In perfused rat liver stimulation of the hepatic nerve plexuses increased via a,-receptors glucose and lactate output decreased flow and caused an overflow of noradrenaline into the hepatic vein. Infusion of noradrenaline and adrenaline also elicited similar metabolic and hemodynamic alterations via a,-receptors, whereas infusion of isoproterenol via P,-receptors enhanced glucose output and slightly reduced lactate release without affecting flow. The influence of circulating catecholamines on the nerve stimulationdependent changes was investigated.
Noradrenaline (100 nmol/L) or adrenaline (40 nmol/L) but not isoproterenol(1 pmol/L), which themselves caused about half-maximal alterations, strongly inhibited the nerve stimulation-induced increase in glucose and lactate output and decrease in flow but had no effect on noradrenaline overflow.
The protein kinase C activator (4P)phorbol 12myristate, 13-acetate (100 nmol/L) but not its analog (4a)phorbol 12,13-didecanoate (100 nmol/L) strongly inhibited the metabolic and hemodynamic changes caused by nerve stimulation or noradrenaline infusion. The protein kinase C inhibitor H7 (20 pmol/L) partially prevented the inhibition of the nerve actions by noradrenaline.
The results lead us to conclude that noradrenaline and adrenaline inhibited the metabolic and hemodynamic nerve actions by means of a mechanism involving protein kinase C rather than presynaptic a-receptors or P-receptors. The catecholamines apparently increased via a,-receptors inositol 1,4,5trisphosphate, which in turn enhanced cytosolic Ca2 + and thus altered metabolism and in part hemodynamics, and diacylglycerol, which in turn activated protein kinase C and thus feedback inhibited the signal chain from a,-receptors via G proteins to phospholipase C. (HEPATOLOGY 1992;15:477-484.)