Changes in Testicular Weight and Serum Gonadotropin and Testosterone Levels before, during, and after Birth in the Perinatal Rat*

Abstract

Changes in serum and pituitary LH [lutropin] and FSH [follitropin] concentrations have been measured in the newborn male rat before, during and up to 24 h after birth. A sudden and transient increase of serum and pituitary gonadotropins was observed at birth, which was followed by a rapid increase of absolute and relative testicular wt between 2-12 h (P < 0.0001) and by a transient increase of serum testosterone between 0 h in utero (810 .+-. 26 pg/ml) and 2 h (2820 .+-. 318 pg/ml; P < 0.0001). Premature newborn rats obtained by cesarian delivery on day 20 of gestation also exhibited an increase in testicular weight between 0-6 h and an increase in serum testosterone levels between 0 h (730 .+-. 170 pg/ml) and 2 h (3400 .+-. 300 pg/ml; P < 0.001) with only a slight increase in serum LH. The hypophyseo-testicular axis of the rat is stimulated at the moment of birth. The factors responsible for this stimulation are discussed. This transient testicular crisis occurring at birth could affect the process of masculinization of the CNS of the rat.