Yamato S, Rattan S
Division of Gastroenterology, Beth Israel Hospital, Harvard Medical School, Boston, Massachusetts 02215.
J Clin Invest. 1990 Aug;86(2):424-9. doi: 10.1172/JCI114728.
The purpose of the present investigation was to examine the role of alpha adrenoceptors in the internal anal sphincter (IAS). Studies wer performed on alpha-chloralose anesthetized opossums. Resting pressure in the IAS (IASP) was recorded using low compliant continuously perfused catheters. The effects of the alpha-1 adrenoceptor agonist phenylephrine and alpha-2 adrenoceptor agonist clonidine and their corresponding selective antagonists, prazosin and yohimbine, respectively, were examined on the resting IASP, and on rectal balloon distension (RBD)-mediated IAS relaxation. Phenylephrine caused a rise in the IASP that was blocked by prazosin and not by yohimbine. Phenylephrine had no effect on IAS relaxation caused by RBD. Clonidine on the other hand caused significant suppression of IAS relaxation in response to RBD, but caused minimal changes in the resting IASP. The suppression of IAS relaxation by clonidine was selectively antagonized by yohimbine but not by prazosin. From these studies we conclude that alpha-2 adrenoceptors exert important neuromodulatory influences on rectoanal inhibitory reflex, while alpha-1 adrenoceptors may exert modulatory effects on the resting IAS tone.
本研究的目的是探讨α肾上腺素能受体在肛门内括约肌（IAS）中的作用。研究在α-氯醛糖麻醉的负鼠身上进行。使用低顺应性连续灌注导管记录IAS的静息压力（IASP）。分别研究了α-1肾上腺素能受体激动剂去氧肾上腺素和α-2肾上腺素能受体激动剂可乐定及其相应的选择性拮抗剂哌唑嗪和育亨宾对静息IASP以及直肠球囊扩张（RBD）介导的IAS松弛的影响。去氧肾上腺素使IASP升高，哌唑嗪可阻断此作用，而育亨宾则不能。去氧肾上腺素对RBD引起的IAS松弛无影响。另一方面，可乐定可显著抑制RBD引起的IAS松弛，但对静息IASP的影响极小。可乐定对IAS松弛的抑制作用可被育亨宾选择性拮抗，而哌唑嗪则不能。从这些研究中我们得出结论，α-2肾上腺素能受体对直肠肛门抑制反射发挥重要的神经调节作用，而α-1肾上腺素能受体可能对静息IAS张力发挥调节作用。
