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

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 × 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 ∿5 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.