SUMMARY The radiometric enzymatic technique of Coyle andHenry (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.BECAUSE OF the poor sensitivity of available fluorometric techniques and the low concentrations of circulating catecholamines, fluorometric measurements of these amines have yielded variable results.1 In recent years the introduction of a highly sensitive enzymatic double-isotope technique for the determination of plasma catecholamines has made possible a more accurate estimation of these amines.2 More recently, Coyle and Henry 3 have reported a method for the differential determination of catecholamines and dopamine in tissues. Their technique, based on the same principle as that of Engelman and Portnoy, 2 is more sensitive and considerably less time-consuming than the latter. Although this technique is applicable to small pieces of tissue, it cannot be used on plasma or serum because of the presence of an inhibitor of the activity of catechol 0-methyl transferase (COMT), which is required to convert the catecholamines into tritiated O-methylated compounds in presence of s H-5-adenosine methionine. In our study we modified the technique of Coyle and Henry to prevent the inhibition of COMT. This modified technique can be used to measure, with a high degree of sensitivity, catecholamines in small quantities of serum.Using this technique, we studied serum catecholamines in an experimental model of hypertension as well as in patients with essential hypertension. Our results suggest that circulating catecholamines may play an important role in the development and maintenance of hypertension induced by deoxycorticosterone acetate (DOCA) and sodium. Moreover, it appears that a significant proportion of hypertensive patients...

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Under basal conditions in anesthetized rats, significant concentrations of free norepinephrine (NE), epinephrine (E), and dopamine (DA) were detected in red blood cell (RBC) lysate. These concentrations were not proportional to their respective plasma concentrations and thus RBC-to-plasma concentration ratios were different for each catecholamine (CA). DA was by far the most concentrated amine inside the RBC. An acute increase in plasma NE and E levels, induced by hemorrhagic hypotension in normotensive (NT) rats, did not result in any modification of the RBC CA content. However, chronic elevation of the NE plasma levels in bilaterally adrenalectomized rats and in deoxycorticosterone acetate (DOCA)-salt hypertensive rats (DOCA-salt HT) were associated with increased NE levels in the RBC. In addition, the large elevation in plasma E concentrations following hemorrhagic hypotension in DOCA-salt HT rats, as well as the greater plasma NE response to hypotension in adrenalectomized animals, were accompanied by increases in the respective RBC amine concentrations. During a steady-state intravenous infusion of tritiated NE, we observed a slow accumulation of radioactivity inside the RBC, indicating that CA can enter the RBC from the plasma. Moreover, catechol methyltransferase activity was measured in the cytosolic fraction of the RBC of both NT and DOCA-salt HT rats suggesting that, once inside the RBC, the catecholamines can be metabolized.

The release of neuropeptide Y like immunoreactivity (NPY-li) from the adrenal gland was studied in relation to the secretion of catecholamines (CA: NE, norepinephrine; E, epinephrine) during the left splanchnic nerve stimulation in thiopental-chloralose anesthetized dogs (n = 16). Plasma concentrations of NE, E, and NPY-li were determined in the left adrenal venous and aortic blood. Adrenal outputs of NPY-li, NE, and E were 2.4 +/- 0.4, 1.4 +/- 0.2, and 7.3 +/- 1.7 ng/min, under basal conditions, respectively. These values increased significantly (p less than 0.05; n = 8) in response to a continuous stepwise stimulation at frequencies of 1, 3, and 10 Hz given at 3-min intervals during 9 min, reaching a maximum output of 4.6 +/- 0.9 (NPY-li), 240.2 +/- 50.2 (NE), and 1412.5 +/- 309.7 ng/min (E) at a frequency of 10 Hz. Burst electrical stimulation at 40 Hz for 1 s at 10-s intervals for a period of 10 min produced similar increases (p less than 0.05) in the release of NPY-li (4.8 +/- 1.0 ng/min, n = 8), NE (283.5 +/- 144.3 ng/min, n = 8), and E (1133.5 +/- 430.6 ng/min, n = 8). Adrenal NPY-li output was significantly correlated with adrenal NE output (r = 0.606; n = 24; p less than 0.05) and adrenal E output (r = 0.640; n = 24; p less than 0.05) in dogs receiving the burst stimulation.(ABSTRACT TRUNCATED AT 250 WORDS)