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Effects of alpha‐adrenoceptor and of combined sympathetic and parasympathetic blockade on cardiac performance and vascular resistance.
Author(s) -
Kelbaek H,
Frandsen H,
Hilsted J,
Christensen NJ,
Nielsen SL
Publication year - 1992
Publication title -
british journal of clinical pharmacology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.216
H-Index - 146
eISSN - 1365-2125
pISSN - 0306-5251
DOI - 10.1111/j.1365-2125.1992.tb04073.x
Subject(s) - phentolamine , vascular resistance , propranolol , medicine , blockade , atropine , endocrinology , cardiac output , heart rate , vasoconstriction , chronotropic , anesthesia , hemodynamics , blood pressure , receptor
1. Cardiac performance and vascular resistance was studied in seven healthy men by radionuclide cardiography and venous plethysmography before and after alpha‐adrenoceptor blockade with phentolamine and after combined alpha‐adrenoceptor, beta‐adrenoceptor (propranolol) and parasympathetic (atropine) blockade. 2. During alpha‐adrenoceptor blockade heart rate and cardiac output increased considerably and left ventricular ejection fraction increased because of increased contractility. Systemic vascular resistance fell both during alpha‐ adrenoceptor blockade alone and during combined blockade. The increase in calf blood flow was of the same magnitude after combined blockade and after alpha‐adrenoceptor blockade alone, and was considerably higher than the fall in systemic vascular resistance. Plasma catecholamine concentrations increased after phentolamine, but the changes were blunted when propranolol and atropine were added. 3. These results indicate that peripheral vasoconstriction especially that exerted by alpha‐adrenoceptor nervous tone in skeletal muscle restricts left ventricular emptying of the intact heart. During pharmacologic blockade of the sympathetic and parasympathetic nervous system at rest the chronotropic state is augmented, whereas preload and inotropy are unaffected.