Developmental changes in arginine vasopressin receptors and testosterone stimulation in Leydig cells

The steroidogenic response of purified Leydig cells from mice at various ages (from 10-95 days old) was investigated after exposure of cells to arginine vasopressin (AVP) or oxytocin (OT). A 24-h pretreatment by the neurohypophysial hormones significantly increased the acute (3-h) testosterone production by 1.3- to 3-fold at all ages studied, with the exception of pubertal Leydig cells which responded with a 5- to 7-fold increment of testosterone production (P less than 0.05). The higher responsiveness of pubertal Leydig cells to AVP does not result from an increased sensitivity, since the half-maximal effective doses (ED50) of AVP needed to stimulate testosterone production were quite similar and were in nanomolar range for both pubertal and adult Leydig cells. In addition, the ED50 for OT was 10 times higher than that for AVP. Cycloheximide totally abolished the AVP stimulation, suggesting that the AVP effect is dependent upon new protein synthesis. No modification of hCG-stimulated testosterone production occurred after a 24-h pretreatment of Leydig cells by AVP or OT for all ages studied. A 72-h AVP pretreatment resulted in a marked decrease (50-60%) in acute hCG-stimulated testosterone production in both pubertal and adult Leydig cells. Binding studies of [3H]AVP to purified Leydig cells from prepubertal, pubertal, and adult mice showed the presence of a single set of high affinity V1 sites. The Kd values, in the nanomolar ranges, remained unchanged regardless of age. Maximal capacities were of the same order in the prepubertal and adult Leydig cells (9,460 vs. 10,314 sites/cell), while a 50% decrease (P less than 0.01) in the number of AVP receptors occurred in pubertal Leydig cells (5,048 sites/cell). These data indicate developmental changes in the steroidogenic responsiveness of Leydig cells to neurohypophysial hormones and suggest that AVP receptors might be under a regulatory mechanism(s) during puberty. They provide additional evidence for participation of neurohypophysial hormones in autocrine/paracrine regulation of testicular steroidogenesis.