Binding of luteinizing hormone releasing hormone to human serum proteins--influence of a chronic treatment with a more potent analogue of LH-RH.

Binding of 125I-LH-RH and its analogue, 125I-6-D-Leu-10-Des-Gly-Ethylamide-LH-RH (6-D-LH-RH) in male serum was studied in 10 healthy males and in 11 patients with idiopathic gonadotropin deficiency (IGD) before and during treatment with 6-D-LH-RH. Using either equilibrium dialysis (A) or ethanol precipitation (B) 13.57 +/- 0.69% (A) or 19.32 +/- 1.73% (B) of LH-RH and 7.12 +/- 0.86% (A) or 14.56 +/- 1.06% (B) of the analogue were in the bound form, without difference between normal subjects and IGD. Capacity of this binding was high (greater than 9 less than 18 mu-Mol LH-RH/0.06 mMol of protein), affinity very low, and the binding almost completely disappeared following removal of albumins by affinity chromatography. Chronic treatment with 6-D-LH-RH did not alter these binding characteristics. These observations suggest non specific albumin binding of LH-RH in male serum and stress the role of this decapeptide as a rapid modulating regulator of gonadotropin secreting system.