Development of the epididymal adipose tissue in monosodium glutamate-induced obese mice.
Obesity was induced in neonatal mice by subcutaneous injections of monosodium glutamate (MSG) at an early neonatal stage. The process of adipocyte formation was studied comparatively in the developing epididymal adipose tissue of the MSG-treated mice and in normal mice during the period from the 6th to the 100th postnatal day. Tritiated thymidine autoradiographic studies showed that cell proliferation activity was the highest on the 6th postnatal day both in the MSG-treated and the control mice. In normal mice, however, cell proliferation took place less frequently after 6 days and had almost ceased after 49 days. In the obese mice, as evidenced by relatively high labeling indices, cell proliferation continued to occur even after 49 days. Ultimately there was no difference in the number of adipocytes counted by Hirsch's method in the MSG-treated and the control mice at the 100th postnatal day. The storage of fat droplets became more noticeable in obese mice than in normal mice after 35 days. The mean size of fat droplets of the obese mice was twice as large as that in normal mice on the 49th postnatal day. These results indicate that the MSG-induced obesity is of the hypertrophic type.