MAMM.\RY GLAND AND LACTATION 



613 



There have been several studies on the 

 effects of corticoids and adrenocorti- 

 eotrophin on lactation in the intact animal. 

 ACTH and the corticoids depress lactation 

 in the intact cow (Fig. 10.10) (Cotes, Crich- 

 ton, Folley and Young, 1949; Flux, Folley 

 and Rowland, 1954; Shaw, Chung and 

 Bunding, 1955; Shaw, 1955), whereas in the 

 rat ACTH and cortisone have been reported 

 as exhibiting galactopoietic effects (Meites, 

 private communication; Johnson and 

 Meites, 1958). With larger doses of corti- 

 sone, however, an inhibition of milk secre- 

 tion in the rat has been reported (Mercier- 

 Parot, 1955). 



The main function of the cortical steroids 

 in lactation is still uncertain. They may act 

 in a "supporting" or "permissive" manner 

 (see Ingle, 1954), maintaining the alveolar 

 cells in a state responsive to the galacto- 

 ])oictic complex, or they may act by main- 

 taining the necessary levels of milk precur- 

 sors in the blood. 



Biochemical studies are, however, Ix'gin- 

 ning to add to our information on the role 

 of the corticoids in lactation. In the rat, 

 adrenalectomy prevents the increase in liver 

 and mammary gland arginase which occurs 

 during normal lactation and it has been 

 suggested that this depression of arginase 

 activity interferes with deamination of 

 amino acids, and thereby inhibits any in- 

 crease in gluconeogenesis from protein and 

 thus starves the mammary gland of non- 

 nitrogenous milk precursors (Folley and 

 Greenbaum, 1947, 1948). As there is little 

 arginase in the mammary gland of other 

 species {e.g., rabbit, cow, goat, sheep), this 

 mechanism may not have general validity 

 (for further discussion see Folley, 1956). 

 Other biochemical studies have suggested 

 that the steroids of the adrenal cortex may 

 be concerned in mammary lipogenesis, but 

 the results so far have been conflicting and 

 no firm conclusions can as yet be drawn 

 (see Folley, 1956). 



C. OVARIAN HORMONES 



There is no evidence that ovariectomy has 

 any deleterious effect on lactation (Kura- 

 mitsu and Loeb, 1921; de Jongh, 1932; Fol- 

 ley and Kon, 1938; Flux, 1955); neither 

 is there evidence for the belief, once 



TABLE 10.1 



Replacement therapy in lactating rats 



adrenalectomized on the fourth 



day of lactation 



(From A. T. Cowie and S. J. Folley, 



J. Endocrinol., 5, 9-13, 1947.) 



(Above results from Cowie, 1952) 



(Above results from Cowie and Tindal, 1955) 



(Above results from Cowie and Tindal, 

 unpublished) 



* The litter-growth index is defined as the mean 

 daily gain in weight per litter over the 5-day pe- 

 riod from the 6th to the 11th days. 



t 2 X 11 mg. tablets cortisone giving mean daily 

 absorption of 850 ^ig., and 1 X 50 mg. tablet DCA 

 giving mean daily absorption of 360 ng. 



widely held, that ovariectomy increases 

 and prolongs lactation in the nonpregnant 

 cow (see Richter, 1936). 



Although the integrity of the ovary is 

 not essential for the maintenance of lacta- 

 tion, there can be no doubt that ovarian 

 hormones, in certain circumstances, pro- 

 foundly influence milk secretion. Estrogens 

 have long been regarded as possessing the 

 power to inhibit lactation, a concept on 

 which Nelson based his theory of the mech- 

 anism of lactation initiation (see page 606 1 . 

 Some workers, however, have expressed 

 doubts that the effect is primarily on milk 

 secretion, and have suggested that in ex- 



