Reversible inhibition of testicular androgen secretion by 3-, 5- and 6-month controlled-release microsphere formulations of the LH-RH agonist [ d-Trp 6, des-Gly-NH 210] LH-RH ethylamide in the dog

Abstract

This study examines the effect of treatment with controlled-release poly( dl-lactide-co-glycolide) microsphere formulations of the LH-RH agonist [ d-Trp 6, des-Gly-NH 2 10-LH-RH ethylamide (LH-RH-A) designed to release about 100 or 200 μg of the peptide per day for 3, 5 or 6 months in male dogs. Plasma levels of testosterone and LH-RH-A were measured at 2-day intervals. After the first injection of the 100-μg/day formulation, plasma testosterone increased from 1.6 ± 0.2 to 3.5 ± 0.6 ng/ml for 5–7 days before decreasing and remaining at 0.05 ± 0.008 ng/ml for approximately 150 days (5 months). After two months of recovery, microspheres designed to release 100 μg for 6 months of LH-RH agonist per day were then injected. Plasma testosterone levels showed an elevation from 1.5 ± 0.5 to 4.7 ± 2.0 ng/ml during the first few days before gradually decreasing to castration levels for 200 days (6 months). One month later, plasma testosterone had returned to normal levels. When microspheres designed to deliver an average of 200 μg per day of the peptide for 3 months were injected in another series of animals, castration levels of plasma testosterone were maintained for 95 days with a progressive increase to normal values at later time intervals. The animals of the first series of experiments were then sacrificed after 4 months of recovery following maintenance of plasma testosterone at castration levels for a total period of 11 months. The testes, prostate and pituitary gland were kept for histological examination which was completely normal in all tissues. The efficacy and excellent tolerance of the controlled-release form of LH-RH-A as inhibitor of the pituitary-gonadal axis strongly support the use of such long-term controlled-release formulations of LH-RH agonists for the treatment of sex steroid sensitive diseases.