The effect of copulation on the plasma antidiuretic activity of the male rat

The plasma antidiuretic activity and the content of antidiuretic hormone (ADH) and oxytocin of the neurointermediate lobe were determined in male rats under normal conditions and after copulation. The plasma samples from control rats assayed directly in the water-loaded ethanol-anaesthetized rat had no detectable antidiuretic activity. The same negative result was observed in plasma obtained from male rats during courtship. However, plasma obtained from male rats at different time intervals after copulation had an antidiuretic activity which was maximal one h after ejaculation. When the ADH was extracted from pools of plasma samples, the circulating level of the hormone in control rats was also measured. The plasma antidiuretic activity after copulation was abolished after thioglycolate treatment which inactivates the neurohypophysial hormones. These findings suggest that ADH is released after copulation and that such a release is maintained for at lest 60 min.