Hormonal changes associated with estrogen induced luteolysis in the pregnant hamster: a reevaluation of the luteotropic complex.

Abstract

Hamsters were injected sc on Day 1 of pregnancy (sperm positive) with 50 micrograms estradiol cyclopentylpropionate (ECP) or peanut oil. On Day 5, serum progesterone (P4) was 10.6 ng/ml in controls vs 3.1 ng/ml after ECP. In the ECP group, serum prolactin (PRL) and follicle stimulating hormone (FSH) did not differ from controls but serum luteinizing hormone (LH) was significantly lower than that of the controls, and usually below the sensitivity of the radioimmunoassay (RIA). After ECP, structural signs of luteolysis (weight and histology) and absence of antral follicles characterized the ovary. Injection of an anti-LH serum on Day 4 halved serum P4 levels on Day 5 in control animals but caused no further lowering of P4 in ECP-treated hamsters. Treatment on Days 1-5 with 1.0 IU hCG or 10 micrograms LH plus ECP on Day 1 restored, by the afternoon of Day 5, serum P4 to the control range (9-10 ng/ml) and antral follicles were now present. The results indicate that a large dose of ECP causes luteolysis by reducing LH levels and reinforce the concept of a luteotropic complex in the hamster with PRL and FSH constituting the minimal components and LH serving as a synergist.