Effects of some catecholamines on the cat cardiovascular system: interactions with adrenoceptor antagonists

Area of Science:

• Pharmacology
• Cardiovascular Physiology
• Adrenergic Receptor Research

Background:

• Catecholamines like norepinephrine and epinephrine exert diverse cardiovascular effects.
• These effects are mediated through interactions with alpha and beta-adrenergic receptors.
• The specific roles of beta-1 and beta-2 adrenergic receptors in feline cardiovascular regulation are not fully elucidated.

Purpose of the Study:

• To investigate the roles of alpha and beta-adrenergic receptors in mediating cardiovascular responses to various catecholamines in cats.
• To differentiate the vascular and cardiac effects of selective beta-1 and beta-2 adrenergic receptor stimulation and blockade.
• To explore the presence and function of beta-1 mediated vasodilation and beta-2 mediated cardiac stimulation in feline cardiovascular systems.

Main Methods:

• Intravenous administration of catecholamines (norepinephrine, epinephrine, isoproterenol, N-t-butylnorepinephrine, oxymethyleneisoproterenol, RO363) in anesthetized cats.
• Assessment of hemodynamic parameters: heart rate, mean arterial blood pressure, cardiac output, total peripheral resistance, and stroke volume.
• Administration of adrenergic receptor antagonists (phentolamine, propranolol, atenolol, butoxamine) to identify receptor subtypes involved.

Main Results:

• Pressor responses to norepinephrine and epinephrine were primarily alpha-receptor mediated via increased peripheral resistance.
• Beta-1 receptor blockade (atenolol) abolished dilator responses to norepinephrine and beta-1 selective agonists (oxymethyleneisoproterenol, RO363).
• Beta-2 receptor blockade (butoxamine) abolished dilator responses to epinephrine, N-t-butylnorepinephrine, and isoproterenol, indicating beta-1 vasodilation and beta-2 vasodilation.
• Atenolol showed agonist-dependent inhibition of cardiac responses, suggesting cardiostimulant beta-2 receptors in the feline heart.
• Butoxamine did not exhibit significant agonist-dependent inhibition of cardiac responses.

Conclusions:

• The feline vasculature possesses beta-1 receptors that mediate vasodilation, in addition to beta-2 receptors.
• The feline heart contains cardiostimulant beta-2 receptors.
• The complex interplay of mixed beta-adrenoceptor populations in the feline cardiovascular system complicates the interpretation of catecholamine actions.