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Biology of Reproduction, Vol 22, 269-276, Copyright © 1980 by Society for the Study of Reproduction
1 Medical Research Council Reproductive Biology Unit,
37 Chalmers Street,
Edinburgh EH3 9EW, Scotland Four adult Soay rams were given a daily i.v. injection of 10 µg LHRH agonist [D-Ser (But)6 des
Gly10 LHRH ethylamide] for 8 days and blood samples were collected at 20 min intervals for
6-7 h on the first and the last day of injection and 1 and 23 days after stopping treatment. Four
untreated animals acted as controls. The first injection of agonist induced a supraphysiological
increase in the circulating levels of LH and FSH, but this response was markedly reduced by the
last injection. Treatment with the LHRH agonist also resulted in a reduction in the testicular
response to LH. Twenty-four h after the last injection there were changes in the endogenous
secretion of LH and testosterone; the number of LH pulses in the agonist treated rams was significantly greater (P<0.001) than in controls while the pulse amplitude was significantly lower
(P<0.02). At the same time there was no longer any increase in the plasma concentration of
testosterone in response to the spontaneous episodic pulses of LH in the agonist treated rams.
Also the LH response to a physiological dose of 200 ng LHRH was reduced and was largely ineffective in provoking a testicular response. This testicular refractoriness was overcome within
6 days of stopping treatment with the agonist, although the effects on pituitary responsiveness to
LHRH were more sustained.
Note:
ACKNOWLEDGMENTS
The animals used in this study were kept at the
Animal Breeding Research Organisation’s field station
at Dryden, near Edinburgh and were cared for by
Norah Anderson. The hormone assays were performed
by Diane Blakeley Sharon Kilpatrick and Rhona
Cunningham and their skilled technical help is acknowledged. We thank NIAMDD for the gift of
hormone preparations, Dr. S. Dombey (Hoechst)
for LHRH and the agonist (HOE 766) and Dr. R. M.
Sharpe for helpful discussion.
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