Stimulation of rat prolactin secretion in vivo by arginine vasotocin: Influence of age of solution, nighttime administration, and dose1

In male rats pretreated for 3 days with 50 μg of estradiol benzoate (E) and 25 mg of progesterone (P), the i.v. administration of 1 μg of arginine vasotocin (AVT) from solutions that were 0, 6, 24 or 48 h old caused a significant rise in plasma prolactin (Prl) 10 min after injection. In the 2nd experiment, the i.v. injection of 1 μg AVT into EP-primed adult male rats at either 01:00 (during darkness) or 13:00 h (during light) resulted in a significant and similar elevation in plasma Prl levels. In the 3rd experiment, normal adult male rats under urethane anaesthesia were given an i.v. injection of diluent or of 100 ng, 1 μg or 10 μg AVT. A significant rise in plasma Prl was observed at 10 and 20 min following injection only in the group treated with 1 μg AVT. In none of these experiments did AVT alter the content of pituitary Prl.