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Effect of active immunization against oestrogens on plasma gonadotrophins in the ewe and the response to synthetic oestrogen or LH

Summary. Immunization against oestrogen resulted in elevated LH concentrations, in the form of a pulsatile release, which rose from 3 to as much as 41 ng/ml approximately every 1·5 h, even in the presence of high plasma progesterone concentrations. Elevated FSH concentrations showed only minor oscillations without consistent synchrony to the LH pulses. Injection of 250 µg stilboestrol did not abolish the LH pulses but in 2 out of 8 ewes FSH was initially lowered. Injection of 1 mg stilboestrol abolished the LH pulses within 11 h and decreased FSH values in 2 out of 4 ewes. Between 16 and 35 h after injection there was a large increase in LH and FSH concentrations. Thus, in the ewe, the tonic secretion of LH and FSH is controlled by a negative feedback action of oestrogen, and diethylstilboestrol will exert both positive and negative feedback effects on both gonadotrophins, depending upon dose. Infusion of LH was unable to alter the frequency or height of the LH pulses, thereby excluding regulation of the LH pulses by a short feedback mechansim.