ROLE OF GABA AND OPIOIDS IN THE REGULATION OF THE VASOPRESSIN RESPONSE TO PHYSICAL EXERCISE IN NORMAL MEN

The present study was undertaken in order to establish the possible in volvement of GABAergic and/or opioid pathways in the mechanism underly ing the arginine-vasopressin (AVP) response to physical exercise. Afte r fasting overnight, seven subjects were tested on four mornings at le ast 1 week apart. Exercise was performed on a bicycle ergometer. The w orkload was gradually increased at 3 min intervals until exhaustion an d lasted about 15 min in all subjects. Tests were carried out under ad ministration of placebo, the opioid antagonist naloxone (10 mg as an i .v. bolus injection), the GABAergic agonist sodium valproate (600 mg i n three divided doses orally) or naloxone plus sodium valproate. Plasm a AVP levels rose 4-fold during exercise. The administration of naloxo ne did not modify, whereas sodium valproate completely abolished the p lasma AVP rise during exercise. When naloxone was given together with sodium valproate, AVP rose 3-fold in response to exercise. These data suggest the involvement of a GABAergic mechanism in regulation of the AVP response to physical exercise in men. Furthermore, the data argue against a role of naloxone sensitive endogenous opioids in the control of AVP during exercise, whereas they suggest a partial opioid mediati on of the GABAergic inhibitory action.