Homologous radio-immunoassay of human plasma dopamine-beta-hydroxylase: analysis of homospecific activity, circulating plasma pool and intergroup differences based on race, blood pressure and cardiac function.

We used a homologous human dopamine-beta-hydroxylase (DBH) radio-immunoassay (RIA) to explore reported differences in plasma DBH enzymatic activity among patient groups stratified for race, blood pressure and cardiac function, as well as to determine plasma immunoreactive DBH protein pool and the relative activity of the enzyme in plasma versus human chromaffin tissue storage vesicles. Plasma DBH activity was lower in patients with congestive heart failure than in control subjects (19.9 +/- 4.0 versus 34.4 +/- 5.9 iu/l, P less than 0.05), paralleled by lower immunoreactive plasma DBH protein concentration (3.50 +/- 0.73 versus 6.34 +/- 1.05 micrograms/ml, P less than 0.05). All subject groups had similar plasma DBH homospecific activity (plasma DBH enzymatic activity/immunoreactive plasma DBH protein), ranging from 5.03 +/- 0.28 to 5.84 +/- 0.44 iu/mg. For the entire subject group, there was a significant relationship between plasma DBH activity and plasma DBH immunoreactive protein (r = 0.89, n = 78, P less than 0.01) from which no subgroup deviated systematically. Black hypertensives had lower plasma DBH activity than white hypertensives (23.0 +/- 5.2 versus 42.9 +/- 4.8 iu/l, P less than 0.01), though their plasma DBH homospecific activities and activity/immunoreactive protein plots were indistinguishable. Total circulating plasma DBH pools were large (from 13.1 +/- 3.7 to 27.5 +/- 4.8 mg).(ABSTRACT TRUNCATED AT 250 WORDS)