Initiation of lactation in rats by nonspecific stresses

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Abstract
Sixty mature, virgin female rats were divided into six groups of 10 each and injected subcutaneously for 10 days with 10 µg estradiol in 0.1 cc corn oil. For the following 5 days the groups were treated as follows: 1) controls, 0.1 cc saline injected subcutaneously once daily; 2) severe cold (0°C) 24 hr/day; 3) intense light and heat for 12 hr/day; 4) restraint, 12 hr/day; 5) starvation, no food or water for 5 days; 6) subcutaneous injection of 0.1 cc or 0.2 cc of 10% formaldehyde once daily. The mammary glands of the control rats regressed from a lobulo-alveolar system to a bare duct system during the period of saline injections. The stressed groups all showed variable degrees of lactation after treatment. It is concluded that nonspecific stresses can promote the secretion of prolactin and ACTH from the anterior pituitary in amounts adequate to induce lactation in estrogen-primed rats. The possible role of stresses in initiating lactation at parturition and under other circumstances is considered, and a common mechanism controlling the secretion of ACTH and prolactin is postulated.