In Vitro Simulation of Prepubertal Changes in Pulsatile Luteinizing Hormone Release Enhances Progesterone and 17β-Estradiol Secretion from Immature Rat Ovaries*

Publisher Website
Google Scholar
Abstract
Changes in the episodic pattern of LH [luteinizing hormone] secretion in female rats as they approach 1st ovulation were previously demonstrated. Ovaries were taken from peripubertal rats and perifused in vitro with a medium containing FSH and LH. The concentration of FSH in the medium was kept constantly low; the concentration of LH was modulated, simulating as closely as possible the various episodic secretory profiles previously observed in vivo. Medium from the perifusion chambers were collected every 10 min for 5 h and assayed for progesterone (P) and 17.beta.-estradiol (E2). Exposure of the ovaries to low amplitude LH pulses (20 ng/ml; comparable to those found in the plasma of peripubertal rats during the morning) did not elicit a significant steroidogenic response. Exposure to large amplitude LH pulses (80 ng/ml; as seen during the afternoon) led to a marked increase in the output of both P and E2. Similarly, increased steroid secretion occurred when ovaries were exposed to a 2 h minisurge of LH (160 ng/ml) or to a minisurge preceded by 3 large amplitude pulses (as seen in some animals during the afternoons of the peripubertal period). Continuous exposure to LH at concentrations similar to either the large amplitude pulses or the LH minisurge increased P and E2 release. The increase was not significantly larger than that produced by the discontinuous LH perifusion patterns, even though the total amount of LH reaching the ovaries during the 5 h perifusion period was considerably greater. Apparently. episodic LH secretion is functionally much more efficient at eliciting release of P and E2 from immature ovaries than in continuous LH secretion. Evidently, changes in the LH secretory pulse patterns, as seen in vivo close to the time of puberty, are fundamental for the activation of ovarian steroidogenesis that leads to the 1st preovulatory surge of gonadotropins.