Localization of vasopressin-neurophysin and norepinephrine in the supraoptic nucleus of spontaneously hypertensive rats

Role of brain vasopressin in regulation of blood pressure

Using recent advances in brain physiological, neurohistochemical, and molecular biological techniques, it could be demonstrated that the central action of vasopressin (VP) is important in cardiovascular regulation and in the pathogenesis of hypertension. VP is now known to be located in the area of the brain involved in cardiovascular regulation. Furthermore, in various pathophysiological states, brain VP secretion is regulated separately from the peripheral VP secretion system. The role of brain VP in the regulation of the circadian rhythm of blood pressure is becoming a topic of major interest.

Central cardiovascular effects of AVP and ANP in normotensive and spontaneously hypertensive rats

The purpose of the present study was to compare influence of central arginine vasopressin (AVP) and of atrial natriuretic peptide (ANP) on control of arterial blood pressure (MAP) and heart rate (HR) in normotensive (WKY) and spontaneously hypertensive (SHR) rats. Three series of experiments were performed on 30 WKY and 30 SHR, chronically instrumented with guide tubes in the lateral ventricle (LV) and arterial and venous catheters. MAP and HR were monitored before and after i.v. injections of either vehicle or 1, 10 and 50 ng of AVP and 25, 125 and 500 ng of ANP. Sensitivity of cardiac component of baroreflex (CCB), expressed as a slope of the regression line was determined from relationships between systolic arterial pressure (SAP) and HR period (HRp) during phenylephrine (Phe)-induced hypertension and sodium nitroprusside (SN)-induced hypotension. CCB was measured before and after administration of either vehicle, AVP, ANP, or both peptides together. Increases of MAP occurred after LV administration of 1, 10 and 50 ng of AVP in WKY and of 10 and 50 ng in SHR. ANP did not cause significant changes in MAP in both strains as compared to vehicle, but it abolished AVP-induced MAP increase in WKY and SHR. CCB was reduced in WKY and SHR after LV administration of AVP during SN-induced hypotension. In SHR but not in WKY administration of ANP, AVP and ANP + AVP decreased CCB during Phe-induced MAP elevation. The results indicate that centrally applied AVP and ANP exert differential effects on blood pressure and baroreflex control of heart rate in WKY and SHR and suggest interaction of these two peptides in blood pressure regulation at the level of central nervous system.

Effects of beta 1- and beta 2-adrenoceptor agonists applied into the hypothalamic paraventricular nuclei of spontaneously hypertensive rats on urine production

We investigated effects of beta-adrenoceptor agonists (beta 1-selective: T-1583 and dobutamine, beta 2-selective: fenoterol, non-selective: isoproterenol) on urine outflow rate, blood pressure, heart rate, respiratory rate and rectal temperature. The drugs were applied into the paraventricular nuclei (PVN) of spontaneously hypertensive (SHR), Wistar-Kyoto (WKY) and Wistar rats. Fenoterol and isoproterenol markedly decreased the urine outflow rate, compared with T-1583 and dobutamine in the rats. There was no marked difference among the three strains in responsiveness to fenoterol and isoproterenol. The antidiuretic effects of fenoterol were inhibited by a beta 2-selective antagonist, butoxamine, more markedly than a beta 1-selective antagonist, atenolol, in SHR; and the inhibitory effects of these drugs were partial in WKY. In Wistar rats, the effect of fenoterol was inhibited by a non-selective beta-antagonist, timolol, but not by atenolol or butoxamine. A vasopressin antagonist (i.v.) did not diminish the antidiuretic effect of fenoterol. Fenoterol reduced the blood pressure in SHR and WKY, but not in Wistar rats. It was suggested that there were predominantly beta 2-adrenoceptors mediating antidiuresis in SHR. In WKY and Wistar rats, however, the beta-adrenoceptor subtypes mediating antidiuresis have yet to be determined. The ability of beta-adrenoceptor agonists to decrease urine outflow rates in SHR was not altered as compared to that in the control rats. beta-Adrenoceptor-mediated antidiuresis was not due to vasopressin release.

Vasopressin and oxytocin gene expression in the supraoptic and paraventricular nucleus of the spontaneously hypertensive rat (SHR) during development of hypertension

To study the regulation of hypothalamic vasopressin (VP) and oxytocin (OT) gene expression in relation to the development of hypertension, levels of VP mRNA and OT mRNA were determined in spontaneously hypertensive rats (SHR). Differences in VP and OT mRNA content of the supraoptic nucleus (SON) and paraventricular nucleus (PVN) of 4- and 10-week-old SHR and Wistar-Kyoto controls (WKY) were quantitated by dot-blot and Northern blot analysis. VP and OT pituitary content and VP plasma levels were measured by radioimmunoassays. VP mRNA levels were approximately 2-fold and 3-fold higher in the SON and PVN of 4-week-old SHR, respectively, as compared to controls. The OT mRNA levels were approximately 35% lower in both nuclei of the SHR. There was no difference in VP and OT pituitary content between 4-week-old SHR and WKY, but VP plasma levels were higher in SHR. In the 10-week-old SHR VP mRNA levels were still approximately 30-40% higher and the OT mRNA levels were approximately 40% lower in both nuclei when compared to age-matched WKY. Pituitary VP and OT contents were respectively 1.5-fold higher and 20% lower in the 10-week-old SHR than in 10-week-old WKY. VP plasma levels were still elevated in the SHR. The data indicate that in the hypothalamo-neurohypophyseal system of the SHR the VP system is in a higher state of activity, while the OT system is lower in activity.

Abnormalities in hypothalamic and neurohypophysial vasopressin content are not a consequence of hypertension in the spontaneously hypertensive rat

In order to determine if the decreased hypothalamic and increased posterior pituitary content of vasopressin (VP) observed previously in spontaneously hypertensive rats (SHR) were a secondary consequence of the hypertension, the effect of preventing the development of hypertension on VP content of the hypothalamoneurohypophyseal system was evaluated. Two methods for preventing the hypertension were used: (1) chronic angiotensin-converting enzyme inhibition (oral captopril, 100 mg/kg/day at 4-12 weeks of age); and (2) intraventricular 6-hydroxydopamine (6-OHDA, 200 micrograms at 4 and 5 weeks of age). Both of these treatments markedly attenuated the increase in systolic blood pressure in SHRs at 5-11 weeks of age. The captopril-treated rats had a significant elevation in serum renin activity at 12 weeks of age indicating the presence of chronic converting enzyme inhibition, and the 6-OHDA-treatment resulted in a depletion of hypothalamic (86%) and brainstem (76%) norepinephrine content. Hypothalamic VP content was reduced in untreated SHRs compared to normotensive Wistar-Kyoto rats (WKYs, P = 0.0015). It was not significantly altered in either strain by the 6-OHDA treatment. Captopril caused a reduction in hypothalamic VP content in both SHRs and WKYs (P less than 0.01). Posterior pituitary VP content was elevated in untreated SHRs compared to WKYs (P less than 0.001), and remained elevated with captopril and 6-OHDA treatments. These data indicate that the abnormalities in VP content in the hypothalamus and posterior pituitary of SHRs are not a response to the hypertension. Therefore, they may represent primary abnormalities in the SHR.(ABSTRACT TRUNCATED AT 250 WORDS)