Age, renal perfusion and function in island-dwelling indigenous Kuna Amerinds of Panama

Background/Aims: Among possible contributors to a progressive fall in renal perfusion and function with increasing age, some hypotheses have invoked t he rise in blood pressure that occurs with age, and a high-protein diet typ ical of urban cultures. Kuna Amerinds residing in isolated islands off the Panamanian Coast have a very low protein intake and show no tendency for bl ood pressure to rise with age, thus providing an opportunity to test these hypotheses. Methods: We measured renal plasma flow and glomerular filtratio n rate (PAH and inulin clearance) in 16 Kuna Indians ranging in age from 18 to 86 years (51 +/- 6 years) who have resided on Ailigandi, an isolated Pa namanian island for all of their lives. Inulin and PAH were infused with a battery-driven pump for 60 min, and a metabolic clearance rate used to calc ulate inulin and PAH clearance. For comparison, we employed identical techn iques in 29 residents of Boston, ranging in age from 19 to 79 years (52 +/- 4 years), all normotensive and free of disease or medication use. Twenty-f our were Caucasian. Results: The Bostonian controls showed the anticipated fall in PAH clearance with age (y = 806 - 4.9x; r = -0.82; f = 38.0; p < 0. 0001). Our hypothesis was that the absence of a blood pressure rise with ag e and the low protein intake would flatten the slope relating renal perfusi on to Kuna age. Our finding was a numerically steeper slope relating age an d renal plasma flow in the Kuna (y = 936 - 6.48x; r = -0.81; p < 0.001). Fi ltration fraction rose with age in both populations, and again the rise was steeper in the Kuna. GFR in the Kuna, on the other hand, was very much hig her at any age (139 +/- 4 ml/min/1.73 m(2)) than in Bostonians (112 +/- 3 m l/min/1.73 m(2); p < 0.001). Conclusion: The findings are not in accord wit h the hypothesis that age-related changes in renal perfusion and glomerular filtration rate reflect an important contribution from blood pressure rise and a high protein intake, typical of modern, urban life.