Changes in the concentration of luteinizing hormone in plasma of rams following administration of oestradiol, progesterone or testosterone.

Fluctuations in the basal level of luteinizing hormone (lh) in the plasma of ewes have been measured by the radioimmunoassay technique (Niswender, Roche, Foster & Midgley, 1968; Goding, Catt, Brown, Kaltenbach, Cumming & Mole, 1969). Goding et al. (1969) and Bolt, Kelley & Hawk (1970) reported that the injection ofoestradiol into the ewe caused lh release. In rams, however, the basal level ofplasma lh is not well defined and any effect exerted by exogenous steroids on plasma lh is not known. This study was designed to measure the basal level of lh in the plasma of adult male sheep and to determine whether exogenous oestradiol, progesterone or testosterone would alter the basal lh level. Sixteen sexually active Rambouillet rams, weighing about 100 kg and ranging in age from 2 to 5 years, were divided into four equal groups. One\x=req-\ half of the animals in each group had been vasectomized for at least 1 year. All