S. J. Graafsma

Reproducibility of ambulatory blood pressure monitoring in daily practice

The reproducibility of ambulatory blood pressure monitoring (ABPM) was investigated in 45 untreated hypertensive patients in an out-patient clinic. Subjects with symptoms or diseases which could probably give rise to an increase in blood pressure (BP) variability were excluded. Patients underwent office BP (OBP) measurements and ABPM measurements with the Oxford Medilog device twice. The data were edited following previous set standards. Reproducibility of ABPM was good for the group: 24 h ABPM difference 0/2 mm Hg, standard deviation of the difference (SDD) 12/6 mm Hg for systolic BP and diastolic BP respectively. For OBP the difference between the two visits was 5/2 mm Hg with a SDD of 15/8 mm Hg. Intra-individual reproducibility was poor; almost half of the patients had a systolic difference of more than 10 mm Hg between both ABPM recordings. Reproduciblity of the day–night difference with a BP fall of at least 10% (dipper status) was moderate. About 60% of the subjects were dippers at one of the ABPM recordings but only 42% had a reproducible dip. Possible factors playing a role in the disappointing reproducibility of the ABPM recordings are the difference in daily activities between both recording days, decreased accuracy at higher BP, quality of sleep and the probable lower accuracy of the device during real ambulant conditions. In daily practice ABPM has no better reproducibility than OBP measurements, despite the larger number of measurements.

Kinetics of (-)125Iodocyanopindolol Binding to Intact Human Mononuclear Cells

In association experiments of (-)125Iodocyanopindolol (125ICYP) with human mononuclear cells (MNC) at 70 pM and a temperature of 37 degrees C equilibrium was reached within 30 min. However, when the same experiments were performed at a concentration of 4 pM 125ICYP, equilibrium was only reached after 3 hours. The consequences of incomplete equilibrium for the interpretation of binding experiments under the incorrect assumption that equilibrium has been reached, was investigated at equilibration times of one, two and three hours. The dissociation constant, Kd, decreased from 7.4 +/- 0.2 pM after one hour to 2.5 +/- 0.4 pM after three hours of incubation while the receptor density, RO, decreased from 970 +/- 170 to 713 +/- 58 sites/cell. Analysis of computer simulated binding curves confirmed the decrease in Kd and RO at prolonged incubations. We conclude that in 125ICYP binding in intact MNC one hour of incubation is not sufficient to obtain equilibrium at the lower concentrations. This leads to an overestimation of Kd- and to a lesser extent of RO-values. Extending the incubation time to three hours on the other hand may lead to a loss of cells and therefore to an underestimation of RO.

Forskolin-stimulated adenylyl cyclase activity is decreased but β2-adrenoceptor function is unchanged in primary hypertension

β2-Adrenoceptor function may be decreased in primary hypertension, resulting in increased peripheral resistance. To study the β2-adrenoceptor function, we used circulating mononuclear leukocytes (MNL) as a model system. Twenty untreated hypertensive subjects [(HT) 10 men and 10 women] and 20 age- and sex-matched healthy normotensive (NT) volunteers were studied. The P2-adrenoceptor density was not significantly different between HT and NT, but the dissociation constants for the high- and low-affinity agonist binding states, studied by isoprenaline competition assays, were significantly higher in HT. Stimulation of adenylyl cyclase with isoprenaline (10 μM, β2-adrenoceptor-mediated stimulation) was not significantly different between the two groups. Forskolin-mediated direct stimulation of adenylyl cyclase was significantly higher in women than in men. For both sexes, the forskolin-induced cyclic AMP production was lower in the HT group, reaching statistical significance in the men. No major abnormalities were observed in β2-adrenoceptor function in mononuclear leukocytes. The putative relation between the decreased forskolin-mediated adenylyl cyclase activity and primary hypertension requires further study.

Effects of Isometric Exercise on Blood Cell Adrenoceptors in Essential Hypertension

The effect of handgrip (HG) isometric exercise on plasma catecholamines, α2-adrenoceptors on platelets and β2-adrenoceptors on lymphocytes was studied in normotensive subjects (NT) and essential hypertensive subjects (HT). Whereas systolic blood pressure (SBP) increases were similar in NT and HT subjects, diastolic blood pressure (DBP) and heart rate (HR) increased more in the former group. Baseline values and changes in plasma epinephrine (E) and norepinephrine (NE) did not differ between both groups. No differences were apparent in α2-adrenoceptor density and affinity between NT and HT subjects before or after the test. HG isometric exercise induced a similar increase in β2-adrenoceptors on lymphocytes of 22 ± 7 and 13 ± 5% in NT and HT subjects, respectively. Affinity to the β2-adrenoceptors under baseline conditions was somewhat lower in HT (8.1 ± 0.4 pM) than in NT subjects (6.5 ± 0.5 pM), and this difference persisted during the test. Our results indicate that there are no differences in α2- and β2-adrenoceptor densities either at baseline conditions or after HG isometric exercise between NT and HT subjects. Small differences noted in affinity to the β2-adrenoceptors require further investigation.

Does treatment with beta-adrenergic blocking agents cause a decrease in beta2-adrenoceptor affinity?

SummaryThe effect of β-adrenoceptor antagonists (BAAs) differing in lipophilicity and partial agonist activity (PAA), and a full agonist, on the dissociation constant for [125I]-(−)- iodocyanopindolol binding to β2-adrenoceptors (KD) has been investigated.Twelve healthy, normotensive male volunteers (mean age 22.3 y) were treated with different BAAs according to a cross-over design. The drugs used were propranolol (highly lipophilic BAA, no PAA), pindolol (moderately lipophilic BAA, strong PAA), dilevalol (highly lipophilic BAA, weak PAA) and salbutamol (full agonist). Before and after a single dose and an 8 day course of one of the drugs, blood pressure and the β2-adrenoceptor characteristics of mononuclear leukocytes (MNL) were determined. Between the treatment periods, there was a washout interval of 14 days.All BAAs decreased the blood pressure, but only propranolol lowered heart rate. Treatment with salbutamol decreased the diastolic and increased the systolic blood pressure and heart rate. Three hours after the single dose of any of the BAAs, a more than 2-fold increase in KD was observed, and the increase became larger after 8 days of administration (up to 3.7-fold increase). In contrast, no effect on KD was observed after treatment with salbutamol. BAAs with PAA and salbutamol induced a 30% decrease in β2-adrenoceptor density.It is concluded that treatment with BAAs, irrespective their lipophilicity or PAA, induces a decrease in the affinity of MNL β2-adrenoceptors for antagonists. This phenomenon may help to explain the contradictory relationship between the kinetics and dynamics of BAAs.