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Gonadotropic Activity of Pituitaries from Cows in Different Stages of Pregnancy

University of Wisconsin

Abstract

Current assay methods using laboratory mammals have rated bovine anterior pituitary much lower than other species of farm animals in gonadotropic activity. By intra-muscular implantation of acetone desiccated pituitary powder into immature female rats sufficient ovarian stimulation was obtained to use the results in quantitative studies. Application of this assay method to glands of sheep and cattle showed them to be much more nearly alike in potency than has been shown by other methods. Both the rat implant method and the subcutaneous injection of an aqueous suspension of the pituitary powder into immature cockerels have been used in a study of the changes of the gonad-stimulating activity of cow-pituitaries at different stages of pregnancy. The results indicate that the gonadotropic hormone content is higher at the beginning of pregnancy than it is at later stages (Table 1). The apparent rate of decline during pregnancy varies with the particular assay method used. Basically however it is probably brought about by an increasing action of some inhibitory agent such as estrogen secreted by the placenta.