Yohimbine Increases Cerebrospinal Fluid and Plasma Norepinephrine but Not Arginine Vasopressin in Humans

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Abstract
Previous studies have demonstrated .alpha.2-inhibitory regulation of central nervous system (CNS) noradrenergic and arginine vasopressinergic systems. We tested the hypothesis that .alpha.2-inhibition of CNS noradrenergic and vasopressinergic systems is tonic in nature by measuring the response of cerebrospinal fluid (CSF) norepinephrine (NE) and arginine vasopressin (AVP) to the .alpha.2-antagonist yohimbine in 7 young normal male human subjects. We also evaluated the tonic nature of .alpha.2-inhibition of the sympathetic nervous system (SNS) and of AVP release into plasma by measuring the response of plasma NE and plasma AVP to yohimbine. CSF NE was significantly higher following yohimbine as compared to placebo. In contrast CSF AVP did not differ between yohimbine and placebo conditions. Similarly, plasma NE was significantly higher following yohimbine as compared to placebo, while plasma AVP was unchanged. These results support a tonic .alpha.2-inhibitory regulatory mechanism for both CNS noradrenergic systems and sympathetic outflow. Such tonic .alpha.2-inhibition could not be demonstrated for regulation of AVP levels in CSF or plasma in humans.