Post‐junctional α‐adrenoceptors and basal limb vascular tone in healthy men
Key result
Vasoconstricting post-junctional alpha2-adrenoceptors contribute more to basal vascular tone than alpha1-adrenoceptors, with a greater increase in forearm blood flow upon blockade (5.9 vs 3.4 ml/100 ml/min; P<0.01).
Why the study?
Does sequential alpha-adrenoceptor blockade reveal the relative contributions of alpha1 and alpha2 receptors to basal limb vascular tone in healthy young men?
Population
21 healthy young men (10 in primary group, 4 in separate prazosin group, 7 in separate yohimbine group)
Comparison
Brachial artery administration of prazosin… vs Baseline (pre-drug administration)
Design
Other
Authors
Discussion
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Member takes
Implication
α2-adrenoceptors predominate basal forearm tone; leaves open subtype roles in hypertension and disease.
Key Points
- The study aims to determine the contributions of alpha-adrenoceptor subtypes to basal limb vascular tone.
- Administered prazosin, yohimbine, and phentolamine to 10 young healthy men after beta-adrenoceptor blockade.
- Measured forearm blood flow using venous occlusion plethysmography.
- Confirmed alpha(1)-adrenoceptor blockade and assessed responses to phenylephrine and tyramine.
- Prazosin increased forearm blood flow from 2.4 to 5.8 ml (100 ml)(-1) min(-1) (P < 0.001 vs. baseline).
- Phentolamine further increased blood flow to 11.7 ml (100 ml)(-1) min(-1) (P < 0.001 vs. baseline).
- Removal of alpha(2)-tone increased blood flow significantly more than removal of alpha(1)-tone (5.9 vs. 3.4 ml (100 ml)(-1) min(-1); P < 0.01).
Structured PICO
Does sequential alpha-adrenoceptor blockade reveal the relative contributions of alpha1 and alpha2 receptors to basal limb vascular tone in healthy young men?
P
Population
21 healthy young men evaluated for forearm blood flow responses to brachial artery administration of alpha-adrenoceptor antagonists.
I
Intervention
Brachial artery administration of prazosin (alpha1-adrenoceptor antagonist), yohimbine (alpha2-adrenoceptor antagonist), and phentolamine (non-selective alpha-adrenoceptor antagonist) after local beta-adrenoceptor blockade with propranolol
C
Comparator
Baseline (pre-drug administration)
O
Outcome
Forearm blood flow (FBF) measured by venous occlusion plethysmographysurrogate
Main Result
Absolute Event Rate: 5.9% vs 3.4%
p-value: p=<0.01
In healthy young men, post-junctional alpha2-adrenoceptors contribute significantly more to basal limb vascular tone than alpha1-adrenoceptors.
Cite This Study
Dinenno et al. (2002) studied Healthy (n=21). Alpha-adrenoceptor antagonists (prazosin, yohimbine, phentolamine) vs. Baseline / alpha1 vs alpha2 blockade was evaluated on Calculated increase in forearm blood flow due to removal of alpha2-vasoconstrictor tone vs alpha1-tone (ml/100 ml/min) (p=<0.01). Vasoconstricting post-junctional alpha2-adrenoceptors contribute more to basal vascular tone than alpha1-adrenoceptors, with a greater increase in forearm blood flow upon blockade (5.9 vs 3.4 ml/100 ml/min; P<0.01).