Background: Metabolic acidosis affects both vitamin D and insulin metabolism. Vitamin D is important in modulation of both insulin secretion and insulin sensitivity in uremia. The present study examines the effect of correction of metabolic acidosis on insulin action and secretion as well as 1,25 vitamin D3 concentrations in uremic patients.
Methods: Eight patients (age 18 +/- 1 year) on maintenance hemodialysis with metabolic acidosis were studied before and after two weeks of oral sodium bicarbonate (NaHCO3) treatment to correct the acidosis. To control for the effect of additional sodium, they were also studied after two weeks of an equivalent amount of oral sodium chloride (NaCl). Controls consisted of 7 healthy controls (age 19 +/- 1 year). Insulin sensitivity was measured by the hyperinsulinemic euglycemic clamp technique. Insulin secretion was measured by the hyperglycemic clamp technique.
Results: Oral NaHCO3 treatment led to significant increases in venous pH and serum bicarbonate concentrations but no significant change in intact parathyroid hormone (PTH) concentrations. Circulating 1,25 dihydroxyvitamin [(OH)2] D3 were significantly lower than control values initially and increased significantly after treatment. Oral NaCl did not change any of the biochemical parameters. Before treatment of acidosis, uremic patients had lower insulin sensitivity (insulin resistance) during constant hyperinsulinemia and lower insulin secretion during constant hyperglycemia compared with controls. Following two weeks of NaHCO3 treatment there were significant increases in insulin sensitivity and insulin secretion, although the values did not normalize. There were no changes in insulin sensitivity or insulin secretion following two weeks of NaCl.
Conclusion: Treatment of metabolic acidosis increased both insulin sensitivity and insulin secretion in patients with uremia. This was accompanied by an increase in the circulating levels of 1,25(OH)2D3 but no change in those of parathyroid hormone.