NEL, Testosterone and Hypothalamic Nitric Oxide

OBJECTIVES: To determine the effect of testosterone administration to prepubertal (15 days old) and peripubertal rats (30 days old) on hypothalamic nitric oxide synthetase (NOS), and GnRH release. METHODS: Hypothalamic samples containing the anterior preoptic and medial basal areas (APO-MBH) were incubated for 30 minutes in 500 l of Earle’s medium with glucose (1 mg/ml) and bacitracin (20 mM). GnRH was determined by RIA in the medium and NOS activity was determined in APO-MBH after 10 min of incubation by the conversion of 14 C arginine to 14 C citrulline. RESULTS: Treatment with testosterone propionate, signicantly decreased NOS hypothalamic activity in prepubertal male rats. (Control: 58.41 ± 0.85; Testosterone: 25.61 ± 1.40 , p<0.001) and had no effect in peripubertal male rats (Control 49.28 ± 1.50; Testosterone 51.48 ± 5.2 pmoles NO/10 min/hypothalamus). On the other hand, in prepubertal rats the treatment decreased Gn-RH release (Control: 3.62 ± 0.23; Testosterone: 1.38 ± 0.11 (pg/ ml medium, p<0.001) and had no effect on Gn-RH release in 30 days old rats (Control: 3.65 ± 0.33.;Testosterone: 4.15 ± 0.36 pg/ ml. medium). CONCLUSION: These results clearly demonstrated that testosterone has an inhibitory effect on hypothalamic NOS activity in prepubertal rats while it did not affect the concentration of this neurotransmitter system in peripubertal rats. This pattern is similar to that observed with GnRH hypothalamic release since testosterone has an inhibitoty effect in prepubertal rats and did not modify the GnRH release in peripubertal rats. Taking into account the well known stimulatory effect of NO on GnRH and the decrease in the sensitivity of GnRH-gonadotrophin axis to the inhibitory feedback effect of testosterone during sexual maturation and the onset of puberty, it is proposed that the changes here described are connected with maturational modifications in the sexual hormones on-GnRH axis connected with the onset