Short-term protein loading in diabetics with a ten-year duration of disease
B. H. Brouhard, L. F. LaGrone, G. E. Richards and L. B. Travis
The concept of renal functional reserve has recently been introduced. To
test this ability of the kidneys to increase the glomerular filtration rate
(GFR) above the baseline level, the GFR response to short-term protein load
was measured. Recent studies have provided conflicting data concerning the
GFR response to a protein load in insulin-dependent diabetics who are known
to have increased baseline GFRs. Thus, we studied nine insulin-dependent
diabetics with a disease of at least a ten-year duration (none were
hypertensive or proteinuric) and compared their data with those of five
nondiabetic controls with normal renal function. All the diabetics, except
one, showed a significant increase in GFR (mean +/- SEM, 60 +/- 9 to 74 +/-
14 mL/min/sq m); the controls also had increased GFRs (mean +/- SEM, 53 +/-
6 to 69 +/- 6 mL/min/sq m). The one patient who demonstrated no rise in the
GFR had the lowest GFR measured, 33 mL/min/sq m. To explore the mechanism
of this response, we measured the plasma levels of putative mediators
glucagon and human growth hormone. Although glucagon showed the expected
rise after the protein meal, the variability was so large that no
statistically significant relationship could be identified. Human growth
hormone remained constant and low in the controls and showed more
variability and was higher in the diabetics; again, no relationship to the
GFR could be demonstrated. Thus, our data demonstrated a normal response to
a short-term protein load by a group of well-defined diabetic subjects who
would be at risk to show subtle renal abnormalities.
