Salt sensitivity of plasma renin in normal Sprague Dawley rats

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Abstract

Background: Sodium intake (NaI), renin system activity, and blood pressure regulation are intimately
related. However, precise quantitative insight into these relationships is virtually absent. We
hypothesized that in rats (i) the steady-state plasma renin concentration (PRC) is log-linearly related
to NaI, (ii) the function PRC = f(NaI) is altered by β1 adrenoceptor blockade or by renal denervation,
and (iii) a step-up in NaI generates a new steady-state PRC within 3 d at constant renin mRNA
expression. Methods: In chronically catheterized, conscious rats on low-Na+
diet (0.004 % Na+
), Na+
input was increased by up to 120-fold, in 3-day steps by intravenous infusions of saline with different
[NaCl]. MABP was recorded continuously, PRC measured in arterial blood and GFR measured by
inulin clearance. Metroprolol (1 mg/kg/h) was used to block β1 adrenoceptors; renal denervation was
performed by standard procedures. Results: PRC (mIU/l) was log-linearly related to NaI
(mmol/kg/d): PRC = −9.9log(NaI) + 21.6; metoprolol and renal denervation had no effect. MABP
and GFR were markedly salt sensitive: MABP [mmHg] = 4.9log(NaI) + 99.3, and GFR [ml/min] =
1.4log(NaI) + 8.3. Metoprolol, but not denervation, reduced blood pressure and heart rate (p<0.001)
as well as glomerular filtration rate (p<0.01). Salt-sensitivity of GFR was not observed in denervated
rats. With increase in NaI, PRC decreased with of T½ of 4.6 h. Conclusion: A log-linear relation to
salt intake was found not only for PRC, but also for MABP and GFR, which per decade increase in
NaI changed by 5 mmHg and 1.4 ml/min respectively. PRC = f(NaI) is unaffected by metoprolol or
renal denervation. New steady states are reached within 1 d at constant renin mRNA.
Original languageEnglish
JournalActa Physiologica
Volume206
Issue numberSupplement 691
ISSN1748-1708
Publication statusPublished - 20. Aug 2012

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