STIMULATION OF LEPTIN RELEASE BY ACTINOMYCIN-D IN RAT ADIPOCYTES

A greater understanding of the factors causing the enhanced release of leptin by adipocytes in obesity is needed. Experiments were designed to determine the effects of actinomycin D on leptin release by isolate d rat adipocytes during primary culture for 24 hr. In adipocytes from fed hypothyroid rats, the initial rate of leptin release over the firs t 6 hr was not maintained over the next 18 hr. The decline in leptin r elease by adipocytes in primary culture between 6 and 24 hr was reduce d markedly by either dexamethasone or actinomycin D. Both actinomycin D and dexamethasone also reduced the loss of leptin mRNA seen over the 24-hr incubation. Maximal effects on leptin release and leptin mRNA a ccumulation required only 0.1 mu M of actinomycin D, a concentration t hat had no significant effect on the 18S RNA content of adipocytes at the end of a 24-hr incubation. In contrast to the reduced loss of lept in mRNA seen at 24 hr, the loss of glyceraldehyde 3-phosphate dehydrog enase messenger ribonucleic acid (GAPDH mRNA) was enhanced in the pres ence of 0.1 mu M of actinomycin D. The effects of dexamethasone could be differentiated from those of actinomycin D by the finding that cycl oheximide blocked the reduced loss of leptin mRNA due to dexamethasone while having no effect on that due to actinomycin D. These results po int to a unique regulation of leptin release and leptin mRNA levels by actinomycin D. (C) 1998 Elsevier Science Inc.