Renal functional reserve in obesity hypertension

The capacity to increase glomerular filtration rate in response to an acute oral protein load is known as the renal functional reserve; the loss of such capacity is used as a marker of hyperfiltration. This physiological response in obese hypertensives is not yet fully understood. We aimed to study the interdependent effects of obesity and hypertension on renal reserve, taking into account renal kallikrein and nitric oxide in the modulation of that parameter. Fourteen obese hypertensives (mean age, 50.5 +/- 0.9 years) and nine lean hypertensives (mean age, 50.6 +/- 2.7 years) were evaluated. Renal haemodynamics and the levels of serum nitric oxide and urinary kallikrein were assessed at baseline and after a protein load (1 g/kg of body weight). An increase in the following parameters was observed when comparing obese and lean hypertensives: basal glomerular filtration rate; renal plasma flow; and urinary kallikrein and nitric oxide levels (129.2 +/- 2.9 vs. 101.4 +/- 3.4 ml/min/1.73 m2; 587.5 +/- 18.2 vs. 502.8 +/- 16.7 ml/min/1.73 m2; 0.120 +/- 0.02 vs. 0.113 +/- 0.02 mU/ml; 23.2 +/- 0.8 vs. 19.5 +/- 1.2 mmol/ml, respectively). The renal reserve was lower in obese hypertensives when compared with that of lean hypertensives (4.1 +/- 0.5 vs. 11.8 +/- 0.8 ml/min, p < 0.005). After a protein load, contrasting with the lean group, inability to elevate the nitric oxide serum levels and a lower increase in urinary kallikrein were observed in the obese group. These data suggest that obese hypertensives lose renal reserve earlier in the evolution to renal dysfunction. This may be due to the defective modulation of renal vasodilatation mechanisms by renal kallikrein and nitric oxide production.