Relaxation of guinea pig trachealis during electrical field stimulation increases with age

• Published in: Journal of applied physiology (1985) Vol. 92; no. 5; pp. 1835 - 1842
• Main Authors: Chitano, Pasquale, Cox, Carrie M, Murphy, Thomas M
• Format: Journal Article
• Language: English
• Published: Bethesda, MD Am Physiological Soc 01.05.2002; American Physiological Society
• Subjects: Age; Aging - physiology; Air breathing; Animals; Biological and medical sciences; Bronchoconstriction - drug effects; Bronchoconstriction - physiology; Children & youth; Cyclooxygenase Inhibitors - pharmacology; Electric Stimulation; Fundamental and applied biological sciences. Psychology; Guinea Pigs; In Vitro Techniques; Indomethacin - pharmacology; Male; Medical research; Muscle Contraction - drug effects; Muscle Contraction - physiology; Muscle Relaxation - drug effects; Muscle Relaxation - physiology; Muscle, Smooth - drug effects; Muscle, Smooth - physiology; Respiratory Mucosa - physiology; Respiratory system: anatomy, metabolism, gas exchange, ventilatory mechanics, respiratory hemodynamics; Throat; Trachea - physiology; Vertebrates: respiratory system; Prostaglandin-endoperoxide synthase; Enzyme; Respiratory epithelium; Electrical stimulus; Rodentia; Electrophysiology; Enzyme inhibitor; Respiratory system; Respiratory tract; Ripening; Relaxation; Vertebrata; Mammalia; Guinea pig; Reactivity; Prostanoid; Oxidoreductases; Trachea; Age; Response stimulus relation
• ISSN: 8750-7587; 1522-1601
• DOI: 10.1152/japplphysiol.00688.2001

Department of Pediatrics, Duke University Medical Center, Durham, North Carolina 27710 Our laboratory has previously shown that maturation of airway smooth muscle (ASM) contractility may play a role in the airway hyperresponsiveness displayed by juveniles of many species, including humans (Chitano P, Wang J, Cox CM, Stephens NL, and Murphy TM. J Appl Physiol 88: 1338-1345, 2000). ASM relaxation, which could also contribute to airway hyperresponsiveness, has neither been described nor quantified during maturation. Therefore, we studied ASM relaxation during and after electrical field stimulation (EFS) in tracheal strips from 1-wk-old, 3-wk-old, and 3-mo-old guinea pigs. Strips were stimulated (60 Hz, 18 V) at their optimal length for 15, 20, and 25 s, with and without the cyclooxygenase inhibitor indomethacin. To evaluate the role of the epithelium, deepithelialized strips from adult animals were also studied. New indexes were developed to quantify relaxation during EFS. We measured the time course of tension relaxation and its maximum rate (RTR) during the EFS, as well as the residual tension at the end of the EFS (TCT end ). After EFS, we measured the maximum RTR and the time needed to reduce to half the TCT end . Relaxation during the EFS significantly increased with age. Indomethacin reduced this age difference by increasing relaxation in strips from younger animals. By contrast, removal of the epithelium in adult strips decreased relaxation. Relaxation after EFS decreased with age and was not affected by indomethacin. In adult strips, it was further reduced by epithelium removal. Our results show that during EFS 1 ) airway smooth muscle relaxation increases with age, 2 ) cyclooxygenase metabolites oppose relaxation in younger animals, and 3 ) epithelium removal inhibits relaxation. We suggest that a reduced ASM relaxing ability during stimulation may be involved in juvenile airway hyperresponsiveness. airway responsiveness; epithelium; indomethacin; maturation