Animal Reproduction Science, 23 (1990) 123-133 123 Elsevier Science Publishers B.V., Amsterdam Sex-related differences in the control of gonadotropin concentrations in neonatal pigs A.J. Ziecik 1, K.L. Esbenshade 2, H.J. Howard and J.H. Britt Department of Animal Science, North Carolina State University. Raleigh, NC 27695-7621 (U.S.A.) (Accepted 7 March 1990) ABSTRACT Ziecik, A.J., Esbenshade, K.L., Howard, H.J. and Britt, J.H., 1990. Sex-related differences in the con- trol ofgonadotropin concentrations in neonatal pigs. Anim. Reprod. Sci., 23:123-133. Two experiments were conducted to examine gonadal regulation ofgonadotropin secretion in male and female neonatal piglets. In the first experiment, a single i.p. injection of charcoal-treated porcine follicular fluid (pFF) lowered (P< 0.05 ) concentrations of plasma follicle-stimulating hormone (FSH) at 6 and 12 h after administration in 7-day-old intact male piglets, but failed to alter FSH in castrated male or intact female piglets. In the second experiment, administration ofpFF twice daily from day 0 to 14 of life caused an increase in plasma FSH levels in intact males, but did not significantly alter FSH in females or in males castrated at birth. Plasma LH did not differ between male and female piglets, but FSH was significantlylower in males than in females. Castration of males at birth resulted in lower testosterone and estradioi-17fl levels and resulted in a gradual increase in concentrations of FSH over the 14-day experimental period. Treatment of neonatal pigs with pFF altered concentra- tions of FSH in intact males, but not in intact females, indicating a divergence between the sexes in the postnatal control of FSH secretion. INTRODUCTION Gonadotropins are first detected in the circulation of fetal pigs around 70 to 80 days of gestation and there are no obvious differences between male and female piglets in peripheral concentrations ofluteinizing hormone (LH) dur- ing fetal and perinatal periods (Colenbrander et al., 1977, 1987; Hennen et al., 1982 ). Secretion of LH in fetal and neonatal pigs is under hypothalamic control because administration ofgonadotropin-releasing hormone (GnRH) increased peripheral concentrations ofLH (Bruhn et al., 1984; Colenbrander et al., 1987 ) and addition of GnRH to incubations of pituitary gonadotrops of fetal origin stimulated release of LH (Elsaesser et al., 1988 ). 'Present address: Institute of Animal Physiology, University of Agriculture and Technology, 10- 718 Olsztyn (Poland) 2Reprint requests. 0378-4320/90/$03.50 © 1990 -- Elsevier Science Publishers B.V.