NDGA and indomethacin. 7. In summary, these results show that metabolites of AA, through both the COX and the lipoxygenase pathways, are involved in the NA-induced contractions in the rat mesenteric bed. The lipoxygenase metabolites are likely to be formed in the vascular endothelium, whereas the COX metabolite, which could be PGF2alpha, is apparently formed within the vascular smooth muscle.

Time-course of the alterations in prostanoid production and in contractile responses of mesenteric beds isolated from streptozotocin diabetic rats.

The prostanoid production and the effect of indomethacin on the noradrenaline-induced contractions were studied in the mesenteric bed of rats at different times (1-8 weeks) after the administration of streptozotocin (STZ). The production of prostacyclin (measured as 6-keto-PGF1alpha) and prostaglandin (PG) E2 was unchanged one week after STZ, but it was reduced to 50% of control values 4 weeks after STZ without further changes 8 weeks after the treatment. The release of thromboxane (TX) A2 (measured as TXB2) and PGF2alpha, increased by 100% one week after STZ and returned to basal values at 3 weeks. TX release was below control values 8 weeks after STZ. The ratio 6-keto-PGF1alpha/TXB2 was reduced one week after STZ, recovered to control values at 4 weeks and augmented at 8 weeks. Indomethacin (10 microM) reduced the contractile responses to noradrenaline in the controls, whereas in STZ-treated rats this effect was observed solely 8 weeks after the treatment. Since this recovery coincided with an increase of the vasodilator/vasoconstrictor prostanoid ratio, a time-dependent compensation of the vascular alterations caused by STZ can be proposed from the present results.

Effect of dipyridamole on prostanoid production in rat isolated atria.

The effect of 0.01 microM dipyridamole on prostanoid production was studied in atria from normal, acute diabetic and insulin-treated diabetic rats. Diabetes was induced by i.v. administration of 65 mg/kg of streptozotocin (STZ) and the rats were killed 5 days later. Atria were incubated during 60 min in Krebs solution. The prostanoids 6-keto-prostaglandin (PG) F1alpha (6-keto-PGF1alpha) and thromboxane (TX) B2, stable metabolites of prostacyclin and TXA2, respectively, as well as PGE2 were measured by reversed phase high-performance liquid chromatography-UV. In diabetic atria, 6-keto-PGF1alpha production was reduced by 50% whereas TXB2 release was increased two-fold compared to the controls, with a significant decrease in the 6-keto-PGF1alpha/TXB2 ratio. The preincubation with 0.01 microM dipyridamole for 30 min increased 6-keto-PGF1alpha production in control, diabetic and insulin-treated diabetic atria whereas TXB2 release was not modified. This effects provoked an significant increase in the 6-keto-PGF1alpha/TXB2 ratio. In conclusion, STZ diabetes reduces the 6-keto-PGF1alpha/TXB2 ratio impairing the functional status of the atria. Dipyridamole increased this ratio in atria from diabetic and insulin-treated diabetic rats, thus opposing the effects of STZ diabetes. This fact suggests the possibility of a participation of the drug in pathologies characterized by an imbalance in the production of vasodilator and vasoconstrictor prostanoids.

Effects of aging on ATP sensitive K(+) channels and on prostanoid production in the rat mesenteric bed.

The aim of the present work was to evaluate, in the rat isolated mesenteric bed, whether increasing age is associated with alterations in the ATP sensitive K(+) channels functionality. Moreover, studies were performed in order to evaluate the effects of aging on the synthesis of vascular prostanoids as well as on its possible contribution to the pressor responses of this vascular bed. Male Wistar rats of 3 month (adults) and 24 month (aged) were used. Although no differences were found among adult and aged rats in pressor responses to 2-30 nmol noradrenaline and to 40-160 nmol KCl, the relaxant responses to the K(+) channel opener, 10(-6) M cromakalim, were significantly diminished in the aged group compared to the adults. On the other hand, whereas PGF2α and 6-keto PGF1α production was not modified with age, the thromboxane B2 and prostaglandin E2 production in the mesenteric bed from 24 month old rats was significantly increased compared to the adult group. Furthermore, the cyclooxigenase synthesis inhibitor, 10(-5) M indomethacin reduced the pressor responses induced by noradrenaline in the mesenteric beds from adults but not from aged rats. It is concluded that there is an age related reduction in the functionality of the ATP sensitive K(+) channels in the rat mesenteric bed. In addition, aging produces an increase in the release of vasoconstrictor as well as of vasodilator prostanoids, whose contribution to noradrenaline induced pressor responses appears to be less relevant in the older animals.