Vasopressin antagonist disrupts the circadian rhythm of water intake on suprachiasmatic injection.

The present study makes an attempt to find out the action of arginine vasopressin (AVP) and its antagonist d-(CH2)5 Tyr (Me) AVP applied at the suprachiasmatic nuclei (SCN) on the circadian rhythm of water intake. Chronic implantation of a 22 G stainless steel cannula for injection was performed using a stereotaxic technique under Nembutal anesthesia. AVP and its antagonist were injected into the SCN of free-moving rats at the beginning of light and dark phases of the light-dark (LD) cycle. Injections of AVP during either phase did not disrupt the circadian pattern of water intake while the injections of the antagonist disrupted it. The findings are suggestive of the involvement of AVP as a mediator of the circadian rhythm of water intake at the level of the neural pacemaker, SCN.