BINDING OF LUTEINIZING-HORMONE RELEASING HORMONE TO HUMAN-SERUM PROTEINS - INFLUENCE OF A CHRONIC TREATMENT WITH A MORE POTENT ANALOG 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 or ethanol precipitation (13.57 ± 0.69% or 19.32 ± 1.73% of LH-RH and 7.12 ± 0.86% or 14.56 ± 1.06% of the analogue were in the bound form, without difference between normal subjects and IGD. Capacity of this binding was high (> 9 < 18 μ-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.