In vitro responses of rainbow trout (Oncorhynchus mykiss) somatotrophs to carp growth hormone-releasing factor (GRF) and somatostatin.

To study the hypothalamic control of growth hormone (GH) release in lower vertebrates, we employed an in vitro technique using a monolayer cell culture system of rainbow trout pituitary glands. Two newly purified carp brain growth hormone-releasing factors, carp GRF(1-45) and carp GRF(1-29), and synthetic somatostatin-14 (SST-14) were applied to the cultured pituitary cells. The results indicate that: (1) The carp GRFs had a dose-related potency in stimulating growth hormone release. The dose of half maximum effect (ED50) for carp GRF(1-45) was 0.107 nM, and an equal potency for carp GRF(1-29) was 0.388 nM. (2) SST-14 inhibited GH release having a dose-dependent potency with an ED50 of 0.186 nM. (3) Osmotic pressure did not influence SST-14 inhibited GH secretion but did affect spontaneous GH release. (4) The response of cultured cells was not affected by length of incubation period with SST-14 or carp GRF but was affected by cell density.