Renal functional reserve and microalbuminuria in offspring of hypertensive parents
Renal functional reserve, microalbuminuria, and plasma atrial natriuretic factor were measured in 21 offspring (9.5 +/- 0.5 years of age, mean +/- SEM) of hypertensive parents and in eight children (10 +/- 0.5 years of age) with no family history of hypertension who were used as a control group. Renal functional reserve was evaluated by measurement of the changes in creatinine clearance after an oral protein load of 45 g/m2. Atrial natriuretic factor levels were determined before and 60 minutes after the protein load, and microalbuminuria in fractional urine before and 120 minutes after the same stimulus as well as in a 24-hour urine collection. All children in the control group significantly increased their creatinine clearance after the protein load (preload, 122 +/- 12; 60 minutes, 144 +/- 9; 120 minutes, 154 +/- 11; 180 minutes, 144 +/- 9 ml/min/1.73 m2; all values were significant vs. preload, p less than 0.005). In contrast, only 13 of 21 offspring of hypertensive parents increased their creatinine clearance to values within 2 SD of the increase shown by the control group (preload, 144 +/- 11; 60 minutes, 153 +/- 7; 120 minutes, 202 +/- 13 ml/min/1.73 m2; p less than 0.001 vs. preload; 180 minutes, 214 +/- 19 ml/min/1.73 m2, p less than 0.001 vs. preload). The remaining eight offspring of hypertensive parents showed no detectable changes (nonresponders) (preload, 189 +/- 18; 60 minutes, 146 +/- 11; 120 minutes, 170 +/- 14; 180 minutes, 168 +/- 13 ml/min/1.73 m2; all values p = NS). No changes in atrial natriuretic factor after the protein load were observed in any group. Offspring of hypertensive parents presented higher microalbuminuria levels in 24-hour urine specimens (3.1 micrograms/min, tolerance factor [TF]2.2) than controls (2.1 micrograms/min, TF 1.5) (p less than 0.05). Although microalbuminuria increased significantly after the water load in the control group (p less than 0.05) and in the offspring of hypertensive parents (p less than 0.01), it returned to baseline at 120 minutes in the former but not in the latter (p less than 0.05 vs. baseline). The lack of renal functional reserve in nonresponders was significantly related (p less than 0.05) to the presence of higher levels of microalbuminuria. We conclude that the absence of renal functional reserve and increased microalbuminuria in some normotensive children who are offspring of essential hypertensive parents can indicate that subtle alterations in renal function may precede the onset of clinical hypertension.