Need of luteinizing hormone for early pregnancy in the golden hamster (Mesocricetus auratus).

Hypophysectomy performed at any stage of pregnancy has been reported to be deleterious for maintenance of gestation in the hamster (Greenwald, 1967). On the basis of his observation that a combination of follicle stimulating hormone (fsh) and prolactin could maintain pregnancy in hypophysectomized pregnant hamsters, Greenwald (1967) suggested that the luteotrophic complex in this animal is made up of fsh and prolactin. Luteinizing hormone (lh), however, has been shown to promote progesterone synthesis in a wide variety of species including the rat (Kilpatrick, Armstrong & Greep, 1964; Armstrong & Black, 1966; Savard, Marsh &Rice, 1965). Recently, it has been shown that neutraliza¬ tion of endogenous lh in the pregnant rat by administration of a highly specific lh antiserum results in termination of gestation in this species (Madhwa Raj, Sairam & Moudgal, 1968; Madhwa Raj & Moudgal, 1970). It was therefore considered of interest to study the effect of lh antiserum on pregnancy in the hamster. The following is a preliminary account of such a study. Colony-bred hamsters, weighing 100 to 120 g, were mated to proven males and the first day on which spermatozoa were found in the vagina was taken as Day 1 of pregnancy. Before starting the treatment, hamsters were subjected to exploratory laparotomy on Day 6 of pregnancy and only those which showed normal numbers of implantation sites were used for further experimentation. Autopsies were performed at various stages of pregnancy and the nature and number of implantation sites were noted. The details of the immunization schedule and the characterization of the antiserum have been reported earlier (Madhwa Raj & Moudgal, 1970). The rabbit antiserum to ovine lh, absorbed free ofantibodies to normal sheep serum proteins, could neutralize the lh activity of hamster pituitary extracts as assayed by the ovarian ascorbic acid depletion test. Incubation of undiluted lh antiserum with 125I-labelled highly purified ovine lh, fsh or prolactin resulted