Neural stimulation of gluconeogenesis in isolated pyruvate-perfused rat kidneys

To estimate peritubular norepinephrine concentration during renal nerve stimulation, we compared gluconeogenic responses in isolated pyruvate-perfused rat kidneys with electrical nerve stimulation and exogenous norepinephrine. During 2 and 4 Hz stimulation, venous norepinephrine was 1.7 +/- 0.4 and 2.7 +/- 0.9 nmol/L, respectively. Intra-arterial norepinephrine infusion of 60 pmol/min for 20 min (an amount corresponding to that released during 4 Hz stimulation) resulted in venous norepinephrine levels of 3.6 +/- 0.6 nmol/L. Electrical stimuli (1, 2, and 4 Hz) sustained increases in vascular resistance of 2, 5, and 11% during 20 min of stimulation, while the norepinephrine infusion increased resistance gradually by 8% and a bolus (12.5 nmol/L) transiently increased resistance by 2%. All electrical and norepinephrine interventions, except 1 Hz, decreased fractional Cl excretion. Decreased glomerular filtration rate was observed only during 4 Hz stimulation. Gluconeogenesis transiently increased during stimulation at 2 or 4 Hz (12% (p = 0.056) and 15% (p = 0.028]. The 5% increase in gluconeogenesis during norepinephrine infusion did not differ from the increase during 4 Hz stimulation (p = 0.45). An exogenous norepinephrine bolus (12.5 nmol/L) increased gluconeogenesis 60% for 15 min, four time more than the response to 4 Hz nerve stimulation (p = 0.012). Therefore, we conclude that nerve stimulation sufficient to produce sustained vasoconstriction and antinatriuresis raised norepinephrine concentration less than 12 nmol/L on the peritubular surface of the S1 proximal tubule, thus accounting for the small gluconeogenic response.