Quantitative evaluation of myocardial injury induced by acute cerebral ischaemia and its prevention by beta 1-adrenergic blockade. An ultrastructural morphometry study.

The protective effects of beta 1-adrenergic blockade with metoprolol (Betaloc Astra) were demonstrated in the gerbil model of myocardial injury provoked by acute ischaemic brain lesions. The myocardial injury was reversible and lipid droplet accumulation was its most striking morphological feature. These droplets were easy to measure in EM photographs and their size was expressed as percentage of sarcoplasmic volume. The EM data of fat accumulation were compared in hearts of carotid-ligated animals with and without metoprolol pretreatment, and in animals with the carotid isolated only, at standard intervals 3-48 h after operation. While in carotid-ligated-only animals the average myocardial fat contents rose to a peak of 1.9% at 10 h, in metoprolol pretreated animals the amount of fat was always significantly lower and started to return earlier to basal values (peak at 6 h, 1.1%). In carotid-isolated-only animals, fat accumulation peaked at 6-10 h (1.1%) and returned quickly to normal levels (0.34 +/- 0.18%). This effective pharmacological blockade with metoprolol strongly supports the concept of catecholamine mediation between acute intracranial lesions and myocardial injury. The background and significance of myocardial fat accumulation is discussed. The EM morphometry of fat droplets appears to be a suitable tool for quantification of reversible myocardial damage most useful for experimental evaluation of cardioprotective measures. As changes in succinic dehydrogenase histochemistry (from 'myofibrillar' to 'granular' pattern) correlated with EM measured fat accumulation, the simplicity and speed of the SDH method recommends itself for fast orientation about presence of myocardial damage.