Comparison of angiotensin II (Ang II) effects in the internal anal sphincter (IAS) and lower esophageal sphincter smooth muscles

• Published in: Life sciences (1973) 2002-03, Vol.70 (18), p.2147-2164
• Main Authors: Rattan, Satish, Fan, Ya-Ping, Puri, Rajinder N
• Format: Article
• Language: English
• Subjects: 1-(5-Isoquinolinesulfonyl)-2-Methylpiperazine - analogs & derivatives; 1-(5-Isoquinolinesulfonyl)-2-Methylpiperazine - pharmacology; Anal Canal - drug effects; Anal Canal - physiology; Angiotensin II (Ang II); Angiotensin II - pharmacology; Animals; Dose-Response Relationship, Drug; Drug Combinations; Esophagus - drug effects; Esophagus - physiology; Female; Flavonoids - pharmacology; Genistein - pharmacology; Imidazoles - pharmacology; Internal anal sphincter (IAS); Losartan - pharmacology; Lower esophageal sphincter (LES); Male; Muscle Contraction - drug effects; Muscle Contraction - physiology; Muscle, Smooth - drug effects; Muscle, Smooth - physiology; Nicardipine - pharmacology; Opossums; Pyridines - pharmacology; Rabbits; Signal transduction; Species Specificity; Tonic smooth muscle; Tyrphostins - pharmacology
• ISSN: 0024-3205; 1879-0631
• DOI: 10.1016/S0024-3205(01)01527-2

Studies were performed to compare the actions of Ang II in the internal anal sphincter (IAS) vs. lower esophageal sphincter (LES) smooth muscles in vitro, in opossum and rabbit. Studies also were carried out in isolated smooth muscle cells. In opossum, Ang II produced no discernible effects in the IAS, but did produce a concentration-dependent contraction in the LES. Conversely, in the rabbit, while Ang II caused a modest response in the LES, it caused a significant contraction in the IAS. The contractile responses of Ang II in the opossum LES were mostly resistant to different neurohumoral antagonists but were antagonized by AT 1 antagonist losartan. AT 2 antagonist PD 123,319, rather than inhibiting, prolonged the contractile action of Ang II. The contractile actions of Ang II in the opossum LES were not modified by the tyrosine kinase inhibitors (genistein and tyrphostin 1×10 −6 M) but were partially attenuated by the PKC inhibitor H-7 (1×10 −6 M), Ca 2+ channel blocker nicardipine (1×10 −5 M), Rho kinase inhibitor HA-1077 (1×10 −7 M) or p 44/42 MAP kinase inhibitor PD 98059 (5×10 −5 M). The combination of HA-1077 and H-7 did not cause an additive attenuation of Ang II responses. Western blot analyses revealed the presence of both AT 1 and AT 2 receptors. We conclude that Ang II-induced contraction of sphincteric smooth muscle occurs primarily by the activation of AT 1 receptors at the smooth muscle cells and involves multiple pathways, influx of Ca 2+, and PKC, Rho kinase and p 44/42 MAP kinase.