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Biology of Reproduction, Vol 22, 781-790, Copyright © 1980 by Society for the Study of Reproduction

Prolactin, Testicular Growth and LH Receptors in the Ram Following Light and 2-Br-agr-Ergocryptine (CB-154) Treatments

B. BARENTON 1, and J. PELLETIER 1

1 Institut National de la Recherche Agronomique, Station de Physiologie de la Reproduction, 37380 Nouzilly, France


The influence of prolactin (PRL) on testicular growth and luteinizing hormone receptors (LH-R) in the ram has been investigated. Unoccupied LH-R were estimated in the 5000 x g testicular membrane fraction. The specific activity of the [125I]-oLH (enzymatically radioiodinated) was 20-40 µCi/µg and maximum binding activity reached 15-25%. Kinetic curves indicated that incubation for 20 h at 20°C was the optimum condition to obtain the maximum specific binding activity. Enzymatic treatment has demonstrated the lipoprotein structure of the LH-R. The specificity of the assay was confined to LH or human chorionic gonadotropin molecules. The equilibrium association constant (Ka) of the LH/receptor interaction was 1010 M-1 and the number of LH-R determined using Scatchard analysis was sim5 fmoles/mg membrane protein. The precision of the assay was 18%.

Plasma prolactin levels decreased by CB-154 treatment or increased by photostimulation did not change either the LH-R number or the equilibrium association constant. However, in the two experiments, a delay in the beginning of testicular growth was observed in rams treated with CB-154. In contrast to what has been found in rodents, these results suggest that, in the case of seasonal variations, high plasma prolactin levels influence changes in testicular activity without any involvement of the speculated regulation by prolactin of the LH-R number.

Note:
ACKNOWLEDGMENTS The authors wish to thank SANDOZ Ltd for the gift of the 2-Br-agr-Ergocryptine and NIH for the various hormone preparations. This work was supported by grant A.T.P.-Centre National de la Recherche Scientifique no. 65-13563 (Physiological Ecology). We thank M. J. Maugie for typing this manuscript.

Submitted on August 7, 1979
Accepted on January 18, 1980




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