RENAL FUNCTIONAL-RESPONSE TO PROTEIN LOADING IN TYPE-1 (INSULIN-DEPENDENT) DIABETIC-PATIENTS ON NORMAL OR HIGH-SALT INTAKE

Insulin-dependent diabetes mellitus (IDDM) patients may have an increa sed intrarenal angiotensin II activity. In diabetic patients, captopri l increases the renal hemodynamic response to an amino acid infusion. We investigated the effects of two salt diets on arterial pressure and renal response to a protein load in 10 normotensive (blood pressure < 140/90 mm Hg) IDDM patients (aged 30 +/- 3 years) who had diabetes fo r 7 +/- 4 years and normoalbuminuria levels [albumin excretion rate 4. 8 (2.5-19.1) mu g/min]. After 1 week of normal (approximate to 100 mmo l/day; approximate to 100 mEq/l) and 1 week of high (approximate to 30 0 mmol/day; approximate to 300 mEq/l) salt intake, renal hemodynamic s tudies were performed at baseline and after a protein load (meat meal) of 100 g/1.73 m(2). The mean 24-hour urinary sodium excretion levels were 99 +/- 27 and 293 +/- 80 mmol (mEq) with normal and high salt int ake, respectively. No significant changes were seen in plasma sodium a nd glucose control with the normal and high salt diets, respectively: plasma sodium 135 +/- 3 vs. 137 +/- 1 mmol/l (mEq/l), (p = 0.08) and g lycated hemoglobin 9.1 +/- 1.9 vs. 9.4 +/- 2.1% (p = 0.36). The body w eight (70.9 +/- 12 vs. 71.8 +/- 13 kg; p = 0.015) was significantly hi gher with a high salt diet. The mean arterial pressure was similar wit h both diets (normal vs. high salt diet 91 +/- 9 vs. 89 +/- 6 mm Hg, p = 0.25). The plasma renin concentration [28 +/- 15 vs. 16 +/- 6 mu U/ ml (168 +/- 90 vs. 96 +/- 36 pmol/l), p = 0.013] and angiotensin II [8 .8 +/- 4.4 vs. 6.4 +/- 3.5 pg/ml (0.052 +/- 0.025 vs. 0.038 +/- 0.021 nmol/l), p = 0.016] were significantly lower with the high salt diet. Following protein loading, the glomerular filtration rate increased wi th both diets: normal salt diet 114 +/- 26 vs. 128 +/- 30 ml/min/1.73 m(2) (1.9 +/- 0.43 vs. 2.13 +/- 0.50 ml/s/1.73 m(2)), p = 0.04; high s alt diet 118 +/- 23 vs. 127 +/- 29 ml/min/1.73 m(2) (1.97 +/- 0.38 vs. 2.12 +/- 0.48 ml/s/1.73 m(2)), p = 0.13. The change in renal plasma f low was similar to that of the glomerular filtration rate with normal and high salt intake, respectively: 566 +/- 94 vs. 617 +/- 142 ml/min/ 1.73 m(2) (9.44 +/- 1.57 vs. 10.29 +/- 2.37 ml/s/173 m(2)), p = 0.0017 ; 572 +/- 125 vs. 600 +/- 110 ml/min/1.73 m(2) (9.54 +/- 2.08 vs. 10.0 0 +/- 1.83 ml/s/1.73 m(2)), p = 0.057. In this subset of normotensive normoalbuminuric IDDM patients, a high salt intake did not promote an exaggerated renal response to the protein load despite inhibition of t he renin-angiotensin system.