Insulin counters the glycogenolytic effect of arginine vasotocin in liver pieces from the axolotl, Ambystoma mexicanum, cultured in vitro.

In organ cultures of liver tissue from the axolotl, Ambystoma mexicanum, 1 nmol/l arginine vasotocin (AVT) increased tissue cyclic AMP (cAMP) concentration, activated glycogen phosphorylase, and caused glycogen breakdown and glucose release. Addition of 10 nmol/l insulin had no effect on any of these parameters. Addition of glucagon together with AVT caused a further increase in tissue cAMP but not in glucose release. Ten nanomoles per liter of insulin added to the cultures 5 min before 1 nmol/liter AVT inhibited all the above actions of AVT. This inhibitory action of insulin was not apparent in the presence of the cAMP phosphodiesterase inhibitor isobutylmethylxanthine (IBMX), which indicates that insulin activates cAMP phosphodiesterase and so reduces the concentration of cAMP in the tissue. This cannot occur in the presence of IBMX. These findings confirm previous reports that AVT causes hepatic glycogenolysis in the axolotl via an increase in tissue cAMP level.