To define alterations in myocardial mitochondrial function due to hypoperfusion, oxidative phosphorylation was simultaneously studied in 17 control (stable perfusion pressure) rat hearts and 17 hypoperfused isolated rat hearts. Hypoperfusion for 30 minutes was achieved by a reduction in coronary perfusion pressure from 77.8 +/- 1.2 mm Hg (mean +/- SEM) to 20.2 +/- 1.8 mm Hg in the experimental group (control perfusion pressure after 30 minutes 75.6 +/- 1.2). Hypoperfusion caused a reduction in left ventricular developed pressure to 20.5 +/- 1.5 mm Hg (versus control 74.8 +/- 3.3, p less than 0.0001), a reduction of coronary flow rate to 4.9 +/- 0.3 ml/min (versus control 19.4 +/- 1.2, p less than 0.0001), and a drop in myocardial oxygen consumption to 0.06 +/- 0.005 ml O2/min (versus control 0.17 +/- 0.01, p less than 0.0001). Myocardial lactate production was increased by hypoperfusion (3.0 +/- 0.6 mumol/min) compared with controls (0.7 +/- 0.5, p less than 0.02), but myocardial creatine kinase release was similar in the hypoperfused and control groups. Hypoperfusion was associated with an augmentation of state 3 mitochondrial respiration with glutamate and malate as respiratory substrates (448.8 +/- 14.0 ng atoms O/min/mg mitochondrial protein versus controls 290.7 +/- 13.4, p less than 0.001). When rates were normalized for mitochondrial malate dehydrogenase (MDHm), state 3 respiration was still increased in hypoperfused hearts (24.1 +/- 2.1 ng atoms O/min/IU MDHm) compared with controls (15.5 +/- 1.6, p less than 0.02). The rates of dinitrophenol-uncoupled electron transport were similar to the rates of state 3 respiration in both the hypoperfused and control groups.(ABSTRACT TRUNCATED AT 250 WORDS)