High-energy phosphates, myocardial contractile function and material properties after short periods of oxygen deficiency.

To investigate myocardial performance and diastolic properties after repeated periods of oxygen deficiency auxotonic and isovolumic measurements were performed after three periods (4 min) of asphyxia in Wistar rats (n = 19). Additionally, the response of the peak isovolumic left ventricular pressure to postextrasystolic potentiation was measured. The hemodynamic results were compared to the levels of high-energy phosphates. Already after 15 min of recovery from asphyxia auxotonic measures of systolic function were completely normal compared to the control group (n = 19). Isovolumic measurements after 20 min of postasphyctic recovery, however, demonstrated a considerable reduction of the peak left ventricular pressure (226.5 +/- 7.5 mm Hg vs. 262.6 +/- 3.4 mm Hg in controls, mean +/- SEM (p less than 0.01) indicating persistence of decreased postischemic contractile performance. The relative effect of postextrasystolic potentiation was similar in both groups, but could not compensate for the reduced performance of the postasphyctic hearts: the absolute postextrasystolic peak isovolumic pressure of the postasphyctic hearts was lower than the value of the regular isovolumic peak pressure in the controls. Diastolic properties (pressure/volume and stress/strain relationships) of the postasphyctic myocardium remained unchanged. The total sum of the adenine-nucleotides decreased from 7.2 +/- 0.2 to 5.6 +/- 0.3 mumol/gww (p less than 0.01). ATP was reduced from 4.8 +/- 0.2 to 3.9 +/- 0.3 mumol/gww (p less than 0.01). Phosphocreatine was elevated to 7.0 +/- 0.6 mumol/gww, x +/- SEM (p less than 0.01). Our results demonstrated normal postasphyctic basal hemodynamics and material properties. Thus, the energy supply was sufficient to maintain steady state conditions - in spite of decreased overall adenine-nucleotide levels. Isovolumic measurements and postextrasystolic potentation tests, however, indicated that the contractile performance of the postischemic myocardium was still reduced. This functional limitation cannot be explained by altered material properties and is probably not causally related to the decreased overall ATP content.