Function of vasopressinergic neurons in rats under conscious and anesthetized conditions

The responses of vasopressinergic neurons to acute salt loading and to graded hemorrhage were studied in rats under conscious and anesthetized conditions. Chronically cannulated rats were used in this study so that pre- and postanesthetic conditions could be studied in the same animals. Anesthesia induced by a combination of ketamine hydrochloride and pentobarbital sodium (Nembutal) did not cause a release of vasopressin-associated neurophysin (VP-RNP). In response to infusion of 18% saline, animals in the anesthetized state had significantly greater increases in plasma osmolality (Posmol) and plasma sodium concentration than animals in the conscious state. However, the rate of increase in plasma VP-RNP concentration ([VP-RNP]) as well as the relationship between [VP-RNP] and Posmol were not significantly different for the two states. Graded hemorrhage caused similar rates of increase in [VP-RNP] for animals under conscious and anesthetized conditions. These data suggest that anesthesia induced by ketamine plus pentobarbital sodium does not change the responsiveness of vasopressinergic neurons to acute salt loading and to graded hemorrhage.