MAMMARY GLAND AND LACTATION 



605 



been emiiha.-^ized by the recent experiments 

 of Jacobsohn and her colleagues. Following 

 on the work of Salter and Best (1953) who 

 showed that hypophysectomized rats could 

 be made to resume body growth by the in- 

 jections of long-acting insulin, Jacobsohn 

 and her colleagues (Ahren and Jacobsohn, 

 1956; Ahren and Etienne, 1958; Ahren, 

 1959) found that treatment with estrogen 

 and progesterone would stimulate consid- 

 erable mammary duct growth in hypophy- 

 sectomized-gonadectomized rats when given 

 with suitable doses of long-acting insulin 

 (Fig. 10.7). This growth-supporting effect 

 of insulin could be nullified if cortisone was 

 also administered (Ahren and Jacobsohn, 

 1957) but could be enhanced by giving thy- 

 roxine (Jacobsohn, 1959). 



The thyroid would thus appear to be an- 

 other endocrine gland whose hormones affect 



mammary growth intlirectly by altering the 

 metabolic environment. Studies in this field, 

 reviewed by Folley (1952a, 1956), indicate 

 that in the rat some degree of hypothyroid- 

 ism enhances alveolar development wdiereas 

 in the mouse, hypothyroidism seems to 

 inhibit mammary development. Chen, John- 

 son, Lyons, Li and Cole (1955) have shown 

 that mammary growth can be induced in 

 hypophysectomized - adrenalectomized-thy- 

 roidectomized rats by giving estrone, pro- 

 gesterone, prolactin, STH, and Cortisol, no 

 replacement of the thyroid hormones being 

 necessary. 



These investigations on the effect of the 

 metabolic environment on mammary devel- 

 opment seem to ])e opening up new avenues 

 of approach to the advancement of our 

 understanding of the mechanisms of mam- 

 mary growth and we would recommend. 



0-5 cm. 



Fig. 10.7. Whole mount preparation of .second thoracic mammary gland of : ^. Ovariec- 

 tomized rats injected with estrone and progesterone. B. Hypophysectomized-ovariectomized 

 rat injected with estrone and progesterone. C. Hypophysectomizcd-o\ariectomized rat. D. 

 Hypophysectomized-ovariectomized rat injected with estrone, progesterone, and insulin. 

 (From K. Ahren and D. Jacobsohn, Acta physiol. scandinav., 37, 190-203, 1956.) 



