STUDY OF THE EFFECT OF VARIOUS DRUGS AND IONS ON THE FROG’S HEART Li Jingxin Physiologcal Department

THEORY Ions 1.The fluids perfusing the heart must contain a proper balance of the three essential ions i.e. sodium ions, potassium ions and calcium ions. 2. If these three ions are present proper proportions, the heart is able to maintain its normal contracti1ity for hours in an oxygenated environment. 3. If the concentrations of ions are abnormal, then the heart will what happen?

1). If concentration of these ions is altered then heart rate and contractility are changed. e.g. excess of potassium ions in the fluids perfusing the heart causes the heart to become dilated and slows the heart rate and may stop heart during diastole .

2).An excess of sodium ions depresses cardiac function like potassium ions excess but for an entirely different reason. Sodium ions compete with the calcium ions at the same point in the excitatory or contractile process of the heart muscle .

3). Excess calcium ions in the fluids enhance myocardial contractility 3).Excess calcium ions in the fluids enhance myocardial contractility . When large amount of calcium ions are infused into the experimental animals, the heart relaxes less during diastole and eventually stops in systole (calcium rigor). A deficiency of calcium ions causes cardiac flaccidity.

Drugs 1.The intrinsic properties of the heart are inf1uenced by autonomic nervous system. Sympathetic and parasympathetic nerve 2.Various drugs acting on specific receptors present in the heart also influence the cardiac activity.

Acetylcholine(Ach) acts on the M- receptors present in the heart and causes the decrease in the heart rate and cardiac contractility.

Adrenalin (Adr) acts on alpha and beta-adrenergic receptors Adrenalin (Adr) acts on alpha and beta-adrenergic receptors. It has positive chronotropic (increased heart rate) and positive inotropic (increased force of contraction)effects .

PROCEDURE 1.Expose the frog’s heart As compared to human heart, in the frog’s heart, there are five chambers ie one ventricle, two atrium, one sinus venosus ,one truncus arteriosus There is no special conducting tissue. There is no coronary circulation in the frog’s heart

ventricle Truncus arteriosus atrium sinus venosus

a. The parietal layer of the membranous pericardium if easily removable but the visceral layer is firmly attached to the heart muscle. b. The wall of single ventricle is thicker than that of atria. c. The truncus arteriosus lies anteriorly to the ventricle near it base and divides into two aorta. d. Sinus venosus lies posteriorly and superior and inferior vena cava empty into it. e. The color of the ventricle is seen to become pale during contraction.

f. During contraction, size of the ventricle is decreased and during relaxation size is increased due to distension g. The two atria are separated from the ventricle by atrio-ventricular groove. h. A careful observation will show a white line at the junction of the sinus and atria. i. Sequence of heartbeat is the sinus, atria, ventricle and finally the truncus arteries. If we remove the heart from the animal’s body and immerse it in Ringer solution placed, the various parts of the heart are seen to continue to beat in the usual regular sequence. This indicates that the heartbeat originates from the heart itself.

PROCEDURE 3. Adjust the velocity and sensitivity ,record normal curve. 2. Connect the heart clip with the apex of the ventricle. Lift the heart gently by raising the lever and adjust its position so that the beating heart produces good movements. Pour Ringer solution on the heart from time to time . 3. Adjust the velocity and sensitivity ,record normal curve.

PROCEDURE 4. Pour 0.65% NaCl solution(deficiency of calcium ) on the frog’s heart and record its effect on the cardiac activity. 5. 1%KCl solution 6. 1%CaCl2 solution 7.1/10000 acetylcholine solution 8. 1/10000adrenalin solution