Endothelial dysfunction after repeated Chlamydia pneumoniae infection in apolipoprotein E-knockout mice.

BACKGROUND: Arterial relaxation is largely regulated by endothelial nitric oxide (NO). Its diminished activity has been associated with incipient atherosclerosis. We investigated the endothelium-dependent relaxation of aorta in apolipoprotein E-knockout (apoE-KO) mice exposed to single or repeated Chlamydia pneumoniae inoculation. METHODS AND RESULTS: Forty-eight apoE-KO mice, 8 weeks old, were inoculated intranasally with C pneumoniae (n=24) or saline (n=24) every 2 weeks over a 6-week period. Twenty mice (10 infected and 10 controls) were killed at 2 weeks and 6 weeks, respectively, after the first inoculation. The smooth muscle tone of aortic rings was measured in vitro at both time points. The norepinephrine-precontracted thoracic aortic rings were successively exposed to methacholine in the absence and presence of N:(G)-nitro-L-arginine methyl ester (L-NAME) and diclofenac. The methacholine-induced relaxation was attenuated in the infected mice at 6 weeks in both the absence and presence of L-NAME (P:<0.05 and P:<0.01, respectively). When administered together with L-NAME, diclofenac enhanced the relaxation of the L-NAME-pretreated aortas in infected mice at 2 weeks (P:<0.05) but not in noninfected mice. The relaxation response from infected mice tended to differ in the same manner at 6 weeks (P:<0.1). No intimal thickening was detected at either time point. CONCLUSIONS: C pneumoniae impairs arterial endothelial function, and the NO pathway is principally involved. Cyclooxygenase-dependent vasoconstricting products may also account for the infection-induced impaired relaxation. These findings further support the role of C pneumoniae infection in atherosclerosis development.

Infection-associated intimal thickening in the coronary arteries of children.

OBJECTIVES: based on autopsy material from children this study investigated the possible relationship of clinically evident infection prior to death with intimal thickening of the coronary arteries. BACKGROUND: viral infections are suggested to be associated with intimal thickening in the coronary arteries both in animals and man. METHODS: the coronary arteries were examined in 175 autopsied children 0-15 years of age (median 7 days). Semi-serial cross sections of the coronary arteries were screened for maximal intimal thickening at 0.2 mm intervals. The length of the internal elastic lamina, the areas of arterial media and intima were measured from cross-sections. Irregular linings of the arteries were mathematically transformed to circles. The percentage of intimal and musculoelastic layer area to luminal area encircled by arterial media was calculated. RESULTS: intimal thickening increased with age but was also associated with the presence of infectious disease at death. Already in the newborn children, who died shortly after the birth, the percentage of intimal and musculoelastic layer area to luminal area encircled by arterial media was big, maximally 55%. In the left coronary artery the mean percentages were 32 and 21% in the groups with viral and bacterial infections, respectively as compared to 16% in the group with no evidence of infection. CONCLUSION: infections in general and viral infections in particular, seem to be associated with intimal thickening, which may predispose coronary arteries to atherosclerosis. Atherogenesis might have a rapid dynamic component.

Analeptic effect of centrally administered histamine H2-receptor agonist dimaprit but not impromidine in urethane-anesthetized rats.

Intracerebroventricularly administered dimaprit decreased the depth of urethane anaesthesia. Ventilatory stimulation, positive corneal reflex and increased susceptibility to pain were observed. Furthermore, dimaprit decreased the lethal effect of large doses of urethane. The analeptic property of dimaprit was not shared by the potent H2-receptor agonist, impromidine, Histamine increased ventilatory tidal volume but no other stimulatory effects were observed. These findings suggest that the analeptic effects of dimaprit were not mediated by H2-receptors. Among the analeptic effects of dimaprit, only the protection against urethane toxicity was antagonized by metiamide. However, this phenomenon appeared to be due to the nonspecific interaction between the three bradypnoeic drugs metiamide, dimaprit and urethane. The histamine-induced increase in ventilatory tidal volume was not antagonized by diphenhydramine or metiamide, suggesting the existence of a novel histaminergic mechanism in the central nervous system.

Respiratory mu-opioid and benzodiazepine interactions in the unrestrained rat.

Interactions of mu-opioid receptors with the benzodiazepine system were studied by examining the modulatory effects of flumazenil (a benzodiazepine antagonist) and alprazolam (a benzodiazepine agonist) on the respiratory effects of the opioid peptide dermorphin. Dermorphin, 1-30 nmol administered i.c.v., to conscious, unrestrained rats decreased ventilation rate (VR) and minute volume (MV) dose-dependently. The ventilatory depression was antagonized by naloxone and by the benzodiazepine antagonist flumazenil. The benzodiazepine alprazolam potentiated the respiratory inhibition of a small (1 nmol) dose of dermorphin but antagonized that of a higher dose (3 nmol). The results suggest that the benzodiazepine/GABA receptor complex modulates respiratory depression induced by central mu-receptor stimulation in the rat.

Evidence for differential opioid mu 1- and mu 2-receptor-mediated regulation of heart rate in the conscious rat.

The possibility that mu-opioid-induced tachycardia and bradycardia could be mediated by different subtypes of the mu-receptor was studied in conscious Sprague-Dawley rats. The selective mu-receptor agonist dermorphin and its analog, TAPS (Tyr-D-Arg-Phe-sarcosine), a putative mu 1-receptor agonist, were given centrally. Tyr-D-Arg-Phe-sarcosine increased the heart rate, the response being inversely correlated to the dose (an increase of 71 +/- 22, 49 +/- 14 and 30 +/- 17 beats/min at doses of 0.3, 3 and 30 pmol, respectively). Dermorphin induced less clear changes in heart rate (maximum increase of 39 +/- 14 beats/min at the dose of 1 pmol). After treatment with the mu 1-selective antagonist naloxonazine (NAZ), TAPS 30 pmol and dermorphin 1 pmol decreased heart rate by -22 +/- 10 and -24 +/- 7 bpm, respectively. The bradycardiac effect of larger doses of dermorphin was potentiated by NAZ (from -25 +/- 8 to -97 +/- 22 bpm) but abolished by the non-selective antagonist naloxone. These data suggest that the high affinity mu 1-opioid receptors mediate tachycardic responses and mu 2-receptors mediate bradycardic responses.

Synthesis and antihypertensive activity of some new quinazoline derivatives.

A series of substituted 2-piperidino-4-amino-6,7-dimethoxyquinazolines was synthesized and screened as potential antihypertensive agents. The hypotensive effect of all the new compounds was studied after intravenous administrations in urethane-anesthetized normotensive rats. The furoylpiperazine moiety in the prazosin molecule could be replaced by a more stable substituted piperidine group without loss of the blood pressure lowering activity. However, the nature of the substituent profoundly influenced the hypotensive potency as well as the duration of the hypotensive action. Some of the new compounds were found to be as potent as prazosin. On the basis of potency and the duration of the hypotensive action in the anesthetized rats, five of the most promising compounds were selected for further studies. Each of these agents exerted an antihypertensive effect upon oral administrations in conscious spontaneously hypertensive rats. At small doses, the new compounds appeared to be somewhat less potent than prazosin, but at the higher doses of 10-100 mumol/kg, two of them appeared to be even more efficacious antihypertensive agents than prazosin.

Involvement of bradykinin B1 and B2 receptors in relaxation of mouse isolated trachea.

1. The aim of the present study was to investigate the effects of bradykinin and [des-Arg9]-bradykinin and their relaxant mechanisms in the mouse isolated trachea. 2. In the resting tracheal preparations with intact epithelium, bradykinin and [des-Arg9]-bradykinin (each drug, 0.01-10 microM) induced neither contraction nor relaxation. In contrast, bradykinin (0.01-10 microM) induced concentration-dependent relaxation when the tracheal preparations were precontracted with methacholine (1 microM). The relaxation induced by bradykinin was inhibited by the B2 receptor antagonist, D-Arg0-[Hyp3,Thi5,D-Tic7,Oic8]-bradykinin (Hoe 140, 0.01-1 microM) in a concentration-dependent manner whereas the B1 receptor antagonist, [des-Arg9,Leu8]-bradykinin (0.01-1 microM), had no inhibitory effect on bradykinin-induced relaxation. [des-Arg9]-bradykinin (0.01-10 microM) also caused concentration-dependent relaxation after precontraction with methacholine. The relaxation induced by [des-Arg9-bradykinin was concentration-dependently inhibited by the B1 receptor antagonist, [des-Arg9,Leu8]-bradykinin (0.01-1 microM), whereas the B2 receptor antagonist, Hoe 140 (0.01-1 microM) was without effect. 3. In the presence of the cyclo-oxygenase inhibitor, indomethacin (0.01-1 microM), the relaxations induced by bradykinin and [des-Arg9]-bradykinin were inhibited concentration-dependently. 4. Two nitric oxide (NO) biosynthesis inhibitors NG-nitro-L-arginine methyl ester (L-NAME, 100 microM) and NG-nitro-L-arginine (L-NOARG, 100 microM) had no inhibitory effects on the relaxations induced by bradykinin and [des-Arg9]-bradykinin. Neither did the selective inhibitor of the soluble guanylate cyclase, 1H-[1,2,4]oxadiazolo[4,3-a]quinoxalin-1-one (ODQ, 10 microM) inhibit the relaxations induced by bradykinin and [des-Arg9]-bradykinin. 5. Prostaglandin E2 (PGE2, 0.01-33 microM) caused concentration-dependent relaxation of the tracheal preparations precontracted with methacholine. Indomethacin (1 microM) and ODQ (10 microM) exerted no inhibitory effects on the relaxation induced by PGE2. 6. The NO-donor, sodium nitroprusside (SNP; 0.01-100 microM) also caused concentration-dependent relaxation of the tracheal preparations precontracted with methacholine. ODQ (0.1-1 microM) concentration-dependently inhibited the relaxation induced by SNP. 7. These data demonstrate that bradykinin and [des-Arg9]-bradykinin relax the mouse trachea precontracted with methacholine by the activation of bradykinin B2-receptors and B1-receptors, respectively. The stimulation of bradykinin receptors induces activation of the cyclo-oxygenase pathway, leading to the production of relaxing prostaglandins. The NO pathway is not involved in the bradykinin-induced relaxation. The relaxation caused by NO-donors in the mouse trachea is likely to be mediated via activation of soluble guanylate cyclase.

Replacement of salt by a novel potassium- and magnesium-enriched salt alternative improves the cardiovascular effects of ramipril.

1. The influence of salt (sodium chloride; NaCl) (an additional 6% in the diet) and that of a novel sodium-reduced, potassium-, magnesium-, and L-lysine-enriched salt alternative on the cardiovascular effects of ramipril was studied in stroke-prone spontaneously hypertensive rats in a 6-week study. The intake of sodium chloride was adjusted to the same level by adding the salt alternative at a 1.75 times higher amount than regular salt. 2. Salt produced a marked rise in blood pressure and induced cardiac hypertrophy and significant mortality, while the salt alternative neither increased blood pressure nor caused any mortality and produced less cardiac hypertrophy than salt. 3. Ramipril treatment at a daily dose of 3 mg kg-1 normalized blood pressure and prevented the development of cardiac hypertrophy of rats on control diet. These effects of ramipril were blocked by the addition of salt but were only slightly attenuated by the addition of the salt alternative. The mortality in the salt group was prevented by ramipril. 4. Responses of mesenteric arterial rings in vitro were examined at the end of the study. Salt, but not the salt alternative, increased vascular contractile responses to noradrenaline. Ramipril treatment improved the arterial relaxation responses to acetylcholine and to sodium nitroprusside. The vascular relaxation enhancing effect of ramipril was blocked by salt but only slightly attenuated by the salt alternative. 5. Ramipril treatment did not significantly increase plasma renin activity in the presence or in the absence of salt supplementation. The salt alternative did not cause hyperkalaemia, either alone or in combination with ramipril treatment. 6. Both salt supplementations, irrespective of ramipril treatment, induced a six to eight fold increase in the urinary excretion of calcium. There was an expected 90 to 140% rise in the urinary excretion of magnesium and 200% rise in the urinary excretion of potassium in the salt alternative group. Salt also produced an approximately 50% increase in magnesuria.7. Our findings suggest that replacement of salt by the potassium-, magnesium- and L-lysine-enriched salt alternative improves the cardiovascular effects of ramipril. In the present study the beneficial effect was related to the increased intakes of potassium and/or magnesium and L-lysine from the salt alternative because the amount of sodium chloride was the same.

Randomized comparison of oral and transdermal hormone replacement on carotid and uterine artery resistance to blood flow.

OBJECTIVE: To compare the long-term effects of oral and transdermal hormone replacement therapy (HRT) on carotid and uterine vascular impedance. METHODS: Sixty-three postmenopausal women were randomized to 1 year's treatment with oral or transdermal sequential combined HRT. Carotid and uterine artery pulsatility indices (PIs) were assessed by color Doppler at baseline, and after 2, 6, and 12 months of treatment. Fifty-eight women completed the trial, 27 in the oral and 31 in the transdermal group. In a subgroup of 30 women, we also performed Doppler measurements in the estrogen-progestin combined phase. The study had 90% power to detect a difference between treatment groups of 0.05 in the carotid artery and of 0.25 in uterine artery PI at the 5% significance level. RESULTS: The carotid PI decreased significantly (P < .001) and similarly during both regimens. This drop was already clearly detectable during the second month, from 0.97 (0.95, 1.01) (mean and 95% confidence intervals [CII) to 0.94 (0.91, 0.97) in the oral and from 0.98 (0.94, 1.00) to 0.92 (0.89, 0.95) in the transdermal group, but it continued up to 12 months (0.85 [0.82, 0.88], 13% of baseline values in the oral group and 0.84 [0.81, 0.871, 14% in the transdermal group). In the uterine arteries, the drop in PI was steeper and greater and reached its maximum at 6 months (39% and 40%, respectively). Drops in carotid and uterine PI correlated positively with baseline PI values, but were not affected by patient age, time from menopause, previous HRT and smoking. Addition of norethisterone acetate did not counteract drops in carotid and uterine PI in either group. CONCLUSION: Oral and transdermal sequential HRT are similarly effective at 1 year in reducing impedance to flow in carotid and uterine circulation. This long-term vascular effect might explain how HRT protects women from cardiovascular disease.

Selective cardiorespiratory activity of an iodinated analog of thyrotropin-releasing hormone (TRH).

The biological activity of thyrotropin-releasing hormone (TRH) and its analogs 4(5)-I-Im-TRH and 2,4(5)-I2-Im-TRH was assessed by means of their effects on: 1) the mean arterial pressure (MAP), 2) heart rate (HR), 3) ventilation minute volume (MV), 4) contractility of the rat duodenum, and 5) concentrations of thyrotropin (TSH) or prolactin (PRL) in serum. Also their binding to TRH-receptors in brain homogenates was studied. In urethane-anesthetized rats TRH ICV increased MAP, HR and MV. 4(5)-I-Im-TRH was equally as active as TRH on HR and MV but a significant elevation in MAP was observed only at a dose 100-fold to that of TRH. However, the maximal responses of 4(5)-I-Im-TRH and TRH did not differ. In conscious rats, TRH 1A elevated MAP and HR but 4(5)-I-Im-TRH was active on MAP only. 2,4(5)-I2-Im-TRH was devoid of cardiorespiratory activity. TRH dose-dependently inhibited the contractions of the rat duodenum while the iodinated analogs lacked such an activity. To induce a significant release of TSH several hundred times more of 4(5)-I-Im-TRH and over 1000 times more of 2,4(5)-I2-Im-TRH were needed as compared to TRH. The iodoanalogs elevated PRL levels only at doses 2000-fold higher than those of TRH. The iodoanalogs displaced [3H][3-Me-His2]TRH [( 3H]MeTRH) from its binding sites at concentrations about 1000 times higher than those of TRH. Substitutions of the histidyl moiety of TRH in 4(5)-I-Im-TRH and 2,4(5)-I2-Im-TRH resulted in substantial loss of the endocrine activity. While the di-iodinated analog was practically devoid of any biological activity the monoiodinated analog exerted similar cardiorespiratory activity to that of TRH.

Role of peripheral and central catecholaminergic and cholinergic mechanisms in the cardiovascular effects of thyrotropin-releasing hormone.

The mechanisms of the cardiovascular effects of i.c.v. administered thyrotropin-releasing hormone (TRH) were studied in anesthetized rats. The pressor response to TRH was blocked after depletion of catecholamines by i.p. reserpine whereas vagotomy or i.v. methylatropine reduced the TRH-induced tachycardia. Centrally administered catecholaminergic or cholinergic receptor antagonists failed to block the cardiovascular effects of TRH. However, centrally administered reserpine reduced the pressor response to TRH and the affinity of its specific binding in brain homogenates. Similar reduction in the affinity of TRH binding was observed after depletion of brain serotonin with p-chlorophenylalanine (PCPA), which was earlier shown to antagonize the TRH-induced pressor effect. It was concluded that TRH acts through a central mechanism to enhance the sympathetic outflow and to attenuate the vagal cardiac activity which leads to hypertension and tachycardia. Central serotonergic mechanisms rather than those related to catecholamines appear to be involved in the pressor response to TRH.

Central and peripheral type benzodiazepine ligands displace [3H][3-ME-HIS2]TRH from its binding sites in the brain and the anterior pituitary and antagonize the effect of TRH in the rat duodenum.

The effects of central (clonazepam, an agonist, and FG 7142, an inverse agonist), mixed (diazepam) or peripheral type (Ro 5-4864) benzodiazepine receptor ligands on the action of TRH on the transmurally stimulated rat duodenum and binding of [3H][3-Me-His2] TRH in the rat anterior pituitary, hypothalamus, cortex and brainstem have been studied. TRH dose-dependently inhibited the contractions of transmurally stimulated rate duodenum. Clonazepam (5 x 10(-6) M), diazepam (10(-5) M), Ro 5-4864 (10(-5) M) or FG 7142 (10(-5) M) attenuated the response of TRH in the rat duodenum. The action of these compounds was antagonized neither by the central type benzodiazepine antagonist flumazenil nor by peripheral type antagonist PK 11195 but instead PK 11195 itself counteracted TRH. TRH displaced [3H][3-Me-His2]TRH with Ki-values ranging 0.08 to 0.31 microM. Ki-values for clonazepam diazepam, Ro 5-4864, PK 11195 and FG 7142 ranged 6-117 microM, 3-23 microM, 20-67 microM, 20-40 microM and 260-420 microM, respectively, demonstrating fairly weak affinity to TRH-receptors. In saturation experiments, clonazepam and PK 11195 significantly increased KD but not Bmax of the labelled ligand while Ro 5-4864 increased both KD and Bmax. This indicates that all these compounds competitively inhibit the binding of [3H][3-Me-His2]TRH in the CNS which may also be the mechanism for their antagonism of the effect of TRH in the rat duodenum.

Vagally mediated bradycardiac effect of prazosin in anaesthetized rats.

Prazosin at doses of 100 or 1000 nmol/kg i.v. induced bradycardia in urethane-anaesthetized rats. The bradycardia was completely abolished by atropine pretreatment or vagotomy. Prazosin also stimulated gastric acid secretion. This effect was completely abolished by vagotomy. The maximal hypotensive effect after prazosin i.c.v. occurred 10 min later than with i.v. administration. It is concluded that prazosin possesses vagal a stimulating property that may in part explain its modest tachycardiac effect seen in clinical use. The mechanism of vagal stimulation by prazosin remains unclear. The present findings suggest that prazosin does not exert any direct effects on central vagal structures accessible from the ventricular space.

Effects of K+ channel inhibitors on the basal tone and KCl- or methacholine-induced contraction of mouse trachea.

The present study examined the effects of K+ channel inhibitors on the basal tone and on KCl- or methacholine-induced contraction of the mouse-isolated trachea. Glibenclamide and iberiotoxin, procaine, quinine and tetraethylammonium did not induce any contraction of the indomethacin-treated mouse trachea. 4-Aminopyridine induced concentration-dependent contraction. This action of 4-aminopyridine was abolished by atropine and reduced by tetrodotoxin and nifedipine. Glibenclamide failed to modify KCl- or methacholine-induced contraction. Iberiotoxin and 4-aminopyridine potentiated KCl- and methacholine-induced contractions. Nifedipine, procaine, quinine and tetraethylammonium inhibited KCl- and methacholine-induced contractions. These data suggest that the closure of large Ca2+-dependent K+ channels can potentiate KCI- and methacholine-induced contraction. The effects of 4-aminopyridine on the mouse trachea reflect chiefly activation of muscarinic receptors. Procaine, quinine and tetraethylammonium inhibit depolarization-induced and receptor-mediated contractions of the mouse-isolated trachea.

Further evidence for central histamine H2-receptor involvement in the hypotensive effect of clonidine in the rat.

In urethane-anaesthetised rats, the administration of the specific histamine H2-receptor antagonist metiamide intracerebroventricularly (i.c.v.) raised the blood pressure and increased the heart rate. Metiamide (i.c.v.) antagonised the hypotensive effect of clonidine (i.c.v.) in an apparently competitive manner. 4-Methylhistamine i.c.v. did not significantly change the blood pressure. The results are consistent with the concept that the hypotensive effect of clonidine is at least partly due to a stimulation of cerebral H2-receptors. The existence of cerebral H2-receptors mediating hypotensive effects is supported by the hypertensive effect of metiamide but not by the lack of hypotensive effects of 4-methylhistamine.

Cardioventilator effects of TRH in anaesthetized rats: role of the brain stem.

Cardioventilator responses were studied in anaesthetized rats after injections of TRH into either the lateral (i.c.v. lat) or the fourth (i.c.v. IV) cerebral ventricles. TRH induced a more rapid hypertensive effect i.c.v. IV than i.c.v. lat. Blocking of the cerebral aqueduct abolished the hypertensive and tachypnoeic effects of TRH i.c.v. lat but not those of TRH i.c.v. IV. It is concluded that TRH increased blood pressure and ventilation rate via brain stem structures close to the fourth ventricle.

Econazole, miconazole and SK & F 96365 inhibit depolarization-induced and receptor-operated contraction of guinea-pig isolated trachea in vitro.

Econazole, miconazole, SK & F 96365 and nifedipine inhibited Ca2+- and depolarization-induced and receptor-operated contraction of guinea-pig isolated trachea. Econazole, miconazole and SK & F 96365 inhibited histamine- and methacholine-induced tracheal contraction more than nifedipine. Nifedipine was more potent in inhibiting KCl-induced contraction. Nifedipine, salbutamol and theophylline, but not econazole, miconazole or SK & F 96365, relaxed KCl, histamine-, and methacholine-precontracted trachea. It appears that in the guinea-pig tracheal smooth muscle, econazole, miconazole and SK & F 96365 behave differently from nifedipine, theophylline and salbutamol. Econazole, miconazole and SK & F 96365 are thus introduced as novel antagonists of receptor-operated airway smooth muscle contraction.

Receptor binding of fluorinated histidine analogs of thyrotropin-releasing hormone in various regions of the rat brain.

Binding properties of [4(5)-fluoro-imidazole-His2]-TRH (4(5)-F-TRH), [2-trifluoromethyl-imidazole-His2]-TRH (2-CF3-TRH) and [4(5)-trifluoromethyl-imidazole-His2]-TRH (4(5)-CF3-TRH), three novel TRH analogs, have been evaluated in rat pituitary, hypothalamus, brainstem and cortex tissue. 4(5)-F-TRH, previously shown to elicit arterial pressor responses and prolactin release similar to those of TRH, binds to TRH receptors with low, micromolar affinity (Ki = 7.5-13.5 microM). 2-CF3-TRH, an analog of less cardiovascular but increased prolactin-releasing activity, shows Ki values of 3.3-4.9 microM. 4(5)-CF3-TRH, which shows comparable biological activity to 2-CF3-TRH, demonstrates a binding affinity which is virtually nonspecific (Ki = 0.39-1.01 mM). It is therefore concluded that the biological effects of these analogs are mediated either through low affinity TRH binding sites not recognized by [3H][3Me-His2]-TRH or through mechanisms not involving TRH receptors as such.

The long-term effects of oral and transdermal postmenopausal hormone replacement therapy on nitric oxide, endothelin-1, prostacyclin, and thromboxane.

OBJECTIVE: Oral postmenopausal hormone replacement therapy (HRT) decreases the risk of cardiovascular disorders, but the mechanisms of this protection are largely unknown. We compared the long-term effects of sequential oral HRT and transdermal HRT on vasodilatory nitric oxide and prostacyclin as well as vasoconstrictive endothelin- and thromboxane A2, all of which may be factors in the protective effect of HRT against cardiovascular disorders. DESIGN: Prospective, randomized study. SETTING: Department of Obstetrics and Gynecology at a university hospital. PATIENT(S): Fifty-two healthy postmenopausal female nonsmokers (n = 42) or smokers (n = 10) who had climacteric symptoms. INTERVENTION(S): The women received either oral HRT (2 mg of estradiol on days 1-12, 2 mg of estradiol plus 1 mg of norethisterone acetate on days 13-22, and 1 mg of estradiol on days 23-28; n = 21) or transdermal HRT (50 microg/d of estradiol on days 1-28 followed by 250 microg/d of norethisterone acetate on days 14-28; n = 21) for 1 year. Ten female smokers received transdermal HRT for 1 year. MAIN OUTCOME MEASURE(S): Plasma levels of nitrate as an index of nitric oxide production, endothelin-1, and urinary output of the prostacyclin metabolite (2,3-dinor-6-keto-PGF1alpha) and that of the thromboxane A2 metabolite (2,3-dinorthromboxane B2) were measured before and during the combined phases of the 2nd, 6th, and 12th treatment months. RESULT(S): Both regimens increased plasma estradiol levels and alleviated vasomotor symptoms. Neither regimen caused significant changes in nitrate, endothelin-1, prostacyclin, or thromboxane A2 in nonsmoking women. Female smokers had significantly higher levels of endothelin-1, which were significantly reduced by transdermal HRT at 6 months of treatment. CONCLUSION(S): Nitric oxide, endothelin-1, prostacyclin, and thromboxane A2 are not of primary importance in the protective effect of sequential oral HRT against cardiovascular disorders in otherwise healthy nonsmoking postmenopausal women. In this regard, transdermal HRT appears comparable to oral HRT. Postmenopausal female smokers have high levels of endothelin-1 that are reduced by transdermal HRT.

Serotonergic involvement in the cardiovascular stimulation by thyrotropin-releasing hormone (TRH) in anesthetized rats.

The cardiovascular effects of intracerebroventricularly administered thyrotropin-releasing hormone (TRH) were studied in anesthetized rats in the presence of serotonin (5-HT) depletion induced by pretreatments with p-chloroamphetamine (PCA) or p-chlorophenylalanine (PCPA). After PCA the reduction of the whole brain 5-HT and 5-HIAA (5-hydroxy-indoleacetic acid) was 53% and 32% of control, respectively. PCPA reduced the brain 5-HT and 5-HIAA levels even to a greater extent, corresponding levels were 9% and 17% of control. TRH 1-100 nmol/kg increased dose dependently blood pressure and heart rate. PCPA pretreatment significantly attenuated the pressor effect and the tachycardia induced by TRH, whereas PCA did not modify the effects of TRH, which may be related to its weaker capacity to deplete 5-HT in TRH sensitive brain areas. These results suggest the involvement of the central serotonergic system in the TRH-induced cardiovascular stimulation.