Calb M, Goldstein R, Pavel S
Acta Endocrinol (Copenh). 1977 Mar;84(3):523-6. doi: 10.1530/acta.0.0840523.
The pineal content of arginine vasotocin in the male rat is subject to diurnal changes, having a high value around noon and a low value around midnight. Since in rats exposed to 24 h constant light the pineal content in arginine vasotocin decreases, and in the rats exposed to 24 h constant darkness the pineal content in arginine vasotocin increases, it appears that during the night both the synthesis and release of arginine vasotocin is enhanced.