The antilipolytic effect of insulin was investigated in obese subjects before and after 7 days of total fasting, and 1 h after oral refeeding with 100 g glucose. Isolated fat cells were prepared from subcutaneous gluteal adipose tissue and incubated in vitro. Specific insulin receptor binding and insulin inhibition of basal and isoprenaline-stimulated lipolysis were determined. During the fasting period, a 15% increase (P less than 0.05) in high-affinity insulin binding and a concomitant 3-4-fold increase in insulin sensitivity were noted, and there was a marked enhancement of the maximum insulin-induced inhibition of basal lipolysis, from 4 to 10 mumol of glycerol/10(7) cells/2 h. The maximum insulin-induced inhibition of isoprenaline-induced lipolysis was similar before and after fasting, about 10 mumol/10(7) cells/2 h. Glucose refeeding induced a 30% decrease (P less than 0.02) in high-affinity insulin binding and a 20-60-fold decrease (P less than 0.01) in the sensitivity of the antilipolytic effect of insulin under basal conditions and in the presence of isoprenaline. The maximum antilipolytic effect of insulin, however, was not altered by glucose refeeding. Thus, in the basal state, maximum antilipolytic effect was larger after refeeding as compared with that before fasting. The high-affinity insulin binding and insulin sensitivity were significantly lower after refeeding than before fasting. Before the fasting period, neither the insulin binding nor the antilipolytic effect of the hormone was altered by oral glucose. It is concluded that fasting and glucose refeeding are associated with marked alterations in the antilipolytic effect of insulin on human fat cells of obese subjects.(ABSTRACT TRUNCATED AT 250 WORDS)