Cudd T A
Department of Physiology, University of Florida, Gainesville 32610-0274, USA.
Can J Physiol Pharmacol. 1998 Feb;76(2):118-24.
Thromboxane A2 (TxA2), well known as a vasoconstrictor and activator of platelets, also stimulates reflex cardiovascular, pituitary, adrenocortical, and blood gas responses, although the site of action is unknown. Previously we determined that the site of these actions is perfused by the carotid vasculature. The purpose of the present study was to test the hypothesis that TxA2 stimulates these responses by acting at the carotid sinus. The TxA2 mimetic U46619 (1 microgram.kg-1.min-1) or saline was infused into the carotid artery (CA) or vena cava in conscious, chronically instrumented carotid sinus denervated (CSD) or sham-operated sheep. Mean arterial pressure increased in all groups receiving U46619. Heart rate increased only in the CSD group receiving CA infusions of U46619. Adrenocorticotropic hormone (ACTH) and cortisol increased in the sham and CSD groups receiving CA U46619, and responses were not different between sham and CSD groups. PaCO2 values were higher in all CSD treatment groups compared with sham treatment groups. Arterial pH increased and PaCO2 decreased in both the sham and CSD groups in response to CA U46619. Although PaCO2 values were higher overall in the CSD group, the magnitude of change in response to U46619 infusions was similar in sham and CSD animals. There was no difference in pHa between CSD and sham groups. Hematocrit and PaO2 did not change. We conclude that TxA2 does not act at the carotid sinus, as responses to U46619 infusions in CSD animals were not different in the cases of ACTH, cortisol, and blood gases, or were enhanced rather than diminished in the case of heart rate. These findings support a hypothesis that TxA2 acts at the brain to mediate cardiovascular, pituitary, adrenocortical, and blood gas responses.
血栓素A2（TxA2）作为一种血管收缩剂和血小板激活剂广为人知，它还能刺激心血管、垂体、肾上腺皮质和血气的反射性反应，尽管其作用部位尚不清楚。此前我们确定这些作用的部位由颈动脉血管系统灌注。本研究的目的是检验TxA2通过作用于颈动脉窦来刺激这些反应的假说。将TxA2模拟物U46619（1微克·千克-1·分钟-1）或生理盐水注入清醒、长期植入仪器的颈动脉窦去神经支配（CSD）或假手术绵羊的颈动脉（CA）或腔静脉。接受U46619的所有组平均动脉压均升高。仅在接受CA注入U46619的CSD组心率升高。接受CA注入U46619的假手术组和CSD组促肾上腺皮质激素（ACTH）和皮质醇升高，且假手术组和CSD组之间的反应无差异。所有CSD治疗组的PaCO2值均高于假手术治疗组。在接受CA注入U46619后，假手术组和CSD组的动脉pH均升高而PaCO2均降低。尽管CSD组的PaCO2值总体较高，但假手术组和CSD组动物对U46619注入的反应变化幅度相似。CSD组和假手术组之间的动脉血pH无差异。血细胞比容和PaO2未改变。我们得出结论，TxA2并非作用于颈动脉窦，因为在CSD动物中，在ACTH、皮质醇和血气方面，对U46619注入的反应并无差异，或者在心率方面反应增强而非减弱。这些发现支持了TxA2作用于大脑以介导心血管、垂体、肾上腺皮质和血气反应的假说。
