The Lack of Relationship between Luteinizing Hormone Receptors in the Rat Corpus Luteum and the Critical Need for Luteinizing Hormone in the Luteotropic Process*

Publisher Website
Google Scholar
Abstract
To see if the apparently crucial need for LH as a luteotropin (LH dependency) or the absence of such a need could be correlated with differences in the characteristics of the LH or PRL receptors in the rat's corpus luteum, the binding of radioiodinated hCG and PRL to homogenates of two kinds of corpora lutea was studied. One was the corpus luteum of the decidual tissue (DT)-bearing pseudopregnant rats; it apparently becomes LH dependent on day 9, since the injection of a specific antiserum to LH (LHAS) into such rats on but not before day 9 (day 1 = ovulation) induces luteolysis. The other was the corpus luteum of rats that had been hypophysectomized and pituitary autotransplanted on day 2; it apparently is LH independent, since LHAS treatment of such rats does not induce luteolysis. Corpora lutea from both kinds of rat were collected for receptor measurements on days 5, 9, 10, and 12. In addition, in other groups of these kinds of rat, LHAS or normal horse serum (NHS) as a control was injected on day 9, and the corpora lutea were collected on days 10 and 12 to see the effect of LHASinduced luteolysis in the DT-bearing rats on either kind of receptor. The concentration of progesterone in peripheral blood serum was also measured at each of the times noted in both kinds of rat. There was no difference in the amount of binding of hCG or PRL between the NHS-treated DT-bearing rats and the NHSor LHAS-treated pituitary-autotransplanted rats on any of the 4 days studied. The affinities of the luteal cell receptors for hCG, determined on day 9, were also the same in both kinds of rat. There was no difference in the amount of hCG or PRL binding on any of the 4 days. In the DT-bearing rats, the serum progesterone level fell markedly within 24 h after LHAS treatment. This was accompanied by only a very slight fall in hCG binding 24 h after treatment and by a 50% fall 72 h after LHAS treatment; no change in PRL binding occurred at either interval. There can be little question that a luteolytic response to LHAS indicates LH dependency. Our results show that the absence of a luteolytic response to LHAS is not ascribable to any difference in LH or PRL receptors from those receptors in corpora lutea in which LHAS induces luteolysis. The inability of LHAS to induce luteolysis, therefore, is a reliable indication of the absence of LH dependency. Thus, our findings support the idea that the rat's corpus luteum under certain conditions can secrete progesterone independently of any effect of LH.

This publication has 14 references indexed in Scilit: