Effect of a synthetic LH-RH agonist on the endocrine function of the testis, adrenocortex and thyroid gland in cocks.

Testosterone, progesterone, thyroxine and triiodothyronine levels in peripheral plasma of cocks and capons were determined by RIA, corticosteroid contents by CPB method 10, 20 and 30 min as well as 1, 2 and 4 hr following a single intravenous injection of 0.5 micrograms/kg D-Lys6-LH-RH ethylamide. Testosterone level increased after 30 min, reached a peak after 1 hr, and returned after 4 hr to the control level in cocks. Plasma concentrations of progesterone and triiodothyronine did not change in response to the treatment. Thyroxine plasma level increased in cocks simultaneously with the decrease of testosterone contents between 1 and 2 hr. In capons, the increase of thyroxine did not occur, thus the promoting factor was probably not LH-RH but rather the decrease of the high testosterone level. Corticosterone level increased between the 2nd and the 4th hr in cocks and between the 1st and 4th hr in capons. This increase might have been due to the increase in thyroxine level (cocks) and the immediate stimulatory effect of the LH-RH analogue of not the C-RH type (cocks, capons).