Effects of nerve stimulation and zymosan on glycogenolysis in perfused livers from cold-exposed rats

The effects of sympathetic nerve stimulation and zymosan (cell wall particles from yeast) on glycogenolysis were studied in perfused livers from rats kept for 5 and 20 days at 4 degrees C. The rate of glycogenolysis induced by nerve stimulation decreased significantly without any decrease in norepinephrine outflow during cold exposure, and the rate induced by norepinephrine did not change. By contrast, the rate of zymosan-induced glycogenolysis increased markedly during cold exposure. The rats with denervated hepatic nerves did not show the increased response to zymosan. In cold-exposed rats, both mepacrine and ibuprofen inhibited the effects of zymosan and of nerve stimulation without any inhibition of the outflow of norepinephrine. Neither inhibitor had any effect on the effects of norepinephrine. The metabolic effects of nerve stimulation and zymosan were not additive in cold-exposed rats. These results suggest that cold exposure may modulate the metabolism of arachidonic acid in Kupffer cells via hepatic nerve and decrease the eicosanoid-dependent glycogenolysis by nerve stimulation.