VARIATIONS IN STORED AND PLASMA CONCENTRATIONS OF ANDROGENS AND LUTEINIZING HORMONE DURING SEXUAL DEVELOPMENT IN THE COCKEREL

SUMMARY The concentrations of luteinizing hormone (LH) and testosterone in the plasma and the stored levels of LH, testosterone and androstenedione were measured in cockerels aged 8–29 weeks. The onset of puberty occurred between 16 and 24 weeks of age, when the testes entered a phase of rapid growth and spermatogenesis was completed. The following sequence of endocrine events was found to be associated with the onset of puberty: a fall in the amount of androstenedione in the testes before any evidence of increased testicular growth; an increase in the total amount of LH in the pituitary gland as the testes started to enlarge; an increase in the total amount of testosterone in the testes and in the concentration of LH in the plasma; an increase in the concentration of testosterone in the plasma. An increase in the rate of growth of the comb and testes preceded a detectable increase in the levels of LH and testosterone in the plasma. The increase in the amount of testosterone in the plasma which occurred after the initial increase in the concentration of LH was associated with the final stages of spermatogenesis, a decrease in the rate of body growth and a temporary reduction in the amount of LH secreted.