Onset of glomerular hypertension with aging precedes injury in the spontaneously hypertensive rat
The changes in renal hemodynamics that develop with aging in spontaneously hypertensive rats (SHR) were examined. Micropuncture studies revealed that glomerular capillary pressure was elevated in SHR at 9 mo of age compared with 3-mo-old SHR and 9-mo-old normotensive Wistar-Kyoto rats. Glomerular hypertension developed because of a small increase in systemic blood pressure and a decline in preglomerular vascular resistance, allowing transmission of elevated systemic pressure to the glomerular capillaries. The hemodynamic alterations were not a compensatory response to injury, inasmuch as vascular and glomerular morphology were normal in 9-mo-old SHR. To determine the mechanism of these changes, the activity of several vasoactive systems was examined. Similar changes in renal hemodynamics were observed in young and old SHR after blockade of nitric oxide production and after intravenous administration of endothelin. However, ANG II produced a proportionally greater reduction in glomerular filtration rate than renal blood flow in older SHR. These data suggest that reduced endogenous activity of the renin-angiotensin system leads to glomerular hypertension in aging SHR. Late development of glomerular hypertension may contribute to the subsequent appearance of glomerular sclerosis and progressive renal failure in these rats
Does essential hypertension cause end-stage renal disease?
The number of patients developing end-stage renal disease (ESRD) as a consequence of hypertension is increasing and accounts for 25% of new cases of ESRD in the United States. However, the diagnosis of hypertensive ESRD is one of exclusion and no pathologic data corroborate this classification. Undoubtedly, these patients suffer from a variety of diseases, including accelerated hypertension and atherosclerotic disease of the large arteries. Also included are patients with an undiagnosed primary renal disease. The prevalence of these conditions in the hypertensive population is unknown. It is also proposed that mild to moderate hypertension can lead to ESRD. In support of this view, early investigators noted that nephrosclerosis was correlated with hypertension and/or left ventricular hypertrophy. More recently, in the Hypertension Detection and Follow-up Program, renal function was found to decline in some patients despite treatment. Data from the Baltimore Longitudinal Study of Aging indicate that the rate at which creatinine clearance declines with aging is correlated with blood pressure. A recent retrospective study reported that serum creatinine increased significantly in approximately 15% of treated hypertensive patients. However, in none of these studies was the presence of intrinsic renal disease definitively excluded. Furthermore, although an increase in serum creatinine or decline in clearance has been reported, progression to end-stage renal disease has not been documented. Therefore, additional studies are necessary to determine the frequency with which essential hypertension leads to end-stage renal disease