AJP - Regulatory, Integrative and Comparative Physiology, Vol 258, Issue 3 729-R735, Copyright © 1990 by American Physiological Society
Hematocrit modulates response of ANP to volume expansion in immature rats
R. L. Chevalier, B. A. Thornhill, M. J. Peach and R. M. Carey
Department of Pediatrics, University of Virginia, Charlottesville 22908.
Compared with the adult, the immature kidney responds to acute volume
expansion (VE) with reduced diuresis and natriuresis. The underlying
mechanisms are poorly understood. Diuresis and natriuresis are blunted
despite a lower hematocrit (Hct) in the immature rat, which should enhance
the response to VE. The present study was designed to evaluate the role of
atrial natriuretic peptide (ANP), its second messenger, guanosine
3',5'-cyclic monophosphate (cGMP), and Hct in the regulation of the renal
response to acute saline VE (3% body wt) during postnatal development in
rats. Anesthetized Sprague-Dawley rats were studied in the preweaning
(group P) or postweaning period (group W). In additional groups, Hct was
increased in preweaned rats (group PI) and decreased in postweaned rats
(group WD) by isovolemic exchange transfusion before VE. Although control
plasma ANP concentration [( ANP]) was not different among the four groups,
the increased diuretic and natriuretic response to VE in group W was
associated with a greater increase in [ANP] and urinary cGMP excretion
(UcGMPV) than in group P (P less than 0.05). Experimental increases in Hct
in group PI resulted in greater [ANP] after VE but a reduction in UcGMPV
and diuresis (P less than 0.05), whereas decrease in Hct in group WD
increased UcGMPV without a significant effect on [ANP], diuresis, or
natriuresis. We conclude that ANP may contribute to the increasing renal
response to VE with maturation and that Hct modulates ANP release, UcGMPV,
and the renal response to VE in postnatal maturation.
