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Investigations were performed in a modified heart-lung preparation of the rat in situ to ascertain to what extent the myosin isoenzyme pattern affects the catecholamine-induced increase in myocardial oxygen consumption. Accordingly, the myocardial oxygen consumption was measured in young Wistar rats with mostly VM-1 myosin and older spontaneously hypertensive rats with mostly VM-3 myosin, both under control conditions and after 0.05 mg/kg orciprenaline. In the controls (73.7 +/- 3.35% VM-1) the oxygen consumption related to TTI increased from 0.098 +/- 0.003 to 0.129 +/- 0.004 microM O2/g X beat under orciprenaline (+32%, p less than 0.005). In the SHR (27.8 +/- 0.58% VM-1) there was no significant increase in O2-consumption related to TTI (control conditions 0.093 +/- 0.003; orciprenaline 0.095 +/- 0.004 microM O2/g X beat; +2%, n.s.). Our investigations demonstrate that the degree of catecholamine-induced increase in myocardial O2-consumption depends on the isoenzyme pattern of myosin.
Kissling et al. (Wed,) studied this question.