Complex sensory nerve endings, functioning as stretch receptors
exist within the vessel walls of both the high and low pressure vascular
systems. The reflex effects of stimulation of receptors in the high
pressure system (arterial baroreceptors) are known in some detail; less
is known regarding the function of receptors in the low pressure system.
The work reported here is concerned with the reflex responses to
stimulation of unencapsulated nerve endings found within the endocardium
of the left atrium and having myelinated afferent fibres in the vagus
nerves (left atrial receptors).
Evidence is presented that stimulation of left atrial receptors
leads to complex and highly specific reflex responses. Stimulation of
left atrial receptors causes a reflex increase in heart rate which is
mediated mainly through the cardiac sympathetic nerves. There is also a
reflex decrease in renal vascular resistance, although the resistance in
other vascular beds remains unaltered. Stimulation of atrial receptors
did not cause any change in respiratory rate or tidal volume.
Stimulation of atrial receptors is associated with a diuresis and under
some circumstances a natriuresis. At least a part of the diuresis
appeared to be dependant on a decrease in the concentration of
vasopressin in the plasma. More recently it became possible to measure
the plasma concentration of vasopressin by radioimmunoassay and it was
shown that stimulation of atrial receptors caused a reflex decrease in
plasma vasopressin concentration. The recent demonstration that the
atrial myocytes produce a natriuretic peptide (atrial natriuretic
factor), which is released during atrial distension, adds another
dimension to the control of blood volume. The release of this peptide
was not influenced by atrial receptor stimulation.
The atrial receptors appear to provide one mechanism by which either
total blood volume, or the filling of the heart may be detected. The
reflex increase in heart rate induced by atrial receptor stimulation may
act along with the "Starling Mechanism" to maintain heart volume
constant. Continued stimulation of atrial receptors, acting through the
renal nerves and a reduction in plasma vasopressin, will promote the
excretion of water and salt and tend to reduce blood volume.
LIST OF CONTENTS:
1. Ledsome, J.R., Linden, R.J. & O'Connor, W.J. (1961). The mechanisms
by which distension of the left atrium produce diuresis in
anaesthetized dogs. J. Physiol. 159, 87-100.
2. Ledsome, J.R. & Linden, R.J. (1964). A reflex increase in heart
rate from distension of the pulmonary vein-atrial junctions. J.
Physiol. 170, 456-473.
3. Ledsome, J.R. & Linden, R.J. (1967). The effects of distending a
pouch of the left atrium on the heart rate. J. Physiol. 193,
121-129.
4. Ledsome, J.R. & Linden, R.J. (1968). The role of the left atrial
receptors in the diuretic response to left atrial distension. J.
Physiol. 198, 487-503.
5. Carswell, F., Hainsworth, R. & Ledsome, J.R. (1970). The effects of
distension of the pulmonary vein-atrial junctions upon peripheral
vascular resistance. J. Physiol. 207, 1-14.
6. Ledsome, J.R. & Hainsworth, R. (1970). The effects upon respiration
of distension of the pulmonary vein-atrial junctions. Respiration
Physiol. 9, 86-94.
7. Carswell, F., Hainsworth, R. & Ledsome, J.R. (1970). The effects of
left atrial distension upon urine flow from the isolated perfused
kidney. Quart. J. exp. Physiol. 55, 173-182.
8. Mason, J.M. & Ledsome, J.R. (1971). The effects of changes in the
rate of infusion of vasopressin in anaesthetized dogs. Can. J.
Physiol. 49, 933-940.
9. Ledsome, J.R. & Mason, J.M. (1972). The effect of vasopressin on
the diuretic response to left atrial distension. J. Physiol. 221,
427-440.
10. Albrook, S.M., Bennion, G. & Ledsome, J.R. (1972). The effects of
decerebration on the reflex response to pulmonary vein distension.
J. Physiol. 226, 793-803.
11. Lawrence, M., Ledsome, J.R. & Mason, J.M. (1973). The time course
of the diuretic response to left atrial distension. Quart. J. exp.
Physiol. 58, 219-227.
12. Burkhart, S.M. & Ledsome, J.R. (1974). The response to distension
of the pulmonary vein-left atrial junctions in dogs with spinal
section. J. Physiol. 237, 685-700.
13. Mason, J.M. & Ledsome, J.R. (1974). Effects of obstruction of the
mitral orifice or distension of the pulmonary vein-atrial junctions
on renal and hind limb vascular resistance in the dog. Circulation
Research 35, 24-32.
14. Burkhart, S.M. & Ledsome, J.R. (1977). The response to distension
of the pulmonary vein-left atrial junctions in anaesthetized dogs
after section of the rostral medulla. J. Physiol. 273, 57-67.
15. Burkhart, S.M., Funnell, L. & Ledsome, J.R. (1977). The effects of
medullary lesions on the reflex responses to carotid occlusion,
aortic nerve stimulation, and distension of the pulmonary vein-left
atrial junctions in the anaesthetized dog. J. Physiol. 273, 69-81.
16. Kidd, C., Ledsome, J.R. & Linden, R.J. (1978). The effect of
distension of the pulmonary vein-atrial junction on activity of left
atrial receptors. J. Physiol. (1978). 285, 445-453.
17. Ledsome, J.R., Wilson, N. and Ngsee, J. (1982). Time course of
changes in plasma vasopressin during atrial distension. Can. J.
Physiol. Pharmacol. 60, 1210-1218.
18. Ledsome, J.R., Ngsee, J. and Wilson, N. (1983). Plasma vasopressin
concentration in the anaesthetized dog before, during and after
atrial distension. J. Physiol. 338, 413-422.
19. Wilson, N. and Ledsome, J.R. (1983). Distension of the pulmonary
vein-atrial junctions and plasma vasopressin in the chloralose
anaesthetized dog. Can. J. Physiol. Pharmacol. 60, 905-910.
20. Ledsome, J.R. and Wilson, N. (1984). The relationship between
plasma vasopressin concentration and urinary excretion during left
atrial distension in anaesthetized dogs. Pflugers Arch. 400,
381-387.
21. Ledsome, J.R., Wilson, N. and Courneya, C.A. (1985). Plasma
vasopressin during increases and decreases in blood volume in
anaesthetized dogs. Can. J. Physiol. Pharmacol. 63, 224-229.
22. Ledsome, J.R. (1985). Atrial receptors, blood volume and
vasopressin. Life Sciences 36, 1315-1330.
23. Ledsome, J.R., Wilson, N., Courneya, C.A. and Rankin, A.J. (1985).
Release of atrial natriuretic peptide by atrial distension. Can. J.
Physiol. Pharmacol. 63, 739-742.
24. Ledsome, J.R., Wilson, N., Rankin, A.J. and Courneya, C.A. (1985).
Time course of release of atrial natriuretic peptide in the
anaesthetized dog. Can. J. Physiol. Pharmacol. 64, 1017-1022.
