Aging as a factor in the renal hemodynamic changes induced by a standardized pyrogen.

The functional and anatomic changes of the kidney associated with increasing age have been demonstrated convincingly. The evaluation of renal function in aged persons has demonstrated a progressive decrease in the urea clearance (1), glomerular filtration rate, effective renal plasma flow, and renal tubular transfer maxima (2, 3). These decreases in function fit well with the anatomic studies which hold that the degree of renal arteriosclerosis present in the aging population is sufficient to account for the decrease in renal parenchyma on a basis of restricted blood supply (4-7). The anatomic studies also agree that the predominant picture of arterial degeneration is that of intimal thickening (lumen attenuation and occlusion) in the larger arteries (interlobar and interlobular) with progressively less sclerosis in the vessels as the observations extend toward the glomerulus. Even in the age group beyond 80 years, Bell notes that only about 20 per cent of the renal arterioles are involved in the sclerotic process, and this involvement is not severe (7). In his study of the relationship of age to renal atrophy in non-hypertensive individuals free from renal disease, Bell states, "Areas of atrophy are wedgeshaped and are caused by intimal atherosclerosis with occlusion of fairly large branches of the renal artery." The present study is concerned with an evaluation of the functional status of the renal arterioles in an aging population free of hypertension and demonstrable renal disease. Since it is believed that the increase in renal blood flow following the intravenous administration of a pyrogen is in large part mediated through a decrease in renal arteriolar tonus (8), we have employed a standard1 Present address: Department of Medicine, Peter Bent Brigham Hospital, Boston, Mass. ized pyrogen test to assay the capacity of the renal arterioles to dilate.