Cellular lipid accumulation in different regions of myocardial infarcts in cats during beta adrenergic blockade with timolol

The effects of non-selective beta adrenergic blockade on intracellular lipid accumulation in hearts with acute ischaemia were studied by electron microscopy of myocardial biopsy specimens using quantitative stereological techniques. Pentobarbital anaesthetised cats with coronary ligation were divided into eight controls and eight cats treated with timolol intravenously just before ligation. Biopsy specimens were collected from ischaemic, borderline, and normally perfused myocardium, defined by an in vivo injection of fluoresceine and verified by regional myocardial blood flow measurements with 15 μm radiolabelled microspheres. During a 3 h occlusion period timolol treated cats had a lower heart rate, left ventricular dP/dt, and plasma free fatty acid concentration. In control cats the cytosolic volume fraction of lipids was 0.71 × 10−3 in non-ischaemic myocardium, 2.63 × 10−3 in central ischaemic tissue, and 6.53 × 10−3 in borderline tissue. Timolol reduced the appreciable lipid accumulation in borderline tissue by 24% (to 4.97 × 10−3) compared with controls, whereas accumulation in central ischaemic tissue was not affected. Thus timolol diminished lipid accumulation in borderline myocardial tissue. The mechanism is most likely related to reduced ischaemic intensity and better preserved metabolic function.