Biology of Reproduction, Vol 23, 621-627, Copyright © 1980 by Society for the Study of Reproduction

Interrelationships Between Follicular Fluid Steroid Levels, GonadotropiC Stimuli, and Oocyte Maturation During Preovulatory Development of Porcine Follicles

¹ Animal Research Institute, Ottawa, Ontario, Canada K1A 0C6
² Department of Obstetrics and Gynecology and Department of Physiology, University of Western Ontario, London, Ontario, Canada N6A 5A5
³ Department of Animal Science, Macdonald Campus of McGill University, Ste. Anne de Bellevue, Quebec, Canada H9X 1C0

Prepubertal gifts were treated with 750 IU pregnant mare serum gonadotropin (PMSG) and 72 h later with 500 IU human chorionic gonadotropin (hCG) to induce follicular growth and ovulation. Laparotomies were carried out on groups of four or five gilts 24, 48, 72, 76, 88, 96, 102, or 108 h after PMSG treatment, and follicular fluid (FF) was aspirated from developing follicles. In most cases FF collected from each ovary of individual gilts was pooled, and the concentration of estrone (E₁), estradiol-17 (E₂), androstenedione (A), testosterone + 5-dihydrotestosterone (T+DHT), and progesterone (P) in each sample was determined by radioimmunoassay. The FF concentrations of A and T+DHT remained relatively constant throughout the preovulatory development of the Graafian follicle. The FF concentrations of E₁, E₂, and P increased until 72 h after administration of PMSG. Following hCG treatment the FF concentrations of E₁ and E₂ declined rapidly to levels below those observed 24 h after PMSG treatment and remained at these levels, whereas the levels of P remained relatively constant until 30 h after hCG was given and then increased sharply. Resumption of meiosis was first evident by 16 h after injection of hCG and coincided with the decline in FF estrogen concentrations. These results indicate that the microenvironment of the Graafian follicle during preovulatory growth and development undergoes an orderly sequence of changes in steroid hormone concentrations which appear to be modulated by exposure of the developing follicle to gonadotropic stimuli.

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