AJP - Regulatory, Integrative and Comparative Physiology, Vol 273, Issue 2 578-R582, Copyright © 1997 by American Physiological Society
Age-related changes in the pressure diuresis and natriuresis response
F. Vargas, M. C. Ortiz, L. A. Fortepiani, N. M. Atucha and J. Garcia-Estan
Departamento de Fisiologia, Facultad de Medicina, Granada, Spain.
The renal-excretory responses to changes in renal perfusion pressure (RPP)
were studied in anesthetized young (3 mo old), adult (12 mo old), and
senescent (24 mo old) rats to evaluate whether the pressure diuresis and
natriuresis mechanism is altered as a function of age. Experiments were
performed in anesthetized animals in which nervous and systemic hormonal
influences to the kidney were fixed. Mean arterial pressure was similar in
all three groups: 97.6 +/- 2.6, 102.1 +/- 3.7, and 95.2 +/- 5.2 mmHg in
young, adult, and senescent rats, respectively. The relationships between
RPP and diuresis/natriuresis or fractional excretions of water and sodium
were similar in young and adult rats. However, in senescent rats the
pressure-diuretic and pressure-natriuretic responses were slightly shifted
to the right, so that diuresis and natriuresis were significantly lower at
higher levels of RPP. Glomerular filtration rate was well autoregulated,
and there were no differences between young and adult rats at each level of
RPP. However, a significantly lower glomerular filtration rate was observed
in senescent rats. These results indicate an age-related decline in the
pressure-dependent sodium and water excretion that appears to be due to a
decrease in glomerular filtration and an increase in tubular sodium
reabsorption.
