Mechanical stimulation of mammary gland development in virgin and pregnant rats

The mammary glands of pregnant Sprague-Dawley rats prevented from self-licking by collars around the neck (n = 9) were only about 50% as developed as those of pregnant rats without collars (n = 9). However, when the ventral body surface of pregnant collared rats was stimulated mechanically (n = 9), mammary glands increased in size, underwent lobuloalveolar growth, and secreted milk in a manner similar to normal pregnant rats.When virgin rats were stimulated mechanically for 22 days (n = 9), their mammary glands had significantly greater secretory tissue and lobuloalveolar development than did the glands of nonstimulated virgin rats (n = 9).Stimulated rats were tied to the stimulating device under ether anesthesia. Because ether and restraint have been shown under some conditions to be Stressors that increase development of the mammary glands, two additional pregnant collared control groups were added. One was restrained on the device without stimulation (n = 9). The other was lightly anesthetized with ether (n = 10). Mammary underdevelopment occurred in both groups. This suggested that stress of ether and restraint were unlikely causes of the mammary development in the stimulated group.