Platelet and plasma vasopressin in dog during hydration and vasopressin infusion

Dog platelets contain a substance immunologically similar to arginine vasopressin. In conscious and anesthetized dogs under basal conditions, platelet immunoreactive vasopressin accounts for approximately 40% of the total circulating immunoreactive vasopressin. When the plasma vasopressin concentration in the anesthetized dog was lowered 75% by intravenous infusion of isotonic dextrose solution for 2 h, the platelets failed to discharge a significant quantity of immunoreactive vasopressin. Subsequently, when the plasma vasopressin concentration was elevated to a level 10-fold greater than the initial levels by intravenous infusion of arginine vasopressin, there was no statistically significant increase in the estimated platelet vasopressin content measured 1 and 2 h after the start of the infusion, although there was the suggestion that the platelets had indeed taken up some vasopressin after 2 h of vasopressin infusion. Thus immunoreactive vasopressin in dog platelets does not appear to exchange readily with plasma vasopressin. The physiological role of platelet immunoreactive vasopressin remains to be determined.