Role of the pituitary in the effects of tonin on adrenal secretion of the rat.

Chronically catheterized conscious rats were infused intravenously with tonin at 2.4 and 12 micrograms x kg-1 x min-1 for 2 h. Plasma aldosterone concentration (PAC) at the end of the experiment was 11.2 +/- 2.4 ng% in controls, 8.5 +/- 2.8 ng% in rats infused with tonin at the lower rate, and 26.2 +/- 3.6 ng% (p less than 0.01 vs. controls) in rats infused at the higher rate. Plasma corticosterone (PC) was significantly higher (p less than 0.05) in the group infused at the high rate while plasma renin activity (PRA) was significantly reduced in this group of rats. Plasma angiotensin II (AII) concentration was similar in all three groups. PAC was elevated after tonin infusion in the presence of AII blockade. PAC in conscious sodium-depleted rats infused with tonin was not significantly changed, but PRA was significantly reduced (p less than 0.01). In chronically hypophysectomized rats, PAC remained unchanged by tonin infusion. The failure of tonin to stimulate aldosterone in hypophysectomized animals indicates a role of a pituitary hormone (probably ACTH) in the effect of tonin on adrenal secretion.