Mechanisms of changes in nitrogen washout and lung volumes after saline infusion in humans

This study was performed to determine the roles of increased intrathoracic blood volume and increased vagal tone in the changes in lung volume and nitrogen washout produced by saline infusion. In the first study, measurements of TLC, VC, FRC, ERV, and slope of phase III nitrogen washout (delta N2) were made on 8 subjects before, during, and after inflation of the leg compartments of medical anti-shock trousers (MAST). In the second study, 13 volunteers were infused intravenously with warm saline (30 ml/kg) for 30 min. Repeat measurements were made approximately 20 and 40 min after infusion. Each subject then received intravenously 0.03 mg/kg atropine, and measurements were repeated. In 7 of these subjects, a third study was performed in which the atropine was injected before saline infusion. Inflation of the MAST (see figures 5 and 6) caused a 1.9% decrease in VC, 5.3% decrease in FRC, and no change in delta N2. Saline infusion caused decreases in TLC, VC, and FRC (4.0, 3.1, and 10.1%, respectively) and a 15.0% increase in delta N2. Atropine reversed the change in delta N2 after saline infusion and prevented these changes when given prior to saline. Atropine had no effect on lung volumes whether given before or after saline infusion. We speculate from our data that saline infusion has 2 effects on the lung. One is a simple displacement of air by increased intravascular volume producing the reduction in lung volumes. The second is an increase in small airways resistance that is mediated by vagal reflex and blocked with atropine.

[Effect of dihydroergotamine (DHE) on blood volume and circulation in the calf in peridural anesthesia in the human]

Dihydroergotamine (DHE) preferentially constricts capacitance vessels in the skin and striated musculature, thereby redistributing blood in favor of the pulmonary vascular bed in the presence of neurogenic vascular tone. The aim of this study was to see if DHE would act likewise when neurogenic vascular tone is absent. Filling and blood flow of the calves were measured plethysmographically in six healthy, supine male volunteers before and during peridural anesthesia (PDA) to the level of at least T5 and, in the denervated state, after the injection of DHE 7.5 micrograms/kg intravenously. Arterial blood pressure, central venous pressure (CVP), and heart rate were also determined. Both blood flow (+2.2 ml/min per 100 ml tissue) and volume (+1 ml/100 ml tissue) of the calves increased while CVP and systolic arterial pressure decreased during PDA (Table 1). DHE did not affect the PDA-included increase in blood flow, but strongly reduced calf volume (-1.7 ml/100 ml tissue). This was accompanied by an increase in CVP and systolic blood pressure (Fig. 1). In the absence much as in the presence of neurogenic vascular tone, DHE preferentially constricts capacitance but not resistance vessels. Thus, DHE counteracts the vascular effects of PDA, as it improves cardiac filling and consequently raises arterial blood pressure by redistributing blood from the dilated capacitance vessels without curtailing blood flow. It would appear, therefore, that DHE is a rational alternative to fluid therapy for the prophylaxis of arterial hypotension during major conduction anesthesia.

Anti-shock effect of ACTH: haematological changes and influence of splenectomy

ACTH-(1-24), injected i.v. into rats subjected to otherwise invariably fatal bleeding, at the dose of 160 micrograms/kg, causes a prompt and sustained increase in mean arterial and pulse pressure, with survival of all treated animals, at least for the first 2 hr. This is associated with a 100% increase in the volume of circulating blood, which is of normal composition, so that also the number of circulating red cells is doubled as compared to controls. Splenectomy greatly impairs the beneficial effect of ACTH on blood pressure, blood volume and survival. It is concluded that, in cases of acute hypovolemia, ACTH-(1-24) induces a recall of blood from storage sites and its redistribution, though the precise mechanism is as yet unknown.

Effects of physiological manipulations on locus coeruleus neuronal activity in freely moving cats. II. Cardiovascular challenge

Several cardiovascular manipulations were examined for their effects on single-unit activity of locus coeruleus noradrenergic (LC-NE) neurons in unanesthetized, unrestrained cats: hydralazine (1 mg/kg, i.v.) was administered to present a tonic hypotensive stimulus, and to activate preferentially the neural component of the sympathoadrenal system; hemorrhage was used to decrease blood volume and to activate both the neural and hormonal components of the sympathoadrenal system; intravenous infusion of isotonic saline was used to increase blood volume. LC-NE neurons were activated by hydralazine, in parallel with the sympathetic response (indicated by elevated heart rate and plasma NE). LC-NE unit activity was decreased following a volume load. However, contrary to previous findings in anesthetized animals, hemorrhage had no effect on LC-NE unit activity, but did activate both components of the sympathetic response. It is concluded that: (1) cardiovascular stimuli can influence the activity of LC-NE neurons, though they show less sensitivity to such stimuli than do primary regulatory mechanisms; (2) the response of LC-NE neurons to physiological stimuli can occur independent of changes in behavioral state; (3) these neurons do not appear to play a specific role in cardiovascular regulation, but may respond to physiological challenges in general; (4) finally, in agreement with previous studies, our data show that LC-NE neurons are generally co-activated with the sympathetic nervous system, but also that the two can be dissociated (e.g. hemorrhage).

Effects of afterload reduction (diuretics and vasodilators) on left ventricular volume and mitral regurgitation in severe congestive heart failure secondary to ischemic or idiopathic dilated cardiomyopathy

The mechanism by which afterload reduction increases left ventricular stroke volume while decreasing left ventricular filling pressure has not previously been established. In 15 patients with severe congestive heart failure due to ischemic or idiopathic dilated cardiomyopathy, absolute ventricular volume, ejection fraction and total stroke volume from radionuclide ventriculography were compared with thermodilution stroke volume before and after intensive afterload reduction with vasodilators and diuretics titrated to hemodynamic goals. After 48 to 72 hours, pulmonary artery wedge pressure decreased from 32 +/- 8 to 16 +/- 4 mm Hg and systemic vascular resistance from 1,960 +/- 700 to 1,200 +/- 400 dynes s cm-5. End-diastolic volume decreased from 390 +/- 138 to 301 +/- 126 ml (p less than 0.01) and end-systolic volume from 316 +/- 127 to 241 +/- 111 (p less than 0.01). Ejection fraction did not change and total stroke volume decreased from 74 +/- 22 to 59 +/- 20 ml (p less than 0.01). Simultaneous forward stroke volume by thermodilution increased from 37 +/- 14 to 52 +/- 14 ml (p less than 0.01), and forward fraction increased from 0.55 +/- 0.40 to 0.96 +/- 0.42. Intensive reduction of ventricular filling pressure and systemic vascular resistance decreased total ventricular stroke volume by 20% but increased forward stroke volume by 40%. The major effect of intensive afterload reduction for severe congestive heart failure may be the reduction of ventricular volume and mitral regurgitation.

Failure of autoregulation of cerebral blood flow in neonates studied by pulsed Doppler ultrasound of the internal carotid artery

To reveal the influence of therapeutically induced changes of arterial blood pressure on cerebral circulation, pulsed Doppler measurements of blood velocity in the right internal carotid artery were performed in 23 neonates. A positive correlation between mean arterial blood pressure and time-averaged maximum blood velocity (change more than 0.5%/torr) could be noticed in 16 infants. These infants were supposed to have loss of autoregulation. The main characteristics in this non-autoregulating group were: gestational age less than 31 weeks, birth weight less than 1501 g and mean carotid blood velocity less than 20 cm/s. In accordance with animal experiments we assume that autoregulation does not work below a definite lower limit of brain perfusion, which is reflected by carotid blood velocity in our study. Patients below/equal 1500 g or 30 gestational weeks very often do not exceed this limit and thus do not reach the "range of autoregulation".

Effects of leukotriene D4 on glomerular dynamics in the rat

Glomerular micropuncture studies were performed in euvolemic, anesthetized, adult, male Munich-Wistar rats to evaluate the glomerular microcirculatory actions of leukotriene D4 (LTD4). In preliminary experiments, intrarenal arterial administration of LTD4 (1 microgram X kg-1 X min-1) was found to cause a rise in mean systemic arterial pressure, a loss of plasma volume, and a fall in renal blood flow, effects identical to those previously reported for LTC4. To assess the local glomerular actions of LTD4 independently of these systemic effects, glomerular microcirculatory dynamics were assessed during LTD4 infusion while constancy of renal perfusion pressure and plasma volume were maintained by partial aortic constriction and isoncotic plasma infusion, respectively. To ascertain the LTD4 actions that are independent of angiotensin II, saralasin (5 micrograms X kg-1 X min-1 iv) was also given throughout the study. LTD4 caused a significant increase in efferent arteriolar resistance in association with a fall in glomerular plasma flow rate (QA) and a rise in glomerular capillary hydraulic pressure. Despite the latter, single-nephron filtration rate fell due to combined reductions in QA and the glomerular ultrafiltration coefficient. These local glomerular constrictor actions of LTD4 support the possibility that this eicosanoid might play an important intermediary role in the functional impairment accompanying some forms of inflammatory injury.

Misoprostol-induced changes in gastric mucosal hemodynamics. A double-blind parallel study in human volunteers

The effects of misoprostol on human gastric mucosal hemodynamics were examined in a double-blind, placebo-controlled, parallel study in 12 healthy male volunteers. Six subjects received 200 micrograms of misoprostol and six received placebo. The index of mucosal blood volume and mucosal blood hemoglobin oxygen saturation (Hb-SO2) were measured at 20 locations in the stomach using reflectance spectrophotometry during endoscopy prior to and after administration of the study drug. Mucosal blood volume index increased by approximately 10 to 25 percent throughout the stomach without a significant change in mucosal Hb-SO2 following treatment with misoprostol. The increase in mucosal blood volume index was statistically significant for 16 of the 20 locations (p less than or equal to 0.05). Placebo produced no significant change in mucosal blood volume and mucosal Hb-SO2. These findings suggest that misoprostol may have the potential effect of accelerating gastric ulcer healing by improving gastric mucosal hemodynamics, in addition to its gastric acid antisecretory activity.

Involvement of the reflex increase in heart rate in the differences in urinary responses to stimulation of atrial receptors in dogs with different blood volumes

The effect of increasing heart rate by increasing the rate of atrial pacing in the absence of any reflex effects from atrial receptors, by cooling the vagi to 12 degrees C, was studied in two groups of dogs with different blood volumes. In one group of nine dogs with a high blood volume increasing heart rate, by an amount similar to that reflexly obtained in response to stimulation of atrial receptors, resulted in significant increases in urine flow and sodium excretion; in another group of eight dogs with a low blood volume similar increases in heart rate did not result in a diuresis or natriuresis. The findings suggest that the effects of an increase in heart rate in combination with differences in blood volume could contribute to the previously reported differences in the urinary responses that result from stimulation of atrial receptors in dogs with different blood volumes.

Peripheral circulatory control of preload-afterload mismatch with angiotensin in dogs

To determine whether changes in the venous circulation were responsible for preload-afterload mismatch with angiotensin, we examined the changes in the heart and the peripheral circulation in six splenectomized dogs after ganglion blockade during an angiotensin infusion to increase mean aortic pressure 25 and then 50%. The peripheral circulation was evaluated by measuring mean circulatory filling pressure (MCFP), arterial compliance, and venous compliance. A 25% increase in mean aortic pressure increased MCFP from 6.2 +/- 0.3 to 7.6 +/- 0.3 mmHg (P less than 0.001) but did not change cardiac output, heart rate, or stroke volume. Systemic vascular resistance increased (P less than 0.01) from 0.50 +/- 0.02 to 0.59 +/- 0.03 mmHg X min X kg X ml-1. Arterial and venous compliances decreased (P less than 0.01) from 0.08 +/- 0.03 to 0.06 +/- 0.03 ml X mmHg-1 X kg-1 and from 2.1 +/- 0.1 to 1.6 +/- 0.1 ml X mmHg-1 X kg-1, respectively. A 50% elevation in mean aortic pressure increased MCFP from 7.1 +/- 0.4 to 9.5 +/- 0.9 mmHg (P less than 0.001) but did not change heart rate. At this level of aortic pressure, cardiac output and stroke volume decreased (P less than 0.01) 12 and 19%, respectively, whereas systemic vascular resistance increased (P less than 0.001) from 0.48 +/- 0.03 to 0.83 +/- 0.05 mmHg X min X kg X ml-1. Arterial and venous compliances decreased (P less than 0.01) from 0.08 +/- 0.01 to 0.05 +/- 0.01 ml X mmHg-1 X kg-1 and from 2.1 +/- 0.1 to 1.4 +/- 0.1 ml X mmHg-1 X kg-1, respectively.(ABSTRACT TRUNCATED AT 250 WORDS)

Relation between oxygen consumption and pressure-volume area of in situ dog heart

We studied the relation between O2 consumption (VO2) and the systolic pressure-volume area (PVA) in the left ventricle of open-chest dogs. PVA and the slope (Emax) of the end-systolic pressure-volume line were determined by an abrupt occlusion of the ascending aorta. VO2 linearly correlated with PVA in control contractile state, where Emax was 15.8 +/- 4.4 (SD) mmHg/ml with intact reflexes and 11.5 +/- 1.2 mmHg/ml with blocked reflexes. Emax and the VO2 axis intercept of the VO2-PVA line were greater in the in situ heart than in the excised cross-circulated dog heart in our previous study. Enhancement of contractile state by dobutamine increased Emax by 60-80% and shifted the VO2-PVA line upward, increasing the VO2 axis intercept by 38% with intact reflexes and by 79% with blocked reflexes. The slope had a tendency to increase with dobutamine, but the increase was statistically insignificant. We conclude that PVA and Emax obtained by the aortic-occlusion method can account for changes in VO2 with changes in loading conditions and contractility in an in situ dog heart.

Inhibition of VP and OT release by water in hypovolemia is independent of opioid peptides

Overhydration inhibits release of vasopressin (VP) and oxytocin (OT) from the hypothalamo-neurohypophysial system during hypovolemia. We investigated whether opioid peptides mediate the inhibitory effect of water on secretion of these hormones. Conscious male rats were made hypovolemic by hemorrhage (HEM, 0.51 ml/min) of 20 and 35% of the blood volume or by injection of either subcutaneous polyethylene glycol (PEG, 20,000 mol wt, 35 ml/kg) or intraperitoneal histamine (HIS, 15 mg/kg, 1 ml/kg). Animals were intubated orally 1-4 min (HEM, HIS) or 6.75 h (PEG) later with or without administration of water (40 ml/kg). Four to seven min after intubation rats were injected with saline (1 ml/kg) or naloxone (2 or 5 mg/kg) and then decapitated 6-10 min later. Control animals were treated similarly but were not stimulated by hypovolemia. VP and OT were extracted from plasma and quantified by radioimmunoassay. Data were analyzed by analysis of variance. In HEM animals blood pressure fell and plasma osmolality increased, both of which correlated positively with the rise in plasma [VP] and [OT]. Overhydration lowered the plasma osmolality, attenuated the fall in blood pressure, and reduced [VP] and [OT] in plasma of HEM animals. The opiate receptor antagonist, naloxone, did not alter these changes in blood pressure or plasma osmolality, or the plasma [VP] after HEM in rats treated with or without water. Plasma [OT] was, however, increased by naloxone in both normally hydrated and overhydrated rats. Thus, regardless of the hydrational state of the animal, opioid peptides inhibited release of OT but not VP during hemorrhage. Data consistent with this interpretation were also obtained from rats made hypovolemic with PEG or HIS.(ABSTRACT TRUNCATED AT 250 WORDS)

Spinal cord blood flow during spinal anesthesia in dogs: the effects of tetracaine, epinephrine, acute blood loss, and hypercapnia

To examine the effects of subarachnoid tetracaine and epinephrine on spinal cord blood flow (SCBF), lumbar SCBF and cerebral blood flow (CBF) were measured simultaneously by the hydrogen clearance technique in dogs (n = 45) anesthetized with halothane. The lumbar subarachnoid administration of tetracaine, 5 mg dissolved in 1 ml of a 7.5% dextrose solution had no significant effect on either SCBF or CBF for 4 hr even though arterial blood pressure and heart rate decreased significantly. After subarachnoid epinephrine alone (100, 300, and 500 micrograms), SCBF varied widely but did not change significantly with any of the injections, nor did CBF. Responses of SCBF to hypercapnia and to acute blood loss during spinal anesthesia with tetracaine were also examined. Increased PaCO2 (from 35 to 57 mm Hg) increased both SCBF and CBF similarly before and after subarachnoid tetracaine; SCBF increased from 26.8 +/- 9.0 ml X 100 g-1 X min-1 (mean +/- SD) before to 34.2 +/- 13.6 ml X 100 g-1 X min-1 during hypercapnia during spinal anesthesia, which was almost identical to the increase (from 31.5 +/- 8.1 ml X 100 g-1 X min-1 to 39.9 +/- 6.0 ml X 100 g-1 X min-1) before spinal anesthesia. Whereas acute blood loss (approximately 20% of estimated blood volume) during spinal anesthesia with tetracaine caused a 23% reduction of SCBF (P less than 0.05), in the absence of tetracaine SCBF remained unchanged during hemorrhagic hypovolemia.(ABSTRACT TRUNCATED AT 250 WORDS)

NADH fluorescence in vivo: changes in cerebral oxidative metabolism and perfusion induced by pentobarbital, indomethacin, and salicylate

The effects of two prostaglandin synthesis inhibitors on brain oxidative metabolism and cerebral blood volume were studied by the nicotinamide adenine dinucleotide (reduced) (NADH) fluorescence technique in rats. Indomethacin (5, 10, and 15 mg/kg) and sodium salicylate (50, 100, and 300 mg/kg) were administered intravenously to groups of rats anesthetized with either nitrous oxide or pentobarbital (40 mg/kg, i.p.). The effects of pentobarbital alone were also examined: pentobarbital induced a progressive reduction in blood volume 4 min following intraperitoneal administration. A reduced NADH fluorescence (oxidation) was noted approximately 9 min after pentobarbital treatment. In N2O-anesthetized rats, the effects of salicylate were dose-dependent. Low doses (50 and 100 mg/kg) decreased both blood volume and NADH fluorescence; in contrast, salicylate at 300 mg/kg increased blood volume and NADH fluorescence. Following pentobarbital, the effects of salicylate (50 and 100 mg/kg) were reversed: increases in both blood volume and NADH fluorescence were seen. In the absence of pentobarbital, it would appear that salicylate induces a cerebral vasoconstriction, an effect that may be obscured by a central stimulation provoked by this drug. Under N2O anesthesia, indomethacin, in a dose-related manner, induced a decrease in blood volume that was accompanied by a dose-related increase in NADH fluorescence (reduction). The changes induced by the highest dose of indomethacin (15 mg/kg) were essentially abolished by pentobarbital. These results support those studies in which indomethacin-induced cerebral vasoconstriction could be abolished by barbiturates. Furthermore, our experiments demonstrate, following indomethacin infusion, a decrease in brain oxidative metabolism.(ABSTRACT TRUNCATED AT 250 WORDS)

Alteration of blood flow distribution and vascular capacitance during induced hypotension in deafferented dogs

The effects of three hypotensive agents, sodium nitroprusside (SNP), nitroglycerin (NTG), and adenosine triphosphate (ATP), on blood flow distribution and vascular capacitance were examined in dogs anesthetized with sodium pentobarbital. To eliminate the modification by the baroreflex, carotid sinus was denervated and aortic and cardiopulmonary vagal fibers were sectioned. Total systemic circulation was divided into two parallel compartments, splanchnic (SP) and extra-splanchnic (ESP) vascular beds. Alteration of vascular capacitance was assessed by a change in systemic blood volume with constant cardiac output and constant venous pressure using a total heart-lung bypass. SNP- and ATP-induced hypotension caused blood flow redistribution from the SP to ESP beds, and this redistribution is greater (P less than 0.01) with ATP than that with SNP. In contrast, NTG-induced hypotension did not significantly cause redistribution. Systemic blood volume was increased during NTG- (10.4 +/- 2.2 ml/kg), and SNP-induced (4.8 +/- 1.1 ml/kg) hypotension. The increase by NTG was significantly greater (P less than 0.05) than that by SNP. In contrast, ATP-induced hypotension did not significantly change systemic blood volume. Since redistribution can result in a passive change in vascular capacitance, the differences in capacitance among SNP, NTG, and ATP can be explained in part by differences in redistribution of blood flow. Redistribution of blood flow from SP to ESP beds can increase venous return due to increasing the slope of the venous return curve. The results suggest that redistribution should be taken into consideration in evaluating the hemodynamic changes during induced hypotension.

Does vasopressin-induced vasoconstriction persist during prolonged infusion in dogs?

I have examined the systemic and regional hemodynamic effects of an intravenous arginine vasopressin (AVP) infusion at a rate of 220 pg X kg-1 X min-1 maintained for 48 h in 12 conscious dogs. Plasma AVP concentration increased from 2.8 +/- 1.1 to 8.2 +/- 1.4 pg/ml, and plasma osmolality fell from 294.8 +/- 1.4 to 287.1 +/- 1.5 mosmol/kg. Mean arterial pressure increased slightly but significantly despite a reduction in blood volume. Contrary to what we previously observed with 1-h AVP infusion at the same rate, cardiac output and heart rate did not decrease, and total peripheral resistance did not increase. Most vascular beds sensitive to the acute vasoconstrictor effects of AVP, such as those of the skeletal muscle, fat, colon, and skin, did not show any significant reduction in blood flow after 48 h. Only in the pancreas and in the thyroid gland was there a significant flow decrease, which was similar in magnitude to that measured after 1 h of infusion. It therefore appears that vasoconstriction induced by modest increases in plasma concentrations of AVP is not maintained during prolonged administration in most vascular beds. However, injection of a specific antagonist of the pressor action of AVP [1-(beta-mercapto-beta,beta-cyclopentamethylenepropionic acid), 2-(O-methyl)tyrosine]arginine vasopressin, 10 micrograms/kg, induced a significant increase in cardiac output and heart rate, as well as a fall in total peripheral resistance and significant increases in myocardial, fat, and skin blood flows after 48 h of AVP infusion.(ABSTRACT TRUNCATED AT 250 WORDS)

[Comparative analysis of the changes in the organic blood flow in the brain, kidneys, intestines and hindlimbs of cats as affected by adrenaline and noradrenaline]

In experiments on anesthetized cats by using the method of hydrogen clearance it was found that noradrenaline and adrenaline at doses of 0.01-10 micrograms/kg intravenously produced dose-dependent various changes in organ blood flow that were caused by differences in the action on adrenoreceptors and the degree of hypertensive reaction. The vessels of the intestine and kidneys possessed the highest sensitivity to noradrenaline and the cerebral vessels had the least sensitivity.

The effects of cremophor EL in the anaesthetized dog

The effects of cremophor EL were studied in 13 anaesthetized, paralyzed and ventilated dogs. Twenty per cent cremophor EL in a dose of 4.3 +/- 0.92 ml was infused at a rate of 30 ml X hr-1. In seven dogs, thoracopulmonary compliance, heart rate, systemic arterial pressure (SAP), pulmonary pressures (PAP, PCWP, RAP), cardiac output (CO) and platelet and white cell counts, were measured before the injection of cremophor EL, at the end of infusion and 5, 10, 30 and 150 minutes after the end of infusion. In six dogs, SAP, CO, and blood volume were measured before the injection of cremophor EL, at the end of infusion and 10, 30, 90 and 150 minutes after the end of infusion. Plasma histamine and catecholamines were assayed before the injection of cremophor EL and 2, 5, 10, 30, 90 and 150 minutes after starting the infusion. Cremophor EL induced a marked, sustained and significant decrease in SAP at the end of infusion and at 5, 10 and 30 minutes after the completion of the infusion (-68, -71, -70 and -43 per cent respectively), in PCWP, RAP and CO (-78 per cent at the end of infusion, -32 per cent 150 minutes after the end of infusion). Heart rate and systemic vascular resistance did not vary significantly. Pulmonary vascular resistance increased at the end of infusion, five and ten minutes after the end of infusion (+734, +548 and +439 per cent respectively). Plasma volume decreased 10 and 30 minutes after the end of infusion (-28 and -30.5 per cent respectively).(ABSTRACT TRUNCATED AT 250 WORDS)

Cardiorespiratory effects of protamine sulphate in man: intra-aortic vs intra-right atrial rapid administration after cardiopulmonary bypass

The effects of protamine sulphate on several cardiorespiratory variables were studied under clinical situations in twenty patients following cardiopulmonary bypass. Because recent reports suggest that there may be advantages of intra-aortic versus intra-venous administration we prospectively evaluated cardiorespiratory features 1 and 10 minutes after rapid administering of protamine sulphate either into the aortic arch (through a catheter percutaneously inserted via the radial artery for monitoring purposes) or into the right atrium. Significant variations in some parameters were found in the patients receiving the drug via the aorta, such as a drop of systemic vascular resistances (p less than 0.05), of coronary perfusion pressure (p less than 0.05), of aortic systolic pressure (p less than 0.01), of diastolic (p less than 0.01) and mean blood pressure (p less than 0.05) and a rise in the respiratory quotient (p less than 0.05). It is concluded that the results do not confirm the superior safety of intra-aortic administration of protamine particularly when replenishment of intravascular volume is not provided.

Intestinal vascular obstruction shock in the rat. Effect of 2 dextran solutions on blood and plasma volumes, cardioinhibitory activity in blood and pulmonary platelet trapping

Pathophysiologic mechanisms involved in the dextran effect on mortality in intestinal shock in rats were studied, using a standardized model for intestinal vascular obstruction. Both dextran 70 and dextran 40 (respective mean molecular weights 70 X 10(3) and 40 X 10(3) d) given to shocked rats reduced but did not prevent the cardioinhibitory action of intestinal venous plasma in vitro. Both dextrans prevented platelet trapping in the lungs. Reduction in blood and plasma volumes was found in shocked rats given saline or dextran 40, but not following dextran 70. These differences were found after 120 min, but not after 240 min, when all shocked groups had lower blood and plasma volumes than in non-shocked controls. The results indicate that several mechanisms influence the effect of dextran 70 on mortality of rats in intestinal shock. Previously observed difference in mortality rates after infusion of dextran 70 and dextran 40 could not be explained by mechanisms studied in this series of experiments.

[Erythrocytic reactions and metabolic shifts in long-term experimental hypercatecholaminemia]

The experiments on intact dogs have revealed that daily two-hour infusions of stressor norepinephrine doses are accompanied by the elevation in erythrocyte, hematocrit and hemoglobin levels, changes in circulating blood volume and signs of compensated metabolic acidosis. These adaptive responses become excessive in persistent hypercatecholaminemia and promote the development of stress-induced organic lesions.

Alterations in systemic haemodynamics induced by atriopeptin III

The mechanism of the hypotensive response to the intravenous administration of atriopeptin III was investigated in rats of the Wistar-Kyoto (WKY) and spontaneously hypertensive (SHR) Okamoto strains. Cardiac performance and the systemic haemodynamic response to acute volume loading were evaluated before and during atriopeptin infusion. Cardiac output was measured by a thermo-dilution technique in conscious rats, and left ventricular pressures with differential (dP/dt) calculations were obtained in anaesthetized animals. Bolus injections followed by a 1-h continuous infusion of atriopeptin caused a progressive decrease in mean arterial pressure (MAP) and cardiac output with no significant change in heart rate. In addition there was a transient decrease, maximal at 5 min, and a subsequent increase in peripheral resistance. Atriopeptin did not alter the maximal cardiac output achieved following acute volume expansion. In the anaesthetized animals, bolus injection with a subsequent 15-min continuous infusion of atriopeptin III significantly reduced left ventricular pressures, dP/dt and mean arterial pressure. Volume expansion fully restored intraventricular pressures and dP/dt while increasing mean arterial pressure toward baseline. We conclude that the steady decrease in mean arterial pressure produced by atriopeptin III is due to a decrease in cardiac output secondary to a fall in stroke volume caused by a lowered filling pressure.