A study of nephron function in normal tropical residents using the creatinine and lithium clearances

Abstract

The kidney bears the brunt of the demands of a tropical climate for water and electrolyte homeostasis. We hypothesised that a tropical climate may cause adaptive changes in the entire organism leading to altered renal function in our subjects. Hence renal function data for residents of a temperate climate may not be applicable to tropical residents. We therefore sought to elucidate renal function in subjects residing in a tropical climate. We used lithium clearance, CLi, a non-invasive tool for assessing proximal tubular function in humans, and endogenous creatinine clearance, CCr, to estimate proximal tubular function and glomerular function, respectively, in our subjects. We did this in order to establish whether or not nephron function in our subjects differs from that for residents of a temperate climate. Nineteen male and 12 female Ghanaian subjects aged between 15 and 48 years were studied. The estimated GCr was 117.3 +/- 6.6 ml/min for male subjects and 97 +/- 6.4 ml/min for female subjects. CLi was 20.3 +/- 1.6 ml/min for male and 19.1 +/- 0.4 ml/min for female subjects, respectively. The estimated absolute reabsorption rate of fluid of proximal tubules was 97.0 +/- 6.0 ml/min for males and 78.1 +/- 6.0 ml/min for females. The percentage proximal fluid reabsorption for male and female subjects was 81.2 +/- 1.4 and 79.5 +/- 1.6, respectively. The differences between male and female values (mean +/- SEM) were not statistically significant. The data suggest that the proximal tubule in residents of a tropical climate may reabsorb more fluid compared to that in residents of a temperate climate. Our values for proximal tubular reabsorption are higher than those reported for residents of a temperature climate. Our estimate of glomerular filtration, however, is similar to published data for Caucasians. The difference in proximal tubular function may reflect possible renal adaptation to a hot, humid climate. We conclude that renal function of tropical residents differs from that of residents of a temperate climate. This difference may be due to renal adaptation to the hot, tropical climate.