Owen M P, Quinn C, Bevan J A
Am J Physiol. 1985 Aug;249(2 Pt 2):H404-14. doi: 10.1152/ajpheart.1985.249.2.H404.
The effect of the alpha 1, alpha 2-antagonist phentolamine (PTA) on neuromuscular transmission and exogenous norepinephrine (NE) was assessed in arteries of diminishing diameter possessing a substantial adventitiomedial junction adrenergic innervation in the rabbit ear, i.e., central ear artery (CEA), unstretched lumen diameter (ULD) approximately equal to 300 microns; main side branch (MSB) off the CEA (ULD approximately equal to 150 microns); and terminal branch (TB) off the MSB (ULD approximately equal to 75 microns). With increasing PTA concentrations, contractile responses to transmural nerve stimulation (TNS) were decreased proportionately less in TB than in MSB and CEA. PTA (4 X 10(-6) M, a competitive antagonist concentration) blocked the tetrodotoxin-sensitive TNS-induced contractions of CEA segments at 2, 4, and 8 Hz. The response at 8 Hz was reduced at least 98% in MSB and 86% in TB. However, responses to 8 Hz were not abolished in MSB and TB until 2 X 10(-5) and 3 X 10(-5) M PTA, respectively. PTA (3 X 10(-5) M) possessed nonspecific depressant properties in addition to its alpha-antagonist properties. We conclude that the sympathetic nervous system influences tone through alpha-adrenoceptors in the CEA and in the MSB and TB at lower frequencies. Responses in the MSB and TB at higher frequencies of nerve stimulation are mediated predominately through alpha-receptors. If the possibility of a nonadrenergic transmitter is discounted, the possibilities that the small PTA-resistant component of the neurogenic response is due to a high concentration of NE acting on alpha-adrenoceptors and/or a high threshold site cannot be distinguished.
在兔耳中，对直径逐渐减小且在外膜中层交界处具有大量肾上腺素能神经支配的动脉，即中央耳动脉（CEA），未拉伸管腔直径（ULD）约为300微米；CEA的主要侧支（MSB）（ULD约为150微米）；以及MSB的终末支（TB）（ULD约为75微米），评估了α1、α2拮抗剂酚妥拉明（PTA）对神经肌肉传递和外源性去甲肾上腺素（NE）的影响。随着PTA浓度的增加，与MSB和CEA相比，TB对跨壁神经刺激（TNS）的收缩反应下降比例较小。PTA（4×10⁻⁶M，竞争性拮抗剂浓度）在2、4和8Hz时阻断了CEA节段对河豚毒素敏感的TNS诱导的收缩。在MSB中，8Hz时的反应至少降低了98%，在TB中降低了86%。然而，直到分别使用2×10⁻⁵M和3×10⁻⁵M的PTA，MSB和TB中8Hz的反应才被消除。PTA（3×10⁻⁵M）除了具有α拮抗剂特性外，还具有非特异性抑制特性。我们得出结论，交感神经系统在较低频率时通过CEA、MSB和TB中的α肾上腺素能受体影响张力。在较高频率的神经刺激下，MSB和TB中的反应主要通过α受体介导。如果排除非肾上腺素能递质的可能性，那么神经源性反应中对PTA耐药的小成分是由于高浓度的NE作用于α肾上腺素能受体和/或高阈值位点这两种可能性无法区分。
