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THE UNUSUAL EFFECT OF GONADECTOMY ON PITUITARY GONADOTROPHINS IN THE MALE BOVINE

Summary.: The concentration of FSH and LH was determined in individual anterior pituitaries of the `intact' (bull) and gonadectomized (steer) male bovine, by differential biological assay methods. The validity of the use of NIH-FSH-ovine and NIH-LH-ovine reference preparations for these bioassays was established. The mean FSH concentration for two groups of bulls was very low: 1·4 µg and 2·1 µg NIH-FSH-S1/mg dry weight. By comparison with male rat anterior pituitary FSH concentration, bull FSH concentration was approximately one hundred times lower, so that the total amounts of FSH in a bull and in a rat anterior pituitary are approximately equivalent. The mean LH concentration for two groups of bulls was rather high: 10·5 and 13·5 µg NIH-LH-S1/mg dry weight. Measured approximately 1 year after gonadectomy, steer anterior pituitary FSH concentration had approximately doubled while the anterior pituitary LH concentration had decreased to less than half that in the `intact' bull. This response of male bovine pituitary LH to the effect of long-term gonadectomy contrasts strikingly with the response of the male rat, in which pituitary LH increases five to tenfold after gonadectomy. These data support the concept of species differences in the mode of regulation of pituitary gonadotrophins.