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Biology of Reproduction, Vol 25, 153-161, Copyright © 1981 by Society for the Study of Reproduction

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

A. L. JOHNSON 1, and A. van TIENHOVEN 1

1 Department of Poultry and Avian Sciences, Cornell University, Ithaca, New York 14853


Experiments were conducted to investigate changes in plasma LH, 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 first ovulation in a sequence.

Injection of 2.0 mg T (i.m.) induced premature ovulation in four of five hens. Plasma concentrations of LH and P4 in T-injected hens, compared with corresponding values from control hens, were significantly increased in all five 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 (SEM) 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 µg of centrally injected T. In an experiment in which hens served as their own controls and in which the control (vehicle) and 20 µg 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 first sampling period (30 min) after injection, suggesting some leakage of T from the site of injection into the peripheral circulation.

Four of the five hens injected i.v. with 20 µg LHRH responded with significant elevations in plasma LH, P4, and T by the first sampling period after injection and with premature ovulation. Analysis of data from hens injected centrally with doses of LHRH from 0.001 to 5.0 µg revealed a significant dose-response regression (P<0.01) with an ED50 of 0.53 µg. Five of six hens injected centrally with 5 µg LHRH responded with a premature ovulation, and all six 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.

We conclude that peripheral injections of unphysiologically high doses of T are capable of inducing premature ovulation, but that this effect is not mediated by T at the site of the hypothalamo-hypophyseal axis. In addition, LHRH injected i.v. or centrally 14-12 h prior to the first ovulation in a sequence is capable of inducing significant and sustained release of LH, P4, and T and premature ovulation.

Note:
ACKNOWLEDGMENTS We wish to thank Ms. R. D. Karaka and Mrs. V. Eisner for excellent technical assistance, Dr. F. J. Cunningham for LH assay materials, and Ms. P. A. Johnson for reviewing the manuscript.

Submitted on December 17, 1980
Accepted on April 2, 1981






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Copyright © 1981 by the Society for the Study of Reproduction.