SMOKING INCREASES CONVERSION OF LACTATE TO GLUCOSE DURING SUBMAXIMAL EXERCISE

We examined the hypotheses that 1) smoking acutely before exercise (AS ) results in a higher rate of lactate production during exercise compa red with chronic smoking with preexercise abstinence (CS) and 2) smoke rs have a higher rate of lactate conversion to glucose during exercise compared with nonsmokers (NS). To test our hypotheses, seven male smo kers and seven nonsmokers were studied by using a primed continuous in fusion of [3-C-13]lactate during 90 min of rest and 60 min of exercise on a cycle ergometer at 50% peak O-2 consumption; smokers were studie d twice: once after an overnight smoking abstinence and once after smo king three cigarettes before exercise. The rates of lactate appearance and conversion to glucose were increased markedly with exercise compa red with rest in all groups (P < 0.05); the rate of lactate appearance for AS was significantly greater (7.87 +/- 0.77 mg . kg(-1). min(-1)) than for both CS (4.64 +/- 0.33 mg . kg(-1). min(-1)) and NS (5.57 +/ - 0.60 mg . kg(-1). min-1) (P < 0.05). The rate of lactate conversion to glucose was similar between CS and AS (6.49 +/- 1.82 and 6.30 +/- 1 .69 mg . kg(-1). min(-1), respectively) during exercise; NS had a sign ificantly lower rate (3.31 +/- 0.90 mg . kg(-1). min(-1)) compared wit h CS and AS (P < 0.05). In summary, acute smoking increases lactate fl ux during exercise; in addition, smokers have a higher rate of lactate to glucose conversion during exercise compared with nonsmokers, which may indicate an increased glucose dependency.