Testicular arginine vasopressin in the developing rat: a possible physiological role

Testicular immunoreactive arginine vasopressin (irAVP) has been shown to inhibit testosterone production by the Leydig cell in vitro. We studied pre- and postpubertal rats and the results are in agreement with the notion that such inhibition might occur in vivo and, therefore, could have physiological significance. Testicular irAVP and serum testosterone levels were measured in 14-, 21-, 28-, 35-, 42-, and 70-day-old rats. The testicular irAVP concentration was lowest in early prepubertal rats, increased significantly to the highest level at 35 days, then decreased at 42 days, and plateaued at 70 days of age. A pubertal increase in serum testosterone was observed at 42 days when AVP was decreasing. Thus, an inverse relationship was observed at the onset of pubertal maturation. These parameters were also measured in 3 groups of rats 1 week after hemicastration which was performed at the ages of 28, 35 and 70 days. In the 28-day-old rats there was a significant decrease in irAVP 1 week later, in contrast to the intact animal, whereas hemicastration performed at 35 and 70 days of age had no impact on irAVP. Our data suggest that the role of AVP may be physiologically relevant during the peripubertal period of testicular maturation in the rat.