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

Summary 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 (C_in), para-amino-hippuric acid (C_PAH), sodium (C_Na), and lithium (C_Li) 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 C_in, C_PAH and filtration fraction were comparable in IDDM and control subjects, whereas C_Na 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 C_in, increased C_PAH (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 C_Na (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.Abbreviations IDDM Insulin-dependent diabetes mellitus - GFR glomerular filtration rate - RPF renal plasma flow - C_in clearance of inulin - C_PAH clearance of para-amino-hippuric acid - C_Na clearance of sodium - C_Li clearance of lithium - APR_Na absolute proximal tubular reabsorption of sodium - FPR_Na fractional proximal tubular reabsorption of sodium - ADR_Na absolute distal tubular reabsorption of sodium - FDR_Na fractional distal tubular reabsorption of sodium - FIRI free plasma immunoreactive insulin - TG serum triglycerides - NEFA serum non-esterified fatty acids - MCR metabolic clearance rate of glucose - FF filtration fraction - ANOVA analysis of variance