Abstract
Experimental evidence has been presented (Nelson, 1 Nelson and Smelser 2 ) which has been interpreted as indicating the existence of a reciprocal relationship between the ovaries and the anterior hypophysis in the control of mammary gland development and lactation. This hypothesis, which is related to that of Moore and Price 3 regarding the control of sex rhythms, held that while the female sex hormones are responsible for the mammary gland development of pregnancy they also inhibit the secretion of the anterior lobe hormone responsible for lactation. With removal of the inhibition at parturition the hormone is secreted and lactation occurs. It is evident that this conception correlates at least most of the known facts relating to normal and induced lactation. Recently, Smith and Smith, 4 and Selye, Collip, and Thomson 5 have presented evidence which supports this hypothesis.
Supporting the earlier experiments with non-pregnant female and male guinea pigs are the following observations from a series of studies on pregnant animals. It will be seen that they offer important evidence in support of the reciprocal relationship concept.
1. The injection, into pregnant guinea pigs, of a potent anterior lobe extract terminated pregnancy and induced lactation (8 cases).
2. Extirpation of the ovaries did not invariably lead to abortion (7 out of 21 cases went to term). Lactation occurred only after foetal expulsion whether abortive or at term.
3. Surgical removal of the the entire pregnant uterus did not cause lactation unless the anterior lobe extract was administered (11 cases).
4. Surgical removal of the uterus and the ovaries did induce lactation (5 cases).
5. Surgical removal of the ovaries and the fertile uterine horn only, in cases of unilateral pregnancy, resulted in lactation (4 cases).
These experiments further confirm the original contentions and are especially pertinent as they deal with the pregnant animal.
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