Fig. 3.

Time course of leptin synthesis and secretion by isolated white adipocytes upon stimulation by insulin. Adipocytes were isolated from rat epididymal tissue by the collagenase technique and incubated in the presence or not of insulin (10 nM). Insulin is known to stimulate leptin secretion by adipocytes. Cells as well as media were sampled at regular time points and assessed for intracellular leptin content and amounts of leptin released in the culture medium. In the absence of insulin (basal condition), the amounts of leptin in the medium increase regularly over time while intracellular content of leptin remains unchanged. Upon stimulation by insulin, leptin in the medium increases much faster than under basal condition, while leptin intracellular content increases significantly reflecting stimulation of leptin synthesis by the cells. However, we can notice that upon stimulation of leptin secretion by insulin, the response of the cells is quite slow since it takes about 60 min for the increases in leptin to be significant.