Milk-ejection responses following administration of tap stimuli and posterior pituitary extracts.

Since the original work of Ely and Petersen(1941),various views(Andersson, 1951;Cross,1953,1954,1955;Cross and Harris,1953;Whittlestone ,1952,1954 a, b,c;see review:Petersen,1948;Folley 1952;Folley and Malpress ,1948;Macaulay, 1950)have been accumulated as to the mechanism of milk"let-down"(or ejection,in the terminology since suggested by Cowie,Folley,Cross,Harris,Jacobsohn, and Richardson,1951;see also Yokoyama,1954).These evidences put forward the hypothesis that the mechanical stimulation of the teats of the lactating animal had induced the reflex release of oxytocic hormone from the posterior lobe of pituitary gland.Oxytocic hormone thus secreted,provoked a contraction of the myoepithelial cells of mammary gland and caused milk ejection response(Richardson,1949;Linzell,1952). On the other hand,there were some observations which tended to indicate that the mechanical stimulation of the teat was also important for the secretion of prolactin(Selye,1934;Hooker and Williams,1940;Meites and Turner,1942) and the maintenance of milk secretion(galactopoiesis:see review,Cowie and Folley,1955;Folley and Malpress,1948).Prolactin and the other galactopoietic hormone accepted to be originated from the anterior pituitary gland(Cowie and Folley,1955;Folley,1952;Folley and Malpress,1948). Involvement of the hypothalamus in the control of the release of these hormones,i.e.oxytocic and galactopoietic hormones,were well known but distinct relationship between the release of these hormones had not been studied. It is of great interest to study the mechanism of the release of these hormones, which was caused by suckling stimulus,under the light of the hypothalamic control. But prior to the investigation of this mechanism,following experiments were performed in order to determine the type of milk ejection responses to posterior pituitary extracts and to"tap"stimuli,and the effect of adrenaline on these responses.