Luteotropic Complex of the Hamster

Abstract

Hypophysectomy, at any stage of pregnancy, interrupted gestation in the hamster. Pituitary removal at day 1, 4 or 8 of pregnancy resulted in rapid regression of the corpus luteum (CL), whereas after day 12, when the placenta has been established, the histologic integrity of the CL was maintained. After hypophysectomy at day 4 of pregnancy, the daily injection of prolactin, but not FSH [follicle-stimulating hormone] or LH [luteinizing hormone] maintained the CL as a histologic entity, but pregnancy was terminated. Treatment with prolactin and FSH increased the vascularity of the CL and maintained pregnancy in the majority of animals; hence, the concerted interaction of these 2 hormones constituted the minimal luteotropic complex (LtH) of the hamster. Evidence is presented that the activity of FSH cannot be attributed to contamination with LH. The addition of exogenous LH to the LtH complex had dose-dependent effects in hamsters hypophysectomized on day 4 of pregnancy. High daily doses of LH (50-100 [mu]g) interrupted pregnancy in all animals and led to a marked increase in ovarian weight due to excessive development of the interstitium. On the other hand, low doses of LH (1 or 10 [mu]g) increased the size of the CL, increased the number of antral follicles and did not interfere with the pregnancy-maintaining activity of the LtH complex. A single injection of estradiol cyclopentylpropionate (ECP) along with daily injection of the LtH com?lex maintained pregnancy at day 8 in hypophysectomized hamsters and also increased the size and hyperemia of the CL. However, ECP alone or combined with prolactin did not maintain pregnancy. Following hypophysectomy at day 12 of pregnancy, treatment with only FSH was necessary to maintain pregnancy until term. Thus, the hamster represents a transitional stage between species which rely exclusively on the pituitary for LtH activity during pregnancy and those which ultimately shift to placental sources.