Biological and binding activities of pituitary hormones from the ostrich, Struthio camelus

Abstract

Biological and binding activities of adenohypophysial hormones purified from the ostrich (ost), Struthio camelus, were compared to those of the corresponding hormones derived from mammalian and other avian species. The potency of ostrich prolactin was comparable to those of other avian preparations and slightly less active than the ovine hormone when tested in the pigeon crop-sac assay, but ostrich growth hormone (GH) was more potent than several other avian preparations and was comparable to mammalian GH in the rat tibia bioassays. Marked discrepancies were evident in the activities of both ostrich gonadotropins (ostGn) when they were tested in a variety of in vivo and in vitro bioassays and radioreceptor assays (RRAs). Both the ostrich follicle-stimulating hormone (ostFSH) and luteinizing hormone (ostLH) were among the most potent tested thus far in in vivo bioassays for total gonadotropin in a lizard and a cockerel; a high sialic acid content may account for these high potencies. OstFSH was also the most potent nonmammalian Gn tested in two FSH specific mammalian bioassays, an in vivo (ovarian augmentation) and an in vitro (cAMP production) rat bioassay; in fact, ostFSH behaved more like a mammalian than an avian hormone in these assays. However, the binding activity of ostFSH was not unlike that of other avian FSH preparations when tested in either mammalian or nonmammalian FSH-RRA systems. OstLH was more potent than other avian preparations in an in vitro mammalian bioassay, but not in avian or amphibian LH bioassays; species specificity was pronounced among these LH assays. Binding activities of ostLH in mammalian and avian LH-RRAs were generally consistent with potencies in the two species of bioassays. However, a marked discrepancy was apparent in the behavior of ostLH in FSH-RRAs. Although ostLH had very low FSH activity when tested by radioimmunoassay, by bioassay, or by FSH-RRA with avian gonads, it was equipotent to ostFSH in competing for FSH-binding sites on the mammalian gonad; in this respect it was more like turkey than chicken LH. The ability of ostLH to antagonize the biological activities of ostFSH in the stimulation of cAMP by rat seminiferous tubules confirms that ostLH binds to the same functional receptors as FSH on the rat testis, even though it does not induce the characteristic physiological response associated with FSH.