Homologous radioimmunoassay for bullfrog growth hormone

Abstract

Antiserum against bullfrog growth hormone (fGH) was produced by immunizing rabbits with the highly purified fGH obtained from adenohypophyses of adult bullfrogs. Histological studies on bullfrog adenohypophyses revealed that the cells that immunologically reacted with the antiserum against fGH corresponded to the ones positively stained with the antiserum against rat GH. The antiserum together with fGH and 125I-fGH was employed to develop a radioimmunoassay (RIA) for fGH. Several dilutions of plasma and of pituitary homogenate of both adult and larval bullfrogs yielded dose-response curves which were parallel to the standard curve. Ovine prolactin (PRL), and growth hormone (GH); eel and salmon GHs; and bullfrog LH, FSH, TSH, PRL, and neurointermediate lobe homogenate did not react in this assay. Plasma from hypophysectomized bullfrogs had no detectable immunoreactive GH. Pituitary homogenates of Bufo japonicus, Xenopus laevis, and Cynops pyrrhogaster gave inhibition curves which did not parallel the standard. The homologous RIA for bullfrog GH thus developed was applied for the determination of plasma and pituitary GH levels in the larvae and adults. Plasma GH levels were relatively low during preclimax period and rose as metamorphosis progressed. Plasma GH concentrations were maximum in the juvenile frogs and decreased as the animals grew up. Pituitary GH concentrations also increased as metamorphosis progressed. After metamorphosis, pituitary GH concentrations declined as the frogs gained weight. There was no sex difference in plasma and pituitary GH levels in the adult.