Biology of Reproduction, Vol 22, 832-836, Copyright © 1980 by Society for the Study of Reproduction

Response of Plasma Testosterone to Human Chorionic Gonadotropin Stimulation in the Ram

¹ Laboratoire INRA 54 189, Service de Biochimie, Ecole Nationale Vétérinaire de Lyon, Marcy-l’Etoile, 69260 Charbonnières, France
² Unité de Recherches sur le Contrôle Hormonal des Activités Cellulaires, INSERM U 162, Hôpital Debrousse, 29 Rue Soeur Bouvier, 69322 Lyon Cedex 1, France

The kinetics of responsiveness of sheep testes to hCG stimulation was studied following injection of 6000 IU hCG. When 4 rams received a single i.v. injection each, plasma testosterone (T) increased sharply (0.81 ± 0.27 to 3.76 ± 0.41 ng/ml) within 2 h, decreasing thereafter to reach control levels at about 10 h, despite the fact that hCG levels were still high. Subsequently, T levels increased to reach the 2 h levels at 20 h. A second delayed peak (7.16 ± 0.47), significantly higher (P<0.001) than that observed at 2 h was seen between 96 and 120 h. T levels declined thereafter to reach the control levels 8 to 9 days after the first injection. Two rams received 2 i.v. injections at 24 h intervals. The profile of plasma T after the first injection was similar to that observed in the first experiment. The second injection of hCG did not induce a significant modification of T levels. The second delayed peak of plasma T was seen at 120 h and was followed by a decline in plasma T levels. A third injection of hCG 8 days after the first induced a rapid increase of plasma T, the levels being similar to those of the second peak, but significantly higher than those observed at 2 h.

Note:
ACKNOWLEDGMENTS The authors are thankful to Dr. M. G. Forest for her generous supply of anti-testosterone antibodies, Dr. M. Donaldson for his editorial help and Ms. J.-Bois for her expert secretarial assistance. This work was supported by grants from INSERM (ATP 71-78-103) and Fondation pour la Recherche Médicale Francaise.