Source of Secretion of Milk “Let-Down” ∗ Hormone in Domestic Mammals

Abstract

Summary and Conclusions

1. The neurohypophyses of a series of animals were separated into the median eminence, stalk and posterior lobe. The acetone-dried tissue in each division was extracted and assayed for milk “let-down” hormone content, using lactating sows as assay animals, 2. The median eminence usually contained an insufficient amount of hormone to cause milk “let-down” in the sow. In a few cases some activity was observed. 3. It was concluded that the milk “let-down” hormone is either not secreted in the hypothalamus or, if secreted there, exists in an inactive form which becomes active only as it passes down the stalk into the posterior lobe. Since the posterior lobe contained roughly 10 times the amount of hormone present in the stalk per unit of dry matter, it seems more probable that the posterior lobe is the source of the milk “let-down” hormone.