Modulation of serum and pituitary luteinizing hormone bioactivity by androgen in the rat.

The biological and immunological activities of serum and pituitary LH were analyzed in normal and castrated rats using the rat interstitial cell testosterone assay and RIAs for intact rat LH (rLH), rLH alpha, and rLH beta. After castration, the bioactivity to immunoactivity ratio of both serum and pituitary LH decreased by about 50% between the 5th and 25th days and returned to normal by 60 days. This decrease in the bioactivity to immunoreactivity ratio of LH in castrated males was not due to increased subunit production and was prevented by the administration of testosterone propionate (50 micrograms/day) from the time of castration. These observations indicate that androgens of their metabolites modify the bioactivity of the circulating and stored forms of the LH molecule.

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