Production of Pseudo-Pregnancy by Mechanical Stimulation of the Nipples

Abstract

We have previously described experiments on lactating rats in which we found that the nervous stimulus of suckling could maintain the dioestrus of lactation after all galactophores had been transcised. 1 , 2 It was also observed that in such animals, from which escape of milk to the litter was prevented, the mammary gland did not undergo rapid involution, but remained in an actively secreting state for some time in spite of the accumulation of the products of secretion.

The escape of milk is therefore not an essential condition for the continuation of dioestrus or for the maintenance of secretory activity in the mammary glands. Accordingly, the questions arise whether the influence of suckling could produce dioestrus in the absence of actively lactating glands and whether, since suckling will maintain the secreting gland, it could lead to a regeneration once involution has set in.

In order to answer these questions we performed the following experiments on rats.

The animals used fall into 3 groups: first, adult virgin rats; second, animals whose litters have been weaned at the end of a normal lactation and which have been seen to be normally cyclic for at least 3 cycles; and third, lactating mothers deprived of their litters on the third day postpartum and studied daily until one or 2 oestrus cycles had appeared. To all animals a strong suckling stimulus was applied, and in order to keep the young alive they were exchanged with the well nourished litter of a normally lactating mother on alternate days, the young of the normal mother being transferred on these days to the experimental animal. Thus the rats under observation were continuously exposed to the suckling stimulus.