Higher than normal levels of catecholamines are found in heart failure patients (Anker et al. 1997) and may, through a process of myocyte death, be involved in a progressive functional deterioration of the skeletal musculature as well as the heart. In our studies using a rat model, we have observed both myocyte necrosis and apoptosis in the soleus muscle after administrating the synthetic catecholamine, isoprenaline, in the form of a single injection. Male Wistar rats (Rattus norvegicus) weighing 302.6 ± 3.4 g were used, with all experimental procedures carried out under the UK Animals (Scientific Procedures) Act, 1986. Fibre damage via necrosis was detected in vivo using an anti-myosin monoclonal antibody that only permeates the disrupted sarcolemmal membranes of necrotic fibres. All animals were injected I.P. with 1 mg kg^-1 of the myosin antibody 1 h before S.C. administration of various doses (ranging from 0.0001 to 5.0 mg kg^-1) of isoprenaline. Twelve hours later, rats were killed by cervical dislocation and the soleus muscles quickly isolated and snap frozen. The myosin antibody and an antibody directed against caspase 3 (R and D Systems), an enzyme that is activated during apoptosis, were detected on 5 mm cryo-sections using immunofluorescence. Fluorescein anti-mouse conjugated secondary antibody and Texas red anti-rabbit conjugated secondary antibody (Vector Labs) were used to visualise necrosis and apoptosis, respectively. The number of fibres damaged was counted in at least three random fields (~500 fibres) using image analysis and the results (Fig. 1) expressed as the percentage of the total number of fibres.

A one way ANOVA was employed to analyse the data for necrosis and Tukey’s post-hoc analysis was used to locate the differences. For apoptosis, a Krustal-Wallis test was employed, followed by Mann-Whitney U tests to locate the differences. No cell death was detected in control animals which received the saline vehicle only. In contrast, both myocyte necrosis and apoptosis were detected after administering 0.0001 mg of isoprenaline kg^-1 each reaching a maximum after 5 mg kg^-1 (Fig. 1). Roughly similar amounts of death occurred through both processes with some co-localisation between apoptotic and necrotic fibres being observed.

Catecholamine-induced damage in skeletal muscle appears to involve both apoptosis and necrosis. Whether these represent two independent processes or not, and consequently the ability of satellite cells to regenerate these severely injured fibres, will be discussed.

The research was supported by the BHF and NHRF.

All procedures accord with current UK legislation.