HF van der Heijden, PN Dekhuijzen, H Folgering and CL van Herwaarden
Department of Pulmonary Diseases, University Hospital Nijmegen, The Netherlands.

The aim of this study was to investigate whether the positive inotropic effects of the beta 2-adrenoceptor agonist salbutamol are increased by foreshortening of the diaphragm, and to determine the mechanism of action of these effects. Diaphragm strips were studied either at optimal resting length (Lo) or at approximately 70% Lo. In an initial experiment (Experiment I) salbutamol was added to the tissue baths in concentrations of 10 micrograms/L or 80 micrograms/L. In a second experiment (Experiment II), the effect of salbutamol (80 micrograms/L) was measured in the presence of 1 microM ryanodine, a sarcoplasmatic reticulum (SR) Ca(2+)-release inhibitor. Each experiment had a time- matched control group. Foreshortening reduced twitch force (Pt), maximal tetanic force (Po), and force-frequency curves. Salbutamol increased Pt and Po both at Lo and approximately 70% Lo. These inotropic effects were significantly greater after foreshortening. The force-frequency curve was shifted upward by salbutamol at both lengths. Force-frequency curves relative to maximal percent of Po were depressed by salbutamol at stimulation frequencies of 80 to 160 Hz. Ryanodine blocked the inotropic effect of salbutamol at both muscle lengths, indicating that these inotropic effects are probably mediated by increased SR Ca2+ release.

This article has been cited by other articles:

				L. M. A. Heunks, H. A. Machiels, R. de Abreu, X. Ping Zhu, H. F. M. van der Heijden, and P. N. R. Dekhuijzen Free radicals in hypoxic rat diaphragm contractility: no role for xanthine oxidase Am J Physiol Lung Cell Mol Physiol, December 1, 2001; 281(6): L1402 - L1412. [Abstract] [Full Text] [PDF]

				U. Hatipoglu, F. LAGHI, and M. J. TOBIN Does Inhaled Albuterol Improve Diaphragmatic Contractility in Patients with Chronic Obstructive Pulmonary Disease? Am. J. Respir. Crit. Care Med., December 1, 1999; 160(6): 1916 - 1921. [Abstract] [Full Text]

				P N R Dekhuijzen, H A Machiels, L M A Heunks, H F M van der Heijden, and R H H van Balkom Athletes and doping: effects of drugs on the respiratory system Thorax, November 1, 1999; 54(11): 1041 - 1046. [Full Text]

				H. F. M. van der Heijden, L. M. A. Heunks, H. Folgering, C. L. A. van Herwaarden, and P. N. R. Dekhuijzen beta 2-Adrenoceptor agonists reduce the decline of rat diaphragm twitch force during severe hypoxia Am J Physiol Lung Cell Mol Physiol, March 1, 1999; 276(3): L474 - L480. [Abstract] [Full Text] [PDF]

				H. F. M. Van Der Heijden, W. Z. Zhan, Y. S. Prakash, P. N. R. Dekhuijzen, and G. C. Sieck Salbutamol enhances isotonic contractile properties of rat diaphragm muscle J Appl Physiol, August 1, 1998; 85(2): 525 - 529. [Abstract] [Full Text] [PDF]

				H. F. M. Van Der Heijden, P. N. R Dekhuijzen, H. Folgering, L. A. Ginsel, and C. L. A. Van Herwaarden Long-term effects of clenbuterol on diaphragm morphology and contractile properties in emphysematous hamsters J Appl Physiol, July 1, 1998; 85(1): 215 - 222. [Abstract] [Full Text] [PDF]