Improved myocardial efficiency in the working perfused heart of the spontaneously hypertensive rat.

Abstract

SUMMARY We assessed the relationship between determinants of myocardial oxygen demandwall stress, peak rate of change of pressure and heart rate-and measured myocardial oxygen consumption over a range of loading conditions in the perfused, working heart of 6-month-old spontaneously hypertensive rats (SHR) and control Wistar-Kyoto rats (WKY). Two isolated heart preparations, an aortic-ejecting heart and an isovolumically contracting preparation with and without isoproterenol (10~7 M) added, were employed. Under a constant perfusion pressure of 110 mm Hg, the heart rate, developed wall stress, and peak rate of change of pressure were not different between the two groups, but coronary flow and myocardial oxygen consumption were significantly lower in the SHR. Systolic values of myocardial high energy phosphate compounds (adenosine 5-triphosphate, phosphocreatine) and myocardial lactate in the two preparations were not significantly different between SHR and WKY. Following adenosine infusion at maximum developed pressure (isovolumic preparation), both SHR and WKY demonstrated preservation of coronary reserve. These results indicate that cardiac hypertrophy represents a compensatory adaptation with improved mechanical efficiency in the 6-month-old SHR when maximally stressed and may be related to the shift from V, to V 2 and V 3 isomyosin phenotypes that was observed in the hypertensive animals. (Hypertension 10: 396-403, 1987) KEY WORDS • hypertension • spontaneously hypertensive rats • heart enlargement • left ventricular hypertrophy • heart physiology • left ventricular function • oxygen consumption • myosin isoenzymes C ARDIAC hypertrophy secondary to pressure overload is a common finding in the clinical setting. 1 " 5 Experimental studies using papillary muscles from hypertrophied rat hearts have demonstrated improved economy of myocardial contraction.6 ' 7 In contrast, the majority of studies performed in vivo in several animal species and in humans have failed to confirm these findings. 1 -38 "" In vivo, hearts from hypertensive animals not only work against an increased afterload but are also exposed to a higher Received January 30, 1987; accepted March 19, 1987. coronary perfusion pressure, making comparative studies more difficult. Therefore, we studied the relationship between myocardial oxygen consumption (MVo 2 ) and workload in 6-month-old spontaneously hypertensive rats (SHR) and their corresponding controls, Wistar-Kyoto rats (WKY), using isolated, perfused heart preparations, which permit increases in workload while maintaining a constant coronary perfusion pressure. Materials and Methods AnimalsSix-month-old male SHR and WKY were obtained from Taconic Farms (Germantown, NY, USA). Rats were individually caged and fed standard rat chow and water ad libitum. Rats were trained to remain quiet in a restrainer; blood pressure was measured at 28 to 30°C by tail-cuff manometry in the unanesthetized animal. The average of the last three daily measurements before death was used for comparison. Isola...

Mechanical and energetic changes in short-term volume and pressure overload of rabbit heart

“…Similarly, in the rat after a short-or long-term pressure overload caused by abdominal aortic stenosis, myocardial mechanical efficiency remained unchanged [26]. However, oxygen consumption studies on hearts obtained from 6-month-old spontaneously hypertensive rats did reveal a higher mechanical efficiency than that of age-matched Wistar-Kyoto control rat hearts [27]. It is important to realize that in whole heart studies, the efficiency measure usually incorporates the basal oxygen consumption in the denominator and hence an increase in the mechanical efficiency may, in fact, be due to a decrease in the energetic cost of the basal metabolism.…”

Age-related decline of PCr/ATP-ratio in progressively hypertrophied hearts of spontaneously hypertensive rats

“…17,18 Previous studies have demonstrated that there is a normal energy metabolism in hearts of young SHR (12-25 weeks). 14,19 On the other hand, only very few data exist concerning the myocardial energy metabolism of aged SHR (Ͼ40 weeks) suffering from progressive myocardial dysfunction. Carlier et al 11 found reduced PCr in the isolated hearts of 72-week-old SHR, and Mochizuki et al 10 in the hearts of 44-week-old SHR after an ischemic period compared with control hearts.…”

Glycolysis in heart failure: a31P-NMR and surface fluorometry study

“…31p-NMR data are shown for healthy and myopathic hamster hearts. The sugar phosphates were identified as described by Chance et al (29). The intracellular pH was calculated as described in methods.…”