We have recently demonstrated that adipose tissue can produce lactate independently of lipolysis in insulin-resistant rats and that lactate production depends on alpha 1-adrenergic stimulation. In this study, we have investigated the influence of aging on norepinephrine-and-phenylephrine-stimulated lactate production and glycerol production. We showed that basal and norepinephrine stimulated lactate production were significantly increased in adipocytes isolated from old vs. young rats (0.165 +/- 0.006 vs. 0.055 +/- 0.008 for basal and 0.567 +/- 0.026 vs. 0.277 +/- 0.019 mumol lactate/10(6) cells/15 minutes for norepinephrine-stimulated lactate production, respectively, p < 0.05). The sensitivity of lactate production to norepinephrine stimulation in adipocytes isolated from old rats was significantly decreased (EC50 = 523 +/- 63.7 vs. 46.7 +/- 6.34 nM, respectively, p < 0.05). Maximal lactate production obtained with norepinephrine and phenylephrine was not significantly different in either group (0.567 +/- 0.026 vs. 0.520 +/- 0.036 in old and 0.277 +/9 0.019 vs. 0 275 +/- 0.017 mumol/10(6) cell/15 minutes in young rats, respectively, ns). Lactate production by adipocytes isolated from old rats were significantly less sensitive to phenylephrine stimulation compared with young (EC50 = 3.67 +/- 1.16 vs. 0.07 +/- 0.01 nM, respectively, p < 0.05) indicating that the effects of aging on norepinephrine and phenylephrine stimulation were probably induced by a decreased number of alpha 1-adrenoceptors. The mechanism by which aging increases adipocyte responsiveness of lactate production has not yet been elucidated.