The influence of mammalian and teleost somatostatins on the secretion of growth hormone from goldfish (Carassius auratus L.) pituitary fragments in vitro.
The effect of various vertebrate somatostatins (SRIF) on basal growth hormone (GH) secretion from goldfish pituitary fragments was studied using an in vitro perifusion system. SRIF-14 caused a rapid and dose-dependent decrease in the rate of GH release from goldfish pituitary fragments. The half-maximal effective dose (ED50) of SRIF-14 was calculated as 1.3 nM following exposure to two minute pulses of increasing concentrations of SRIF-14, whereas the ED50 of SRIF-14 calculated after continuous exposure to sequentially increasing doses of SRIF-14 was 65 nM. This difference suggests that the pituitary fragments were less responsive to SRIF-14 in the latter experiment, possibly as a result of previous exposure to SRIF-14. SRIF-28 was found to be equipotent with SRIF-14 in decreasing basal GH secretion from the goldfish pituitary. In contrast, catfish SRIF-22, a uniquely teleost SRIF isolated from catfish pancreatic islets, did not alter GH secretion. These results provide further support for the hypothesis that SRIF-14 or a very similar molecule functions as a GH release-inhibiting factor in teleosts, indicating that this action of SRIF-14 has been fully conserved throughout vertebrate evolution.