Abstract
The ability of an inhibitory analogue of L.H.-releasing hormone (L.H.R.H.) to suppress the release of luteinising hormone (L.H.) and follicle-stimulating hormone (F.S.H.) after administration of a small dose of L.H.R.H. was tested in four men. A single intramuscular injection of 90 mg (D-Phe-2,D-Trp-3,D-Phe-6)-L.H.R.H. diminished the gonadotrophin response to 25 μg of L.H.R.H. given 1, 4, 8, and 24 hours afterwards. Basal levels of L.H. and F.S.H. were not lowered. The results demonstrate that an inhibitory analogue of L.H.R.H. is active in man and suggest the possibility that inhibitors of L.H.R.H. might eventually form the basis of a new method of birth control.