Perivascular nerve stimulation and phenylephrine responses in rat liver. Metabolic effects, Ca2+ and K+ fluxes.

Electrical stimulation of perivascular nerves (20 Hz/2 ms/20 V) in perfused rat liver led to a transient increase of 14CO2 production from [1-14C]glutamate, glutathione and thiol efflux, an increase in the lactate/pyruvate and the 3-hydroxybutyrate/acetoacetate ratio, glucose release and of portal pressure. These metabolic effects were accompanied by a Ca2+ release from the liver within the initial 2 min, being followed by Ca2+ reuptake, which lasted about 3 min. The initial Ca2+ release was 67 nmol/g liver and was smaller than that observed after phenylephrine (5 microM) addition (156 nmol/g liver). Hepatic Ca2+ release following nerve stimulation or phenylephrine was not significantly affected when the hemodynamic changes were largely prevented by sodium nitroprusside (10 microM). Although the amounts of Ca2+ released were different, the glycogenolytic responses, but not the other metabolic effects, were quantitatively similar with nerve stimulation and phenylephrine. Within the first 3 min of nerve stimulation there was a K+ uptake by the liver being followed by a K+ release over the next 5-6 min and a subsequent slow K+ uptake phase. These changes resembled those observed with phenylephrine. Phentolamine, an alpha-adrenergic antagonist, abolished the Ca2+ and K+ movements following nerve stimulation as well as glucose release and the hemodynamic changes. During continuous infusion of phenylephrine, nerve stimulation led still to an increase of portal pressure; however, the effects of nerve stimulation on Ca2+ and K+ fluxes and glucose release were largely suppressed. It is concluded that the metabolic effects of electrical nerve stimulation are mediated by a redistribution of cellular Ca2+ following alpha-receptor activation. Nerve stimulation involves Ca2+ and K+ fluxes across the plasma membrane. The metabolic effects are qualitatively similar to those induced by phenylephrine. The quantitative difference between nerve stimulation and phenylephrine is explained by a differential subacinar response, with fewer cells being reached by nerve stimulation than cells containing alpha-receptors. The hemodynamic changes of nerve stimulation point to the existence of sphincters near the inflow of the sinusoidal bed.