Abstract
Prolactin was injected to the normally lactating and unilaterally ligated mice in order to ameliorate or maintain the respiratory activity of the mammary gland From the results of the histological observation and litter's growth curve in addition to the respiratory activities, it was suggested that prolactin might exert some influence on metabolic or synthetic process, qualitatively but not quantitatively. And it was discussed that there might exist a certain optimum dose according to the condition of mammary gland for prolactin to exert stimulatory effect on the mammary respiratory activity. However, prolactin, in adopted doses, did not prevent the involution occurring in the ligated gland six days after unilateral ligature. From these results it may be possible to conclude that the removal of milk might be a limiting factor, and further, prolactin may be effective for maintaining the mammary gland in the functioning state, although the dosage of hormone in connection with the stage of lactation is an important factor.
