Luteinizing Hormone in the Cat. II. Mating-Induced Secretion*

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Abstract
In cannulated female cats, LH concentrations increased within 5 min after mating and usually reached a maximum within 20 min if the animals were limited to a single copulation. The dynamics of such LH release were similar to those observed after the iv injection of gonadotropin-releasing hormone (GnRH). A second mating, 1 h after the first, resulted in a second, similar increase in concentrations of LH without evidence of a priming effect of the first mating on the LH release mechanism. When female cats were permitted to mate at their own pace, copulations were frequent during the first 2 h, with LH release being evident during the first 90 min. However, the copulatory stimulus became ineffective (or nearly so) at inducing LH release when matings continued beyond this period. In all types of cats studied (spontaneous estrous, estrogentreated, intact, and estrogen-treated castrate), the LH response to a single coitus varied considerably and was not correlated with plasma concentrations of estradiol or progesterone. Some intact animals failed to release LH, making it evident that the hormonal conditions which elicited mating behavior were dissociable from those which optimized postcopulatory LH release. Thus, it would appear that other factors may be more important than estradiol in controlling the magnitude of the preovulatory LH surge. We hypothesize that repeated matings trigger episodes of GnRH release and thereby produce cumulative increments in plasma LH concentrations. The possible role of pituitary sensitization to GnRH in this process is discussed. The mechanisms by which the system eventually becomes refractory to the mating stimulus are not defined, but may involve either a decrease in GnRH release or a decrease in the responsiveness of the pituitary gland.