Effect of age and COX-2-derived prostanoids on the progression of adult vascular dysfunction in the offspring of diabetic rats.

BACKGROUND AND PURPOSE: The present study was designed to determine how diabetes in pregnancy affects vascular function in their offspring, the influence of age and whether COX activation is involved in this effect. EXPERIMENTAL APPROACH: Relaxation responses to ACh were analysed in mesenteric resistance arteries from the offspring of control rats (O-CR) and those of diabetic rats (O-DR) at 3, 6 and 12 months of age. TxB2, PGE2 and PGF(2α) release were determined by enzyme immunoassay. COX-1 and COX-2 expression were measured by Western blot analysis. KEY RESULTS: O-DR developed hypertension from 6 months of age compared with O-CR. In O-DR, relaxation responses to ACh were impaired in all ages studied and were restored by COX-2 inhibition. TP receptor blockade (SQ29548) restored ACh relaxation in arteries from 3-month-old O-DR while TP and EP receptor blockade (SQ29548 + AH6809) was required to restore it in 6-month-old O-DR. In 12-month-old O-DR, ACh relaxation was restored when TP, EP and FP receptors were blocked (SQ29548 + AH6809 + AL8810). ACh-stimulated TxB2 was higher in all O-DR. ACh-stimulated PGE2 release was increased in arteries from 6- and 12-month-old O-DR, whereas PGF(2α) was increased only in 12-month-old O-DR. COX-2, but not COX-1, expression was higher in O-DR than O-CR. CONCLUSIONS AND IMPLICATIONS: The results indicate an age-dependent up-regulation of COX-2 coupled to an enhanced formation of vasoconstrictor prostanoids in resistance arteries from O-DR. This effect plays a key role in the pathogenesis of endothelial dysfunction, which in turn could contribute to the progression of vascular dysfunction in these rats.

Effects of K+channels inhibitors on the cholinergic relaxation of the isolated aorta of adult offspring rats exposed to maternal diabetes.

Vascular disease has importance in chronic diabetes mellitus but long-term impact of maternal diabetes (MD) on vascular function in the offspring is poorly investigated. This study aimed to examine the alterations produced by MD in K (+) channels activity on endothelium-dependent aortic relaxation induced by acetylcholine (ACh) in adult offspring rats. Diabetes mellitus was induced in female Wistar rats by streptozotocin (STZ; 42 mg/kg, i. p.) injected on the 7 (th) day of pregnancy. Body weights of offspring rats from diabetic mothers (O-DR) were significantly lesser than those of offspring rats from control mothers (O-CR). At 120 days of age, triglyceride but not glucose and cholesterol level was significantly higher in O-DR than in O-CR. In aortic preparations from O-DR, norepinephrine (NE)-induced contractions were significantly higher than those observed in O-CR. In aortic preparations from O-DR precontracted with NE (1 muM), vasorelaxant response to either ACh (0.1, 1 and 10 muM) or sodium nitroprusside (0.1, 1 and 10 nM) was significantly reduced when compared to O-CR. In both groups, vasorelaxant responses to ACh were reduced in the presence of tetraethylamonium chloride and 4-aminopyridine. However, pretreatment with glybenclamide reduced vasorelaxant effects of lowest concentration (0.1 muM) of ACh only in preparations from O-CR. Our results suggest a reduced K (+)(ATP) activity in the cholinergic relaxation of aortic rings of adult offspring born to STZ-diabetic mothers.

Effects of long-term pretreatment with isoproterenol on inotropic responsiveness to alpha-adrenoceptor stimulation: study in isolated perfused rat hearts.

The effects of chronic pretreatment with isoproterenol (5 mg kg(-1)) daily for 10 days on cardiac alpha-adrenergic responsiveness in Langendorff heart preparations were investigated. Isoproterenol pretreatment caused cardiac hypertrophy (29%) as shown by a significant increase in the ratio of ventricular dry weight to body weight. In preparations from isoproterenol-pretreated rats, both maximum increases in left ventricular systolic pressure and heart rate elicited by isoproterenol (10(-12) to 10(-4) M) were significantly reduced (the isoproterenol concentration producing 50% of the maximum positive inotropic and chronotropic responses was enhanced almost 32- and 4-fold, respectively), while the positive inotropic response to phenylephrine (10(-12) to 10(-4) M) was significantly enhanced (the phenylephrine concentration producing 50% of the maximum positive inotropic effect was reduced almost 100-fold), compared with saline-pretreated rats. In preparations from both groups, phenylephrine infusion induced non-significant changes in heart rate and its positive inotropic response was reduced in the presence of propranolol (10(-7) M) in the perfusion medium. Even under beta-adrenoceptor blockade, the curve for the phenylephrine-induced positive inotropic effect remained shifted upward after isoproterenol pretreatment. Chronic isoproterenol pretreatment induces the expected cardiac beta-adrenoceptor desensitization while simultaneously enhancing the positive inotropic responsiveness to phenylephrine in Langendorff heart preparations. These findings support the hypothesis that cardiac alpha1-adrenoceptor stimulation may contribute to the maintenance of myocardial function under conditions in which beta-adrenoceptor function is compromised.

Effects of long-term pretreatment with isoproterenol on bromocriptine-induced tachycardia in conscious rats.

It has been shown that bromocriptine-induced tachycardia, which persisted after adrenalectomy, is (i) mediated by central dopamine D2 receptor activation and (ii) reduced by 5-day isoproterenol pretreatment, supporting therefore the hypothesis that this effect is dependent on sympathetic outflow to the heart. This study was conducted to examine whether prolonged pretreatment with isoproterenol could abolish bromocriptine-induced tachycardia in conscious rats. Isoproterenol pretreatment for 15 days caused cardiac hypertrophy without affecting baseline blood pressure and heart rate. In control rats, intravenous bromocriptine (150 microg/kg) induced significant hypotension and tachycardia. Bromocriptine-induced hypotension was unaffected by isoproterenol pretreatment, while tachycardia was reversed to significant bradycardia, an effect that was partly reduced by i.v. domperidone (0.5 mg/kg). Neither cardiac vagal nor sympathetic tone was altered by isoproterenol pretreatment. In isolated perfused heart preparations from isoproterenol-pretreated rats, the isoproterenol-induced maximal increase in left ventricular systolic pressure was significantly reduced, compared with saline-pretreated rats (the EC50 of the isoproterenol-induced increase in left ventricular systolic pressure was enhanced approximately 22-fold). These results show that 15-day isoproterenol pretreatment not only abolished but reversed bromocriptine-induced tachycardia to bradycardia, an effect that is mainly related to further cardiac beta-adrenoceptor desensitization rather than to impairment of autonomic regulation of the heart. They suggest that, in normal conscious rats, the central tachycardia of bromocriptine appears to predominate and to mask the bradycardia of this agonist at peripheral dopamine D2 receptors.

Cardiovascular effects of the essential oil of Croton nepetaefolius in rats: role of the autonomic nervous system.

Cardiovascular effects of intravenous (i.v.) treatment with the essential oil of Croton nepetaefolius (EOCN) were investigated in rats. Additionally, this study examined the importance of the autonomic nervous system in mediation of the EOCN-induced changes in mean aortic pressure (MAP) and heart rate (HR). In both pentobarbitone-anaesthetised and conscious rats, i.v. bolus injections of EOCN (1 to 50 mg/kg) elicited dose-dependent decreases in MAP and HR. Both decreases were of the same order of magnitude or duration, irrespective of whether the animal was under general anaesthesia. Pretreatment of anaesthetised rats with bilateral vagotomy reduced the magnitude of EOCN-induced bradycardia without affecting hypotension. Likewise, i.v. pretreatment of conscious rats with either methylatropine (1 mg/kg) or hexamethonium (30 mg/kg) significantly decreased the bradycardic effects of EOCN by the same order of magnitude. Neither compound influenced the hypotensive effects elicited by EOCN. This is the first physiological evidence that i.v. treatment with EOCN in either anaesthetised or conscious rats elicits hypotension and bradycardia. EOCN-induced bradycardia appears dependent upon the presence of an intact and functional parasympathetic nerve drive to the heart. However, EOCN-induced hypotension appears independent of the presence of an operational sympathetic nervous system. This suggests that EOCN may be a direct vasorelaxant agent.

Bromocriptine-induced tachycardia in conscious rats: blunted response following isoproterenol pretreatment for 5 days.

Previous studies have shown that tachycardia induced by intravenous injection of bromocriptine, which persisted after adrenalectomy, was mediated by central dopamine D2 receptor stimulation. Such stimulation could activate central sympathetic outflow to the heart. To test this hypothesis, we investigated whether pretreatment with isoproterenol, known to induce cardiac beta-adrenoceptor desensitization, could reduce bromocriptine-induced tachycardia. A 5 day pretreatment with isoproterenol (5 mg/kg/day) induced a 21% increase in the ratio of ventricular dry weight to body weight, compared with saline-pretreated rats. In isolated perfused heart preparations from isoproterenol-pretreated rats, the isoproterenol-induced increase in left ventricular systolic pressure and heart rate was significantly reduced, compared with saline-pretreated rats (the isoproterenol concentration producing 50% of the maximal positive inotropic and chronotropic responses was increased approximately 5- and 4-fold, respectively). In conscious control rats, intravenous injection of bromocriptine (50, 150 and 250 micrograms/kg) decreased mean aortic pressure and increased heart rate in a dose-related manner. Pretreatment with isoproterenol for 5 days reduced bromocriptine-induced tachycardia without affecting hypotension. Cardiac autonomic tone remained of the same order of magnitude irrespective of whether the animal was pretreated with isoproterenol. These results indicate that isoproterenol pretreatment reduces bromocriptine-induced tachycardia mainly through desensitization of cardiac beta-adrenoceptors rather than via an impairment of autonomic regulation of the heart. This supports the hypothesis that bromocriptine-induced activation of central dopamine D2 receptors increases heart rate via activation of central sympathetic outflow to the heart.

Hypotensive action of bromocriptine in the DOCA-salt hypertensive rat: contribution of spinal dopamine receptors.

To assess the role of spinal dopamine receptors in mediation of hypotension induced by systemic administration of the dopamine D2 receptor agonist, bromocriptine, conscious deoxycorticosterone acetate (DOCA)-salt hypertensive rats were pretreated with either intravenous (i.v.; 500 micrograms/kg) or intrathecal (i.t.; 40 micrograms/rat at T9-T10) domperidone, a selective dopamine D2 receptor antagonist that does not cross the blood-brain barrier. In DOCA-salt hypertensive rats, i.v. administration of a sub-maximal dose of bromocriptine (150 micrograms/kg) induced a significant decrease in mean aortic pressure (MAP) which was greater and longer lasting than that in uninephrectomized control rats. Intravenous or i.t. pretreatment with domperidone reduced partially, but significantly, the hypotensive effect of bromocriptine (reduction of about 57% and 45% of the maximal effect, respectively). The remaining responses observed during the 60 min postinjection period were still statistically significant as compared with vehicle injection. In contrast, the bromocriptine-induced hypotension was fully abolished by i.v. pretreatment with metoclopramide (300 micrograms/kg), a dopamine D2 receptor antagonist that crosses the blood-brain barrier, or by combined pretreatment with i.v. and i.t. domperidone. These results suggest that, in DOCA-salt hypertensive rats, the hypotension induced by i.v. bromocriptine is mediated partly through a peripheral D2 dopaminergic mechanism and partly through stimulation of spinal dopamine D2 receptors, has been demonstrated in conscious normotensive rats.

Central dopaminergic origin of bromocriptine induced tachycardia in normotensive rats.

OBJECTIVES: This study was undertaken to investigate the mechanism of the tachycardic effect of bromocriptine, a specific dopamine D-2 receptor agonist, which is not abolished, as previously reported, by intravenous domperidone, a selective dopamine D-2 antagonist unable to cross the blood brain barrier. Two hypotheses were tested: (1) that the increase in heart rate after intravenous treatment with bromocriptine could be related to central dopamine receptor stimulation and (2) that it could be induced by a release of adrenaline from the adrenal medulla. METHODS: Changes in mean aortic pressure and heart rate, induced by treatment with 150 micrograms.kg-1 bromocriptine intravenously, were measured in conscious or anaesthetised normal or adrenalectomised rats submitted to various pretreatments. RESULTS: In conscious intact rats, intravenous bromocriptine decreased mean aortic pressure (-11 (SEM1) mm Hg) and increased heart rate (62(12)) beats.min-1). Both effects were prevented by intravenous pretreatment (0.3 mg.kg-1) with dopamine D-2 receptor antagonists able to cross the blood brain barrier, such as haloperidol, sulpiride, and metoclopramide. In anaesthetised rats, domperidone (50 and 20 micrograms.kg-1) given via a lateral cerebral ventricle abolished the bromocriptine induced tachycardia without affecting the hypotensive response. Both effects were unchanged after bilateral adrenalectomy but were completely abolished by intravenous haloperidol pretreatment (0.3 mg.kg-1) in conscious adrenalectomised rats. CONCLUSIONS: These results suggest that in anaesthetised and conscious normotensive rats, the bromocriptine induced tachycardia is not related to a release of adrenaline from the adrenal medulla but could be elicited by central dopamine D-2 receptor stimulation through a possible increase in cardiac sympathetic tone.