1. The regulation of angiotensin I1 (AII) receptor subtypes was studied in peripheral tissues of 20 week old male spontaneously hypertensive rats (SHR) and age-matched normotensive Wistar-Kyoto (WKY) rats.2. A11 receptor binding was determined by a quantitative in vitro autoradiography using [125I]-[Sar1,Iles]AII as a ligand on the kidney, adrenal gland, thoracic aorta and heart. CV-11974, a specific AT1 receptor antagonist, and CGP42112B, a specific AT2 antagonist, were used in competition with [125I]-[Sarl,Iles]AII to differentiate AT1 and AT2 receptor binding.3. The relative abundance of each subtype was very similar between SHR and WKY rats. In both strains of rats, the adrenal cortex contained predominantly AT1 receptors, while AT2 receptors predominated in the adrenal medulla. The kidney contained exclusively AT1 receptors over glomeruli, proximal tubules and outer medulla. AT1 receptors were predominant in the thoracic aorta and heart. 4.As for relative receptor density, important differences were observed between SHR and WKY rats. In SHR, the adrenal cortex, outer medulla of the kidney, and heart displayed higher AT1 receptor density than WKY rats. 5.These results indicate that the expression of AT1 receptors is differently regulated in some important targets of A11 in SHR, and suggest that the altered regulation of AT1 receptor presented in this study should be relevant to the pathophysiological features of SHR.

Inhibition of angiotensin (Ang) II type 1 (AT1) receptors in various target tissues of adult Sprague-Dawley rats was studied after single oral administration of TCV-116. The effects of TCV-116 on Ang II-receptor binding were assessed by quantitative in vitro autoradiography using 125I-[Sar1,Ile8]Ang II as a ligand. Four hours after the administration of TCV-116 (1 mg/kg), Ang II-receptor binding was markedly inhibited in the kidney (20% of control), adrenal cortex (27%), thoracic aorta (57%), heart (55%) and testis (76%) where AT1 receptors predominate. In the brain, orally administered TCV-116 produced a significant inhibition of binding both to the circumventricular organs (38%), which are devoid of the blood-brain barrier (BBB), and to the discrete regions within the BBB such as the paraventricular hypothalamic nucleus (48%), nucleus of the solitary tract (60%). Twenty-four hours after the administration, Ang II-receptor binding had partly recovered to approximately 50-85% of control levels. In contrast, throughout the experimental period, Ang II-receptor binding was little affected in sites where Ang II type 2 (AT2) receptors predominate such as the adrenal medulla and the nucleus of the inferior olive. These data indicate that orally administered TCV-116 specifically binds to AT1 receptors both in peripheral tissues and the central nervous system.

Angiotensin II (AT2) has been implicated in the growth and/or differentiation of its target tissues. In the present study, testicular AT2 receptor and its subtypes in hypophysectomized rats were examined using quantitative in vitro autoradiography and Northern blot analysis in an attempt to determine possible involvement of pituitary hormones in their expression. Prepubescent (3 weeks of age) male Sprague-Dawley rats underwent hypophysectomy or sham operation. From 10 days thereafter, they were treated with vehicle, growth hormone, human chorionic gonadotrophin or human menopausal gonadotrophin for 10 days. Testicular AT2 receptors were labelled with 125I-[Sar1,Ile8] AT2 and differentiated into its subtypes (AT1 and FAT2) according to their susceptibility to AT1 (losartan, 5 microM) and AT2 (CGP42112B, 1 microM) antagonists. Hypophysectomy led to a marked increase in AT2 receptor concentration (sham-operated rats: 0.7 +/- 0.2 fmol/mg protein, hypophysectomized rats: 2.5 +/- 0.6 fmol/mg protein, mean +/- SEM, n = 11-12, p < 0.01) with predominant occurrence of AT1 receptors. Both human chorionic gonadotrophin and human menopausal gonadotrophin decreased testicular AT2 receptor concentration, whereas growth hormone did not affect AT2 receptor expression. Northern blot analysis revealed both testicular AT1 and AT2 receptor mRNA expression to be significantly increased after hypophysectomy and reduced by gonadotrophin treatment. These results suggest that the expression of testicular AT2 receptors is regulated by pituitary gonadotrophins and that AT2 may play a role in testicular growth and/or differentiation.

The study results indicated that raloxifene can transiently reduce the levels of bone metabolism markers and might be useful for preventing fractures in postmenopausal women with end-stage renal failure, although raloxifene use over the long term may not have adequate efficacy in the absence of appropriate concomitant active vitamin D therapy.

We examined the responses on blood pressure when the renal vasoactive system such as renin-angiotensin-aldosterone system (RAAS) and kallikrein-kinin system (KKS) was activated by dietary salt restriction in the congenitally bilateral hydronephrotic rat (BHN). In a low salt diet (LS)-normotensive and normal kidney control rats after 8 weeks from initiating dietary salt restriction, the plasma sodium concentration (PNa) was retained at a level similar to that in the normal diet (ND)-control rats, and plasma renin activity (PRA), plasma aldosterone concentration (PAC) and urinary kallikrein activity (UKA) were about 1.8-, 9.4- and 1.7-fold higher, respectively, than those in the ND-control rats. In addition, LS-control rats had a significantly (p < 0.001) high systolic blood pressure (163 ± 2.0 mm Hg) compared with that (136 ± 5.8) of ND-control rats. These results suggest that the activated renal vasoactive system acted for not only sodium retention but also for elevation of blood pressure in LS-control rats. In LS-BHN at week 8, PNa was also retained at a nearly normal level. However, the renal vasoactive system activation for sodium retention was higher than that of LS-control rats; that is, increase of PRA, PAC and UKA were about 3.8-, 24.7- and 10.0-fold, respectively, than in ND-BHN. The higher activation of RAAS, nevertheless, does not affect blood pressure in BHN; that is, both hypertension of BHN fed LS and ND developed similarly. These findings suggest that dietary salt restriction could markedly activate the renal vasoactive system for sodium retention without elevating blood pressure in BHN different from control rats.