Luteolysis in the hamster: abrogation by gonadotropin and prolactin pretreatment

The luteolysis which terminated pseudopregnancy (PSP) in superovulated hamsters was studied. Spontaneous luteolysis occurred before 1100 on Day 7 of PSP and was characterized by a rapid decline in circulating progesterone levels. Luteolysis induced by prostaglandin F2 alpha (PGF2 alpha) on Day 5 of PSP displayed a similar rapid reduction in progesterone over 24 hours. In both cases levels of the progesterone metabolite 20 alpha hydroxypregn-4-ene-3-one (20 alpha-OHP) were less than 2 percent of progesterone levels and declined in a manner similar to progesterone. This suggests that conversion of progesterone or its precursors to 20 alpha-OHP was not a functional aspect of luteolysis in the hamster. Pretreatment with either prolactin (PRL), luteinizing hormone (LH) or follicle stimulating hormone (FSH) failed to prevent PGF2 alpha-induced luteolysis on Day 5 in the superovulated PSP hamster. Combinations of PRL and LH, LH and FSH or PRL and FSH were also unsuccessful in abrogating luteolysis. However, pretreatment with a combination of PRL, FSH and LH prevented luteolysis in 11/14 animals. These results suggest that luteotropic agents can reverse the luteolytic effects of PGF2 alpha in the hamster.