Development of Neural Regulation of Follicle Stimulating Hormone (FSH) Secretion

Abstract

Hypothalamic follicle stimulating hormone releasing factor (FSHRF) content, pituitary and plasma follicle stimulating hormone (FSH) concentrations have been determined in female rats between 5 and 75 days of age. FSHRF was present by at least 10 days of age and at levels that exceeded those observed at any age thereafter. No fluctuations in FSHRF were detected during the estrous cycle. Plasma FSH levels determined by radioimmunoassay increased threefold between 5 and 15 days of age, at which time, values were approximately 1,300 ng/ml. At no other age were levels of this magnitude observed. During the estrous cycle, values ranged between 136 and 261 ng/ml, with the lowest during the morning of proestrus and the highest, the morning of estrus. Pituitary FSH stores during the cycle determined by bioassay were 16.5 (proestrus), 19.5 (estrus), 22.8 (metestrus), and 21.2 µg (diestrus) per pituitary. Neural regulation of FSH secretion exists by at least 10 days of age in the female rat. FSH secretion decreases between 15 days of age and puberty, and fluctuates at least twofold during the adult cycle.

Adrenal Involvement in Determining the Time of Onset of Puberty in the Rat1

“…Prior to the peak, FSH levels are low but are higher in the female than in the male. A second peak at ovulation is seen, of the same magnitude as the peaks that occur during the estrous cycle (113).…”

Vasoactive intestinal peptide enhances aromatase activity in the neonatal rat ovary before development of primary follicles or responsiveness to follicle-stimulating hormone.

“…Indeed, specific binding of gonadotropins (FSH or LH/human chorionic gonadotropin) is not demonstrable in neonatal rat ovaries prior to days 4-5 (26, 27), an observation that is in keeping with the belief that initial organization of both primordial and primary follicles is independent of the pituitary (24,25). Furthermore, despite the fact that gonadotropin levels are elevated throughout the first 2 weeks of life in the rat (28,29) responsiveness of the ovary to gonadotropins in terms of cAMP formation (30, 31) and steroidogenesis (32) is delayed until at least postnatal day 4 (33).…”

Landmarks in the development of the female reproductive system

“…Folliclestimulating hormone, FSH FSH levels increase shortly after birth to a maximum on Day 12 then declines to about one-fifth of the Day 12 values by the end of the juvenile period (Kragt and Dahlgen, 1972;Ojeda and Ramirez, 1972;Dohler and Wuttke, 1974).…”

“…Plasma luteinizing hormone (LH) levels are also higher in neonatal-infantile rats than in juvenile rats and are characterized by sporadic surges (Kragt and Dahlgen, 1972;Ojeda and Ramirez, 1972;Dohler and Wuttke, 1974;MacDonald et al, 1987). These surges disappear completely by the juvenile phase and LH levels remain low during this period.…”