Breslow M J
Department of Anesthesiology and Critical Care Medicine, Johns Hopkins Medical Institutions, Baltimore, Maryland 21205.
Am J Physiol. 1992 May;262(5 Pt 2):H1317-30. doi: 10.1152/ajpheart.1992.262.5.H1317.
Before 1986, little was known concerning regulation of blood flow to adrenal medulla and cortex. With the introduction of a radiolabeled microsphere methodology, which permitted independent measurement of blood flow to the two regions, it became apparent that medulla and cortex regulate blood flow independently and that both regions receive levels of blood flow considerably in excess of that required for nutrient delivery. It is likely that abundant blood flow serves to speed entry of adrenal secretory products into the systemic circulation. Coupling of blood flow with secretion is particularly apparent in medulla, where severalfold increases in blood flow occur during catecholamine secretion elicited by hemorrhage, hypoxia, and splanchnic nerve stimulation. Both catecholamine secretion and medullary vasodilation are neurally mediated. The two responses can be pharmacologically dissociated, suggesting possible direct innervation of adrenal vessels. However, morphological confirmation of vascular innervation is not available, and effects of released chromaffin cell products on adjacent vessels are also possible. In contrast to medulla, cortical secretory activity is not associated with altered blood flow. However, neural elements are found in close proximity to cortical vessels, and the cortical vasculature responds to changes in O2 tension and to a number of pharmacological agents. In addition, several studies indicate that cortical secretory activity can be modulated by changes in blood flow. The response of both vasculatures to pharmacological agents is, in many instances, different from responses observed in other vascular beds. These data indicate that the adrenal has evolved unique vasoregulatory mechanisms, either because vasoactive compounds are present in such high concentration, or because blood flow plays an important role in the secretory process.
1986年以前，人们对肾上腺髓质和皮质血流调节知之甚少。随着放射性微球技术的引入，该技术能够独立测量两个区域的血流，结果表明髓质和皮质独立调节血流，且两个区域的血流水平大大超过营养物质输送所需的水平。丰富的血流可能有助于肾上腺分泌产物快速进入体循环。血流与分泌的耦合在髓质中尤为明显，在出血、缺氧和内脏神经刺激引起的儿茶酚胺分泌过程中，髓质血流会增加数倍。儿茶酚胺分泌和髓质血管舒张均由神经介导。这两种反应可以通过药理学方法分离，提示肾上腺血管可能有直接神经支配。然而，目前尚无血管神经支配的形态学证据，嗜铬细胞释放的产物对邻近血管的作用也有可能。与髓质不同，皮质分泌活动与血流变化无关。然而，在皮质血管附近发现了神经成分，皮质血管系统对氧张力变化和多种药理试剂有反应。此外，多项研究表明，皮质分泌活动可受血流变化的调节。在许多情况下，两种血管系统对药理试剂的反应与在其他血管床中观察到的反应不同。这些数据表明，肾上腺已经进化出独特的血管调节机制，要么是因为血管活性化合物浓度很高，要么是因为血流在分泌过程中起重要作用。
