Ablation of the area postrema in rats prevents sustained hypertension during angiotensin II infusion and after unilateral renal artery constriction (two-kidney, one clip hypertension). The current ...experiment was performed to determine whether an intact area postrema is required for hypertension development in a low renin model of experimental hypertension in rats. In 11 rats, the area postrema was destroyed using electrical current; the extent and specificity of each lesion was confirmed later by blind histological analysis. In 12 rats, sham operations were performed. All rats were uninephrectomized and drank saline. During once-weekly injections of deoxycorticosterone pivalate (5 mg/wk) for 4 weeks, sham-operated rats (n = 10) showed a significant increase in mean arterial pressure (Days 6-28) and saline intake (Days 12-28), but no significant increase in sodium or water retention. Deoxycorticosterone-treated rats with area postrema ablation (n = 9) exhibited no change in arterial pressure, sodium retention, or water retention, but a significant increase in saline intake (Days 17-28). Plasma renin activity was equally suppressed in both groups of rats. The depressor response to ganglion blockade with hexamethonium (20 mg/kg i.v.) was significantly increased during the 2nd, 3rd, and 4th weeks of steroid treatment in sham-operated, but not area postrema-ablated, rats. Four rats (2 sham-operated; 2 ablated) showed no change in any variable over 28 days in the absence of steroid treatment. It is concluded that the area postrema may be important in some non-angiotensin-dependent forms of experimental hypertension, possibly by affecting neurogenic control mechanisms.
It has been hypothesized that moderately increased blood levels of arginine vasopressin (AVP) contribute to the development and/or maintenance of hypertension. In this study, male Sprague-Dawley rats ...on a fixed 1 meq daily sodium intake received 10-day intravenous infusions of 0.2 and 2.0 ng.kg-1.min-1 AVP. The higher infusion rate was above the acute vasoconstrictor threshold for AVP administration and also produced a maximal antidiuretic effect. During chronic AVP administration, however, daily mean arterial pressure, heart rate, and body fluid composition were not changed, despite a maintained antidiuresis. To test the hypothesis that circulating AVP failed to cause hypertension as a result of sensitization of the baroreflex or a direct sympathoinhibitory effect of the peptide, additional experiments were performed in rats subjected to sinoaortic denervation (SAD) or ablation of the area postrema (APX). Infusion of AVP for 10 days into SAD or APX rats caused a sustained antidiuresis but did not change arterial pressure, heart rate, or body fluid composition. In all groups of rats, the depressor response to ganglionic blockade (20 mg/kg hexamethonium) was used to estimate the autonomic component of resting arterial pressure; no change in autonomic cardiovascular control was found using this method in any of the groups during AVP infusion. Long-term elevation of plasma AVP in rats, therefore, does not cause hypertension or significantly affect autonomic regulation of arterial pressure.
Two nodule cDNA clones representing genes involved in Alnus glutinosa nitrogen metabolism were analysed. ag11 encoded glutamine synthetase (GS), the enzyme responsible for ammonium assimilation, ...while ag118 encoded acetylornithine transaminase (AOTA), an enzyme involved in the biosynthesis of citrulline, the nitrogen transport form in Alnus. GS mRNA was found at highest levels in root nodules, where it was present in the infected cells as well as in the cells of the pericycle of the vascular system. AOTA transcripts were found at high levels in nodules, confined to the infected cells, suggesting that in nodules of A. glutinosa, citrulline biosynthesis takes place mainly in the infected cells.
A series of new 1,3-dimethyl-7-phenylalkyl-8-3-(4-phenyl-1-piperazinyl)propylamino-purine-2,6-dione derivatives (10-16) was synthesized and their 5-HTIA and 5-HT2A receptor affinities were ...determined. It was found that compounds with the phenylpropyl substituent in position 7 of purine-2,6-dione (12, 14 and 16), or with phenylmethyl in position 7 and 2-OCH3 in the phenylpiperazine part (13) showed a distinct affinity for 5-HTIA receptors (Ki = 8-50 nM). No structural modifications resulted in 5-HT2A ligands, since the affinity of 10-16 for those receptors was insignificant (Ki = 115-550 nM). The new 5-HT1A receptor ligands (12-14, 16) were investigated in vivo to determine their functional activity at those receptors. In behavioral studies, 12-14 and 16 behaved like postsynaptic 5-HTIA receptor antagonists, since they reduced lower lip retraction and the behavioral syndrome induced by 8-OH-DPAT (5-HT1A receptor agonist) in rats. When given alone, none of the compounds investigated in vivo, mimicked 8-OH-DPAT activity in those tests. Derivative 12 did not affect the body temperature in mice, whereas 13, 14 and 16 decreased it. Furthermore, 12 did not change the hypothermia induced by 8-OH-DPAT, and the decrease in body temperature in mice induced by 13, 14 or 16 was not antagonized by WAY 100635 (5-HT1A receptor antagonist); hence in that model neither 12, 13, 14 nor 16 acted as antagonists or agonists, respectively, at presynaptic 5-HT1A receptors.
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