Abstract
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 testicularmembrane fraction.The specificactivityof the (‘25Il-oLH (enzymatically radioiodinated) was 20-40 �iCi4tgand maximum binding activityreached 15-25%. Kinetic curves indicated that incubation for 20 h at 20#{176}C was the optimum condition to obtain the maximum specific binding activity. Enzymatic treatmenthas demonstrated the lipoprotein structure of the LH-R. The specificityof the assay was confined to LH or human chorionic gonadotropin molecules. The equilibrium associationconstant (Ka) of the LH/receptor interactionwas 10i0 M -i and the number of LH-R determined using Scatchard analysis was “vS fmoles/mg membrane protein.The precision of the assay was 18%. Plasma prolactin levelsdecreased by CB-154 treatment or increasedby 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 testiculargrowth was observed in rams treatedwith CB154. In contrast to what has been found in rodents,these resultssuggest that,in the case of seasonal variations,high plasma prolactin levelsinfluencechanges in testicularactivity without any involvement of the speculated regulationby prolactinof the LH-R number.
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