AJP - Regulatory, Integrative and Comparative Physiology, Vol 267, Issue 6 1611-R1616, Copyright © 1994 by American Physiological Society
Pregnant rats are refractory to the natriuretic actions of atrial natriuretic peptide
S. Masilamani, L. Castro and C. Baylis
Department of Physiology, West Virginia University, Morgantown 26506.
Normal pregnant women and rats undergo a volume expansion. Atrial
natriuretic peptide (ANP) is involved in volume homeostasis and is
stimulated in response to volume expansion in nonpregnant animals,
resulting in natriuresis and diuresis. The conscious, chronically
catheterized rat was used to measure mean arterial blood pressure (MABP)
and renal responses to administered ANP (160 ng.kg-1.min-1 i.v.) to
determine if the actions of ANP are altered by pregnancy. These experiments
examined virgin (n = 7) and pregnant rats, studied on gestational days 7-9
(n = 9) and 15-17 (n = 7). Renal clearance studies (with inulin and
p-aminohippurate) were conducted in control conditions and during 60 min of
ANP infusion. After the ANP infusion, plasma ANP concentrations were
measured in virgin and pregnant rats. MABP fell with ANP infusion to
similar absolute values in virgins (112 +/- 2 to 80 +/- 6 mmHg), 7- to
9-day pregnant (114 +/- 2 to 91 +/- 3 mmHg), and 15- to 17-day pregnant
(107 +/- 2 to 88 +/- 4 mmHg) rats although the percent decline in MABP in
15- to 17-day pregnant rats was less than in virgins. Plasma ANP
concentrations were similar in all groups. ANP had no effect on glomerular
filtration rate, renal plasma flow, or renal vascular resistance in virgin
or pregnant rats. ANP increased sodium excretion in virgins and in 7- to
9-day pregnant rats (+102 +/- 27 and +135 +/- 47%, respectively) but not in
15- to 17-day pregnant animals (+23 +/- 22%).(ABSTRACT TRUNCATED AT 250
WORDS)
