Effect of drugs on the coronary blood flow and heart rate using isolated rats heart (Langendorff’s preparation)

[ps2id id=’background’ target=”/]

BACKGROUND

Both sympathetic and parasympathetic nerves innervate the heart and maintain the basic rhythm of the heart along with SA node. Blood is supplied to the heart walls by coronary arteries. There is no parasympathetic innervation to coronary vessels. Post ganglionic sympathetic axons pass from cardiac nerve fiber to coronary vessels. Both alpha and beta 2 adrenoreceptors mediates vasoconstriction and vasodilation in large coronary arteries and smaller vessels respectively. The coronary blood vessels are sensitive to vasodilator mediators released by the myocardial cells under hypoxic conditions and this effect can be observed by using Langendroffs method by perfusing coronary arteries. This technique also called as retrograde perfusion as the aorta is cannulated. The pressure of physiological salt solution (PSS) i.e. Ringers Locke solution closes the aortic valve so that PSS is directly delivered to the coronary arteries without passing through the heart. The aortic valves prevents filling of left ventricle and remains the left side of the heart empty. The right side of the heart receives drained fluid from coronary sinus and the same will be expelled through the cut orifices of inferior vena cava or passess through right ventricle and pumped out through pulmonary artery. In perfused heart, the rate at which fluid leaves the heart reflects the coronary flow. The force of ventricular contractions can be measured by attaching a thread with a pin to the tip of the ventricle through a pulley to transducer and this can be recorded by using a kymograph.¹

[ps2id id=’requirements’ target=”/]

REQUIREMENTS

Animals used: Rats of 200-300 g are selected for the study.

Drugs: Pentobarbitone sodium (45 mg/kg, i.p.), Noradrenaline, isoprenaline and acetylcholine (10 mg/kg stock solution), heparin (300 IU/ml, i.p.), normal saline

Physiological solution: Kreb’s Hanselet buffer (KHB)

Instruments used: Langendroff’s apparatus

[ps2id id=’procedure’ target=”/]

PROCEDURE

Before starting the isolation of heart, set the Langendroff’s instrument and ensure that the perfusion system is working in a good condition. Inject heparin to the animal. After 20 minutes, anaesthetize the rat with pentobarbitone sodium. Then kill the rat by decapitation. Open the thorax immediately, expose and remove the heart and immerse it in ice cold PSS. Then cannulate the heart through aorta using artery cannula and mount the heart on Langendroffs instrument carefully with button thread.

Perfuse the heart at a constant perfusion pressure of 90 cm water with KHB and maintain the temperature at 37^oc and pH 7.4. Maintain the perfusion rate at a rate of 5 ml/minute and saturate the perfusion solution with oxygen at a constant and slow speed. Attach a heart clip with light thread to the tip of the ventricle. Attach the thread to the pulley placed below the heart about 4 mm vertically. Attach the thread to the kymograph and record the heart contractions.

Note the coronary output by counting the drops of the fluid leaving the heart and record the force of contraction by contractions of the heart on kymograph, heart rate by number of beats per minute by using stop clock. Inject 0.1 ml of test drug and measure the coronary outflow after 10 seconds of drug injection. Record the heart rate and the heart contractions for a minute.

[ps2id id=’conclusion’ target=”/]

CONCLUSION

Noradrenaline and isoprenaline produces positive ionotropic and chronotropic effects whereas acetylcholine produces negative ionotropic and chronotropic effects on isolated heart.

OBSERVATION

[ps2id id=’references’ target=”/][ps2id id=’1′ target=”/]

REFERENCES

1. Kulkarni SK. Hand book of experimental Pharmacology. Experiment on intact preparations. Chapter 4. 3^rd edition. Delhi: Vallabh Prakashan publishers; 2007: 159-161.
   
2. Srimachai S, Devaux S, Demougeot C, Kumphune S, Ullrich ND, Niggli E, et al. Bacopa monnieri extract increases rat coronary flow and protects against myocardial ischemia/reperfusion injury. BMC Complementary Alternative Med. 2017;17:117.