The role of lactation and weaning in the pathogenesis of arteriosclerosis in female breeder rats

Abstract

Female breeder rats develop spontaneous arteriosclerosis if they are actively and repeatedly bred. Females which nursed large litters following each pregnancy appeared to develop the most severe arterial disease as well as other degenerative changes. In order to determine how the degree of lactational activity would affect the pathogenesis of the arterial disease female breeder rats were provided with many, few or no pups during the lactation phase following each of 4 pregnancies. To test the effect of abrupt cessation of milk removal vs. complete removal of milk, breeder females were provided with many pups to nurse following each of 4 pregnancies. However, in some cases the young were removed suddenly, i.e., forced weaning, after 23 days of lactation, whereas some females were permitted to nurse their young until they gave up nursing voluntarily, i.e., natural weaning. A special group of breeders completed 1 pregnancy only but was provided with nursing pups for an extended period of time, i.e., 100 days.

The results of these experiments demonstrated, that female breeders which had experienced one or several pregnancies and which had lactated actively followed by abrupt weaning of the young developed grossly visible arteriosclerosis characterized by severe calcific complications. On the other hand, breeders which were permitted to suckle their young until they were weaned naturally were completely free of the severe calcific arterial involvement. However, early microscopic intimal mucopolysaccharide accumulations capped by collagen could be found in all breeders. These intimal lesions are believed to be the forerunners of the more complicated lesions and are believed to be associated with the gestational phase of the reproductive cycle.