Effects of insulin and lipid emulsion on renal haemodynamics and renal sodium handling in IDDM patients.

To evaluate the role of insulin and hypertriglyceridaemia in the regulation of renal haemodynamics and sodium handling in insulin-dependent diabetes mellitus (IDDM), 11 IDDM patients without microalbuminuria and 13 weight-, age-, protein intake- and sex-matched healthy control subjects were studied. Clearances of inulin (Cin), para-amino-hippuric acid (CPAH), sodium (CNa), and lithium (CLi) were measured in four 60-min clearance periods (periods I, II, III and IV) during isoinsulinaemia with lipid emulsion infusion (study 1), a hyperinsulinaemic isoglycaemic clamp with Intralipid infusion (study 2), and during time-controlled isoinsulinaemia (study 3). We found that Cin, CPAH and filtration fraction were comparable in IDDM and control subjects, whereas CNa was decreased in diabetic subjects (2.01 +/- 1.11 vs 3.03 +/- 1.32 ml/min; p < 0.05) due to elevations of proximal tubular fractional and absolute reabsorptions of sodium (p < 0.05). Insulin infusion did not affect Cin, increased CPAH (p < 0.05) and, consequently, lowered the filtration fraction (p < 0.01) in both groups. While acute hyperinsulinaemia resulted in increases in distal tubular fractional and absolute reabsorptions of sodium (p < 0.01) contributing to a fall in CNa (p < 0.01) in control subjects, in diabetic subjects the sodium-retaining effect of insulin was not significant. The lipid emulsion did not alter any of the estimated parameters. We conclude that IDDM without microalbuminuria is associated with a tendency to sodium retention which is not aggravated by insulin when compared to control subjects. Acutely induced hypertriglyceridaemia does not alter renal haemodynamics or renal sodium handling.