Stimulation by angiotensins I and II of ACTH release from goldfish pituitary cell columns

Dispersed, superfused goldfish anterior pituitary cell columns were stimulated with pulses of salmon angiotensin I (sAI), human angiotensin I (hAI), and human angiotensin II (hAII). Human AII stimulated the greatest release of ACTH. The dose-response curves for hAI and sAI were similar and revealed that hAI and sAI were about one-tenth as potent as hAII in stimulating ACTH release. In mammals, AI must be converted to AII in order to stimulate ACTH release. In goldfish, the angiotensin-converting enzyme inhibitor captopril, which inhibits the conversion of AI to AII, was not able to block sAI-stimulated ACTH release. This finding suggests that the angiotensin receptor of the goldfish corticotrope is less discriminating than that of the mammalian corticotrope and recognizes both AI and AII. This hypothesis was supported by the observation that sarcosine analogs of AII, which block AII-stimulated ACTH release in mammals, failed to block hAII-stimulated ACTH release in goldfish. Saralasin showed negligible, [Sar1,Thr8]-AII slight, and [Sar1, Ile8]-AII moderate, intrinsic ACTH-releasing activity. These findings suggest that the ACTH-releasing activity of angiotensin appeared early in the evolution of the vertebrate pituitary.