Salt sensitivity of renin secretion, glomerular filtration rate and blood pressure in conscious Sprague-Dawley rats

AimWe hypothesized that in normal rats in metabolic steady state, (i) the plasma renin concentration (PRC) is log-linearly related to Na+ intake (NaI), (ii) the concurrent changes in mean arterial pressure (MABP) and glomerular filtration rate (GFR) are negligible and (iii) the function PRC=f(NaI) is altered by (1)-adrenoceptor blockade (metoprolol) and surgical renal denervation (DNX). MethodsIn catheterized, conscious rats on low-Na+ diet (0.004% Na+), NaI was increased by up to 120-fold, in four 3-day steps, by intravenous saline infusion. MABP was recorded continuously, PRC measured in arterial blood, and GFR estimated by inulin clearance. ResultsSteady states were achieved within 3days. PRC [mIUL(-1)] was log-linearly related to NaI [mmolkg(-1)day(-1)]: PRC=-9.9log (NaI)+ 22. Set point (22mIUL(-1) at NaI=1) and slope (9.9mIU per decade NaI) were independent of metoprolol administration and DNX. MABP and GFR were markedly salt-sensitive: MABP [mmHg]=4.9log (NaI)+ 99 (P<0.01), and GFR [mLmin(-1)]=1.4log (NaI)+8.3 (P<0.01). MABP increased similarly (approx. 10%, P<0.001) irrespective of pre-treatment. Metoprolol, but not DNX, reduced MABP, HR, and GFR (all P<0.01). Salt sensitivity of GFR was not observed in DNX rats. ConclusionLog-linear relations to sodium intake exist not only for PRC, but also for MABP and GFR, which per 10-fold increase in sodium intake rose by 5mmHg and 1.4mLmin(-1) respectively. Steady-state levels of PRC appear independent of renal nerves. MABP and GFR seem markedly salt sensitive in normal rats.