Spontaneous changes in guinea‐pig respiratory pattern during barometric plethysmography: role of catecholamines and nitric oxide

Abstract

Barometric plethysmography for unrestrained animals is a non-invasive method that allows repetitive measurements of pulmonary function, but habituation of the conscious animal to this technique has not been explored. Respiratory frequency (f R ) and 'enhanced pause' (P enh ) were measured by barometric plethysmography for a period of 8 h in guinea-pigs. Compared with basal values, during the first hour of recording a progressive increase in P enh (up to 25-50%) and a corresponding decrease in f R were recorded, followed by a relative plateau in each for up to 8 h. These changes were avoided by a 30-min pretreatment with propranolol and L-NAME (nitric oxide synthase inhibitor), with P enh values as high as this plateau phase since the beginning of recording. Atropine, salbutamol or budesonide did not modify the progressive increment in P enh . We concluded that catecholamines and nitric oxide are released when guinea-pigs are introduced into the plethysmographic chamber, leading to initial low P enh values. These mediators probably diminish owing to habituation of the animal to the new environment, with an apparent progressive increment in P enh . These spontaneous changes in P enh and f R must be taken into account during barometric plethysmography in order to avoid misinterpretation of the results.

Respiratory changes during adaptation to stress induced by movement restriction in rabbits

“…We found that Penh in rabbits had a progressive decrease in the first 60 min of recording. This is contrary to Penh changes occurring in guinea pigs during barometric plethysmography [10]. Thus, in guinea pigs, Penh values were relatively low immediately after the animal entered the chamber, but these were followed by a progressive increase in the next 90 min.…”

“…This last method is remarkably useful due to its simplicity and because it allows the animal to stay in an unrestrained state and even to eat and drink at libitum. Some years ago, it was reported that guinea pigs submitted to barometric plethysmography have an initial period of adaptation to the confinement inside the plethysmographic chamber, which takes up to 90 min to stabilize [10]. Changes observed during this period were probably due to stress and consisted of a decreasing trend of respiratory frequency that was mirrored by an increasing trend in a surrogate of lung resistance.…”

β1‐integrins shedding in a guinea‐pig model of chronic asthma with remodelled airways

“…The dose–response curve was stopped when Penh reached three times its baseline level. Once Penh had returned close to the initial baseline value (<50% increment) [14], OVA challenge was administered. The second curve was performed 3 h after OVA challenge.…”

“…One hour after concluding the second histamine curve, and when at least 50% of baseline Penh was reached [14], animals were overdosed with an intraperitoneal injection of pentobarbital sodium (65 mg/kg) and the trachea was cannulated. Using a syringe, 5 mL of saline solution (37 °C) was introduced through the tracheal tube and gently recovered 1 min later.…”

Interstitial collagen turnover during airway remodeling in acute and chronic experimental asthma

“…Airway hyperresponsiveness was evaluated in sensitized animals from the 35 and 125 days model using 2 nebulized histamine dose-response curves, practiced prior and following an OVA challenge as previously described (31,32). In the guinea pig, histamine aerosol administration induces an all-or-none response (33).…”