Advertisement

Pflügers Archiv

, Volume 403, Issue 1, pp 21–27 | Cite as

Relative roles of vagal and sympathetic effector mechanisms in the baroreflex control of myocardial contractility in conscious rabbits

  • P. E. Aylward
  • R. J. McRitchie
  • M. J. West
  • J. P. Chalmers
Heart, Circulation, Respiration and Blood; Environmental and Exercise Physiology

Abstract

The relative roles of vagal and sympathetic effector mechanisms in the baroreflex control of myocardial contractility have been assessed in the conscious normotensive and hypertensive rabbit. Graded increases in mean arterial pressure (MAP) were produced by inflation of a balloon occluder around the abdominal aorta. Stimulus response curves relating the change in MAP to the induced change in peak rate of change of left ventricular pressure (peak LVdP/dt) were produced when heart rate was allowed to change and when it was held constant by atrial pacing. These curves were repeated after sympathetic blockade with propranolol, vagal blockade with methylscopolamine and combined blockade with the two drugs together.

Increase in MAP produced a reflex fall in peak LVdP/dt which was due to two components. There was a reflex negative inotropic effect which was independent of heart rate, occurring in animals in whom heart rate was held constant by atrial pacing, and there was also a reduction in peak LVdP/dt which was caused by the reflex bradycardia when the heart rate was allowed to change. Both sympathetic and vagal efferents contributed to the reflex fall in peak LVdP/dt seen after elevation of MAP, the sympathetic being primarily responsible for the direct negative inotropic effect and the vagus for the bradycardia and hence the secondary effects on peak LVdP/dt.

The slope of the stimulus response curves relating the fall in peak LVdP/dt to the increase in MAP was similar in intact normotensive and hypertensive rabbits, both with and without atrial pacing. This indicates that the sensitivity of the baroreceptor-myocardial contractility reflex was not impaired in the hypertensive animals, 6 weeks after renal wrapping, even though reflex control of heart rate is blunted at this time. Furthermore, the relative contribution of the vagus and the sympathetic to the control of contractility was similar in normotensive and hypertensive animals when heart rate was allowed to change. On the other hand, when the heart rate was held constant with atrial pacing, vagal blockade with methyl scopolamine revealed a contribution of the vagus to the reflex negative inotropic effect in hypertensive rabbits that was not evident in normotensive animals.

Key words

Baroreflex Myocardial contractility Hypertension sympathetic Vagus Peak LVdP/dt Mean arterial pressure Autonomic effectors 

Preview

Unable to display preview. Download preview PDF.

Unable to display preview. Download preview PDF.

References

  1. Angell-James JE (1973) Characteristics of single aortic and right subclavian baroreceptor fibre activity in rabbits with chronic renal hypertension. Circ Res 32:149–161Google Scholar
  2. Aylward PE, McRitchie RJ, Chalmers JP, West MJ (1983) Baroreflex control of myocardial contractility in the conscious normotensive and renal hypertensive rabbit. Hypertension 5:916–926Google Scholar
  3. Barry WH (1975) Effects of varying differentiator frequency response on recorded peakdP/dt. Cardiovasc Res 9:433–439Google Scholar
  4. Blix AS, Folkow B (1983) Adjustments to diving in mammals and birds. Handbook of physiology, section 2, vol 3, chapter 25, Am Physiol Soc, pp 917–945Google Scholar
  5. Cotten MD, Moran NC (1957) Effects of increased reflex sympathetic activity on contractile force of the heart. Am J Physiol 191:461–468Google Scholar
  6. De Geest H, Matthew NL, Zieske H (1964) Carotid sinus baroreceptor reflex effects upon myocardial contractility. Circ Res 15:327–341Google Scholar
  7. Dorward PK, Anderson MC, Burke SL, Oliver JR, Korner PI (1982) Rapid resetting of the aortic baroreceptors in the rabbit and its implications for short-term and longer term reflex control. Circ Res 50:428–439Google Scholar
  8. Ferrante FL, Opdyke DF (1969) Mammalian ventricular function during submersion asphyxia. J Appl Physiol 26:561–570Google Scholar
  9. Fletcher PJ, Korner PI, Angus J, Oliver JR (1976) Changes in cardiac output and TPR during development of renal hypertension in the rabbit. Circ Res 39 (5):633–637Google Scholar
  10. Gersh WL, Hahn CEW, Prys-Roberts C (1971) Physical characteristics for the measurement of left ventricular pressure and its derivative. Cardiovasc Res 5:32–40Google Scholar
  11. Gribbin B, Pickering TG, Sleight P, Peto R (1971) Effect of high blood pressure on baroreflex sensitivity in man. Circ Res 29:424–431Google Scholar
  12. Guo GB, Abboud FM (1983) Temporal sequence of impairment of baroreflex control of heart rate and lumbar sympathetic nerve activity in renal hypertensive rabbits. Fed Proc 42 (No 3):481Google Scholar
  13. Guo GB, Thames MD, Abboud FM (1982) Differential baroreflex control of heart rate and vascular resistance in rabbits. Relative role of carotid, aortic and cardiopulmonary baroreceptors. Circ Res 50:554–565Google Scholar
  14. Guo GB, Thames MD, Abboud FM (1983) Arterial baroreflexes in renal hypertensive rabbits. Circ Res 53:223–234Google Scholar
  15. Korner PI, Shaw J, West MJ, Oliver JR (1972) Central nervous system control of baroreceptor reflexes in the rabbit. Circ Res 31:637–652Google Scholar
  16. Lindgren P, Manning J (1968) Decrease in cardiac activity by carotid sinus baroreceptor reflex. Acta Physiol Scand 63:401–408Google Scholar
  17. Mancia G, Ferrari A, Gregorini L, Parati G, Ferrari MC, Pomidossi G, Zanchetti A (1979) Control of blood pressure by carotid sinus baroreceptors in man. Am J Cardiol 44:895–902Google Scholar
  18. McCubbin JW, Green JH, Page IH (1956) Baroreceptor function in chronic renal hypertension. Circ Res 4:205–210Google Scholar
  19. McRitchie RJ, Blood R, Chalmers JP (1984) Measurement of myocardial contractility in conscious rabbits. Am J Physiol 246:H293–295Google Scholar
  20. Sarnoff SJ, Gilmore JP, Brockman SK, Mitchell JH, Linden RJ (1960) Regulation of ventricular contraction by the carotid sinus. Its effect on atrial and ventricular dynamics. Circ Res 8:1123–1135Google Scholar
  21. Wallenstein S, Zucker CL, Fleiss JL (1980) Some statistical methods useful in circulation research. Circ Res 47:1–9Google Scholar
  22. West MJ, Korner PI (1974) The baroreceptor-heart rate reflex in renal hypertension in the rabbit. Clin Exp Pharmacol Physiol 1:231–239Google Scholar
  23. West MJ, Angus JA, Korner PI (1975) Estimation of non-autonomic and autonomic components of iliac bed vascular resistance in renal hypertensive rabbits. Cardiovasc Res 9:697–706Google Scholar
  24. West MJ, Blessing WW, Chalmers JP (1981) Arterial baroreceptor reflex function in the conscious rabbit after brainstem lesions coinciding with the A1 group of catecholamine neurons. Circ Res 49:959–970Google Scholar
  25. Yoran C, Higginson L, Romero MA, Covell JW, Ross J Jr (1981) Reflex sympathetic augmentation of left ventricular inotropic state in the conscious dog. Am J Physiol 241:H857-H863Google Scholar

Copyright information

© Springer-Verlag 1985

Authors and Affiliations

  • P. E. Aylward
    • 1
  • R. J. McRitchie
    • 1
  • M. J. West
    • 1
  • J. P. Chalmers
    • 1
  1. 1.Department of MedicineFlinders Medical CentreBedford ParkAustralia

Personalised recommendations