Evidence for the Release of Vasopressin and Oxytocin into Cerebrospinal Fluid: Measurements in Plasma and CSF of Intact and Hypophysectomized Rats

Abstract

Arginine-8-vasopressin (AVP) and oxytocin (OXT) were measured by radio-immunoassay (RIA) in cerebrospinal fluid (CSF) and plasma of Wistar rats under various conditions. In addition, basal plasma levels of OXT were measured in Brattleboro rats, either homozygous or heterozygous for diabetes insipidus (Ho-DI or He-DI respectively). The basal OXT plasma level of Ho-DI rats was elevated as compared to He-DI and Wistar rats. Water deprivation caused a gradual increase of plasma OXT levels in Wistar rats. CSF was collected from Wistar rats by withdrawal from the cisterna magna under pentobarbitone anesthesia. Anesthesia induced a rise of the plasma AVP level as well as of the plasma OXT level. Withdrawal of CSF caused a dramatic rise of plasma AVP levels and, to a minor extent, of plasma OXT levels. In rats studied at 4 weeks after hypophysectomy plasma AVP levels were only detectable after CSF withdrawal. CSF levels of AVP were elevated in these animals. In intact and hypophysectomized rats, basal OXT plasma levels and the increased levels after anesthesia were the same. The OXT release into the blood was partly impaired after hypophysectomy because CSF withdrawal did not result in a further rise of plasma OXT levels. CSF oxytocin levels were the same in intact and hypophysectomized rats. A difference of the effect of hypophysectomy was thus observed with respect to the presence in CSF and plasma for AVP but not for OXT. It is concluded that the regeneration of AVP and OXT fibers is different which leads to a different release of the hormones into CSF and plasma.