Stimulation of Rat Prolactin Secretion in vivo by Arginine Vasotocin: Influence of Age of Solution, Nighttime Administration, and Dose

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Abstract
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.