BROXATEROL INCREASES FORCE OUTPUT OF FATIGUED CANINE DIAPHRAGM MORE THAN SALBUTAMOL

We previously demonstrated that broxaterol enhanced recovery of fatigu ed canine diaphragm. The aim of this study was to compare the inotropi c effects of salbutamol and broxaterol on fatigued canine diaphragm. L ow-frequency fatigue was induced in 14 mongrel dogs by electrophrenic stimulation, which was continued until transdiaphragmatic pressure (Pd i) at 20 Hz was reduced by 50% or for 1 h. After stabilization of fati gue, the animals received a bolus (18.5 mu g/kg) of either broxaterol or salbutamol, followed by a continuous infusion (0.43 mu g/kg/min). A second bolus of 74.0 mu g/kg, followed by a continuous infusion of 1. 72 mu g/kg/min, was given after 90 min. Both drugs significantly incre ased twitch Pdi. Twitch Pdi measured 90 min after the first and second doses of broxaterol increased by 28 +/- 23% and 42 +/- 34%, respectiv ely, whereas the salbutamol-induced increase was clearly smaller (9 +/ - 10% and 17 +/- 15%, respectively). Broxaterol increased Pdi at 20 Hz by 25 +/- 28% with the first dose and by 29 +/- 21% with the second d ose. In contrast, salbutamol did not alter Pdi at 20 Hz. Neither drug affected Pdi at 100 Hz. We conclude that broxaterol promoted recovery of low-frequency fatigue of the canine diaphragm in vivo in a dose-dep endent manner, whereas salbutamol only minimally improved force produc tion by the fatigued diaphragm.