Increased myothermal economy of isometric force generation in compensated cardiac hypertrophy induced by pulmonary artery constriction in the rabbit. A characterization of heat liberation in normal and hypertrophied right ventricular papillary muscles.
Year: 1982
Type: article
Abstract: Initial, recovery, and resting heat were measured in normal and hypertrophied papillary muscles in order to monitor the energetic consequences of the subcellular changes accompanying hypertrophy.The pulmonary artery was constricted in rabbits 4 weeks prior to measurements.Right ventricular papillary muscles were stimulated at 0.2 Hz and 21 °C in Krebs-Ringer solution under isometric conditions at optimum length.Peak twitch tension was 5.90 ± 0.25 g/mm 2 (SEM) in normal muscle (N) and 5.11 ± 0.47 g/mm 2 (NS) in pressure overload muscle (P).The maximal rate of tension generation decreased 26% (P < 0.02) from 15.9 ± 0.85 g/mm 2 sec (N) to 11.7 ± 1.37 g/mm 2 sec (P).Time-to-peak tension increased 30% (P < 0.001) from 627 ± 20 msec (N) to 816 ± 21 msec (P).The total activity related heat production per beat decreased 36% (P < 0.001) from 3.92 ± 0.26 mcal/g (N) to 2.51 ± 0.29 mcal/g (P).Initial heat was reduced 37% (P < 0.001) from 1.66 ± 0.10 mcal/g (N) to 1.04 ± 0.12 mcal/g (P).The isometric heat coefficient increased 43% (P < 0.005) from 8.76 ± 0.54 (N) to 12.5 ± 1 (P) showing increased economy in hypertrophy.There was an early fast phase (1.29 ± 0.12 mcal/g per sec) of initial heat lasting 396 ± 25 msec which was related to tension build-up.A slow phase (1.05 ± 0.07 mcal/g per sec) accompanied relaxation.In hypertrophy, the fast phase was 32% (P < 0.05) slower than normal and lasted 27% (P < 0.02) longer; the slow phase was 48% (P < 0.001) slower than normal.The ratio of recovery to initial heat (1.37 ± 0.09) was not different in N and P muscles.Resting heat was 2.08 ± 0.35 mcal/g per beat in N and 1.35 ± 0.23 mcal/g per beat in P muscles.Our present results and previous enzymatic and mechanical studies suggest that the relation between the compensated pressure overload hypertrophied and normal hearts is similar to the relation between slow and fast skeletal muscle.The changes in the heart that undergoes hypertrophy secondary to pressure overload are beneficial, since they meet the new hemodynamic demands with increased economy of force production.(Circ Res 50: 491-500, 1982) Circulation Research/Vol.50, No. 4, April 1982because the controls in the earlier series of five muscles liberated 40% more initial heat per gram of muscle than did the present controls.We believe the present values, obtained from a much larger population, to be a better representation of rabbit papillary muscle energetics. Methods Animals and Surgical PreparationExperiments were performed on 38 male albino rabbits weighing 2.44 ± 0.09 kg at the time of sacrifice.Experimental animals (1.7 ± 0.04 kg body weight) were anesthetized with Phenergan (20 mg/animal) and sodium pentobarbitol (20 mg/kg).Positive pressure respiration with 95% C>2-5% CO2, partially saturated with halothane, was established after tracheal intubation.The central end of the pulmonary artery was exposed and freed of surrounding connective tissue through an incision at the second intercostal space on the left side of the animal.A spiral monel metal coil (inside diameter 2.9 mm; length 6.6 mm; 2.5 turns; 0.7 mm diameter wire) was applied to the outside surface of the artery by threading the spiral around the artery in a screw-like manner (Hamrell and Alpert, 1977).Animals recovered (3-5 hours) in a warm compartment (28 °C) which was continuously supplied with a moisturized, 95% C>2-5% CO2 gas mixture.The surgical trauma and the 67% constriction of the pulmonary artery caused 50% of the animals to die within 72 hours of surgery.Experiments were performed 32 days after surgery.Right ventricular blood pressure was measured directly in five representative experimental and control animals under standard anesthesia by needle puncture of the thorax and right ventricular wall (18-gauge, 5-cm hypodermic needle connected to the AILTECH, MSIOD pressure transducer).Papillary muscles were not taken from these animals. * The high-energy phosphate concentration in heart muscle
Source: Circulation Research
Authors: N R Alpert, L A Mulieri
Language: English
Subfield: Cardiology and Cardiovascular Medicine
Field: Medicine
Domain: Health Sciences
Open Access status: bronze
Funder: National Institutes of Health
OpenAlex ID: W2127892601