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The Specificity of the Lactogenic Hormone in the Initiation of Lactation¹

Department of Dairy Husbandry, University of Missouri, Columbia, Missouri²

ABSTRACT

A study is reported with the "laetogenic hormone" and the "thyro-tropic and other hormone" fraction of the anterior pituitary on lactogenesis in the pseudo-pregnant rabbit.

When the "laetogenic hormone" fraction was injected at the rate of 1 mg. per 100 grams body weight (+) to (++) glands were obtained, the average rating being 1.67. When 1.5 mg. was given (+++) to (+++) glands were obtained the average rating being 3.17, which is considered in the range for a unit response. At this level approximately 52 mg. containing 260 McShan-Turner pigeon units were required.

A group of rabbits injected with 2 mg. per 100 gm. body weight of the "thyrotropic and other hormone" fraction showed no evidence of lactation. At the 5 mg. and 10 mg. levels six animals in each group survived the test period. Only one rabbit in each group showed any evidence of lactation.

In a group of five thyroidectomized rabbits injected with 5 mg. of the "thyrotropic and other hormone" fraction per 100 grams body weight (++) lactation was initiated in two animals but little or none in the other three. Another group of seven thyroidectomized rabbits injected at the 10 mg. level gave mostly (+) to (++) glands, the average rating being 1.43. All the animals survived the test period.

The average gland rating was increased from 1.67 for 1 mg. of lactogenic hormone per 100 grams body weight, to 1.86 when supplemented by 1 mg. of the "thyrotropic and other hormone" fraction. When the level of injection of the latter was 2 mg. the average gland rating was increased to 2.60.

These results are taken to indicate that the primary function of the lactogenic hormone, which also possesses the ability to proliferate the pigeon crop gland, is to initiate and maintain established lactation. Extracts rich in the thyrotropic and other hormones, but containing only traces of the lactogenic hormone, do not possess the ability to initiate lactation in doses as high as could be tolerated. This fraction, however, has a supplementing effect on established lactation.

¹ Contribution from the Department of Dairy Husbandry, Missouri Agricultural Experiment Station, Journal Series No. 684.

² This study has been aided in part by grant from the Committee on Research in Endocrinology of the national Research Council.