Homologous regulation of human platelet vasopressin receptors does not occur in vivo.

Large variations in the functional responsiveness of human platelets to arginine vasopressin (AVP), related to maximal platelet AVP-binding capacity, have been observed among individuals. The effects of dehydration and overhydration on maximal platelet AVP-binding capacity, plasma AVP, platelet-associated AVP, and AVP-induced platelet aggregation were examined in healthy human volunteers to determine whether homologous regulation of platelet AVP receptors occurs in vivo within the physiological range of circulating AVP fluctuations. Although significant variations of plasma AVP were observed under both conditions, no correlation could be found in the same individual with any change in 1) the maximal AVP-binding capacity, 2) platelet aggregatory responses to AVP, or 3) the platelet AVP fraction. Moreover, there was no relationship between the number of detectable platelet AVP receptors and the amount of AVP associated with platelets. These data show that homologous regulation of platelet AVP receptors by AVP does not occur in vivo over the time investigated, at least within the physiological range of AVP. Nonetheless, regulation at the platelet precursor stage appears to be highly probable in view of the relationship between plasma AVP and platelet AVP binding capacity observed among different individuals.