Plasma LH and androgen levels in the red-winged blackbird ( Agelaius phoeniceus) treated with a potent GnRH analogue

Abstract

1. 1. Low doses of GnRH-A (0.01-0.10-1.0 μg) given during the annual testes growth period did not clearly affect plasma LH and androgen levels 10 min following the injection. 2. 2. The first injection of high doses ofGnRH-A (2.0-10.0-20.0 μg) markedly increased plasma LH and androgen levels measured 10 min following the injection. The increase in plasma LH level was dose-dependent and the maximal LH level was obtained with 10.0 μg of GnRH-A. 3. 3. Impairment of the LH response to GnRH-A was assessed by comparing the first and the fourteenth injection of high doses of GnRH-A. Evidences of pituitary gland desensitization are reported since plasma LH levels were reduced following the fourteenth injection in all groups. 4. 4. Plasma androgen levels following high doses of GnRH-A were not clearly affected in red-winged blackbirds.