Reflexes elicited by acute stretch of atrial vs. pulmonary receptors in conscious dogs

Abstract

We measured hemodynamics and renal function in conscious dogs while partially obstructing blood flow at various sites within the thorax. Inflation of a balloon in the left atrium increased left atrial pressure (LAP) by 9 mmHg and caused a parallel increase in pulmonary arterial pressure (PAP); heart rate, arterial pressure, and total peripheral resistance increased; stroke volume and right atrial pressure decreased; and cardiac output remained unchanged. The increase in LAP was accompanied by a fourfold increase in urine flow and a threefold increase in sodium excretion. Plasma vasopressin (AVP) and renin activity (PRA) decreased. On the other hand, partial occlusion of the pulmonary veins or the main pulmonary artery produced similar increases in PAP without affecting LAP, systemic hemodynamics, renal function, or plasma AVP. Similarly, inflation of a balloon in the right atrium failed to alter renal function, plasma AVP, or PRA. Finally, constriction of the thoracic inferior vena cava decreased LAP and increased PRA. In summary, these data emphasize that inflation of a balloon in the left atrium of the conscious dog produces a composite response consisting of alterations in cardiovascular function, renal function, and circulating hormones. Moreover, our data indicate that the response is mediated by a reflex initiated from receptors located in the left atrium; we detected no evidence that receptors located in the pulmonary vasculature or right heart contribute to this response.

Serotonergic mechanisms of the lateral parabrachial nucleus in renal and hormonal responses to isotonic blood volume expansion

“…The present results suggest the involvement of LPBN serotonergic mechanisms in the regulation of urinary sodium, potassium and water excretion, and hormonal responses to acute isotonic blood volume expansion. serotonin; natriuresis; atrial natriuretic peptide; oxytocin; vasopressin ISOTONIC BLOOD VOLUME expansion, by reflex mechanisms, induces a series of regulatory responses, including the inhibition of the sympathetic outflow to the kidney, heart, and blood vessels, reduction of renin and vasopressin (VP) secretion, and increase in the levels of circulating atrial natriuretic peptide (ANP) and oxytocin (OT) that leads to diuresis and natriuresis (1,2,12,14,20,24,45,53).There are several reports demonstrating the correlation between natriuresis and diuresis and plasma ANP levels in response to systemic volume expansion, e.g., atrial balloon inflation, blood volume expansion, salt load, and water immersion (4,7,17,32,50,59). These responses depend on the activation of sinoaortic baroreceptors and/or cardiopulmonary receptor afferents located in the atria, lungs, great veins, and ventricles that project to the nucleus of the solitary tract (NTS) (1, 12, 22).…”

“…The present results suggest the involvement of LPBN serotonergic mechanisms in the regulation of urinary sodium, potassium and water excretion, and hormonal responses to acute isotonic blood volume expansion. serotonin; natriuresis; atrial natriuretic peptide; oxytocin; vasopressin ISOTONIC BLOOD VOLUME expansion, by reflex mechanisms, induces a series of regulatory responses, including the inhibition of the sympathetic outflow to the kidney, heart, and blood vessels, reduction of renin and vasopressin (VP) secretion, and increase in the levels of circulating atrial natriuretic peptide (ANP) and oxytocin (OT) that leads to diuresis and natriuresis (1,2,12,14,20,24,45,53).…”

Responses of renal hemodynamics and function to acute volume expansion in the conscious dog.

“…The mechanism for this reflex appears to be mechanoreceptors situated in the cardiopulmonary area activating the vagal and/or sympathetic afferent fibers to control renal function. Although increases in renal excretory function have been repeatedly demonstrated by mechanical stretch of the atria (Lydtin and Hamilton, 1964;Linden, 1973;Goetz et al, 1975;Fater et al, 1982;Schultz et al, 1982), distention of the left atrium by balloon inflation (Ledsome et al, 1961;Kappagoda et al, 1974;Zehr et al, 1976), and volume expansion (Gilmore and Weisfeldt, 1965;Fater et al, 1982), it remains controversial whether the responses of renal function are mediated by vagal afferents. For example, Gilmore and Weisfeldt (1965) failed to demonstrate any difference in the natriuretic response of the kidney to acute volume expansion before and after bilateral vagotomy in the anesthetized dog.…”

Absence of reflex vascular responses from the intrapulmonary circulation in anaesthetised dogs

“…However, these studies have not reported responses to distension of the pulmonary circulation with the more moderate pressures likely to be encountered in life. Furthermore, in many the stimuli were not adequately localised to the intrapulmonary circulation so that changes in pressure in the main pulmonary trunk (Daly et al 1937;Schultz et al 1982) and to other reflexogenic regions would be likely to have complicated the interpretation of any results. The present study was undertaken with the objective of investigating the vascular responses during intrapulmonary arterial and or venous distension particularly over the physiological range.…”