Glomerular adaptations with normal aging and with long-term converting enzyme inhibition in rats

Normal aging is accompanied by renal functional and structural deterioration. To examine the hemodynamic and growth-related mechanisms of age-associated nephron loss, as well as the potential beneficial effects of antihypertensive therapy, studies were performed in normal aging Munich- Wistar rats, and in rats receiving long-term antihypertensive therapy with the converting enzyme inhibitor (CEI) enalapril. In protocol 1, rats were treated from the age of 3 mo. Compared with young rats, untreated old rats studied at 2.5 yr of age exhibited normal blood pressure but increased glomerular capillary pressure due to a reduction in afferent arteriolar resistance. Glomerular size increased proportionately to changes in body weight, while kidney weight increased to a lesser degree. Albuminuria rose significantly after 10 mo of age and was accompanied by development of modest, but significant, glomerular sclerosis. CEI therapy from the age of 3 mo lowered systemic and glomerular capillary pressures, did not affect glomerular size, and significantly ameliorated development of albuminuria and structural injury. In protocol 2, untreated rats were compared with a treated group in which enalapril therapy was delayed until the age of 1 yr, when albuminuria was already rising. Subsequent increases in albuminuria and development of sclerosis were significantly attenuated, although not entirely prevented. These findings suggest that hemodynamic maladaptations may contribute to age-related loss of renal function in the rat and that antihypertensive therapy may serve to delay this process.