Hypothalamic control of prolactin and growth hormone secretion in different vertebrate species

Abstract

Pituitaries from different vertebrates representing mammals, birds, reptiles, and amphibians, were incubated in vitro with various hypothalamic extracts (HE). Prolactin and growth hormone (GH) in medium and pituitary were measured by densitometry after polyacrylamide gel electrophoretic separation (PAGE). Rat ( Rattus norvegicus), chicken ( Gallus domesticus), terrapin ( Chrysemys picta), and toad ( Xenopus laevis) pituitaries were incubated with homologous HE. Rat HE inhibited prolactin release. In the other species the HE stimulated prolactin release. In all four species GH release was stimulated by HE. The effects on prolactin and GH release were proportional to the dose of HE added. Chicken pituitaries were incubated with chicken HE together with rat HE. The rat HE inhibited the chicken HE-stimulated release of prolactin, as measured by radioimmunoassay. Heterologous incubations were used to test HE for prolactin releasing and inhibiting factors and for GH releasing and inhibiting factors. Chicken pituitaries were incubated with HE from the eel ( Anguilla anguilla), the cod ( Gadus gadus) and the flounder ( Pleuronectes flesus) as well as from the other species listed. Both cod and flounder HE marginally inhibited autonomous chicken prolactin release. HE from these species dose-responsively inhibited chicken HE-stimulated prolactin release. Cod HE also inhibited chicken HE-stimulated GH release. HE from the eel, the terrapin and the toad stimulated chicken prolactin release. Hormone release from terrapin and toad pituitaries incubated with heterologous HE was consistent with hypothalamic control via releasing factors in these species.