Phentolamine-resistant neurogenic constriction occurs in small arteries at higher frequencies

摘要: The effect of the alpha 1, 2-antagonist phentolamine (PTA) on neuromuscular transmission and exogenous norepinephrine (NE) was assessed in arteries diminishing diameter possessing a substantial adventitiomedial junction adrenergic innervation rabbit ear, i.e., central ear artery (CEA), unstretched lumen (ULD) approximately equal to 300 microns; main side branch (MSB) off CEA (ULD 150 microns); terminal (TB) MSB 75 microns). With increasing PTA concentrations, contractile responses transmural nerve stimulation (TNS) were decreased proportionately less TB than CEA. (4 X 10(-6) M, competitive antagonist concentration) blocked tetrodotoxin-sensitive TNS-induced contractions segments at 2, 4, 8 Hz. response Hz reduced least 98% 86% TB. However, not abolished until 2 10(-5) 3 M PTA, respectively. (3 M) possessed nonspecific depressant properties addition its alpha-antagonist properties. We conclude that sympathetic nervous system influences tone through alpha-adrenoceptors lower frequencies. Responses higher frequencies are mediated predominately alpha-receptors. If possibility nonadrenergic transmitter is discounted, possibilities small PTA-resistant component neurogenic due high concentration NE acting and/or threshold site cannot be distinguished.