Submitted September 7, 2007
Returned for revision October 10, 2007
Accepted November 28, 2007
Pituitary
Weaning and the Developmental Changes in Follicle-Stimulating Hormone, Pituitary Adenylate Cyclase-Activating Polypeptide, and Inhibin B in the Male Rat
Joseph Patrick Moore, Jr. *
and
Stephen J. Winters
* To whom correspondence should be addressed. E-mail: jpmoor03{at}louisville.edu.
Abstract
Pituitary Fshb concentrations increase markedly and selectively beginning on Postnatal Day 20 in the male rat. To evaluate the factors potentially responsible for this rise in FSH, we adjusted the time of weaning that is generally also on Day 20. Male rat pups were provided nutrients by suckling only, and were weaned to lab chow earlier (Day 17) or later (Day 23) than normally performed in animal facilities (Day 20). Between ages 17 and 29 days, serum LH (1.4-fold) and FSH (2.4-fold) levels, pituitary expression of Lhb (5.4-fold), Fshb (21.3-fold), and Inhbb (2.26-fold) mRNAs, and testicular expression of Inhbb (10-fold) mRNA increased significantly. Concurrently, significant decreases in serum Inhibin B levels (1.8-fold), pituitary Adcyap1 (4.2-fold), total follistatin (Fst, 3.5-fold), and follistatin-288 (Fst-288, 5.6-fold) mRNAs, and testicular expression of Inhba (8.2-fold) mRNA occurred. Early weaning significantly increased serum FSH, but not LH, and increased pituitary expression of Fshb and GnRH receptor (Gnrhr) mRNAs, but not Lhb. Early weaning also significantly decreased serum Inhibin B, but increased testicular expression of the Inhbb subunit. Early weaning also caused pituitary expression of follistatin and Adcyap1 to decline earlier than in the control group. Immediately after weaning growth accelerated substantially, and the time of weaning produced significant and differential effects on circulating leptin levels that were not related to indices of FSH production. From these observations, we propose the novel hypothesis that the increase in growth rate subsequent to weaning signals circulating inhibin B levels to fall and pituitary Adcyap1 and consequently follistatin expression to decrease, and these events together facilitate the rise in Fshb and Gnrhr expression by increasing pituitary activin signaling.
Key words:
Pituitary •
Follicle-stimulating hormone •
Inhibin •
Luteinizing hormone •
Male sexual function
