The half-life of luteinizing hormone in intact and castrated quail during photoperiodic stimulation.

In the Japanese quail (Coturnix coturnix japonica) the plasma concentration of luteinizing hormone (LH) depends on the physiological state of the animal. Low levels are found in sexually immature birds on short days (0.8 +/- 0.1 (n = 20) ng/ml) while after exposure to long days, sexually mature birds have a significantly higher LH level (4.4 +/- 0.4 (n = 20) ng/ml). Castration of long day males results in an even higher rise in LH concentration to 16.8 +/- 1.8 (n = 16) ng/ml. When the half-life (t1/2) of circulating LH was determined it was found to have two components: a fast t 1/2 of about 6 min and a slower component of either 20 min (determined by a radioisotope method), or 40 min (following hypophysectomy). No significant difference was observed in either of these components between birds in the three physiological states (short days, long days, castration plus long days). It would appear, therefore, that since the half-life of plasma LH remains constant, the difference in circulating LH observed under the various physiological conditions results solely from a change in the rate of LH secretion.