We previously demonstrated that
broxaterol enhanced recovery of fatigued canine diaphragm. The aim of this study was to compare the inotropic effects of
salbutamol and
broxaterol on fatigued canine diaphragm. Low-frequency
fatigue was induced in 14 mongrel dogs by electrophrenic stimulation, which was continued until transdiaphragmatic pressure (Pdi) at 20 Hz was reduced by 50% or for 1 h. After stabilization of
fatigue, the animals received a bolus (18.5 microg/kg) of either
broxaterol or
salbutamol, followed by a continuous infusion (0.43 microg/kg/min). A second bolus of 74.0 microg/kg, followed by a continuous infusion of 1.72 microg/kg/min, was given after 90 min. Both drugs significantly increased twitch Pdi. Twitch Pdi measured 90 min after the first and second doses of
broxaterol increased by 28 +/- 23% and 42 +/- 34%, respectively, 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 dose. 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-dependent manner, whereas
salbutamol only minimally improved force production by the fatigued diaphragm.