Production of pseudo-pregnancy by mechanical stimulation of the nipples.
An experiment was conducted on rats in an effort to answer the following questions: could the influence of suckling produce a dioestrus in the absence of actively lactating glands; and since suckling will maintain the secreting gland, could it lead to a regeneration once involution has set in. The animals used were adult virgin rats, animals whose litters had been weaned at the end of a normal lactation and which have been seen to be normally cyclic for at least 3 cycles, and lactating mothers deprived of their litters on the 3rd day postpartum and studied daily until 1 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 rats under observation were continuously exposed to the suckling stimulus. Only rarely would an animal harm the litter. This was the case no less frequently with lactating mothers than with virgins. In many instances, there was no suckling, either from the unwillingness of the animal to allow it or from the inability of the litter to find the relatively small nipples of virginal and weaned rats. Nipples often became necrotic from the strength of the stimulus, especially in virgins and in animals weaned for a long time. Of 25 animals given litters, active suckling occurred only in 15 cases. For a group of 8 animals, the teats took on the appeareance and flexibility of those of a lactating mother after a few days. These animals became continuously dioestrous, but in some cases an oestrus cycle occurred after the initiation of nursing. As biopsy specimens showed, the mammary gland developed to the same extent as it would in the course of pseudo-pregnancy.