FSH, LH and prolactin levels, ovarian follicular development and ovarian responsiveness to FSH in the Snell dwarf mouse

Abstract

Abstract. The homozygous Snell dwarf mouse is sterile. It has been shown that pituitary hormone levels are low in 3 month old animals except for FSH and LH whose pituitary contents and plasma concentrations are normal. In this study, the pituitary FSH, LH and prolactin (Prl) content, the FSH plasma concentration and the ovarian follicular development of the Snell dwarf mouse were studied at 18, 20, 24, 40 and 80 days of age. Normal mice were also studied at the same age and served as controls. Pituitary FSH was significantly lower in dwarf mice compared with controls during the period days 18 to 30, while plasma FSH was significantly lower during the period days 20 to 80. Pituitary LH was significantly lower in dwarf mice during the period days 18 to 40. In normal mice, pituitary Prl increased with age, but remained consistently low in dwarf mice. The normal number of growing follicles was similar in dwarf mice and controls up to day 30, but thereafter the total number of growing follicles was greater in the controls. In the dwarf mice, the production of antral follicles was low and there were no ovulations. The rates of atresia were similar in the two genotypes. The responsiveness of the dwarf mouse ovary to FSH was then examined. When dwarf and control mice were supplemented with FSH for 5 days starting at 24 days of age, the ovarian and uterine weights increase 6- and 5-fold, respectively, in the dwarf mice, and 2- to 3-fold in the normal mice. When dwarf mice were supplemented with FSH for 4 days starting at 30 to 40 days of age, there was an increase in the total number of growing follicles, a greater number of the more mature classes and a lower rate of atresia compared with untreated dwarf mice. Low FSH levels during the prepubertal period are probably not the sole cause of dwarf mouse sterility. We believe that the dwarf mouse is a good animal model for the study of the role of pituitary hormones in ovarian follicular development.