Role of the kidney in plasma glucose regulation during hyperglycemia

Little is known about the role of the kidney in plasma glucose regulation during hyperglycemia. We studied 12 overnight-fasted conscious dogs after either intrarenal (IR, n = 6) or peripheral (PH, n = 6) dextrose infusion to maintain hyperglycemia without glycosuria. Systemic and renal glucose kinetics were measured with [6-³H]glucose, lactate balance was measured by arteriovenous difference, and glycogen content was assayed in the kidneys. Plasma glucose (~5.5 vs. ~6.3 mM), insulin (~70 vs. ~110 pM), and glucose appearance (~14 vs. ~16 μmol · kg^-1 · min^-1) increased comparably in both groups (P < 0.05). In IR, fractional extraction of glucose (FE(Glc)) increased from 4.1 ± 0.2 to 16.1 ± 0.5% (P < 0.001) and lactate balance reversed to renal output (+ 1.3 ± 0.2 vs. -0.9 ± 0.2 μmol · kg^{- 1} · min^-1, P < 0.01). Glycogen content was twofold higher in the left (127 ± 33 μg/g tissue) than in the right kidney (56 ± 11 μg/g tissue, P < 0.01). In PH, FE(Glc) decreased from 4.9 ± 0.6 to 2.2 ± 0.3% (P < 0.05), renal glucose utilization did not change (~1.3 μmol · kg^-1 · min^-1), and glycogen content was equal in both kidneys (~45 μg/g tissue). We conclude that, although the kidney plays a minor role in plasma glucose disposal in physiological hyperglycemia, increased glucose uptake, glycogen storage, and lactate formation precede glycosuria and may represent important mechanisms by which the kidney contributes to normalization of plasma glucose in diabetes.