Metabolic response to exercise in dialysis patients

Abstract

The metabolic and hormonal response to acute moderate intensity (40% of VO2 max) bicycle exercise was examined in eight uremic subjects maintained on chronic dialysis and in 12 age- and weight-matched controls before and after the administration of low dose, selective (metoprolol) and non-selective (propranolol), beta adrenergic antagonists. The fasting plasma glucose concentration and basal rates of hepatic glucose production (HGP) and tissue glucose disappearance (Rd) were similar in control and uremic subjects. In both groups HGP and Rd increased in parallel during exercise, and the plasma glucose concentration remained constant at the fasting level. However, the increments in Rd (2.27 ± 0.27 vs. 0.87 ± 0.31 mg/kg·min, P<0.01) and HGP (2.47 ± 0.22 vs. 0.92 ± 0.19 mg/kg·min, P<0.01) were 2.5-3 fold greater in the control compared to uremic subjects. Although the VO2max was decreased by 50% (39 ± 2 vs. 20 ± 2 ml/min·kg; P<0.01), the correlation between Rd and VO2 max was weak (r = 0.33, P<0.10), suggesting that factors other than diminished physical fitness contribute to diminished tissue uptake of glucose in the dialyzed uremic patients. Following the cessation of exercise, HGP and Rd promptly returned toward basal levels in both uremic and control subjects. The glucose homeostatic response to exercise was not significantly altered by either propranolol or metoprolol. In the postabsorptive state fasting levels of insulin, glucagon, epinephrine, and norepinephrine all were significantly increased in the uremic group (P<0.01 to 0.05). During exercise in the healthy young controls the plasma insulin concentration declined and plasma epinephrine and norepinephrine levels rose three- to fourfold. In contrast, in uremics plasma insulin failed to fall (P<0.05) and the increase in circulating epineprhine and norepinephrine levels was markedly impaired (P<0.01). The plasma glucagon concentration did not change signficantly from baseline in either the control or uremic groups during exercise. Neither low dose propranolol nor metoprolol altered the hormonal response to exercise in either group.