Adrenergic regulation of the cardiovascular system in the South American rattlesnake, Crotalus durissus.

Click for Abstract : The present study investigates adrenergic regulation of the systemic and pulmonary circulations of the anaesthetised South American rattlesnake,�Crotalus durissus. Haemodynamic measurements were made following bolus injections of adrenaline and adrenergic antagonists administered through a systemic arterial catheter. Adrenaline caused a marked systemic vasoconstriction that was abolished by phentolamine, indicating this response was mediated through ?-adrenergic receptors. Injection of phentolamine gave rise to a pronounced vasodilatation (systemic conductance (Gsys) more than doubled), while injection of propranolol caused a systemic vasoconstriction, pointing to a potent ?-adrenergic, and a weaker ?-adrenergic tone in the systemic vasculature of�Crotalus. Overall, the pulmonary vasculature was far less responsive to adrenergic stimulation than the systemic circulation. Adrenaline caused a small but non-significant pulmonary vasodilatation and there was tendency of reducing this dilatation after either phentolamine or propranolol. Injection of phentolamine increased pulmonary conductance (Gpul), while injection of propranolol produced a small pulmonary constriction, indicating that ?-adrenergic and ?-adrenergic receptors contribute to a basal regulation of the pulmonary vasculature. Our results suggest adrenergic regulation of the systemic vasculature, rather than the pulmonary, may be an important factor in the development of intracardiac shunts.