Received March 25, 2004
Revised May 4, 2004
Accepted after revision July 8, 2004

¹ Instituto Nacional de Enfermedades Respiratorias
² Universidad Nacional Autónoma de México

^* To whom correspondence should be addressed. E-mail: mhvargasb{at}yahoo.com.mx.

	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 (fR) and enhanced pause (Penh) were measured by barometric plethysmography during 8 h in guinea pigs. Compared with basal values, during the first hour of recording a progressive increase in Penh (up to 25-50%) with a mirror decrease of fR were noticed, followed by a relative plateau for up to 8 h. These changes were avoided by a 30-min pretreatment with propranolol and L-NAME (nitric oxide synthase inhibitor), making Penh values as higher as the plateau phase since the beginning of recording. Atropine, salbutamol or budesonide did not modify the progressive increment of Penh. We concluded that catecholamines and nitric oxide are being released when guinea pigs are introduced into the plethysmographic chamber, leading to initial low Penh values. Probably these mediators gradually diminish due to habituation of the animal to the new environment, with an apparent progressive increment of Penh. These spontaneous changes of Penh and fR must be taken into account during barometric plethysmography in order to avoid misinterpretation of the results.

Key Words: Catecholamine, Nitric oxide, Plethysmography