The effects of age, race and heredity on glomerular filtration rate following volume expansion and contraction in normal man

To elucidate racial and age differences in natriuretic responses following volume expansion, we studied GFR, as reflected by endogenous creatinine clearance, in 446 normal persons including 99 blacks and 44 pairs of mono-and dizygotic twins. GFR was measured day and night, under basal conditions, following volume expansion with 2 L intravenous normal saline and volume contraction with 120 mg oral furosemide. Volume expansion and contraction altered GFR to similar degrees in whites and blacks. White exhibited a diurnal variation in GFR (day>night) under all conditions, which was not observed in blacks. Following saline, whites excreted more sodium during the day, but less sodium during the night, than blacks (p<0.05). In whites, UnaV and GFR were correlated only during the day, while in blacks the correlation persisted throughout the night. When the white population was divided into subjects < 40 years and ≥40 years, the responses of the older whites resembled those of blacks. The inverse relationship between GFR and age was steeper in blacks than whites. A twin analysis demonstrated that plasma creatinine, urinary creatinine excretion and creatinine clearance are heritable. The failure of GFR to decrease at night in blacks and older whites may be related to an altered natriuretic capacity. Decreases in GFR with aging are greater in blacks than whites. GFR is partially under the influence of genetic variance.