Plasma dopamine-beta-hydroxylase activity in oral contraceptive hypertension

Blood pressure in women using oral contraceptives: results from the Health Survey for England 1994

OBJECTIVE

To assess whether the blood pressure is higher among women who take oral contraceptives than it is among those who do not.

DESIGN

A cross-sectional survey of a stratified random sample of English adults (aged > or = 16 years).

SETTING

Non-institutionalized households in England during 1994.

PARTICIPANTS

From this sociodemographically representative sample of English adults, 3545 premenopausal women, of whom 892 were current users of oral contraceptives, were evaluated.

INTERVENTIONS

An interviewer-administered questionnaire determined details of menopausal status, use of oral contraceptives and antihypertensive agents and other sociodemographic variables. Measurements of the weight, height and blood pressure (the mean of the last two of three readings taken with a Dinamap 8100 device) were recorded.

MAIN OUTCOME MEASURES

Systolic and diastolic blood pressures adjusted for potential confounders by oral-contraceptive-user status.

RESULTS

Mean blood pressures adjusted for age were significantly higher among oral contraceptive users (125/70 mmHg) than they were among non-users (123/68 mmHg, P < 0.001 both for systolic and for diastolic blood pressures). These results remained unchanged after further adjustment for the body mass index, alcohol intake, physical activity and hypertension treatment. Blood pressure differences tended to be larger among older oral contraceptive users. Oral contraceptives containing progestogen only were not associated with higher blood pressures.

CONCLUSIONS

Despite the fact that most combined oral contraceptives in current use in England contain low doses of oestrogen, slightly but significantly higher blood pressures were observed among oral contraceptive users. Blood pressures should be screened before oral contraceptives are supplied and should be monitored regularly during oral contraceptive use.

The role of the sympathetic nervous system in oestrogen-induced hypertension in rats

Albino rats of either sex received chronic ethinyl oestradiol (EO) treatment (1.5 mg kg-1 daily, i.m.) for 3 weeks. Untreated control rats received arachis oil vehicle alone. Chronic EO treatment resulted in elevation of blood pressure in both sexes. Female rats exhibited significantly greater elevation in blood pressure than males. In chronic EO-treated rats pressor responses to low doses (0.5 micrograms kg-1) of noradrenaline were significantly increased, while those to angiotensin II, acetylcholine and isoprenaline were unaltered. Chronic EO treatment also sensitized the vascular bed of the rats' hindquarters to noradrenaline. EO-induced hypertension was associated with significant increase in dopamine-beta-hydroxylase activity of adrenal glands. Complete bilateral adrenalectomy or chemical sympathectomy prevented the development of EO-induced hypertension. It is suggested that chronic treatment of rats with EO induces and maintains hypertension. The peripheral sympathetic system plays an important role in this phenomenon.

Oral contraceptives and responsiveness of plasma renin activity and blood pressure in normotensive women

In young normotensive women (5 without and 5 with chronic oral contraceptives (= o.c.) cardiovascular homeostasis was challenged by isoproterenol and ergometer exercise, at normal and at resitricted sodium intake. Blood pressure and plasma renin activity (= PRA) did not differ between the 2 groups. Plasma renin substrate was markedly elevated in the o.c. group. Sodium restriction induced similar changes in body weight, urinary sodium excretion, systolic blood pressure and PRA; diastolic blood pressure decreased only in the non-o.c. group (by 6 mm Hg). In both groups isoproterenol and exercise induced similar changes in heart rate and blood pressure, except that after sodium restriction both stimuli caused larger decreases in diastolic blood pressure in the o.c. group. At both levels of sodium intake, PRA increased slightly less during exercise in the o.c. group; following restriction PRA response to isoproterenol was significantly less in the o.c. group. These results indicate that following chronic use of o.c. PRA responsiveness is normal or somewhat blunted. The different responses of diastolic blood pressure to sodium restriction and subsequent isoproterenol or exercise point to subtle changes in the inter-action of aodium and pressor mechanisms during chronic o.c. use.

Dopamine beta-hydroxylase in health and disease

DBH is a copper-containing oxygenase that catalyzes the hydroxylation of the beta carbon of a wide variety of phenylethylamine derivatives using molecular oxygen ascorbate as cofactors. It is a glycoprotein with a molecular weight of 290,000 and consists of four identical subunits, each with a single copper atom and 5% carbohydrate by weight. The enzyme is a constituent of catecholamine storage vesicles in chromaffin cell and adrenergic neurons in the peripheral and central nervous system where it functions to synthesize noradrenaline from dopamine. Although endogenous inhibitors have been isolated, they have not been demonstrated to have a physiological function, and the kinetics of the enzyme in vitro and in vivo suggest that the enzyme is not a rate limiting step in catecholamine synthesis under normal conditions. DBH exists in both a soluble form within vesicles and as a constituent of their membranes with its active site directed inward. The significance of the partition of the enzyme into soluble and membrane forms is not understood, although the soluble form has a fivefold greater homospecific activity. DBH has been one of the most intensively investigated enzymes in neurochemistry for several reasons. It is a readily assayable constitutent of catecholamine storage vesicles and, as such, provides a convenient biochemical marker for subcellular fractionation work and studies of the cellular regulation of catecholamine synthesis, storage, and release. The adrenal medulla is a rich source of the enzyme for purification, and the purified enzyme is highly antigenic, thereby enabling the use of several immunological techniques to study the cellular dynamics of the enzyme and the organelles in which it is located. These include radioimmunoassay, immunohistochemistry, and cytochemistry. This review firstly summarizes the present state of knowledge concerning the molecular properties of DBH. It then describes the tissue, cellular, and subcellular localization of the enzyme and its physiological regulation. The remainder of the review concentrates on those aspects of research on DBH in which the authors have participated that have led to general advances such as the development of the concept of homospecific activity, the introduction of immunohistochemistry for the localization of enzymes involved in transmitter metabolism, the release of macromolecules from synaptic vesicles during the process of exocytosis, the use of antibodies to DBH administered in vivo to study the fate of synaptic vesicle membranes and to produce specific immunological lesions of noradrenergic nerves in the peripheral and central nervous system, the genetic, environmental, and physiological determinants of serum DBH activity as an index of sympathetic function in animals and man, and the question of its diagnostic value in disease.

Plasma dopamine-beta-hydroxylase activity and blood pressure variability in hypertensive man

It has been proposed that measurements of plasma dopamine-beta-hydroxylase (DBH) may allow for assessmetn of adrenergic tone and may elucidate a possible neurogenic contribution to essential hypertension. We performed a series of measurements of DBH in fifty-seven normotensive and fifty hypertensive black and white men in order (1) to compare DBH to selected blood pressure patterns and (2) to evalutate the influence of salt intake, posture and race on plasma DBH. Plasma DBH, measured on unrestricted salt intake with subjects supine, was 42 +/- 4 Units/L in white normotensives, greater (P less than 0.05) than black normotensives (26 +/- 6 Units/L). White hypertensives had greater plasma concentrations of DBH than black (35 +/- 3 VS. 24 +/- 5, P less than 0.05). Normotensives did not differ from hypertensives. Dietary salt restriction and upright ambulation increased plasma DBH activity in hypertensives. Although DBH did not correlate directly with blood pressure, high DBH values were associated with lability of blood pressure in hypertensives but not in normotensives. There are two possible explanations for our results: (1) multiple factors influence plasma DBH activity and plasma levels reflect more than adrenergic function, or (2) essential hypertension is a multifactorial disease and excess sympathetic neuronal activity alone is not sufficient to produce sustained hypertension.

Psychotherapeutic control of hypertension

We conducted a six-month trial to determine the effect of psychologic relaxation on blood pressure. Alterations of peripheral sympathetic-nervous-system activity, as reflected by changes of dopamine-beta-hydroxylase in plasma, were evaluated, and plasma volume and plasma renin activity were measured. Treated patients exhibited significant (P less than 0.05) reductions of blood pressure when supine and upright, and of plasma dopamine-beta-hydroxylase activity, and furosemide-stimulated renin activity when upright. Blood-pressure changes after six months correlated best with differences in plasma activity of dopamine-beta-hydroxylase with patients supine (r = 0.54; P less than 0.05) and upright (r = 0.62; P less than 0.05). These results suggest that reduction of peripheral adrenergic activity contributes importantly to the improvement of hypertension observed with this form of therapy. Furthermore, the decrease of furosemide-stimulated plasma renin activity suggests that alterations of the renin-angiotensin system may help lower blood pressure in certain patients.