Effect of acute changes in left atrial pressure on urine flow in unanesthetized dogs

Abstract

The effect of an acute rise in left atrial pressure on urine flow, urine specific gravity, and sodium excretion was studied in chronic preparations with and without anesthesia and at different hydration levels. Left atrial pressure was changed by an exteriorized purse string about the mitral annulus. In 56 of 58 experiments (including each of the above conditions) a transient increase of urine flow was found during atrial distention, accompanied by an increase in sodium excretion and a fall in urine specific gravity. Absolute volume and percentage increase of the diuresis varied directly with the degree of prehydration. Vasopressin infusions modified the response only in prehydrated animals. Arterial pressure and renal blood flow (electromagnetic flowmeter) were increased during atrial distention. At least two mechanisms interplay in the diuretic response: 1) hemodynamic and 2) humoral (ADH or Jahn's "diuretic factor"). The degree of prehydration seems to determine the threshold of the ADH mechanism. Our data speak against homeostatic fluid volume control by stretch receptors in the left atrium or its inflow tract.

The effects of vasopressin on the diuretic response to left atrial distension

“…It seems reasonable to suppose that in the conscious dog a decrease in antidiuretic activity could occur during atrial distension possibly at a lower range of concentration leading to a greater increase in free water clearance which would be inhibited by smaller doses of vasopressin. Lydtin & Hamilton (1964) provide some support for this speculation.…”

“…The results allow the view that a part of the diuretic response to left atrial distension could depend upon a decrease in the concentration of antidiuretic hormone in the circulating blood. fNTRODUCTION Partial obstruction of the mitral orifice causes an increase in urine flow in anaesthetized (Henry, Gauer & Reeves, 1956) and unanaesthetized dogs (Lydtin & Hamilton, 1964). It has been suggested that the diuretic response is due at least in part to a decrease in the rate of release of antidiuretic hormone from the neurohypophysis (Arndt, Reineck & Gauer, 1963; Johnson, Moore & Segar, 1969) and it has been shown that left atrial distension is accompanied by a decrease in antidiuretic activity in the circulating blood (Shu'ayb, Moran & Zimmerman, 1965).…”

“…It has been suggested that the diuretic response is due at least in part to a decrease in the rate of release of antidiuretic hormone from the neurohypophysis (Arndt, Reineck & Gauer, 1963; Johnson, Moore & Segar, 1969) and it has been shown that left atrial distension is accompanied by a decrease in antidiuretic activity in the circulating blood (Shu'ayb, Moran & Zimmerman, 1965). However, the J. R. LEDSOME AND J. M. MASON diuretic response occurs during infusion of vasopressin adequate to completely inhibit water diuresis in the conscious dog (Ledsome, Linden & O'Connor, 1961;Lydtin & Hamilton, 1964). The part which antidiuretic hormone plays in the diuretic response to left atrial distension is therefore in doubt.…”

Plasma vasopressin concentration in the anaesthetized dog before, during and after atrial distension.

“…We followed changes in plasma AVP concentration for only 10 min.It cannot be assumed that plasma AVP concentration would then remain constant for a long period of atrial distension. When atrial distension is prolonged the diuretic response reaches a peak after 40-50 min and then declines ; Lydtin & Hamilton, 1964;Lawrence, Ledsome & Mason, 1973). Shu'ayb et al (1965) claimed that both ADH and urinary flow started to return to the pre-inflation level in 30-40 min, although this statement was not borne out in all their illustrations.…”

Studies of the mechanism of contralateral polyuria after renal artery stenosis.

“…4). DISCUSSION (17,18) and norepinephrine increases free water clearance in water loaded subjects despite infusion of vasopressin (7). Similarly when the rise in MAP induced by acute renal artery stenosis was prevented by Arfonad in Group II, no change in baroreceptor tone should have occurred, but Uosm fell and free water clearance increased.…”