Effect of acute haemodilution on right atrial type-B receptor activity in anaesthetized cats
Bhunia, S.; Bhattacharya, N.; Fahim, M.
Indian Journal of Physiology and Pharmacology 39(3): 216-222
In order to investigate whether the sensitivity of atrial type-B receptors to its natural stimulus is altered during acute hemodilution, experiments were conducted in nine anaesthetized, artificially ventilated and thoracotomized cats. Hemodilution was achieved by replacement of blood by the same volume of dextran (MW 150000). Atrial receptor activity, arterial blood pressure, right atrial pressure and ECG were recorded. Heart rate was calculated from ECG records. Arterial blood hematocrit was measured. Mean arterial blood pressure and heart rate were not altered by hemodilution even at a hematocrit level of 12.17 +- 0.93 percent. Average activity of type-B atrial receptors, mean right atrial pressure, right atrial peak 'v' pressure, right atrial initial 'v' pressure and right atrial 'v' wave amplitude were changed significantly (r lt 0.05) during acute hemodilution when the hematocrit was 12.17 +- 0.93 percent but the atrial type-B receptor activity per cycle did not show any significant change. Average activity of type-B receptors increased from 8.56 +- 1.02 spikes/sec to 9.56 +- 1.11 spikes/sec. Mean right atrial pressure, right atrial 'v' wave amplitude, right atrial peak 'v' pressure increased significantly (P lt 0.05) from respective control values. Right atrial initial 'v' wave pressure decreased significantly. Heart rate changed from 168.11 +- 5.42 beats/min to 170.89 +- 5.65 beats/min. Mean arterial pressure changed from 134.33 +- 0.89 mmHg to 135.67 +- 1.46 mmHg. The data demonstrated that acute hemodilution caused increase in mean right atrial pressure, peak 'v' wave pressure, 'v' wave amplitude, average activity of type-B atrial receptor and decrease in initial 'v' wave pressure which could be attributed to increase in venous return. The increase in average activity following hemodilution could be attributed to a small increase in activity of atrial type-B receptors per cardiac cycle as there was no significant change in the heart rate.