Biological activity of angiotensin-(1-7) heptapeptide in the hamster heart.
Angiotensin II has been reported to have both a positive inotropic effect and a coronary constrictor action in the hamster heart. To study the contribution to these responses of phenylalanine in position 8, we assessed the direct cardiac effects of angiotensin-(1-7), which lacks phenylalanine in position 8. Syrian hamsters were used to determine the effects of angiotensin-(1-7) on cardiac performance in the diseased and normal hearts. We used the isolated isovolumic heart preparation perfused either at a constant pressure of 50 mm Hg or at a constant coronary (myocardial) flow rate of 7 ml/min (seven cardiomyopathic hamsters [CMH] and seven normal hamsters [NH] in each subgroup). At constant perfusion pressure, coronary (myocardial) flow rate decreased (p less than 0.01) in both CMH and NH (-31 +/- 8% vs. -39 +/- 4% of baseline, respectively); but the percent decrease in left ventricular pressure and the first derivative of left ventricular pressure over time (LV + dP/dt) was significant only in NH (-8 +/- 1% and -9 +/- 4%) but not in CMH (-14 +/- 5% and -21 +/- 8%). On the other hand, at a constant coronary (myocardial) flow rate, left ventricular pressure and LV + dP/dt tended to increase in both CMH and NH (+10 +/- 3% and +6 +/- 2% of baseline vs. +7 +/- 7% and +7 +/- 5%, respectively) but these changes were not significant.(ABSTRACT TRUNCATED AT 250 WORDS)
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