Effect of angiotensin-converting enzyme inhibitor (SQ 20881) on the plasma concentration of angiotensin I, angiotensin II, and arginine vasopressin in the dog during hemorrhagic shock

Systemic and regional hemodynamic effects of enalaprilat infusion in experimental normotensive sepsis

Angiotensin-converting enzyme inhibitors have been shown to improve splanchnic perfusion in distinct shock states. We hypothesized that enalaprilat potentiates the benefits of early fluid resuscitation in severe experimental sepsis, particularly in the splanchnic region. Anesthetized and mechanically ventilated mongrel dogs received an intravenous infusion of live Escherichia coli over a period of 30 min. Thereafter, two interventions were performed: fluid infusion (normal saline, 32 mL/kg over 30 min) and enalaprilat infusion (0.02 mg kg(-1) min(-1) for 60 min) in randomized groups. The following groups were studied: controls (fluid infusion, N = 4), E1 (enalaprilat infusion followed by fluid infusion, N = 5) and E2 (fluid infusion followed by enalaprilat infusion, N = 5). All animals were observed for a 120 min after bacterial infusion. Mean arterial pressure, cardiac output (CO), portal vein blood flow (PVBF), systemic and regional oxygen-derived variables, and lactate levels were measured. Rapid and progressive reductions in CO and PVBF were induced by the infusion of live bacteria, while minor changes were observed in mean arterial pressure. Systemic and regional territories showed a significant increase in oxygen extraction and lactate levels. Widening venous-arterial and portal-arterial pCO2 gradients were also detected. Fluid replacement promoted transient benefits in CO and PVBF. Enalaprilat after fluid resuscitation did not affect systemic or regional hemodynamic variables. We conclude that in this model of normotensive sepsis inhibition of angiotensin-converting enzyme did not interfere with the course of systemic or regional hemodynamic and oxygen-derived variables.

Angiotensin II decreases the rate of production of cerebrospinal fluid

The choroid plexus, which produces cerebrospinal fluid (CSF), contains receptors for angiotensin II and a very high concentration of angiotensin-converting enzyme. Circulating angiotensin II decreases blood flow to the choroid plexus. The first goal of this study was to examine the hypothesis that angiotensin II decreases the production of CSF. The second goal was to determine whether effects of angiotensin II on the production of CSF were receptor-mediated. Production of CSF was measured in chloralose-anesthetized rabbits using ventriculocisternal perfusion of artificial CSF containing blue dextran. Rabbits received either vehicle, angiotensin II, angiotensin II in the presence of an angiotensin II antagonist (saralasin), or saralasin intravenously. Increases in blood pressure, during administration of angiotensin II, were prevented by withdrawal of blood. Under control conditions, CSF production averaged 7.2 +/- 0.2 microliters/min (mean +/- S.E.). Angiotensin II (100 ng/kg/min i.v.) decreased CSF production by 24 +/- 3% (P < 0.05, n = 8). In the presence of saralasin (1 microgram/kg/min i.v.), angiotensin II had no significant effect on CSF production (-4 +/- 6%, P > 0.05, n = 7). Vehicle did not affect CSF production significantly (-2 +/- 6%, P > 0.05, n = 7). Saralasin alone decreased production of CSF (-21 +/- 5%, P < 0.05, n = 7). To test the specificity of saralasin in blocking effects of angiotensin II receptor stimulation on CSF production, the carbonic anhydrase inhibitor acetazolamide was administered in the presence and absence of saralasin.(ABSTRACT TRUNCATED AT 250 WORDS)

Ephedrine in the initial treatment of haemorrhagic shock

The initial treatment for hypotension due to blood loss is intravenous fluids. Occasionally there is need for additional medication, as well as stopping the source of the bleeding. The literature in the main discusses the use of dopamine. Ephedrine has not been reviewed as useful in such situations. This article discusses the immediate use of ephedrine in the treatment of shock due to bleeding; its special quality is as a catecholamine whose venoconstrictor component is stronger than its arterioconstrictor component. Thus, its effect of increasing venous return is more significant than arterial vasoconstriction.

Trauma induced increases in plasma vasopressin and angiotensin II

Previous investigators have shown that hypotension will cause an increase in plasma levels of both vasopressin and angiotensin II. Significant increases in peripheral resistance after thermal trauma suggested that a similar increase in plasma vasopressin and angiotensin II levels might occur under this condition. This possibility has been studied in the pentobarbital anesthetized dog. Peripheral resistance was calculated from measured cardiac output and mean arterial blood pressure. Vasopressin and angiotensin II levels were measured by radio-immunoassay. The results of this study showed that vasopressin plasma levels increase 4 to 6 fold 15 minutes after thermal trauma and remained elevated (3 to 4 fold) for at least 6 hours. Angiotensin II increased in a linear manner from 15 minutes to 6 hours post trauma. At 6 hours post trauma angiotensin II plasma levels were 4 times pretrauma levels. For the first 4 hours post trauma there was a positive correlation between the sum of vasopressin and angiotensin II plasma levels and the increase in peripheral resistance. These results suggest that the trauma induced increase in peripheral resistance is due to increases in plasma vasopressin and angiotensin II.

Naloxone reversal of hemorrhagic hypotension in the conscious guinea-pig is impeded by inhibition of the renin-angiotensin II system

Naloxone reverses hemorrhagic hypotension in the conscious guinea-pig. Captopril and saralasin impede this naloxone effect, suggesting that angiotensin II is involved in naloxone action. This is compatible with previous work which has shown that B-endorphin inhibits the centrally mediated pressor action of angiotensin II, and that naloxone blocks this effect. Naloxone may be interacting with the postulated brain renin-angiotension II system or may be blocking the action of shock-induced circulating angiotensin II on a centrally located area such as the hypothalamus.

Effects of angiotensin II on plasma antidiuretic hormone and renal water excretion

The effects of intravenous (i.v.) and intracarotid (IC) angiotensin II (AII) infusion on systemic and renal hemodynamics, renal water excretion, and plasma antidiuretic hormone (ADH) levels were examined in six conscious dogs under water loaded and hydropenic conditions. In the first group of seven studies, AII in a mean dose of 12.7 ng/kg/min was administered i.v. to water loaded dogs. The infusion induced a significant increase in mean arterial pressure (MAP, 99 to 118 mm Hg, P less than 0.001), and significant reductions in both glomerular filtration rate (GFR, 67 to 57 ml/min, P less than 0.05) and para-aminohippurate clearance (CPAH, 280 to 212 ml/min, P less than 0.005) occurred. Despite this decrement in renal hemodynamics, urine remained maximally dilute (Uosm, 58 to 61 mOsm/kg H2O, NS). Furthermore, plasma ADH was suppressed maximally after water load and did not increase after i.v. AII infusion. The IC infusion of AII (mean dose 5.8 ng/kg/min) produced similar changes in hemodynamics; plasma ADH remained undetectable. When AII was administered i.v. to hydropenic animals (mean dose 8.3 ng/kg/min), MAP again increased (86 to 111 mm Hg, P less than 0.001) as GFR (81.3 to 68.6 ml/min, NS) and CPAH (291 to 223 ml/min, P less than 0.05) declined modestly. In these animals, Uosm decreased significantly (1429 to 1114 mOsm/kg H2O, P less than 0.005) and plasma ADH did not change significantly (1.66 to 1.88 pg/ml, NS). When IC AII (4 ng/kg/min) was repeated in hydropenic dogs pretreated with indomethacin, neither Usom (1787 to 1664 mOsm/kg H2O, NS) nor plasma ADH were altered.(ABSTRACT TRUNCATED AT 250 WORDS)

Plasma concentrations of angiotensin II and aldosterone during acute left ventricular failure in the dog. Effect of converting enzyme inhibition

Acute left ventricular failure was induced in anesthetized dogs by left coronary embolization. Treatment with the converting enzyme inhibitor enalaprilat (MK-422) was then given. Hemodynamic registrations confirmed the development of left ventricular failure. Plasma concentrations of angiotensin II and aldosterone rose significantly. Treatment with enalaprilat was accompanied by significant reductions in heart preload and afterload and in plasma hormone concentrations.

Chronotropic effects of angiotensin I, angiotensin II, bradykinin and vasopressin in guinea pig atria

Chronotropic responses to angiotensin I and angiotensin II, vasopressin and bradykinin were measured in guinea pig isolated right atria. Angiotensin II (100-30,000 pg/ml) was slightly more potent than angiotensin I and caused a maximum tachycardia of 30-40 b/min; only 20% of the maximum response to (--)-noradrenaline. Propranolol (1 micro M) or reserpine pretreatment (1 mg/kg i.p., 24 h) did not alter the response to angiotensin II or bradykinin. Converting enzyme inhibition by captopril (10 micrograms/ml) did not affect resting rate nor the response to angiotensin II but shifted the location of the angiotensin I curve by 40 fold to the right. Bradykinin (5-500 ng/ml) caused small increases in rate while vasopressin 1-100 ng/ml was completely without effect. These results suggest that angiotensin II has a small positive chronotropic effect that is not dependent on tissue noradrenaline release or beta-adrenoceptors and that tissue converting enzyme is active in right atria. Relatively high concentrations of angiotensin and bradykinin were required to directly stimulate the sino-atrial node compared with plasma levels measured during physiological stimuli. Therefore these effects on atria are probably of little physiological significance for peptide concentrations in plasma but may be important in relation to local tissue generation of angiotensin II.

Effect of infused captopril on blood pressure and the renin-angiotensin-aldosterone system in normal dogs subjected to varying sodium balance

Infusion of captopril at 20, 200, 2,000 and 6,000 micrograms/kg/hour into sodium-depleted conscious dogs produced a rapid, dose-dependent decrease in blood pressure and plasma angiotensin II and III, maximal suppression being achieved at 200 micrograms/kg/hour (97 +/- 14 to 65 +/- 8 [standard deviation] mm Hg, 38 +/- 10.6 to 3.2 +/- 1.5 pmol/liter and 7.0 +/- 4.8 to 1 +/- 0.5 pmol/liter, respectively). Angiotensin I concentration increased with each infusion rate to a maximal 16-fold increase at 6,000 micrograms/kg/hour (26 to 416 pmol/liter). For all infusion rates the percentage decrease in blood pressure correlated with the percentage decrease in plasma angiotensin II (r = 0.65, p less than 0.001). Infusion of captopril at 6,000 micrograms/kg/hour into sodium-loaded dogs also produced a decrease in both blood pressure (117 +/- 9 to 96.6 +/- 11 mm Hg) and plasma angiotension II (11.0 +/- 3 to 1.6 +/- 1.3 pmol/liter). Plasma aldosterone concentrations decreased whereas both blood angiotensin I and renin concentration increased. In another experiment angiotensin II was infused at 2, 6, 18 and 54 ng/kg/min into sodium-depleted dogs firstly without modification and secondly combined with captopril (6,000 micrograms/kg/hour) given for 1 hour before the angiotensin dose-response study and continued throughout. Angiotensin II infusion raised mean arterial pressure and plasma angiotensin II in each animal. However, the angiotensin II blood pressure dose-response curve was shifted downwards and to the right in the captopril-treated animals. These results suggest that arterial pressure and aldosterone secretion in normal dogs are partly dependent on the renin-angiotensin system but that not all of the acute decrease in blood pressure produced by captopril can be explained by the suppression of the acute vasoconstrictor effect of circulating angiotensin II.

Effect of captopril on cardiovascular, sympathetic and vasopressin responses to hemorrhage

Spontaneous blood pressure recovery following hemorrhage in anesthetized rats is almost completely blocked by administration of captopril. This occurs despite comparable or enhanced increases in plasma levels of catecholamines and vasopressin. These findings suggest that angiotensin II, the formation of which is blocked by captopril, is essential to acute blood pressure recovery following hemorrhage and that changes in catecholamines or vasopressin are insufficient to sustain pressure recovery. The data also indicate that angiotensin II formation is not essential in the hemorrhagic stimulation of vasopressin or catecholamines.

Effect of osmolality on arginine vasopressin and renin release after hemorrhage

The effects of alterations of plasma osmolality on plasma arginine vasopressin (AVP) and renin activity (PRA) following graded hemorrhage were studied in conscious dogs who were either euhydrated, dehydrated, water loaded, or infused with hypertonic saline. Base-line plasma osmolality and AVP were significantly different in the four treatment groups; however, following hemorrhage the increases in log AVP did not significantly differ. An unexpected finding was that water loading resulted in significant elevations in PRA and plasma aldosterone concentrations, whereas plasma osmolality and AVP were reduced. Prior to hemorrhage, PRA was significantly greater in the water-loaded and dehydrated groups than in the euhydrated or saline-infused groups; following hemorrhage the increases in log PRA were not significantly different in all four treatment groups. The data suggest that, although alterations in osmolality influence base-line levels of AVP, they have no effect on relative (logarithmic) rises in AVP following hemorrhage. Similarly, alterations in AVP may influence base-line PRA, but do not influence relative rises in PRA following hemorrhage.

Prevention of the development of spontaneous hypertension in rats by captopril (SQ 14,225)

Indirect systolic blood pressure (SBP) was monitored in male, weanling, spontaneously hypertensive rats (SHR) maintained on water for 16 weeks (group A) or on captopril therapy (100 mg/kg/day in drinking water) for 4 (group B), 8 (group C), 12 (group D), 16 (group E) weeks. Weanling SHR of group A developed typical, time-related hypertension over a 16-week observation period. In marked contrast, SHR receiving captopril did not develop hypertension. Discontinuation of captopril after 4, 8, 12 or 16 weeks resulted in the usual development of hypertension. There was a transient increase in water consumption of drug treated rats which returned to normal by 8 weeks of dosing. Conversely, when captopril therapy was discontinued after 4, 8 or 12 weeks, there was a transient decrease in water intake, the magnitude of which was inversely related to the duration of drug therapy. These results demonstrate that daily captopril therapy was able to completely prevent the development of spontaneous hypertension. Explanations for the mechanism(s) underlying the influence of captopril on blood pressure and water intake remain speculative.

Role of hepatic portal osmoreception in the control of ADH release

Dogs were prepared for experiments by chronic implantation of catheters into the hepatic portal vein. Intraportal infusions of hypertonic saline, 5 ml/min, increased plasma antidiuretic hormones (rat bioassay) in absence of significant changes in systemic plasma osmolality. In the 5th min of 1.8, 2.7, or 3.6% saline infusion, plasma antidiuretic hormone (ADH) increased significantly from 3.2 +/- 0.7 to 14.3 +/- 3.6 (SE) microU/ml, from 2.3 +/- 0.4 to 42.0 +/- 7.6 microU/ml, and from 1.9 +/- 0.6 to 64.4 +/- 16.8 microU/ml, respectively. In control experiments plasma ADH did not change with isotonic saline infused intraportally or with 3.6% saline given into a systemic vein. The transsection of hepatic vagal afferent fibers abolished plasma ADH increase dependent on hypertonic intraportal infusion. The data support the existence of osmoreceptors within the portal vascular bed and indicate ADH involvement in the control of fluid balance by intrahepatic blood osmalality. The information on osmolality changes is neurally transmitted to the hypothalamus via hepatic vagal afferents. A demonstration of an increase in portal but not systemic blood osmolality following food intake suggests that intrahepatic osmoreception may be important in physiological regulation of water metabolism.

Modification by SQ 14225 of blood pressure and adrenal catecholamine response to hemorrhage

SQ 14225 infusion to cats exposed to hemorrhage suppressed adrenomedullary catecholamine release. The immediate compensatory blood pressure response was unaffected, while the later compensatory response was of a higher magnitude in intact cats that in SQ 14225-treated animals. Adrenal gland blood flow was better preserved in SQ 14225-treated hemorrhaged cats than in cats exposed to hemorrhage only. These data emphasize the role of angiotensin II in adrenal catecholamine and blood pressure responses to hemorrhage.

Inhibitors of the renin-angiotensin system in experimental hypertension, with a note on the measurement of angiotensin I, II and III during infusion of converting-enzyme inhibitor

1 Prolonged infusion (11 h) of both saralasin and angiotensin-converting enzyme inhibitor (SQ20881) gradually lowered BP in two-kidney hypertensive rats to levels similar to that in normotensive rats infused with dextrose. 2 Saralasin did not lower BP in DOCA-salt hypertensive rats. 3 These observations support the notion that in chronic renal hypertension, angiotensin II may maintain hypertension by a slowly developing action. 4 Plasma angiotensin II in rats infused with SQ20881 was suppressed relative to renin, but was not eliminated. 5 Chromatography of angiotensin II extracts from dogs infused with converting enzyme inhibitor (SQ14,225) showed that the very high levels of angiotensin I achieved after treatment with SQ14,225 can lead to falsely high estimated angiotensin II levels as a result of angiotensin I cross-reacting with the angiotensin II assay.

The vasodepressor action of prostacyclin (PGI2) and its effect on plasma angiotensin II and vasopressin in unanaesthetized normotensive and hypertensive rats

The action of prostacyclin (PGI2) on arterial pressure, heart rate, plasma concentration of angiotensin II and vasopressin was studied in groups of normal, renal hypertensive and DOC hypertensive rats. PGI2 was given by continuous iv. infusion at successive doses of 0.25, 0.5 and 1.0 microgram/kg x min, each rate for one hour. Arterial pressure was reduced to normal or below normal in the hypertensive rats, though the fall of blood pressure was greatest in the DOC hypertensive animals. Mean arterial pressure at the end of infusion was 89 mm Hg for normal rats, 87 mm Hg for renal hypertensive rats and 69 mm Hg for DOC hypertensive rats. Diastolic pressure fell more than systolic pressure suggesting a vasodilator mechanism. Heart rate was reduced significantly at the end of the infusion in the three groups of rats. Prostacyclin was also infused for 3 hours at a constant rate of 0.5 microgram/kg x min. The arterial pressure lowering effect was maintained throughout the infusion period.

Correction of renal hypertension in the rat by prolonged infusion of angiotensin inhibitors

Injection of saralasin or converting-enzyme inhibitor produced a small variable reduction of blood-pressure in rats with two-kidney hypertension. Prolonged infusion of the inhibitors gradually reduced blood-pressure to normal. Control infusions of saralasin in normal animals and of dextrose in normal and hypertensive animals did not reduce blood-pressure. Plasma-renin concentration correlated significantly with the early but not with the later fall of blood-pressure. Plasma-concentrations of renin and angiotensin II were closely related except in rats receiving converting-enzyme inhibitor, when angiotensin II was relatively reduced. The gradual reduction of arterial pressure by saralasin was not associated with increased urinary sodium excretion.