Pituitary‐dependent expression of the testicular angiotensin II receptor and its subtypes in rats

Angiotensin II (AT 2 ) has been implicated in the growth and/or differentiation of its target tissues. In the present study, testicular AT 2 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 AT 2 receptors were labelled with 125 I-[Sar 1 ,Ile 8 ] AT 2 and differentiated into its subtypes (AT 1 and FAT 2 ) according to their susceptibility to AT 1 (losartan, 5 μM) and AT 2 (CGP42112B, 1 μM) 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 AT 1 receptors. Both human chorionic gonadotrophin and human menopausal gonadotrophin decreased testicular AT2 receptor concentration, whereas growth hormone did not affect AT 2 receptor expression. Northern blot analysis revealed both testicular AT 1 and AT 2 receptor mRNA expression to be significantly increased after hypophysectomy and reduced by gonadotrophin treatment. These results suggest that the expression of testicular AT 2 receptors is regulated by pituitary gonadotrophins and that AT 2 may play a role in testicular growth and/or differentiation.