Blood hyperosmolality and pulmonary vascular resistance in the cat

Hypertonic saline

A key feature in the successful resuscitation of dehydrated or endotoxemic ruminants is the total amount of sodium administered. Administration of small volumes of HS and HSD offer major advantages over large volumes of isotonic saline because HS and HSD do not require intravenous catheterization or periodic monitoring, and are therefore suitable for use in the field. Hypertonic saline and HSD exert their beneficial effect by rapidly increasing preload and transiently decreasing afterload. Contrary to early reports, HS and HSD decrease cardiac contractility and do not activate a pulmonary reflex. The osmolality of HS and HSD should be 2400 mOsm/L (7.2% NaCl solution, 8 times normal plasma osmolality). Use of HS and HSD solutions of different osmolality to 2400 mOsm/L should be avoided at all costs, as too low a tonicity removes the main advantages of HS (low cost, decreased infusion time), whereas too high a tonicity may cause rapid vasodilation and decreased cardiac contractility, resulting in death. Rapid administration (> 1 mL/kg-1/min-1) of HS (2400 mOsm/L) should be avoided, as the induced hypotension may be fatal when coupled with a transient decrease in cardiac contractility. For treating dehydrated adult ruminants, HS (2400 mOsm/L, 4-5 mL/kg i.v. over 4-5 minutes) should be administered through the jugular vein and the cow allowed to drink water. This means that 2 L of HS should be administered to adult cattle. HSD should be administered in conjunction with isotonic oral electrolyte solutions to all calves 8% or more dehydrated (eyes recessed > or = 4 mm into the orbit, cervical skin tent duration > 6 seconds) or calves with reduced cardiac output (fetlock temperature < 29 degrees C when housed at 10-24 degrees C). For treating dehydrated calves, HSD (2400 mOsm/L NaCl in 6% dextran-70, 4-5 mL/kg i.v. over 4-5 minutes) should be administered through the jugular vein and the calf allowed to suckle an isotonic oral electrolyte solution. This means that 120-200 mL of HSD of HSD should be administered to a calf. HSD should be routinely administered to severely depressed or comatose calves, as HSD provides the fastest method of resuscitation while rapidly reversing the effects of hyperkalemia.

Effects of hypertonic NaCl solution on microvascular haemodynamics in normo- and hypovolaemia

The aims of this study were to investigate possible resuscitation effects of a single, 10-min, 350-microliters intravenous infusion of 7.5% NaCl in hamsters in hemorrhagic shock and to compare the effects of such infusion with an identical one of 0.9% NaCl on the hamster cheek pouch microcirculation during normovolaemia and after acute bleeding to a hypotension level of about 40 mmHg. No significant differences could be detected between the effects of either infusion given to normovolaemic normotensive hamsters. In the animals subjected to haemorrhage, upon bleeding, arterioles larger than 40 microns constricted, arterioles smaller than 40 microns dilated and venular diameter did not change, while blood flow decreased in all vessels. The main differences between the infusions after haemorrhage were a significant increase in mean arterial pressure and arteriolar blood flow, venoconstriction and a tendency for the smaller arterioles to remain more dilated and the larger ones more constricted after the hypertonic infusion. Central nervous and/or reflex excitation of the sympathetic nervous system could account for the constriction of venules and larger arterioles, while a direct effect of hyperosmolarity could explain the dilatation of the smaller arterioles. The study can therefore help to explain some of the mechanisms underlying the reported resuscitation effect of 7.5% NaCl infusion in animals during severe haemorrhagic hypovolaemia.

Regulation of renal blood flow by plasma chloride

Micropuncture studies have shown that glomerular filtration rate (GFR) falls in response to a rise in Na(+) or Cl(-) concentrations in the loop of Henle, whereas studies in isolated kidneys have shown that GFR falls in response to osmotic diuresis. To define the separate effects of an acute increase in plasma sodium (P(Na)), chloride (P(Cl)) or osmolality (P(osmol)), changes in renal blood flow (RBF) and GFR were measured during intrarenal infusions of hypertonic NaCl, NaHCO(3), Na acetate, dextrose, NH(4)Cl or NH(4)acetate to denervated kidneys. The infusions raised P(osmol) at the experimental kidney by 30-45 mosmol. RBF increased abruptly by 10-30% with all hypertonic infusions indicating that an acute increase in plasma tonicity causes renal vasodilatation. Renal vasodilatation persisted or increased further during infusion of dextrose, NaHCO(3) and Na acetate, but GFR was unchanged. In contrast, during infusion of the two Cl-containing solutions, vasodilatation was reversed after 1-5 min and RBF and GFR decreased (P < 0.01) below preinfusion levels. Prior salt depletion doubled the vasoconstriction seen with hypertonic NaCl infusions. Overall, changes in RBF were unrelated to changes in P(Na) or fractional Na or fluid reabsorption but correlated with changes in P(Cl) (r = -0.91) and fractional Cl(-) reabsorption (r = 0.94). The intrafemoral arterial infusion of the two Cl-containing solutions did not increase femoral vascular resistance. In conclusion, hyperchloremia produces a progressive renal vasoconstriction and fall in GFR that is independent of the renal nerves, is potentiated by prior salt depletion and is related to tubular Cl(-) reabsorption. Chloride-induced vasoconstriction appears specific for the renal vessels.

Regulation of renal blood flow by plasma chloride

Micropuncture studies have shown that glomerular filtration rate (GFR) falls in response to a rise in Na(+) or Cl(-) concentrations in the loop of Henle, whereas studies in isolated kidneys have shown that GFR falls in response to osmotic diuresis. To define the separate effects of an acute increase in plasma sodium (P(Na)), chloride (P(Cl)) or osmolality (P(osmol)), changes in renal blood flow (RBF) and GFR were measured during intrarenal infusions of hypertonic NaCl, NaHCO(3), Na acetate, dextrose, NH(4)Cl or NH(4)acetate to denervated kidneys. The infusions raised P(osmol) at the experimental kidney by 30-45 mosmol. RBF increased abruptly by 10-30% with all hypertonic infusions indicating that an acute increase in plasma tonicity causes renal vasodilatation. Renal vasodilatation persisted or increased further during infusion of dextrose, NaHCO(3) and Na acetate, but GFR was unchanged. In contrast, during infusion of the two Cl-containing solutions, vasodilatation was reversed after 1-5 min and RBF and GFR decreased (P < 0.01) below preinfusion levels. Prior salt depletion doubled the vasoconstriction seen with hypertonic NaCl infusions. Overall, changes in RBF were unrelated to changes in P(Na) or fractional Na or fluid reabsorption but correlated with changes in P(Cl) (r = -0.91) and fractional Cl(-) reabsorption (r = 0.94). The intrafemoral arterial infusion of the two Cl-containing solutions did not increase femoral vascular resistance. In conclusion, hyperchloremia produces a progressive renal vasoconstriction and fall in GFR that is independent of the renal nerves, is potentiated by prior salt depletion and is related to tubular Cl(-) reabsorption. Chloride-induced vasoconstriction appears specific for the renal vessels.

Glucose metabolism accelerates the decline of hypoxic vasoconstriction in rat lungs

Isolated lungs lose the vasoconstrictor response to airway hypoxia with time of perfusion. In isolated rat lungs this loss was accelerated by the addition to perfusate of glucose or pyruvate. The addition of 3-0-methyl glucoside (a non-metabolizable glucose analog) or saline (a solvent control) did not change the rate of decline of hypoxic vasoconstriction. An inhibitor of glucose metabolism (2-deoxy-D-glucose) augmented the hypoxic pressor response. Vasoconstrictor responses to angiotensin II and KCL were not affected by any of the additions. There were no differences in perfusate osmolality among groups of lungs. These results suggest that glucose accelerated the decline of hypoxic pulmonary vasoconstriction by a metabolic, not an osmotic, effect. There may be an important link between lung glucose metabolism and the hypoxic pressor response.

Treatment of refractory hypovolaemic shock by 7.5% sodium chloride injections

Injections of hyperosmotic (7.5%) sodium chloride (100-400 ml) were given to 12 patients in terminal hypovolaemic shock who had not responded to vigorous volume replacement and corticosteroid and dopamine infusions. Hyperosmotic sodium chloride promptly reversed the shock in 11 of these patients. The immediate effects of the NaCl injections were a moderate rise in arterial pressure, the resumption of urine flow, and recovery of consciousness. These effects tended to persist for a few hours. The hyperosmotic infusion also reduced isosmotic fluid requirement by 90%.

Hyperosmolality and pancreatic blood flow

In the cat pancreas, close intra-arterial infusions of hypertonic xylose, glucose and sucrose solutions caused a marked vasodilatation but no secretion. The magnitude of the vasodilator response correlated with the degree of induced glandular hyperosmolality but not with the substance per se. Stimulation of the vagus nerve as well as infusion of secretin and/or CCK evoked a pronounced secretion and a small to moderate increase in pancreatic blood flow, but did not significantly change the plasma osmolality in the venous effluent from the gland. Bradykinin, papaverine and isoprenaline caused large increments of pancreatic blood flow; none of these drugs evoked secretion nor did they change the venous osmolality. It is concluded that blood-bone hyperosmolality is a strong stimulus for pancreatic vasodilatation, but the functional hyperaemia of this gland is due to factors other than regional tissue hyperosmolality.

Dynamics of canine pancreatic blood flow and of insulin secretion during an intravenous glucose load

Blood flow through the superior pancreaticoduodenal artery of anaesthetized dogs increases immediately after an i.v. glucose load and parallels to glycemia, but not to insulin output. Flow of superior mesenteric, and femoral arteries as well as of portal vein are also enhanced after rapid i.v. injections of glucose or mannitol. Extent and duration of all flow increases are dose-dependent and strongly related to the alterations of arterial plasma osmolality (maximum increase 24 mosmoles/kg). Heart rate, mean arterial blood pressure, and hematocrit remain unchanged after the first test minute. There is a considerable decrease of peripheral vascular resistance in the circulatory regions investigated. Flow through aorta ascendens is augmented for a short time. Possible mechanisms of vasodilatation are reflexes produced by osmoreceptors and/or local effects of osmolality on the tonus of vascular muscle. Within the physiological range pancreatic perfusion does not determine the amount of insulin released.

The influence of hypertonic mannitol on regional myocardial blood flow during acute and chronic myocardial ischemia in anesthetized and awake intact dogs

The influence of hypertonic mannitol on regional myocardial blood flow and ventricular performance was studied during acute myocardial ischemia in awake, unsedated and in anesthesized dogs and after myocardial infarction in awake unsedated dogs. Regional myocardial blood flow was measured with radioactive microspheres. Generalized increases in regional myocardial blood flow occurred after mannitol in all of the different animal models studied. The increases in coronary blood flow after mannitol were just as impressive in the nonischemic regions as in the ischemic portion of the left ventricle in all of the different models that were examined in this study. Improvement in regional myocardial blood flow to the ischemic area of the left ventricle after mannitol was associated with a reduction in ST segment elevation during acute myocardial ischemia in anesthetized dogs. The increases in regional myocardial flow after mannitol were also associated with increases in contractility, but the increases in flow appeared to be more impressive than the changes in contractility. The data obtained demonstrate that mannitol increases regional coronary blood flow to both ischemic and nonischemic myocardium in both anesthetized and awake, unsedated, intact dogs with acute and chronic myocardial ischemia and that mannitol reduces ST segment elevation during acute myocardial ischemia in anesthetized dogs. Thus the results suggest that under these circumstances the increases in regional myocardial blood flow after mannitol are of physiological importance in reducing the extent of myocardial injury. Since coronary blood flow increased to nonischemic regions the increases in regional myocardial flow demonstrated in this study after mannitol cannot be entirely explained by the mechanism of reduction in ischemic cell swelling.

Circulatory effects evoded by 'physiological' increases of arterial osmolality

The effects of moderate arterial hyperosmolality (+20 mOsm/kg H2O), produced by short term intravenous hypertonic infusion, on vascular resistance in skin, skeletal muscle, intestine, and kidney were analyzed in the anesthetized cat. Vascular resistance decreased in all four regions in response to the hypertonicity both before and after regional sympathectomy and the effects were not significantly altered by beta-adreno-ceptor blockade. Arterial blood pressure rose during the hypertonic infusion despite the decreased vascular resistance and an unchanged heart rate, indicating an increased stroke volume and cardiac output. Similar increases of arterial osmolality are known to occur in heavy exercise and in hemorrhage. The present results may therefore suggest that blood borne hyperosmolality is a factor which can contribute to the overall cardiovascular adjustments in these situations.