Comparison of the Luteolytic Action of LH and Estrogen in the Hamster

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Abstract
Luteal morphology and maintenance of decidual cell response (DCR) or pregnancy were used as end-points in evaluating the effects of bovine luteinizing hormone (NIH-LH-B3) on the corpora lutea (CL) of the hamster. Daily treatment for 5 days with 20 to 100 [mu]g of LH induced luteal regression in pseudopregnant and pregnant animals. However, 50 [mu]g of LH also caused hyperplasis and hypertrophy of the ovarian interstitium which resulted in a positive DCR in pseudopregnant animals despite the involution of the CL. One hundred [mu]g of LH consistently induced ovulation in pseudopregnant and occasionally in pregnant animals. The CL resulting from new ovulations were nonfunctional. FSH [follicle-stimulating hormone], prolactin or a combination of FSH and prolactin did not induce luteolysis. The luteolytic effect of 100 [mu]g of LH was counteracted by prolactin, but not FSH. The ratio of exogenou prolactin and LH was critical for the preservation of the CL. Treatment with combinations of prolactin and LH in ratios of 2.5, 10 and 20 preserved CL in 37.5, 66.7 and 100% of animals, respectively. A single injection of 100 [mu]g of estradiol cyclopentylpropionate or 10-100 [mu]g of estrone consistently induced luteal regression. The luteolytic effect of estrogen was completely reversed by FSH, but not by prolactin. These results, in conjunction with previous studies, suggest that LH exerts a luteolytic effect directly on the functional CL of the hamster. Estrogen exerts its luteolytic action indirectly, by preventing the secretion of FSH which is a component of the luteotropic complex of the hamster.