The effects of a 15-min coronary occlusion and subsequent reperfusion were investigated in conscious dogs previously instrumented for measurement of left ventricular pressure, dP/dt, regional wall thickening, electrograms, and myocardial blood flow. Coronary occlussion reduced overall left ventricular function only slightly but eliminated systolic wall thickening in the ischemic zone and reduced regional myocardial blood flow in the ischemic zone from 1.04 +/- 0.04 to 0.27 +/- 0.02 ml/min per g and the endo/epi flow ratio from 1.23 +/- 0.04 to 0.44 +/- 0.04, while S-T segment elevation increased from 1.1 +/- 0.3 to 8.2 +/- 0.9 mV. After release of the occlusion, S-T segment elevation disappeared within 1 min while reactive hyperemia in the previously occluded artery and a transient increase in cardiac diastolic wall thickness occurred and then subsided by 15 min. In contrast, systolic wall thickening and the endo/epi flow ratio remained significantly depressed for more than 3 h. Thus reperfusion after a 15 minute coronary occlusion results in a prolonged period of reduced regional myocardial blood flow, particularly in the endocardial layers, which correlates with the prolonged depression of regional myocardial shortening and wall thickening.

A B S T R A C T The effects of coronary artery reperfusion at 1 and 3 h after occlusion on infarct size (IS) in the conscious dog were compared with a second group of dogs that were not reperfused (24 h occlusion). Infarct size was calculated from creatine kinase (CK) appearing in blood samples (ISJ) the serial blood CK curve was changed significantly by reperfusion. In dogs with a 24-h occlusion, CK rose gradually to a peak at 11.4±0.5 h. In dogs reperfused at 3 h, CK rose sharply at 3 h and reached a peak at 6.8±0.5 h, significantly earlier (P < 0.01) than occurred in dogs reperfused at 1 h, i.e., when the peak occurred at 4.2±0.4 h. The rapid appearance of CK in blood after reperfusion at 1 and 3 h suggested a washout phenomena. Thus, reperfusion alters the shape ofthe serial blood CK curve and results in a different linear relationship between calculated and measured infarct size, resulting in greater recovery of CK in blood per unit of infarcted myocardium.Dr. Vatner is an Established Investigator for the American Heart Association.

SUMMARY The effects of aging and smooth muscle activation on the elastic stiffness of the aortic wall were assessed in nine unanesthetized adult sheep, seven newborn (<1 week) lambs, and five near term fetal lambs in utero, previously instrumented with pressure gauges and ultrasonic dimension crystals for measurements of internal pressure and external diameter in the proximal third of the descending thoracic aorta. Angiotensin and nitroglycerin were administered as intravenous (iv) boluses to increase or decrease pressure and diameter. The midwall stress (u)-radius data were fitted to an exponential curve (r > 0.95) for each animal. The curves obtained in this way were similar to those obtained by inflating and deflating an implanted hydraulic occluder. Incremental elastic modulus (Einc) was derived as a linear function of stress. Compared at similar a levels, Eiac was significantly (P < 0.05) lower in the adults than in either the newborn or the fetuses. For example, at a -3.30 x 10* dynes/cm 1 , Ei«, was 1.41 ± 0.10 x 10* dynes/cm 1 in the adults, compared with 2.41 ± 0.35 in the lambs and 2.31 ± 0.15 in the fetuses. However, when Eim was calculated at the higher stress value corresponding to baseline mean arterial pressure, {a -6.90 ± 0.59 x 10* dynes/cm* in the adult, 3.36 ± 0.27 in the newborn, 3.62 ± 0.56 in the fetus), E&*. was only slightly higher in the adults (3.67 ± 0.50 x 10' dynes/ cm 1 ) than in the newborns (2.42 ± 0.38) or the fetuses (2.58 ± 0.58). a-Adrenergic activation of aortic smooth muscle, induced by methoxamine infusion, shifted pressure-diameter and stress-radius relationships toward higher pressure or stress for any given radius in the adult, whereas no alteration was observed in unanesthetized fetal or newborn lambs or in adults anesthetized with pentobarbitaL Thus the aortic elastic modulus at any given wall stress is lower in the unanesthetized adult sheep than in the newborn or the fetus. However, the responsiveness of aortic smooth muscle to a-adrenergic stimulation increases with age. Ore Res 44: 1979

A B S T R A C T The effects of right ventricular hypertrophy on the overall and regional distribution of myocardial blood flow in the absence of an elevated coronary arterial driving pressure were evaluated in 18 conscious dogs subjected to a chronic pressure overload of the right ventricle induced by pulmonary artery constriction. The sustained pressure overload for duration of4-6 wk or 4-5 mo resulted in significant increases in right ventricular mass (45 and 110%, respectively) and right ventricular fiber diameter (22 and 60%, respectively). Moreover, the presence *tmoderate and severe hypertrophy was associated with marked increases in transmural blood flow per gram to the right ventricle proportional to the observed increases in mass, i.e., of 36 and 109%, respectively, from a normal value of 0.67+0.04 ml/min per g, whereas left ventricular blood flow remained unaltered from a normal value of 1.00±0.06 ml/min per g. Despite the large increases in blood flow per gram to moderately and severely hypertrophied right ventricle, no significant changes in the ratio of capillary:muscle fiber number were observed. These data suggest that the development of right ventricular hypertrophy is characterized by a sustained compensatory response of the coronary circulation to the augmented work load and mass, and that it is not associated with a proliferative response of the vasculature supplying the enlarged ventricle.

A B S T R A C T The effects of coronary occlusion and of subsequent propranolol administration were examined in 18 conscious dogs. Overall left ventricular (LV) function was assessed by measurements of LV pressure and dP/dt, and regional myocardial function was assessed by measurements of segment length (SL), velocity of SL shortening and regional myocardial "work", i.e., pressure-length loops in normal, moderately, and severely ischemic zones. Regional intramyocardial electrograms were measured from the same sites along with regional myocardial blood flow as determined by the radioactive microsphere technique. Coronary occlusion resulted in graded loss of function from the normal to severely ischemic zones with graded flow reduction and graded elevation of the ST segment. Propranolol depressed overall LV function, function in the normal zone (work fell by 17+4%), and in the majority of moderately ischemic segments (work fell by 7±+-3%). In severely ischemic segments the extent of paradoxical motion and post-systolic shortening was reduced by propranolol. After propranolol regional myocardial blood flow fell in the normal zone (11+2%) and rose in the moderately (15+4%) and severely (63+10%) ischemic zones. Thus, in the conscious dog with regional myocardial ischemia, propranolol induces a redistribution of myocardial blood flow, with flow falling in normal zones and rising in moderately and severely ischemic zones. The improvement in perfusion of ischemic tissue was associated with slight but significant depression of shortening, velocity, and work in the moderately ischemic Dr. Vatner is an Established