Hormonal Regulation of Leptin mRNA Expression and Preadipocyte Recruitment and Differentiation in Porcine Primary Cultures of S‐V Cells

The hormonal regulation of leptin mRNA expression and the association between leptin expression and adipocyte differentiation were examined in primary cultures of porcine S‐V cells with Northern blot and immunocytochemical analysis. Seeding for 3 days with fetal bovine serum (FBS) with varying levels of dexamethasone (Dex) increased levels of leptin mRNA in a dosedependent manner in parallel with increases in the proportion of preadipocytes (AD‐3 positive cells; AD‐3, a preadipocyte marker). Six‐day treatment with 10 or 850 nM insulin after FBS+Dex treatment resulted in a similar increase in leptin mRNA expression and morphological differentiation. However, significantly lower levels of leptin mRNA and smaller fat cells were observed in cultures treated with 1 nM insulin or 10 nM insulin‐like growth factor‐I (IGF‐I). Dex‐induced increases in leptin mRNA levels and AD‐3 cell numbers were blocked completely by the addition of transforming growth factor‐β (TGF‐β) to FBS+Dex‐treated cultures. However TGF‐β significantly increased fat cell size and leptin mRNA expression when added to ITS (insulin, 850 nM; transferrin, 5 μg/ml; and selenium, 5 ug/mL) treated cultures during the lipid‐filling stage. When added with FBS+DEX for the first 3 days, growth hormone (GH) did not influence the Dex‐induced increase in AD‐3 cells and leptin mRNA expression, but GH reduced leptin mRNA levels when added with insulin for 6 days after FBS+Dex. These results demonstrated that regulation of leptin mRNA expression by Dex, insulin, IGF‐I, TGF‐β, and GH may be associated with changes in preadipocyte number and fat cell size.