Secretion of Ovarian Inhibin and Its Physiologic Roles in the Regulation of Follicle-Stimulating Hormone Secretion during the Estrous Cycle of the Female Guinea Pig1

Abstract

To characterize inhibin secretion during the estrous cycle in guinea pigs, the concentrations of plasma inhibin, estradiol, progesterone, and FSH were determined. A significant positive correlation was observed between inhibin and estradiol throughout the estrous cycle. Plasma inhibin and estradiol started to increase a few days before ovulation (Day 0 = day of estimated ovulation), and decreased after ovulation. These two hormones remained low during the luteal phase. The immunoreactivity of inhibin alpha, betaA, and betaB subunits was colocalized in the granulosa cells of one or two healthy large follicles in the ovary before ovulation. There was no positive reaction of inhibin alpha and beta subunits in the corpora lutea or other follicles. Ovariectomy resulted in an abrupt decrease in plasma inhibin and a significant increase in plasma FSH. Injection of anti-inhibin serum into adult female guinea pigs induced an elevation in plasma FSH in a dose-dependent manner. This report presents the first description of sequential changes in plasma inhibin and estradiol during the estrous cycle of guinea pigs. Results suggest that inhibin is secreted mainly by granulosa cells of a few healthy large follicles in the ovary and that it plays an important role in the regulation of FSH secretion during the estrous cycle in guinea pigs.

Role of phosphodiesterase in cyclic AMP signaling in cultured rat granulosa cells

“…Estradiol concentrations in the granulosa cell conditioned medium were determined by RIA [16,17]. The intra-coefficients of variation for estradiol determination in this laboratory were less than 9%.…”

Regulatory Role of Inhibin in Follicle-Stimulating Hormone Secretion and Folliculogenesis in the Guinea Pig.

“…In vivo efficiency of the antiserum was ensured by an increase in plasma concentration of FSH after an i.v. injection of the antiserum, and described previously [29].…”

“…Passive immunization against inhibin can increase the secretion of FSH in female guinea pigs [29] as well as in the other animals [14,16,17,21,26]. However, the mechanism that regulates the onset and completion of the compensatory response to hemiovariectomy remains obscure in guinea pigs.…”

Induction of follicular luteinization by equine chorionic gonadotropin in cyclic guinea pigs

“…An in vitro assay indicated that cells of LUFs were more sensitive to hCG (Westfahl, 1993). The possible reason for this might be that the high dose of eCG can destroy or inhibit granulosa cells, which secrete inhibins to regulate the function of FSH (Shi et al, 1999;Ozawa et al, 2001).…”

“…Guinea pigs are a more reliable reproductive model as compared with mice or rats (Silva et al, 1998;Shi et al, 1999;Kulduk et al, 2014;Sun et al, 2014), because they share similarities with humans and large domestic animals in estrous cycles and prolonged pregnancy (van Kan et al, 2009). Guinea pigs, only ovulate a few oocytes (3.6±0.1) in one typical estrous cycle (Suzuki et al, 1993), and the majority of follicles are lost by atresia (Hermreck and Greenwald, 1964) in the four continuous stages (Wang et al, 2010b).…”