Cardiorenal-endocrine dynamics during and following volume expansion

The relationship between atrial pressure, atrial natriuretic peptide (ANP), the renin-angiotensin-aldosterone system, and renal hemodynamic and excretory function was examined during and following acute 10% body weight saline volume expansion and measurements were made at 3.3, 6.6, and 10% body weight volume expansion in pentobarbital anesthetized dogs (n = 10). Right atrial pressure (RAP), pulmonary capillary wedge pressure (PCWP), fractional excretion of Na (FENa), and ANP all increased in parallel during volume expansion. Plasma renin activity (PRA) and aldosterone decreased in parallel during 10% volume expansion. Following 10% volume expansion, saline was infused at the peak urine flow rate to maintain peak volume expansion. Despite continued saline infusion, RAP, PCWP, and ANP decreased in parallel. In contrast, FENa remained increased, and aldosterone and PRA remained depressed. These studies demonstrate that atrial pressures, ANP, and FENa increase in parallel during volume expansion; this suggests a role for ANP in modulating acute atrial volume overload. During stable volume expansion periods, however, despite a decrease in ANP levels, Na excretion remains elevated, suggesting that non-ANP mechanisms may be important in maintaining natriuresis during stable volume expansion.

Systemic vascular effects of epinephrine administration in man

Although the peripheral vascular effects of epinephrine have been characterized in animal models, similar studies have not been carried out in man. To determine the vascular effects of epinephrine the systemic circuit must be conceptually and surgically opened to allow for independent control of flow and pressure. This unique situation exists in man only while on total cardiopulmonary bypass with an external reservoir and pump interposed between the right atrium and the aorta. Under these conditions, peripheral vascular compliance, arteriolar and venous resistance, and the systemic time constant (a measure of the drainage characteristics of the vascular bed, in units of time) can be determined directly. Nine anesthetized patients undergoing normothermic cardiopulmonary bypass were studied before and during epinephrine infusion (5 micrograms/kg/min) after the aorta was cross-clamped and the heart had been isolated from the rest of the peripheral circulation. At constant blood flow epinephrine infusion increased blood pressure and reservoir volume (effectively decreasing blood volume) by an average of 360 ml. Although systemic vascular compliance decreased (due to venoconstriction), resistance to venous return decreased. Analysis of transient blood volume changes after a step change in right atrial pressure at constant blood flow revealed that blood was effectively draining from two vascular compartments with different time constants, as previously demonstrated in animal experiments. Epinephrine caused redistribution of blood flow away from the compartment with the longest time constant by constricting the arterioles leading to it. This accounts for the major increase in venous return and is almost entirely the mechanism of increased cardiac output in the normal individual after its administration, independent of its effects on the heart. In an attempt to localize the long and short time constant vascular compartments, three normal volunteers were studied. Thallium-201 whole body imaging at rest and after maximal treadmill exercise showed redistribution of blood flow away from the mesenteric bed and towards the muscle compartments. Although two similar compartment models of the circulation have been suggested by others, to our knowledge this type of analysis has not been carried out in man.

Time-course of changes in cardiac hypertrophy and pressor mechanisms in two-kidney, one clip hypertensive rats during treatment with minoxidil, enalapril or after uninephrectomy

In rats with severe two-kidney, one clip (2-K,1C) hypertension the time-course of changes in left and right ventricular (LV and RV) weight and LV dimensions was assessed following initiation of chronic treatment with minoxidil, enalapril or removal of the clipped kidney in relation to changes in blood pressure (BP) and sympathetic activity, as well as plasma and blood volumes. Minoxidil decreased BP markedly, but tolerance to the antihypertensive effect developed after 2-3 weeks. In contrast, enalapril or uninephrectomy caused a rapid and persistent normalization of BP. Significant increases in LV and RV weight occurred after 3-5 weeks of treatment with minoxidil. Left ventricular wall thickness decreased over the initial 1-2 weeks and then returned to untreated levels. Left ventricular internal dimensions showed an increase after 1-2 weeks of minoxidil, which persisted with more prolonged treatment. With enalapril, regression to normal occurred for both LV and RV weight within 1 week of treatment. Following uninephrectomy a more gradual regression took place and normal cardiac weight was not obtained until 3 weeks. Indices of sympathetic activity (plasma catecholamines, BP response to hexamethonium or heart rate) did not differ significantly in minoxidil treatment versus untreated hypertensive rats from 2 to 35 days of treatment. A significant increase in heart rate was found after 1 day of minoxidil and a decrease after enalapril. Plasma and blood volumes were elevated in minoxidil-treated rats from 7 to 35 days, as well as initially after uninephrectomy. Therefore, in 2-K, 1C hypertensive rats long-term treatment with minoxidil induces both RV hypertrophy and LV eccentric hypertrophy. Changes in cardiac volume load may play a major role in the differing effects of different antihypertensive therapies on cardiac hypertrophy.

Immediate hemodynamic response to furosemide in patients undergoing chronic hemodialysis

To evaluate the effect of furosemide on cardiovascular hemodynamics in patients with end-stage renal failure, we studied ten patients undergoing hemodialysis three times a week. Arterial pressure, heart rate, and cardiac output (indocyanine green dye) were measured in triplicate; total peripheral resistance and central blood volume were calculated by standard formulas. Hemodynamics were determined at baseline and 5, 10, 15, and 30 minutes after intravenous (IV) bolus injection of furosemide 60 mg. Furosemide produced a decrease in central blood volume of -13% +/- 2.2% from pretreatment values (P less than .01) that was most pronounced five minutes after injection, together with a fall in cardiac output (from 6.76 +/- 0.59 to 6.17 +/- 0.52 L/min, P less than .10). Stroke volume decreased with a maximum fall occurring after 15 minutes (from 84 +/- 7 to 79 +/- 7 mL/min, P less than .05), and total peripheral resistance increased (from 15.8 +/- 2.1 to 17.8 +/- 2.3 units, P less than .05) after furosemide. Arterial pressure and heart rate did not change. The decrease in central blood volume reflects a shift of the total blood volume from the cardiopulmonary circulation to the periphery, suggesting dilation of the peripheral venous bed. Thus, even in patients undergoing hemodialysis, furosemide acutely decreases left ventricular preload by venous dilation and should therefore prove to be beneficial in acute volume overload.

Effect of hemodilution on cochlear blood flow measured by laser-Doppler flowmetry

The effect of hemodilution on cochlear blood flow was studied in guinea pigs. Hypervolemic hemodilution was accomplished by infusion of 10 mg/kg of body weight of dextran 40 (as a 10% solution in normal saline), which resulted in an average hematocrit decrease from 43 to 32%. Normovolemic hemodilution was accomplished by repeated exchange of 3 ml of whole blood with 3 ml of dextran 75 (6% solution in normal saline) every 5 minutes until the hematocrit reached approximately 5%. The cochlear blood flow was measured by laser-Doppler flowmetry. Irrespective of the dilutional technique, the cochlear blood flow increased as hematocrit decreased to a maximum of approximately 200% of original value at a hematocrit near 20%. The blood pressure was not significantly influenced by the hemodilution until hematocrit values below 15% were reached. The enhancement of cochlear blood flow is consistent with the expected reduction of blood viscosity and increase of cardiac output. Normovolemic hemodilution with dextran 75 causes a smaller disturbance of systemic circulation physiology and has a more lasting effect than dextran 40 infusion.

Effects of chronic salt loading on plasma atrial natriuretic peptide (ANP) in the spontaneously hypertensive rat

Plasma concentrations of immunoreactive atrial natriuretic peptide (ANP) was measured in spontaneously hypertensive rats (SHR) during chronic salt loading (1.5% NaCl in drinking water). During the 3-week experimental period mean arterial blood pressure, heart rate, urinary sodium excretion and body weight was assessed in salt-loaded as well as in control rats. The sodium excretion was more than 10-fold increased in the rats on the high salt diet. The plasma ANP concentration was significantly increased only 24 h after the start of the high salt intake. Thereafter plasma ANP concentrations were not significantly different from values obtained in control rats. The blood pressure was significantly increased after 3 weeks on the high salt diet. At the end of the 3-week experimental period the rats were subjected to a 10 and 20% acute volume expansion with homologous whole blood. During this intervention the increase in plasma ANP concentrations was blunted in the high salt rats compared to the control group. It is concluded that during chronic salt loading in SHR there is an initial rise in plasma ANP levels and that other hormonal and neuronal systems are more important in the long term maintenance of fluid and electrolyte balance.

Chronic effects of vasopressin on fluid volume distribution in conscious dogs

Previous studies have suggested that acute elevations of arginine vasopressin (AVP) may result in an extravascular to intravascular shift of fluid independent of any change in total body H2O (TBW). The present studies examined the chronic influence of elevated AVP on fluid volume distribution in five splenectomized, sodium-deprived conscious dogs (avg body wt = 18.9 +/- 0.7 kg). During 4 days of continuous intravenous AVP infusion (0.36 ng X kg-1 X min-1), the computerized average 24-h total body weight was maintained within 110 g of the control value by means of a sensitive servo-controlled scale device. Urine flow and urine osmolality averaged 335 +/- 52 ml/day and 637 +/- 36 mosmol/kg during the preinfusion period and changed to levels averaging 151 +/- 14 and 1,377 +/- 121 with elevated AVP (P less than 0.05). Chromium-51-labeled red cell volume (51Cr RBC), plasma volume (Evans blue), TBW (3H2O), calculated total blood volume (using 51Cr RBC and Hct), and mean arterial pressure averaged 22 +/- 1 ml/kg, 54 +/- 7 ml/kg, 0.62 +/- 0.04 l/kg, 68 +/- 3 ml/kg, and 99 +/- 3 mmHg, respectively, during the control period and remained unchanged during the AVP infusion period. Plasma protein, sodium, and osmolality averaged 6.4 +/- 0.1 g/dl, 145.7 +/- 0.8 meq/l, and 295.0 +/- 1.5 mosmol/kg during the preinfusion period and also remained unchanged with elevated AVP. We conclude from the present studies that AVP has minimal or no chronic influence on internal volume redistribution.

Analysis of intestinal water absorption and changes in circulating blood volume in rats

To analyze the change in blood volume after intestinal absorption, circulating blood volume was continuously monitored in rats after infusion of various solutions into the small intestine. Arterial and venous catheters were connected to a system for continuous monitoring of blood volume by the dilution method using 51Cr-labeled erythrocytes. Test solutions (tap water, 0.45, 0.9, 1.8% NaCl, 0.45% NaCl with 2% glucose, and 5% glucose) were infused at a rate of 1 ml/100 g body wt. for 10 min through a duodenal catheter. After the infusion, blood volume increased except in the 1.8% NaCl group, which showed a transient decrease in blood volume by about 10%. The rate of blood volume increase was highest in the 0.45% NaCl with 2% glucose group and lowest in the 1.8% NaCl group. The retention ratio of infused solution in the vascular space was almost identical among the groups and was about 22%. These results indicate that the rate of increase in blood volume after intestinal administration of fluid is modified by the osmolality of the fluid and Na-glucose co-transport, whereas the retention ratio of the infused fluid in blood is constant.

Fluid and electrolyte handling in Long Evans and Brattleboro rats following injection of polyethylene glycol

1. Intake and output of water, Na+ and K+ were measured in Long Evans and Brattleboro rats (deficient in hypothalamic and pituitary vasopressin) before and after subcutaneous injection of polyethylene glycol (PEG) sufficient to cause a substantial hypovolaemia. 2. In the Long Evans rats an initial fluid retention (due to oliguria and polydipsia) was accompanied by Na+ retention and K+ loss. On the second day there was a diuresis but Na+ retention persisted until days 3 and 4 when there was a natriuresis. 3. Brattleboro rats initially also showed fluid retention but this was achieved by hypodipsia with a greater oliguria; there was an accompanying retention of Na+ and K+. On the second day, a reduced fluid balance was still accompanied by Na+ retention but associated with kaliuresis. Diuresis and natriuresis occurred on the third day after PEG injection. 4. Thus, rats deficient in vasopressin respond to hypovolaemia by retaining fluid. The renal actions of aldosterone do not explain fully the changes in renal electrolyte handling.

Effects of hydralazine on blood pressure, pressor mechanisms, and cardiac hypertrophy in two-kidney, one-clip hypertensive rats

In 2-kidney, 1-clip hypertensive rats, the time course of changes in blood pressure (BP), heart rate, activity of the sympathetic nervous system and the renin-angiotensin system, plasma and blood volumes, left ventricular (LV) and right ventricular (RV) weight, and LV dimensions were evaluated during treatment with hydralazine 80 and 120 mg/L drinking water for 2 days or 1, 2, 3, 5, and 8 weeks. Hydralazine induced initially a clear antihypertensive effect (mean BP from 170-180 down to 135-145 mmHg (1 mmHg = 133.32 Pa], subsequently tolerance developed. Heart rate, plasma catecholamines, and the blood pressure response to hexamethonium were not affected by treatment. Significant increases in plasma renin activity occurred during the initial 1-3 weeks of treatment. Plasma and blood volumes showed only small increases with prolonged treatment. RV weight and LV internal diameter showed significant increases at 3, 5, and 8 weeks of treatment, LV weight at 5 and 8 weeks. LV wall thickness did not change significantly. Thus, treatment with the arterial vasodilator hydralazine causes both RV hypertrophy and eccentric LV hypertrophy. Intravascular volume expansion, associated possibly with redistribution of blood volume to the central compartment, may play a major role in these cardiac effects. Increased renin release but not a generalized increase in sympathetic tone may play a role in the development of tolerance to the antihypertensive effect.

Antihypertensive effect of synthetic atrial natriuretic factor in vasopressin-infused rats

To assess the pathophysiological role of atrial natriuretic factors in the regulation of blood pressure, we studied the effect of chronic infusion of a synthetic atrial natriuretic factor of 25 amino-acid residues on blood pressure and sodium-water excretion. Experimental subjects were rats with hypertension made by chronic infusion of vasopressin on regular intakes of sodium or on sodium loading with 1% NaCl as drinking water. When a subdepressor dose (150 micrograms/kg/day) of synthetic atrial natriuretic factor was delivered via an osmotic minipump into the jugular vein simultaneously with 7.2 U/kg/day of vasopressin infused intraperitoneally by another osmotic minipump, the expected elevation of systolic blood pressure was completely inhibited. This was not accompanied by any changes in urine volume and urinary sodium excretion. The antihypertensive effect was sustained throughout the experimental period lasting 3 days in rats on regular sodium intake (p less than 0.01) or on sodium loading with 1% NaCl as drinking water (p less than 0.01). These results indicate that a subdepressor dose of synthetic atrial natriuretic factor can modulate the vasopressor effect of vasopressin. Therefore it is suggested that an atrial natriuretic factor may be involved in the regulation of blood pressure via its antagonizing effect to vasopressin.

The influence of furosemide on heart rate and oxygen uptake in exercising man

We recently observed that heart rate (HR) related methods for assessing physical fitness lead to an overestimation of endurance capacity in subjects treated with furosemide. To gain a more detailed description of this effect, the relationships between work load (WL), oxygen uptake (VO2), and HR were determined in the present study. To this end, nine healthy male subjects performed two incremental exercise tests (10 W increase per 30 s) on a bicycle ergometer. In one test 40 mg furosemide (Lasix) was applied orally 90 min before exercise started. Compared with control conditions, furosemide led to a change in mean blood volume of -4.5% (range: +7.8% to -11.5%). Neither the maximal VO2 (VO2max) nor the maximal work load (WLmax) were significantly altered after furosemide application. Though the WL-VO2 relationship was not significantly affected, the HR-VO2 relationship showed significant alterations which depended on both the loss of blood volume (BV) and work intensity: When the reduction in BV was less than approximately 5%, HR was found to be lowered at all workloads. When the BV reduction was greater than about 5% HR was significantly reduced only in the lower ranges of work load but significantly increased at the higher work intensities. Since BV reductions are known to increase HR during exercise, our findings suggest that, in addition to the blood volume induced changes in HR, furosemide exerts further direct or indirect effects on heart rate adjustment.

Postsynaptic alpha 1- and alpha 2-adrenergic receptors in adrenergic control of capacitance vessel tone in vivo

The involvement of postsynaptic alpha 2-adrenergic receptors in the adrenergic constriction of the capacitance vessels was studied in anesthetized, spontaneously breathing dogs under ganglionic blockade (hexamethonium, 10 mg/kg + 10 mg/kg/hr; methylatropine, 0.5 mg/kg). Effective vascular compliance was measured as an indicator of venous tone (blood volume was varied by +/- 4 ml/kg in an 11-minute cycle of infusion, withdrawal, withdrawal, and reinfusion) and was calculated from the correlation between the observed changes in central venous pressure and the changes in blood volume. Sympathetic activity and central venous pressure were lower and effective vascular compliance was higher than values in untreated conscious dogs. The alpha 2-agonist UK 14,304 (5-bromo-6-[imidazolin-2-ylamino]-quinoxaline; 0.04 and 0.12 micrograms/kg/min; n = 6) dose-dependently lowered compliance and increased central venous pressure to levels found in conscious dogs, as did the alpha 1-agonist methoxamine (10 and 30 micrograms/kg; n = 6). Rauwolscine (alpha 2-antagonist), 0.3 mg/kg, significantly attenuated the effects of UK 14,304, but not those of methoxamine, while prazosin (alpha 1-antagonist), 0.12 mg/kg, attenuated the effects of methoxamine, but not those of UK 14,304 (n = 6 each). Under beta-blockade (nadolol, 2 mg/kg; n = 12) venous tone was increased to about physiological levels by norepinephrine, 0.15 micrograms/kg/min i.v., or by neuronal norepinephrine release induced by tyramine, 10 micrograms/kg/min i.v. These increases were significantly attenuated by prazosin as well as by rauwolscine and were abolished by a combination of both. These results indicate that postsynaptic alpha 2-adrenergic receptors (in addition to alpha 1-adrenergic receptors) are functional in the venous system in vivo and contribute substantially to adrenergic sympathetic and humoral regulation of venous tone.

Relationship between the venoconstrictor activity of dihydroergotamine and its pharmacokinetics during acute and chronic oral dosing

In a double-blind, interindividual comparative study 30 healthy volunteers were randomly allocated to oral treatment with 5 or 10 mg of dihydroergotamine (DHE) or placebo once daily for 16 days. Regional basic venous blood volume (BBV), pressure dependent venous capacitance (CV) of the calf, resting heart rate and blood pressure were determined on Days 1 and 15 of treatment. Plasma concentrations of DHE were monitored on Days 2 and 16. Due to spontaneous vasodilation BBV varied considerably, showing that it is an inappropriate parameter for investigating the venoconstrictor activity of DHE. CV remained unchanged after the first dose of DHE but it had declined significantly on both dosage regimens at the end of the treatment phase. In contrast, the blood concentration profiles of DHE were comparable at the beginning and the end of the trial. The discrepancy can best be explained by the existence of an effect compartment, e.g. smooth vascular musculature, which slowly becomes filled with DHE and/or its active metabolites. The venoconstrictor activity of DHE exhibited a significant dose-response relationship.

Effects of a stable enkephalin analogue, (D-Met2,Pro5)-enkephalinamide, and naloxone on cortical blood flow and cerebral blood volume in experimental brain ischemia in anesthetized cats

The effects of intracarotid injection of the stable enkephalin analogue (D-Met2,Pro5)-enkephalinamide (ENK) and intravenous administration of naloxone on the cerebrocortical blood flow (dye dilution method) and cerebral blood volume (CBV) (photoelectric method) were investigated during unilateral brain ischemia in anesthetized cats. Both parameters were measured simultaneously in the intact and ischemic (middle cerebral artery occluded) hemispheres. An intracarotid injection of ENK 0.5 mg/kg induced a significant increase in cortical vascular resistance and a -87% decrease in cerebrocortical blood flow from 25 +/- 3 to 4 +/- 3 ml/100 g/min, without CBV alteration in the ischemic hemisphere. Naloxone (1 mg/kg i.v.), on the other hand, induced a marked two-fold increase in cerebrocortical blood flow and a significant elevation of CBV from 5.9 +/- 0.5 to 7.4 +/- 0.7 vol% in the ischemic hemisphere. No change in cerebrocortical blood flow or CBV was observed in the intact hemisphere either after ENK or after naloxone administration. Arterial blood gases and hematocrit remained unchanged. On the basis of the present findings, we conclude that besides other factors, endogenous opioid mechanisms may also participate in ischemic cerebrovascular reactions and the cerebral circulatory effects of naloxone probably reflect its opiate receptor blocking property and not simply its other non-opiate-related actions.

[Renal effects of dopamine in healthy adults with special reference to the excretion of phosphate and calcium]

The intravenous application of 4 micrograms/kg/min dopamine (DA) over 3 h in 11 healthy volunteers resulted in an increase in inulin clearance and urine volume by about 10%, renal excretion of sodium and calcium being increased by DA by a factor of 5. We found a strong linear correlation between changes of renal excretion of sodium and calcium under DA (r = 0,90). The concentration of ionized calcium in whole blood was absolutely stable under DA in the range of 1.25 to 1.27 mmol/l. The application of the catecholamine also resulted in a significant reduction of plasma volume by a mean of about 10% and in a nonsignificant reduction of intravascular protein mass by 8%. The phosphaturic effect of DA was weak and unpredictable. We suppose that in the intact organism the pharmacologic effect of dopamine on the tubular handling of phosphate which seems to be experimentally proven, may be masked by other mechanisms with an antiphosphaturic action such as increased levels of growth hormone and/or insulin.

Effect of atriopeptin III on hematocrit and volemia of nephrectomized rats

The effect of a synthetic atrial natriuretic peptide (atriopeptin III) on blood pressure, heart rate, and hematocrit was investigated in conscious, nephrectomized (n = 6), and sham-operated (n = 6) rats. Atriopeptin III infusion (1 microgram/min iv for 30 min) decreased mean blood pressure to a similar extent in nephrectomized [from 122 +/- 5 to 108 +/- 3 (SE) mmHg; P less than 0.01] and in sham-operated rats (from 124 +/- 4 to 103 +/- 2 mmHg; P less than 0.01), whereas it had no significant effect on heart rate. Hematocrit rose similarly in nephrectomized (from 45 +/- 1 to 49 +/- 1%; P less than 0.01) and in sham-operated rats (from 46 +/- 1 to 50 +/- 1%; P less than 0.001). Infusion of the vehicle of atriopeptin III to nephrectomized rats (n = 7) did not change any of these parameters. Plasma volume and red cell mass of nephrectomized rats infused with atriopeptin III was measured by use of radiolabeled albumin and erythrocytes, respectively. A plasma volume contraction of approximately 10% (P less than 0.01) was observed, whereas red cell mass did not change. In an additional group of nephrectomized rats (n = 6), Na nitroprusside was infused intravenously at a rate of 2 micrograms/min for 30 min. Na nitroprusside reduced mean blood pressure from 127 +/- 4 to 106 +/- 3 mmHg (P less than 0.001), but hematocrit remained unchanged (46 +/- 1% before vs. 45 +/- 1% after infusion). In four anesthetized rats with both kidneys and the spleen removed atriopeptin III still raised the hematocrit.(ABSTRACT TRUNCATED AT 250 WORDS)

Isosorbide dinitrate and pulsatile arterial haemodynamic variables in hypertension

The effect of a sustained-release oral isosorbide dinitrate (ISDN) preparation on cerebral and forearm circulation was determined in 16 patients with mild to moderate essential hypertension. Measurements were made by pulsed Doppler velocimetry in the common carotid and the brachial arteries. Pulse wave velocity of the forearm was simultaneously recorded by means of strain gauge arterial mechanography allowing non-invasive evaluation of compliance and characteristic impedance of the brachial artery. Four hours after ISDN ingestion, the patients exhibited a significant decrease in blood pressure without a change in heart rate. An increase in carotid and brachial artery diameter was shown whereas blood flow increased only in the forearm. Resistance decreased significantly in both carotid and brachial vascular beds but only in the brachial vascular bed was the baseline resistance directly correlated with the change in brachial bed resistance. Concerning pulsatile large artery parameters, pulse wave velocity and characteristic impedance diminished, and brachial artery compliance increased significantly. The tangential tension of carotid and brachial arteries did not change. An increase in plasma renin activity was observed and related to the vasodilating effect on small arteries of the brachial vascular bed. This study showed that the antihypertensive effects of ISDN were accompanied by a strong vasodilatory action on small and large arteries and by an improvement in the pulsatile behaviour of large arteries.

Response of rat jejunum to changes in sodium and volume balance

Initial studies determined whether a renal factor facilitates decreased jejunal absorption following volume expansion of the anesthetized rat. Volume expansion (VE) decreased jejunal absorption to the same extent in both normal and nephrectomized animals. Furthermore, VE of a donor animal failed to alter jejunal absorption in a recipient following cross circulation. Thus, a hormonal factor is not implicated in the jejunal response to VE. Additional experiments demonstrated that rats ingesting a high-Na diet exhibited levels of jejunal absorption lower than animals fed a normal-Na diet. High-Na animals were not volume expanded. Plasma aldosterone concentrations and plasma renin activity were reduced in high-Na animals. Bilateral adrenalectomy-nephrectomy inhibited jejunal absorption. However, neither bilateral adrenalectomy nor bilateral nephrectomy alone inhibited jejunal absorption. Furthermore, inhibition of angiotensin formation in adrenalectomized animals failed to alter jejunal absorption. Decreased jejunal absorption in high-Na animals is not due to volume expansion or to inhibition of the renin-angiotensin-aldosterone axis.

Blood volume expansion with hetastarch in acute ischaemic stroke: the effects on local cerebral blood flow and computer mapped EEG

Focal cerebral ischaemia was induced in seven anaesthetized monkeys by unilateral middle cerebral artery (MCA) occlusion. Local cerebral blood flow (CBF) and computer mapped EEG (CME) changes were then studied as blood volume and cardiac output (CO) were varied. CO was increased by colloidal volume expansion and decreased by exsanguination. Local CBF fell to 24 +/- 9% of control values in ischaemic areas following MCA occlusion and increased to 43 +/- 19% of control values (p less than 0.01) when CO was increased by 130 +/- 70% with colloid infusion. Local CBF to nonischaemic regions was not altered significantly by blood volume expansion. Exsanguination led to return of CO to control levels and was associated with reduction of local CBF in ischaemic regions to 24 +/- 12% of control values (p less than 0.05). CME showed bifrontal or ipsilateral slow wave foci (delta) following MCA occlusion. Blood volume expansion brought about a marked reduction of this slow wave activity and exsanguination led to recurrence of the slow wave foci. This data demonstrated that colloidal blood volume expansion induced an increase in local CBF and improved neuroelectric status of ischaemic brain following MCA occlusion. It was also shown that a reduction of blood volume and cardiac output resulted in a reduction in local CBF and a worsening of neuroelectric status in ischaemic areas. This study supports the contention that blood volume and cardiac output maintenance is extremely important in the management of acute ischaemic stroke.

[Problems and prospects for the drug correction of orthostatic tolerance in space medicine]

This paper reviews published data concerning physiological mechanisms of man's orthostatic tolerance and its decline under the influence of space flight factors. The principles, goals and potentialities of drug correction of orthostatic intolerance are presented. The applicability of selected drugs used separately or in combination with traditional countermeasures is discussed.