Temporal Relationship Between Serum LH Levels and Oocyte Maturation in Prepubertal Rats Injected with Pregnant Mare's Serum Gonadotropin¹,²

Abstract

Follicular oocytes were examined at various time intervals preceding ovulation in immature rats injected with 10 IU pregnant mare's serum goriadotropin (PMS) on the morning of day 30. A dose of 10 IU PMS was shown to give a physiological number of ova in the oviducts on the morning of day 33. Serum LH levels were determined with a radioimmunoassay and were found to increase on the afternoon of day 32. The earliest detectable change in the process of ovum maturation, viz. loss of the germinal vesicle and the nucleolus, occurred 2–3 hr after the increase in serum LH. This time relationship is very similar to that reported earlier for adult cycling rats. It is concluded that the PMS-injected immature rat is a suitable experimental animal for studies aimed to further elucidate the ovarian mechanisms triggering the resumption of the meiotic division of the follicular oocytes before ovulation. (Endocrinology95: 1762, 1974)