Regulation of luteinizing hormone secretion in prepubertal male and female rats.

The effect of naloxone or clonidine, on serum levels of luteinizing hormone (LH) was investigated in immature male and female rats. After birth, naloxone progressively increased serum LH concentrations in females, reaching maximal effects on the 10th to the 16th day of life. Males failed to respond to naloxone during this period. Clonidine only moderately increased LH in immature female rats. However, immature males displayed a high sensitivity to this alpha 2-adrenoceptor agonist. The secretion pattern of LH caused by clonidine during the first two weeks of life resembled that evoked by naloxone in females. Thus, regulation of LH secretion of immature female rats involves endorphins, while in males control of LH-release is by adrenergic mechanisms.