Prolactin receptors in interstitial cells of testes from rats at different stages of development

The developmental pattern of prolactin receptors was examined in intact interstitial cells isolated from testes of 19‐day old foetuses (F₁₉), 1 to 45‐day immature (N₁ to N₄₅) and adult animals. The prolactin binding activity in F₁₉ interstitial cells is low, being 27% of that found in cells of the adult. There is an abrupt 60% increase in prolactin binding immediately after birth (N₁), followed by a slow, but gradual, increase for the next 34 days. A second rapid increase in prolactin binding occurs between days 34 and adulthood which follows an increment in serum prolactin concentrations after day 24. Equilibrium analysis revealed that the receptors in interstitial cells from N₁, N₃₄ and adults have similar affinity (K_d= 2.7 to 3.3 times 10^‐10M) for prolactin. However, cells from adults contain twice as many prolactin receptors per cell as that of immature animals. This increase in prolactin receptors may play a role in the modulation of interstitial (Leydig) cell function during sexual maturation.