Effect of Beta-Adrenergic Blockade and Sympathetic Stimulation on Canine Bronchial Mast Cell Response to Immune DegranulationIn Vivo

Abstract

We examined the effect of beta-adrenoceptor blockade and residual alpha-adrenoceptor effects during sympathetic stimulation on mast cell secretion of histamine in 12 natively allergic mongrel dogs. Bronchial mast cell response was measured as the arteriovenous difference (AVd) in plasma histamine concentration [H] across the bronchus. Plasma [H] was determined simultaneously from the azygos outflow tract and femoral artery as a marker of mast cell response prior to and for 90 s after intra-arterial injection of sham diluent and 1:100 and 1:30 dilutions of Ascaris suum antigen. Sympathetic (alpha-adrenergic) stimulation was elicited with continuous infusion of the nicotinic agonist, dimethylphenylpiperazinium (DMPP) under conditions of muscarinic blockade with atropine and beta-adrenoceptor blockade with propranolol. Plasma epinephrine (EPI) increased from 315 +/- 106 to 34,127 +/- 10,711 pg/ml (p less than 0.02). Control animals receiving sham infusion in place of sympathetic stimulation additionally had neural blockade with hexamethonium and alpha-adrenoceptor blockade with phentolamine. Plasma EPI was 90 +/- 58 pg/ml and did not change significantly during mast cell degranulation. Significant AVd in [H] was elicited after 1:30 A. suum antigen in both control (72.9 +/- 12.5 ng/ml versus 2.8 +/- 10.1 ng/ml at baseline; p = 0.031) and beta-adrenergically blocked (alpha-stimulated) (106.1 +/- 20.1 versus -1.5 +/- 35.9 ng/ml at baseline; p = 0.031) animals. However, alpha-adrenoceptor stimulation did not elicit significantly augmented secretion of [H]. We demonstrate that beta-adrenoceptor blockade blocks completely the inhibition of mast cell secretion caused by sympathetic stimulation with DMPP. However, alpha-adrenoceptor stimulation does not cause significant augmentation of mast cell secretion in the large airways of the dog.