Hypothalamo-Hypophyseal Sensitivity to Hormones in the Hen. II. Plasma Concentrations of LH, Progesterone, and Testosterone in Response to Peripheral and Central Injections of LHRH or Testosterone

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Abstract
Changes in plasma LH [luteinizing hormone], progesterone (P4) and testosterone (T) and the incidence of premature ovulation in response to peripheral and central injections of T or synthetic LHRH administered 14-12 h prior to the 1st ovulation in a sequence were investigated. Injection of 2.0 mg T (i.m.) induced premature ovulation in 4 of 5 hens. Plasma concentrations of LH and P4 in T-injected hens, compared with corresponding values from control hens, were significantly increased in all 5 birds by 90 min and reached highest concentrations by 180 and 240 min, respectively, following injection. Plasma T was increased to 19.88 .+-. 3.40 ng/ml (standard error of the mean) 30 min following injection of 2.0 mg T and slowly declined throughout the remaining sampling interval. There was no significant (P > 0.05) dose relationship with respect to premature ovulation between 10.0 and 80.0 .mu.g of centrally injected T. In an experiment in which hens served as their own controls and in which the control (vehicle) and 20 .mu.g T intraventricular injections were assigned at random to each hen, T did not affect the incidence of ovulation or concentrations of plasma LH or P4, but plasma T concentration was increased significantly by the 1st sampling period (30 min) after injection, suggesting some leakage of T from the site of injection into the peripheral circulation. Four of the 5 hens injected i.v. with 20 .mu.g LHRH responded with significant elevations in plasma LH, P4 and T by the 1st sampling period after injection and with premature ovulation. Analysis of data from hens injected centrally with doses of LHRH from 0.001-5.0 .mu.g revealed a significant dose-response regression (P < 0.01) with an ED50 of 0.53 .mu.g. Five of 6 hens injected centrally with 5 .mu.g LHRH responded with a premature ovulation, and all 6 treated birds showed increased plasma concentrations of LH, P4 and T within 30 min of the time of injection, compared with values obtained in vehicle-injected birds. Peripheral injections of unphysiologically high doses of T evidently are capable of inducing premature ovulation, but this effect is not mediated by T at the site of the hypothalmo-hypophyseal axis. LHRH injected i.v. or centrally 14-12 h prior to the 1st ovulation in a sequence is capable of inducing significant and sustained release of LH, P4 and T and premature ovulation.