Evaluation of a simple plasma catecholamine extraction procedure prior to high-performance liquid chromatography and electrochemical detection.

The modified extraction method for catecholamines described in this study is reproducible, simple, rapid, economical and relatively hazard-free. This method is based on the principle that plasma catecholamines are selectively adsorbed on acid-washed alumina at pH 8.6 and then eluted at a pH between 1.0 and 2.0. No statistically significant differences were obtained by using either 0.5 or 1.0 ml of plasma with 0.5 or 1.0 ml of Tris buffer. A 15-min mixing time during the adsorption and desorption steps was found to be practical, but any standardized time up to 1 h can be used. If the washing step was omitted, the catecholamines could not be eluted from the acid-washed alumina. To prevent dilution, the alumina had to be centrifuged and not aspirated to dryness after the washing step. An amount of 50 mg of WA-4 alumina was found to be the most practical in this study. Extracted or unextracted plasma as well as catecholamine standards were stable for four months at -20 degrees C.

Cardiovascular adrenoreceptor number and function in experimental hypertension in the baboon.

We studied adrenoreceptor density and affinity in the myocardial and pooled arterial smooth muscle membranes in a baboon model (Grollman 2-kidney, 2-figure-of-8) of hypertension, using tritiated prazosin (alpha 1-antagonist), yohimbine (alpha 2-antagonist) and dihydroalprenolol (beta-antagonist) as ligands. By the end of 24 weeks, mean arterial blood pressure had increased from 105 +/- 3 to 155 +/- 8 mm Hg, and heart rate increased from 102 +/- 6 to 118 +/- 2/min. In the myocardium, there was a significant decrease in alpha 2- and beta-receptor density, and significant decreases in alpha 1-, alpha 2- and beta-receptor KD values. In membranes from arteries, Bmax for alpha 1- and alpha 2-receptors more than doubled, with significantly increased Kd values for both receptor subtypes. The decrease in myocardial beta-receptor density may represent a down-regulatory response to the increased sympathetic activity in this type of hypertension, and the decreased Bmax for myocardial alpha 2-receptors may cause a decreased feedback inhibition of norepinephrine release from sympathetic nerve terminals, contributing to the increased heart rate. The increase in both alpha-receptor subtypes in arteries may be part of the pathogenesis of the hypertension. However, we were unable to show increased chronotropic responses to infused isoproterenol, or increased blood pressure responses to phenylephrine.

Myocardial beta-receptors in experimental renal and aortic coarctation hypertensive rabbits.

We investigated the effect of inducing two-kidney, one clip (2K, 1C) and aortic coarctation (AC) hypertension in rabbits, on myocardial beta-adrenoreceptor number and affinity, using 3H-dihydroalprenolol as a beta-ligand. Six weeks after surgery, mean arterial blood pressures were: sham-operated controls C, 75.6 +/- 2.3 mmHg (n = 11); 2K-1C 96.3 +/- 2.5 mmHg (n = 6, P less than 0.005); and AC, 114.1 +/- 4.8 mmHg (n = 10, P less than 0.0005). Bmax values at six weeks for C, 2K,-1C and AC were 234.5 +/- 35.7, 139.0 +/- 10.3 (P less than 0.05) and 121.0 +/- 12.8 (P less than 0.005) fmol/mg protein respectively. There were no differences in KD. Both 2K, 1C and AC hypertension significantly decreased myocardial beta-receptor density; this may be a 'down-regulatory' response to increased circulating or myocardial catecholamine concentrations or to enhanced sympathetic activity.

Inhibition of adrenaline-forming enzyme in the brain prevents one-kidney, one-clip hypertension and deoxycorticosterone acetate-salt hypertension in the rabbit.

1. Phenylethanolamine N-methyltransferase (PNMT) converts noradrenaline into adrenaline and brain PNMT is elevated in spontaneously hypertensive and deoxycorticosterone acetate (DOCA)-salt hypertensive rats. In view of the evidence for the involvement of central adrenergic neurons in renal hypertension, we measured the blood pressure response in one-clip, one-kidney Goldblatt hypertensive and DOCA-salt hypertensive rabbits to the PNMT inhibitor SK&F 64139, injected into the lateral cerebral ventricles. 2. Intracerebroventricular injection of SK&F 64139 (10 micrograms/kg) significantly attenuated the mean arterial blood pressure rise in one-clip, one-kidney and DOCA-salt rabbits, at 4 and 8 weeks. 3. These findings support the idea the hypertension in this animal model required an intact adrenaline biosynthetic process, and that central catecholaminergic neurons may be involved in the pathogenesis of low-renin dependent forms of hypertension.