Effects of thyrotropin on the proliferation and differentiation of cultured rat preadipocytes.

Thyrotropin receptor (TSHR) is expressed during the differentiation of rat preadipocytes and is highly abundant in mature fat adipocytes, but its physiological role is unknown. In this article, long-term effects of thyrotropin (TSH) on the proliferation and the differentiation were investigated using cultured rat preadipocytes. When TSH was added at the beginning of differentiation, TSH increased the number of preadipocytes and 3H-thymidine uptake. Apoptosis of the cells was not influenced by TSH. Preadipocytes incubated in the presence of TSH had fewer fat droplets, decreased level of mRNA for lipoprotein lipase (LPL), a marker of adipocyte differentiation. Histochemical study showed that the cells that increased their number and expressed lower level of LPL in response to TSH were preadipocytes, and not contaminating fibroblasts. In conclusion, TSH causes the proliferation and inhibits the differentiation of rat preadipocytes. Results suggest that TSH may be a potent regulator of preadipocyte proliferation and differentiation in vivo.