Spontaneous changes in guinea-pig respiratory pattern during barometric plethysmography: role of catecholamines and...

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.