A vitellogenic hormone with a large and a small form from salmon pituitaries

Abstract

Two subfractions, with molecular weights of 25,000 and 45,000, respectively, were discovered in a fraction of chum salmon ( Oncorhynchus keta) pituitary extract, which was not absorbed on concanavalin A (Con A)-Sepharose. This fraction, designated as Con AI, had been rechromatographed on Con A-Sepharose to assure exclusion of the glycoprotein (Con AII) gonadotropin. The two forms of the Con AI hormone displayed vitellogenic activity in the hypophysectomized winter flounder ( Pseudopleuronectes americanus) as evidenced by their ability to stimulate the uptake of H 3 33PO 4 and [ 3H]leucine into the whole fish ovary and the protein fraction of the ovary, as well as the incorporation of the radioisotopes into the lipophosphoprotein fraction in vivo. The absence of any significant interference from the Con AI vitellogenic hormones in the radioimmunoassay for the salmon Con AII hormone, reinforced by an earlier finding of specificity of action of the latter hormone in the chick testicular radiophosphate uptake and immature trout gonadal cAMP production assays ( D. R. Idler, L. S. Bazar, and S. J. Hwang, 1975a, Endocrine Res. Commun., 2, 215–235), provides strong grounds for the contention that two different types of gonadotropic hormones are elaborated by the chum salmon pituitary.