Comparison of the effects of nadolol and bisoprolol on the isoprenaline-evoked dilatation of the dorsal hand vein in man

AIMS

We attempted to explore the possible differential involvement of beta-adrenoceptor subtypes in the dilator response of the human dorsal hand vein to isoprenaline by examining the ability of bisoprolol, a selective beta1-adrenoceptor antagonist, and nadolol, a nonselective beta1/beta2-adrenoceptor antagonist, to antagonize the response.

METHODS

Twelve healthy male volunteers participated in four weekly sessions. In the preliminary session a dose-response curve to the vasoconstrictor effect of phenylephrine was constructed and the dose producing 50-75% maximal response was determined for each individual. In each of the remaining three (treatment) sessions, nadolol (40 mg), bisoprolol (5 mg) or placebo was ingested, and isoprenaline hydrochloride (3.33-1000 ng min(-1)) was infused locally into the dorsal hand vein along with a constant dose of phenylephrine hydrochloride (to preconstrict the vein) 2 h after the ingestion of the drugs. Changes in vein diameter were monitored with the dorsal hand vein compliance technique. Subjects were allocated to treatment session according to a double-blind balanced cross-over design. Systolic and diastolic blood pressure, and heart rate were also measured.

RESULTS

Isoprenaline produced dose-dependent venodilatation which was antagonized by nadolol but remained unaffected by bisoprolol (ANOVA with repeated measures: P < 0.025; Dunnett's test: placebo vs nadolol, P < 0.01; placebo vs bisoprolol, P = NS). Mean log ED50 (ng min-1) was significantly increased in the presence of nadolol and remained unchanged in the presence of bisoprolol (ANOVA, P < 0.025; Dunnett's test: placebo vs nadolol, P < 0.005; placebo vs bisoprolol, P = NS; differences between mean log ED50 [95% CI]: placebo vs bisoprolol -0.11 [-0.38, 0.16], placebo vs nadolol 0.32[0.09, 0.72], bisoprolol vs nadolol -0.43 [-0.71, -0.15]). Mean Emax did not differ in the three treatment conditions.

CONCLUSIONS

The failure of bisoprolol to attenuate isoprenaline-evoked venodilatation in the human dorsal hand vein argues against the involvement of a beta1-adrenoceptor-mediated component in the isoprenaline-evoked venodilatory responses. The possibility cannot be excluded that the consequences of beta1-adrenoceptor blockade by bisoprolol might have been obscured by a possible venodilator effect of bisoprolol.

Comparison of the effects of venlafaxine, desipramine, and paroxetine on noradrenaline- and methoxamine-evoked constriction of the dorsal hand vein

AIMS

To examine whether the antidepressant venlafaxine, a novel serotonin-noradrenaline re-uptake inhibitor (SNRI), can modify alpha-adrenoceptor-mediated venoconstriction in man. The effects of venlafaxine were compared with those of desipramine, a tricyclic antidepressant with noradrenaline uptake inhibiting properties, and paroxetine, a selective serotonin re-uptake inhibitor (SSRI), on noradrenaline-and methoxamine-evoked venoconstriction using the dorsal hand vein compliance technique.

METHODS

Fifteen healthy male volunteers participated in five weekly experimental sessions. Each session was associated with a clinically effective dose of an antidepressant or placebo. The following oral dosages were used: venlafaxine 75 mg, venlafaxine 150 mg, desipramine 100 mg, paroxetine 20 mg, or placebo. A double-blind, cross-over, balanced design was used. In each session, dose-response curves to both locally infused noradrenaline acid tartrate (0.1-33.33 ng min-1 ) and methoxamine hydrochloride (0.5-121.5 microg min-1 ) were constructed. Systolic and diastolic blood pressure and pulse rate were measured in the supine and erect positions. Salivation was measured by the dental roll technique.

RESULTS

Venlafaxine 150 mg and desipramine 100 mg potentiated the venoconstrictor response to noradrenaline (anova of log ED50s: P<0.01; individual comparisons: venlafaxine 150 mg vs placebo: P<0.005; mean difference, 95% CI: -0. 49 (-0.81, -0.17); desipramine 100 mg vs placebo: P<0.005; mean difference, 95% CI: -0.34 (-0.60, -0.09) without affecting the response to methoxamine. Neither paroxetine nor placebo had any effects on the venoconstrictor responses. Both doses of venlafaxine increased systolic blood pressure (supine and erect) and venlafaxine 150 mg increased diastolic blood pressure (supine) (anova, P<0.05). Desipramine increased heart rate (P<0.05). Desipramine and both doses of venlafaxine reduced salivation (P<0.025).

CONCLUSIONS

These results show that, similarly to desipramine 100 mg, venlafaxine 150 mg can potentiate venoconstrictor responses to noradrenaline, consistent with venlafaxine's ability to block noradrenaline uptake in man. The importance of noradrenaline uptake blockade in these observations is confirmed by the lack of effect of the antidepressants on methoxamine-evoked venoconstriction and the failure of paroxetine to modify noradrenaline-evoked venoconstriction.

Comparison of the effects of nadolol and bisoprolol on noradrenaline-evoked venoconstriction in man in vivo

AIMS

In an attempt to explore the possible involvement of venodilator beta-adrenoceptors in the constrictor response of the human dorsal hand vein to noradrenaline, we examined the ability of nadolol, a non-selective beta1/beta2-adrenoceptor antagonist, and bisoprolol a selective beta1-adrenoceptor antagonist, to potentiate the response.

METHODS

Twelve healthy male volunteers participated in three weekly sessions. In each session nadolol (40 mg), bisoprolol (5 mg) or placebo was ingested, and (-) noradrenaline acid tartrate (0.33-33.33 ng min ) was infused locally into the dorsal hand vein 2 h after the ingestion of the drugs. Changes in vein diameter were monitored with the dorsal hand vein compliance technique. Subjects were allocated to treatments and sessions according to a double-blind balanced cross-over design. Systolic and diastolic blood pressure, and heart rate were also measured.

RESULTS

Noradrenaline produced dose-dependent venoconstriction which was antagonized by bisoprolol but remained unaffected by nadolol (ANOVA with repeated measures: F(2,22) = 5.07, P < 0.025; Dunnett's test: placebo vs nadolol; t = 0.35, df = 22, k = 3, NS; placebo vs bisoprolol; t = 2.83, df = 22, k = 3, P < 0.01). Mean (+/- s.e. mean) logED50s (ng min[-1]) were 0.44 +/- 0.15 (placebo), 0.73 +/- 0.11 (bisoprolol) and 0.50 +/- 0.21 (nadolol); mean (95% CI) differences were 0.29 (-0.005, 0.58) for placebo vs bisoprolol and 0.06 (-0.35, 0.46) for placebo vs nadolol. Both active drugs significantly (compared with placebo, P < 0.05) decreased (mean change from pretreatment +/- s.e. mean) heart rate (bisoprolol -16.08 +/- 2.01; nadolol -11.67 +/- 2.06) and systolic blood pressure (bisoprolol -15.0 +/- 0.80; nadolol -9.47 +/- 0.18).

CONCLUSIONS

The failure of nadolol and bisoprolol to potentiate noradrenaline-evoked venoconstriction argues against the involvement of masked venodilator beta-adrenoceptors in the response. The mechanism underlying the antagonism of noradrenaline-evoked venoconstriction by bisoprolol remains to be elucidated.

Bisoprolol attenuates noradrenaline- and phenylephrine-evoked venoconstriction in man in vivo

AIMS

The aim of this study was to examine the effects of bisoprolol (BIS), a selective beta1-adrenoceptor antagonist without partial agonistic activity, on noradrenaline- and phenylephrine-evoked venoconstriction in man using the dorsal hand vein compliance technique.

METHODS

Twelve healthy male volunteers participated in three weekly experimental sessions. Subjects were allocated to treatments and sessions on a double-blind basis. In each session either BIS 5 mg (BIS5), or BIS 10 mg (BIS10), or placebo was administered orally, and noradrenaline acid tartrate (0.1-33.33 ng min (-1) followed by phenylephrine hydrochloride (0.033-10 microg min(-l)) was infused into the dorsal hand vein. Systolic and diastolic blood pressure and heart rate were also measured.

RESULTS

Both noradrenaline and phenylephrine produced dose-dependent venoconstriction: the geometric mean ED50 for noradrenaline was 3.21 ng min(-1) and for phenylephrine 135.04 ng min(-1); the potency ratio (noradrenaline/phenylephrine) was 42. Both BIS5 and BIS10 significantly decreased the venoconstriction to noradrenaline (ANOVA; P<0.005), and to phenylephrine (ANOVA; P<0.001). The antagonism of the venoconstrictor responses was also reflected in a significant increase in logED50 values for both noradrenaline (ANOVA; P<0.005), and phenylephrine (ANOVA; P<0.0025) in the presence of both doses of BIS. Both doses of BIS significantly decreased heart rate (ANOVA; P<0.0001), and systolic blood pressure (ANOVA; P<0.0025).

CONCLUSIONS

Bisoprolol can antagonize alpha1-adrenoceptor mediated venoconstriction in the human dorsal hand vein in vivo through a mechanism which remains to be elucidated.

Cumulative and noncumulative dose-response curves to noradrenaline on the dorsal hand vein

Cumulative and noncumulative dose-response curves to noradrenaline were compared in the human dorsal hand vein (DHV), using the DHV compliance technique. This technique involves recording changes in the diameter of a superficial hand vein at a constant congestion pressure. Twelve healthy male volunteers (20-45 years) participated in one experimental session. Five incremental doses of noradrenaline acid tartrate (0.33-33.33 ng min-1) were infused twice in each subject: first with 5-min washout (5% dextrose saline) periods in between ("noncumulative dose-response curve"), then without interspersed washout periods ("cumulative dose-response curve"). Two-factor analysis of variance (dose of noradrenaline x method of infusion) showed a significant effect of dose (F = 101.53, df = 4.44, p < 0.0001); however, there was no significant effect of method of infusion (F = 0.21, df = 1,11, p > 0.1), indicating that cumulative and noncumulative applications of noradrenaline resulted in similar dose-response curves. Neither method of noradrenaline application had any effect on systemic blood pressure and heart rate. Construction of cumulative dose-response curves allows the study of the interactions of noradrenaline with a systemically taken antagonist during a narrow time window and the construction of more than one dose-response curve within the same experimental session.

The opposite effects of amitriptyline on noradrenaline- and methoxamine-evoked venoconstriction in man

The effects of a single oral dose (100 mg) of amitriptyline on noradrenaline- and methoxamine-evoked venoconstriction were compared, using the dorsal hand vein compliance technique, in 8 healthy male volunteers. Both noradrenaline and methoxamine produced dose-dependent venoconstriction; the geometric mean ED50 for noradrenaline was 4.15 ng min-1 and for methoxamine was 1143.54 ng min-1; the potency ratio (noradrenaline/methoxamine) was 277. Amitriptyline shifted the dose-response curve for noradrenaline to the left (ANOVA: P < 0.025; dose-ratio: 0.38) consistent with potentiation, and the dose-response curve for methoxamine to the right (ANOVA: P < 0.025; dose ratio: 2.72) consistent with antagonism. The potentiation is likely to be due to noradrenaline uptake blockade, whereas the antagonism is likely to reflect the blockade of post-junctional alpha 1-adrenoceptors.

Effects of different congestion pressures on the diameter of the dorsal hand vein and on its apparent sensitivity to noradrenaline

We have measured the diameter of the human dorsal hand vein (DHV) in situ and compared the venoconstrictor dose-response curves to locally infused noradrenaline at different venous congestion pressures using the DHV compliance technique. Congestion pressure was defined as the inflation pressure of a sphygmomanometer cuff on the ipsilateral upper arm. Male healthy volunteers (20-45 years) participated in two experimental sessions. In Session I, DHV diameter was measured at congestion pressures of 20, 25, 30, 35, 40, 45, 50, 55, 60, 65, 70 mmHg. In Session II, venoconstrictor dose-response curves to six doses (0.1-33.33 ng min-1) of (-)noradrenaline acid tartrate were established at congestion pressures 30 and 45 mmHg. DHV diameter increased as a function of congestion pressure. The rate of increase in DHV diameter (mm/5 mmHg) declined at higher values of congestion pressure (e.g. 0.14 mm/5 mmHg between 20 and 45 mmHg, and 0.04 mm/5 mmHg between 45 and 70 mmHg). Noradrenaline was less potent at 45 mmHg than at 30 mmHg. Mean log ED50 was significantly greater at 45 mmHg than at 30 mmHg congestion pressure, while mean E(max) did not differ at the two congestion pressures. The geometric mean ED50 was approximately 195% greater at 45 mmHg than at 30 mmHg. These results show that DHV diameter is positively related to congestion pressure, and that as the congestion pressure increases, the apparent sensitivity of the vein to the venoconstrictor effect of noradrenaline decreases. This latter finding is consistent with the physiological antagonism between congestion-induced venodilatation and noradrenaline-evoked venoconstriction. It is recommended that a standard congestion pressure is used in order to facilitate the comparison of results obtained in different laboratories.

Comparison of the effects of desipramine on noradrenaline- and methoxamine-evoked venoconstriction in man

1. The dorsal hand vein compliance technique was used to investigate the dual effect of tricyclic antidepressants at the noradrenergic synapse (i.e. noradrenaline uptake blockade leading to potentiation and alpha 1-adrenoceptor blockade leading to antagonism of the effect of noradrenaline). The effects of a single oral dose (100 mg) of desipramine (DMI) on venoconstrictor responses to locally infused noradrenaline and methoxamine, a selective alpha 1-adrenoceptor agonist with little affinity for the uptake mechanism, were examined. 2. Eight healthy male volunteers participated in four weekly experimental sessions. Each session was associated with one of the following treatment conditions: noradrenaline/DMI, noradrenaline/placebo, methoxamine/DMI, methoxamine/placebo. Subjects were allocated randomly to treatments and sessions according to a double-blind balanced design. Noradrenaline acid tartrate (0.33-33 ng min-1) and methoxamine hydrochloride (0.0135-135 micrograms min-1) were infused into the superficial dorsal hand vein; each dose was infused for 5-7 min with 5 min intervening washout periods. Systolic and diastolic blood pressure and pulse rate were recorded before the infusion and immediately after the infusion of the highest dose. Salivation, an index of anticholinergic activity of the antidepressant, was measured by the dental roll technique. 3. Both noradrenaline and methoxamine produced dose-dependent venoconstriction: the geometric mean ED50 for noradrenaline was 4.41 ng min-1 and for methoxamine was 2558 ng min-1; the potency ratio (noradrenaline/methoxamine) was 2884. DMI shifted the dose-response curve for noradrenaline to the left (ANOVA: P < 0.025), resulting in a dose-ratio of 0.26. DMI did not affect the dose-response curve for methoxamine significantly; the dose ratio was 1.24. 4. None of the local infusions and/or systemic treatments had any significant effects on supine systolic and diastolic blood pressure and pulse rate. 5. DMI caused a substantial (47.6%) reduction in salivary output that significantly differed from the slight statistically insignificant increase (5.8%) of salivary output recorded after placebo. 6. These results show that a single oral dose (100 mg) of DMI causes significant potentiation of the response to noradrenaline without significantly affecting the response to methoxamine. The potentiation is likely to be due to uptake blockade since the response to methoxamine was not affected. Furthermore, the lack of significant antagonism of the response to methoxamine indicates that a single oral dose (100 mg) of DMI does not cause sufficient alpha 1-adrenoceptor blockade to be detected as a pharmacodynamic change in our test system.