Aims: 

In dogs, plasma renin concentration (PRC) is log-linearly related to sodium intake (NaI) during steady state (Kjølby & Bie, 2008); i.e., PRC is a linear function of log(NaI). Here, we hypothesized that this concept also applies to rats, and that the parameters are changed by chronic blockade of b1 adrenoceptors.

Methods: 

Sprague-Dawley rats were provided with chronic, femoral, arterial and venous catheters and studied after >5 days of recovery and >3 days of low-salt diet. Sodium intake was varied from 0.07 to16 mmol/kg/d by intravenous infusion. PRC was measured at the end of the dark phase of the diurnal periods. Mean arterial blood pressure (MABP) was sampled 20 h/d, and glomerular filtration rate (GFR) measured by inulin clearance using the constant infusion technique. Metoprolol (1 mg/kg/h) was infused intravenously to block b1 adrenoceptors.

Results: 

Over the ~200 fold range of NaI, PRC was log-linearly related to log(NaI). In control experiments, the relation was PRC = -8.2 log(NaI) + 19.6; MABP and heart rate varied significantly with sodium intake, but GFR did not. During chronic metoprolol infusion, MABP was reduced (lowest salt intake: -23 mmHg, p< 0.01), in contrast, the PRC-NaI relation followed PRC = -8.7 log(NaI) +19.6, i.e., a relationship indistinguishable from control.

Conclusion: 

The results confirm in the rat that PRC is a log-linear function of NaI. Surprisingly they indicate either that b1 adrenoceptors are not importantly involved in renin secretion, or that the b1-mediated effect is quantitatively replaced by the effect of hypotension.

Reference: 

Kjølby M. & Bie P. Am.J.Physiol.Regul.Integr.Comp.Physiol. 294:R17–25,2008.