Isotope-derivative Measurements of Plasma Norepinephrine and Epinephrine in Man

S reduced the activity of COMT, but increasing the magnesium concentration in the incubation mixture and the addition of EGTA to plasma samples improved the recoveries. Each sample was corrected for losses incurred during extraction and chromatography by using [Cjmethoxytyramine, [Cjnormetanephrine, and [CJmetanephrine that were added at the end of incubation. Several catechol compounds known to be O-methylated by COMT were examined for cross-reactivity. Of the substances tested, only dihydroxyphenylalanine (DOPA) exhibited cross-reactivity. However, the apparent 30% cross-reactivity of DOPA with dopamine was due to the presence of decarboxylase activity in the COMT preparation. As little as 50 fxl of trunk plasma from decapitated rats was sufficient for the determination of the three catecholamines. (All are verbatim summaries) Louis, W. J.; Doyle, A. E. ; and Anavekar, S. N. (Univ. of Melbourne, Dept. of Med., Austin Hosp., Victoria, Australia): PLASMA NORADRENALINE CONCENTRATION AND BLOOD PRESSURE IN ESSENTIAL HYPERTENSION, PHAEOCHROMOCYTOMA AND DEPRESSION. Clin. Sci. Molec. Med. 48:239, 1975. 1. Mean plasma noradrenaline concentration was elevated in forty-four patients with established essential hypertension. Eighteen of these hypertensive patients had resting plasma noradrenaline concentrations in the normal range. 2. Patients with endogenous depression had higher mean plasma noradrenaline concentrations but significantly lower blood pressure than patients with essential hypertension. 3. Patients with phaeochromocytoma had plasma noradrenaline concentrations twenty-eight times greater than those found in essential hypertension, but blood pressures were less than 20% higher. 4. It is concluded that excess of sympathetic drive only partly explains the level of the blood pressure in essential hypertension. Ben-Jonothan, Nira; and Porter, John C. (Cecil H. and Ida Green Centr. for Reproductive Biology Sciences, the Dept. of Obstetrics and Gyn., and the Dept. of Physiology, the Univ. of Texas Health Science Centr. at Dallas, Southwestern Med. Sch., Dallas, Tex.): A SENSITIVE RADIOENZYMATIC ASSAY FOR DOPAMINE, NOREPINEPHRINE, AND EPINEPHRINE IN PLASMA AND TISSUE. Endocrinology 98:1497, 1976. A double-isotope, radioenzymatic assay for measuring dopamine, norepinephrine, and epinephrine in one sample is described. The assay procedure includes incubation, solvent extraction, and thin-layer chromatography. Dopamine, norepinephrine, and epinephrine were incubated with catechol-O-methyl transferase (COMT) and [H]S-adenosyl methionine ([H]SAM) and were converted to the O-methylated tritiated derivatives: [H]methoxytyramine, [Hjnormetanephrine, and [Hjmetanephrine, respectively. After several extraction steps, the O-methylated products were purified by means of twodimensional, thin-layer chromatography using silica gel. The thin-layer chromatographic system using silica gel. The thin-layer chromatographic system resulted in complete separation of the three O-methylated compounds with an overlap of only 1-2%. The assay was linear from 0 to 5 ng for each catecholamine and had a sensitivity of 10-30 pg. The addition of large amounts of plasma De Champlain, Jacques; Farley, Lise; Cousineau, Daniel; and Van Ameringen, Marie-Reine (Centre de Recherche en Sciences Neurologiques, Dep. de Physiologie, Faculte de Medecine, Universite de Montre'al, Quebec, Canada): CIRCULATING CATECHOLAMINE LEVELS IN HUMAN AND EXPERIMENTAL HYPERTENSION. Circ. Res 38:109, 1976. The radiometric enzymatic technique of Coyle and Henry (J. Neurochem. 21:61-67, 1973) was adapted to the measurement of serum catecholamines. This technique requires less time than other enzymatic techniques and is sensitive to quantities as small as 25 pg. In normotensive subjects lying supine for 20 minutes serum catecholamine levels averaged 0.218 ng/ml, with no obvious sex or age difference. Under these standardized conditions, the circulating catecholamine levels for a given individual are highly reproducible on different days over a period of several months. In 22 patients with essential hypertension, circulating levels were significantly higher, with an average of 0.370 ng/ml. More than 50% of the hypertensive patients had values greater than the highest value measured in normotensives. Systolic blood pressure and heart rate were significantly higher in the hypertensive group with elevated levels of circulating catecholamines than in the hypertensive group with normal levels. In one model of experimental hypertension, produced in the rat by administration of deoxycorticosterone acetate (DOCA) and saline for 4-8 weeks, serum catecholamines were significantly elevated. These findings suggest that the sympathetic system may play an important role in maintaining an elevated blood pressure in experimental hypertension and in a significant proportion of patients with essential hypertension. Johnson, David G. ; Henry, David P.; Moss, Jonathan; and Williams, Robert H. (Divisions of Endocrinology and Clinical Pharmacology, Dept. of Med., Univ. of Washington, Seattle, Wash.): INHIBITION OF INSULIN RELEASE BY SCORPION TOXIN IN RAT PANCREATIC ISLETS. Diabetes 25:198, 1976. Toxin purified from venom of the scorpion Leiurus quinquestriatus was used to release norepinephrine from adrenergic nerve terminals in isolated pancreatic islets perifused in vitro. Addition of toxin (10 /xg./ml.) to the perifusion medium caused a sixfold increase in release of norepinephrine in the presence or absence of 3 X 10"M phenoxybenzamine. During 20 minutes of stimulation with toxin, the pancreatic islets released an average of 15 pg. 1082 DIABETES, VOL. 2 5 , NO. 11