Noncoordinated expression of luteal cell messenger ribonucleic acids during human chorionic gonadotropin stimulation of the primate corpus luteum

Abstract

In nonfertile cycles, the absolute steroidogenic capacity of the primate corpus luteum, as reflected in the expression of messenger RNA (mRNA) for the progesterone biosynthetic enzymes cytochrome P450 cholesterol side-chain cleavage (P450SCC) and 3 beta-hydroxysteroid dehydrogenase (3 beta-HSD), progressively declines until luteal regression. Despite this progressive loss in luteal cell function, the elaboration of CG by the implanted blastocyst is able to prolong the functional lifespan of the corpus luteum. It was the purpose of this study to investigate the relationship between aging of the primate corpus luteum and the cellular mechanisms by which the decline in luteal cell function is arrested by CG. Corpora lutea were obtained from cynomolgus monkeys on days 11 or 16 of the luteal phase after a 7-day treatment period with increasing doses of human CG (hCG) given intramuscularly beginning on days 5 or 10. Corpora lutea were also obtained from control animals on days 5, 10, 11, and 16 of the luteal phase. Human CG treatment significantly (P < 0.05) elevated both serum progesterone and estradiol levels throughout the treatment period; however, progesterone production in animals treated with hCG late in the luteal phase (days 10-16) steadily declined after the third treatment day. Expression of mRNA for P450SCC and 3 beta-HSD was markedly stimulated (P < 0.05) by hCG treatment early in the luteal phase. However, 3 beta-HSD message levels in corpora lutea from animals treated with hCG on days 10-16 were not different from those of day-16 control corpora lutea, whereas P450SCC mRNA was only minimally stimulated. There was a dramatic (P < 0.05) increase in mRNA levels for the aromatase enzyme and low density lipoprotein receptor in animals given hCG in both the early and the late luteal phase. In conclusion, there appears to be a differential responsiveness of the primate corpus luteum to hCG stimulation dependent upon luteal age. The loss in responsiveness to hCG in terms of maintenance of mRNA levels is reflective of the inability of the late luteal phase corpus luteum for continued progesterone biosynthesis in the face of heightened luteotropic stimulation.