Lactogenic Hormone Requirements for Milk Secretion in Intact Lactating Rats.

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Abstract
A technique is described for determination of amount of lactogenic hormone required for milk secretion in intact lactating rats. Rats were isolated from their litters for 12 hours on day 14 post partum, then deeply anesthetized with 4.5 mg/100 g Nembutal (pentobarbital-Na) and all milk withdrawn by 9 young with the aid of oxytocin. With lactogenic hormone discharge blocked and mammary glands empty, significantly less milk (0.85 g/100 g maternal body weight) was obtained following a 2d 12-hour isolation period in comparison with 2.92 g/100 g for unanesthetized controls. Injection of 0.5, 1, 1.5 or 2 mg lactogenic hormone during the 2d isolation period significantly restored milk yield approximately 70%. Yields were, nevertheless, significantly less than controls. No greater milk yield resulted from injection of more than 1 mg lactogen. These data indicate that lactogen is necessary for maintenance of milk secretion in intact rats and strongly imply that since lactogen alone was incapable of restoring milk secretion 100%, other pituitary hormones are necessary for full milk secretion and perhaps might be susceptible to discharge by nursing stimuli.