Studies of a controlled-release microcapsule formulation of an LH-RH agonist (D-Trp-6-LH-RH) in the rhesus monkey menstrual cycle.

It has been shown that continuous administration of LH-RH agonists inhibits ovulation in many species, including human and nonhuman primates. However, the need of daily injections or intranasal application of the LH-RH agonists makes this contraceptive approach impractical. In addition, due to the repeated daily administration of the LH-RH analogues and their bioavailability, serum levels of gonadotropins and estradiol present wide variations and are often associated with irregular bleeding and/or endometrial hyperplasia. This experiment was designed to study the effects on ovulation and the hormonal profile during the rhesus monkey menstrual cycle of a system that continuously delivers a potent agonist of LH-RH (D-Trp-6-LH-RH encapsulated in poly [DL-lactide-co-glycolide]). Subjects were divided into two groups: On day 1 of the cycle, monkeys received a single subcutaneous injection of microcapsules containing D-Trp-6-LH-RH at a release rate of 13.6 micrograms/day (Group 1) or placebo microcapsules (Group 2). Ovulation dates were significantly delayed in animals from Group 1 (50 +/- 3 days) as compared to those in group 2 (20 +/- 2 days). Luteal phases following ovulation were normal in animals of both groups, as determined by length and serum progesterone levels. No significant differences on baseline levels of FSH and LH were observed between the two groups of animals. Post-treatment cycles were ovulatory and presented normal luteal phases and hormone concentrations as compared to the non-treated animals of our colony. The present data show for the first time that a controlled-release microcapsule formulation that delivers an agonist of LH-RH can effectively suppress ovulation when injected in a single dose in non-human primates.