MATERIALS AND METHODS

In this study venous blood samples (10 ml) were obtained from the internal jugular vein of six volunteers at a puncture site above the common facial vein, and simultaneously samples (14 ml) were anaerobically taken from the radial artery. This site of internal jugular vein puncture is routinely utilized in certain types of major cardiovascular surgery in order to insert balloon-tipped flotation-directed catheters into the pulmonary artery via the internal jugular vein and the right atrium and right ventricle (Barash and Dizon, 1977). The volunteers were six healthy subjects, four men and two women, ranging in ages from 27 to 57 years. None of the volunteers had taken any medication within 10 days of the study and all were fully awake and alert during the sampling. The bloods were immediately placed on ice, centrifuged, and the plasma removed. One milliliter of 0.5 M-HCI, 5.0 mg sodium metabisulfite, and 100 ng each of deuterated HVA and 5-HIAA internal standards were added per ml of plasma; the samples were then frozen at-70 C until assayed for free HVA and 5-HIAA. Urine samples were obtained during the 1-3.5 h time period bracketing the plasma sampling procedure and were stored at pH 2.0 with 5.0 mg sodium metabisulfite and 30 pg deuterated HVA and 5-HIAA per ml of urine. Samples were prepared and analyzed by the mass spectrometric technique of selected ion monitoring according to published methodology (Hattox and Crawley, 1979) with the addition of an initial wash with 10 ml hexane. Total urinary HVA was determined according to a modification of the method of Elchisak et al.(1977) by adding 0.1 m10. 5 MH, SO, to 0.1 ml urine followed immediately by hydrolysis in a boiling water bath for exactly 7 min. 5-HIAA was measured as the free compound.

All plasma analyses were determined without knowledge as to whether the samples were from arterial or venous bloods. Quantitation was carried out by using a Finnigan Corporation (Sunnyvale, California) Model 3200 quadrupole mass spectrometer equipped with a programmable multiple ion monitor unit and electron impact ionization. In order to reduce the variance, plasma samples were assayed in duplicate and each of these duplicate samples was injected into the GC-mass spectrometer two or three times. The values from these multiple injections were then averaged to obtain a final value for a given specimen. The values for the duplicate plasma samples were averaged to obtain the final value for plasma HVA and 5-HIAA. Previous experiments have shown that with