Plasma follicle-stimulating hormone during photoperiodically induced sexual maturation in male Japanese quail.

Follicle-stimulating hormone (FSH) was measured in Japanese quail using a heterologous radioimmunoassay, the specificty of which was confirmed by its cross-reactions with purified chicken FSH and luteinizing hormone (LH). Plasma concentrations of FSH, LH and testosterone were determined in quail during the testicular growth and sexual maturation which follows their transfer from short to long daylengths. All three hormones could be detected in short-day birds but their concentrations were greatly increased following photostimulation. Plasma FSH increased 12-fold during the first 9 long days, remained at this level for a week, and then declined steadily so that by the time the birds were sexually mature the level of FSH had decreased to one-third of the maximum level. LH reached a high level (five times the short day level) after 4 long days. Thereafter two patterns of LH secretion could be distinguished. In one experiment the high level of LH was maintained unchanged throughout sexual maturation while in another experiment LH secretion decreased significantly between days 11 and 28 of photostimulation. A strong correlation existed between testicular growth and the plasma FSH concentration. It was maximal during the phase of rapid testicular growth and decreased as spermiogenesis began. The pituitary FSH content increased during photostimulation. Castration caused a 20-fold rise in plasma FSH compared with that in intact quail. The change in LH concentration after castration was about eightfold. The changes in hormone secretion were strikingly similar to those found during sexual development and puberty in the rat.