Effect of angiotensin infusion on regional blood flow and regional vascular resistance in the rat

SARS-CoV-2 infection causes pulmonary shunt by vasodilatation

Patients with severe acute respiratory syndrome coronavirus 2 (SARS‐CoV‐2) may present a significant hypoxemia. The exactly mechanism of such hypoxemia in patients with coronavirus disease 2019 (COVID‐19) is not well described. It has been suggested that microthrombosis contributes to this mechanism, increasing pulmonary dead space. However, dead spaces would not be sensible to oxygen supplementation, and also, enlargement of pulmonary vessels it has been evidenced. Shunt mechanism by vasodilatation, instead, could explain decubitus dependence in oxygenation by blood redistribution as observed in these patients, and moreover, would be more sensible to oxygen supplementation than dead spaces. We hypothesized that SARS‐CoV‐2 causes an intrapulmonary vascular dilatation (IPVD), determining a shunt mechanism by vasodilatation. We performed contrast‐enhanced transthoracic echocardiography to search IPVD shunt in patients with confirmed COVID‐19, hospitalized in an intensive care unit. Ten patients were recruited; one patient was excluded due to low quality of echocardiographic image, and nine patients were included. IPVD was found in seven (78%) patients, with different grades, including patient with normal compliance and the one without invasive ventilation. We demonstrated that shunt by IPVD is present among patients with COVID‐19, and this mechanism is probably implicated in significant hypoxemia observed.

Our study brings to light a novel pathophysiological process about Covid‐19 disease.

We demonstrated that SARS‐CoV‐2 infection cause a shunt mechanism by intrapulmonary vasodilatation, and this finding can be implicated in important hypoxemia observed in these patients.

We hypothesize that bradykinin probably has a key role in this process.

A Nervously-Mediated Action of Angiotensin in Anaesthetised Rats

In rats under chloralose anaesthesia, angiotensin in large doses caused a nervously-mediated vasoconstriction in the vascularly-isolated innervated hind limb, whereas in small doses it caused a nervously mediated peripheral vasodilatation. Noradrenaline over an equipressor dose range caused only a nervously-mediated peripheral vasodilatation. These peripheral responses were abolished by section of the nerves leading to the hind limb.

Comparative pharmacokinetics of coumarin anticoagulants L: Physiologic modeling of S-warfarin in rats and pharmacologic target-mediated warfarin disposition in man

The anticoagulant warfarin exemplifies a type of drug that exhibits high affinity to pharmacologic target sites of limited capacity, resulting in unusual concentration-dependent distribution and elimination properties. The time course of warfarin concentrations in the serum, liver, kidneys, muscle, and abdominal fat of male Sprague-Dawley rats was determined by high-performance liquid chromatography after IV injection of a 0.25 or 1.0 mg/kg dose. The rats were preclassified on the basis of their serum free fraction of warfarin; animals with free fraction values of approximately 0.004 and 0.01 and corresponding differences in elimination half-life were selected for study, yielding four experimental groups. Several rats of each group were sacrificed periodically over approximately 80-240 h for determination of drug concentrations. S-warfarin concentrations in serum declined apparently exponentially over at least one order of magnitude. During this time, concentrations in all other assayed tissues declined much more slowly. In another experiment, S-warfarin concentrations in serum and liver were followed for approximately 50 days after IV injection of a 1 mg/kg dose. This revealed a terminal, very slow elimination phase in serum nearly parallel to the decline in liver drug concentrations. Simultaneous physiologic modeling of all data (30 equations) using ADAPT II (Biomedical Simulations Resource, Los Angeles, CA), with intrinsic clearance, the dissociation constant of the warfarin-high affinity binding site complex, and two binding parameters for the (unassayed) remainder tissue compartment as parameters of unknown value, yielded very good fittings and parameter estimates with relatively small standard deviations. The unusual dose-dependent accumulation characteristics of this type of drug during continuous infusion are demonstrated by computer simulation of published results of warfarin infusions in rats. Utilization of a model premised on similar target-mediated drug disposition also allowed characterization of data from the literature for racemic warfarin pharmacokinetics in man.

CORONARY AND MYOCARDIAL ACTIONS OF ANGIOTENSIN

In the dog heart-lung preparation, single injections of 40 µg angiotensin II produced consistently a biphasic response. Initial impairment of cardiac function was observed with decrease of cardiac output and of ventricular force, and with increase of atrial pressures. After 10 to 20 seconds, there was a positive inotropic effect, with an increase of cardiac output and of ventricular force, and a decrease in atrial pressures. Responses were comparable in reserpinized and nonreserpinized preparations. Tachyphylaxis to angiotensin was found consistently in the heart-lung preparation, with a regular decrease in response following second and third injections. A positive inotropic action of angiotensin II was demonstrated in the cat papillary muscle preparation. These studies demonstrated that angiotensin has a direct cardiac action, namely a positive inotropic effect. This action probably does not depend upon myocardial stores of catecholamines.

When the left anterior descending coronary artery of the dog was perfused with blood at a constant flow, single intracoronary injections of angiotensin (1.0 µg) consistently increased coronary resistance (6% to 92%). Continuous intracoronary infusion of angiotensin increased coronary vascular resistance when blood concentrations were as low as 0.42 µg/ liter. No evidence of initial cardiac depression or of increased coronary vascular resistance was found after norepinephrine.

It is concluded that the initial impairment of cardiac performance following angiotensin is caused at least in part by decreased coronary blood flow. Caution is suggested in the use of angiotensin in the treatment of human shock because of its action upon the coronary circulation.

Atrial natriuretic factor release by angiotensin II in the conscious rat

Since it was previously reported that atrial natriuretic factor (ANF) may exert an inhibitory effect on renin release, the existence of an Angiotensin II (Ang II)-ANF feedback mechanism was investigated. Male rats were infused intraperitoneally for 7 days with either saline, a nonpressor dose of Ang II (200 ng/kg/min), or a pressor dose (800 ng/kg/min) of Ang II. Systolic blood pressure, plasma ANF, 24-hour urinary sodium excretion, urine volume, and water intake were measured. A significant increase in plasma ANF was observed in the group with a pressor response (blood pressure rose from 89.0 +/- 3.9 to 136.7 +/- 11.4 mm Hg; ANF rose from 36.8 +/- 4.9 to 92.7 +/- 17.7 pg/ml). There was no significant time effect on 24-hour sodium excretion, urine volume, and water intake in both Ang II-infused groups. In a second set of experiments, male rats were infused intravenously for 60 minutes with either saline, a nonpressor dose of Ang II (16 ng/kg/min), or a pressor dose (800 ng/kg/min) of Ang II. Left ventricular end-diastolic pressure, right atrial pressure, and mean arterial pressure were monitored. There was a significant increase in plasma ANF and left ventricular end-diastolic pressure only with the pressor dose (blood pressure rose from 85.0 +/- 6.1 to 140.0 +/- 5.5 mm Hg; ANF rose from 22.6 +/- 6.0 to 108.3 +/- 47.7 pg/ml; left ventricular end-diastolic pressure rose from 5.3 +/- 5.7 to 20.8 +/- 7.9 mm Hg). No significant modification of right atrial pressure was recorded.(ABSTRACT TRUNCATED AT 250 WORDS)

Central and regional hemodynamics during the acute onset of renal hypertension in rats

The purpose of this study was to quantitate the regional changes in flow and resistance which occur during the acute onset of two-kidney, one clip renal hypertension. Anesthetized rats were implanted with a Doppler flow probe and balloon occluder on one renal artery. To produce acute hypertension, the occluder was inflated to reduce renal flow velocity by 50%. After 90 minutes, mean arterial pressure increased 25% above the prestenosis control period value as a result of a 22% increase in peripheral resistance. Regional flows and resistances were determined prior to and 90 minutes after renal artery stenosis by injection of labelled microspheres into the left ventricle. Our major findings were that: 1) the regional hemodynamic changes in flow and resistance are unevenly distributed among individual organs; and 2) the major site of increased resistance resides in the splanchnic circulation with the largest increases occurring in the small intestine.

Organ scaling in mammals: the kidneys

Values of kidney weight in adult male and female mammals, both terrestrial and aquatic, as well as values for renal blood flow and glomerular number and diameter, were submitted to linear (log-log) regression analysis. The slope of the regression line for kidney weight in 63 species of adult terrestrial mammals was 0.85 %/- 0.01. No statistically significant difference was found between the slopes of the regression lines for male and female terrestrial mammals. The slope of regression line for kidney weight in eight species of adult aquatic mammals was 0.92 +/- 0.01. Again, no statistically significant difference was found between the slopes for males and females. However, the slope (0.92) of the regression line for aquatic mammals was significantly different from the slope (0.85) for terrestrial mammals (P much less than 0.001). The slope of the regression of renal blood flow on body weight was 0.82 +/- 0.01. This value is consistent with the hypothesis that renal blood flow represents a constant fraction of cardiac output (over about 3.4 orders of magnitude in body weight). The slopes of the regression lines for glomerular number (per kidney) and mean glomerular diameter were 0.59 +/- 0.02 and 0.11 +/- 0.01, respectively. A schematic model representing the scaling of energy-partitioning in mammals is introduced.

Angiotensin-induced sodium excretion patterns in cirrhosis: role of renal prostaglandins

Changes in renal hemodynamics and sodium excretion induced by an angiotensin II (AII) infusion were correlated with urinary prostaglandin E2 (PGE2) excretion in 15 patients with cirrhosis and ascites. All induced natriuretic responses in 47% and antinatriuretic responses in 53% of the patients. Natriuresis was accompanied by an increase; antinatriuresis by a decrease in PGE2 excretion. Although there was no change in GFR (CIn), renal blood flow (CPAH) decreased. Patients were clinically indistinguishable. Antinatriuretic responders tended, however, to have higher baseline PGE2 excretion rates, were more sensitive to effects of prostaglandin blockade, and were less sensitive to the pressor effect of AII. Following partial inhibition of renal prostaglandin synthesis by indomethacin, AII-induced natriuretic responses were accentuated. GFR, RBF, and urine flow rate markedly decreased in both groups. There was no difference in pressor sensitivity to AII following prostaglandin synthesis blockade. We conclude that in patients with hepatic cirrhosis, the sodium excretion pattern induced by an exogenous AII challenge may depend on the prior state of intrarenal prostaglandin activity. Our findings also support the hypothesis that renal hemodynamic parameters in patients with cirrhosis and ascites are crucially dependent on renal prostaglandins.

Cerebral venous pressure during actively induced hypertension and hypercapnia in cats

Superior sagittal sinus pressure, intracranial pressure and arterial pressure were recorded in an experimental series on 10 cats. During drug-induced, severe, acute arterial hypertension and parallel hypercapnia, venous pressure could exceed intracranial pressure in both the supra- and infratentorial compartment. From these data it is concluded that cerebral venous pressure during acute arterial hypertension may contribute to protein extravasation at the postcapillary-venular level.

Microsphere measurement of regional intestinal blood supply and cardiac output in the rat

The regional blood supply to consecutive segments of the small intestine in the anaesthetized rat was investigated with a radioactive microsphere technique. A blood flow gradient with the lowest flow in the distal segments (0.85--0.89 ml/min.g) and the highest in the proximal segments (1.13--1.15 ml/min.g) was observed. Very few microspheres were found in the portal vein blood, indicating negligible arteriovenous shunting in the splanchnic area. The mean cardiac outputs in two consecutive measurements were 27.9 and 28.7 ml/min . 100 g, respectively. The cardiac output and regional blood flow values were in accordance with those obtained with other techniques.

The role of angiotensin in the canine renal vascular response to barbiturate anesthesia

The influence of barbiturate anesthesia on renal blood flow was assessed by the xenon washout method in trained dogs with catheters chronically implanted in the renal artery. Anesthesia induced with either thiopental sodium or pentobarbital sodium resulted in a striking reduction in renal blood flow (4.1 +/- 0.1 vs. 2.6 +/- 0.2 ml/g per min; P less than 0.001) without a change in arterial pressure. The reduction in blood flow was prevented by a high salt intake and partially reversed by agents which interrupt the renin-angiotensin system (BPF 9a; 1-Sar,8-Ala-angiotensin II; propranolol) but not by alpha-adrenergic blocking agents (phentolamine and phenoxybenzamine). Anesthesia blunted the renal vascular response to angiotensin II (P less than 0.0005) whereas responsiveness to norepinephrine was increased (P less than 0.05). We conclude that barbiturate anesthesia induces a major, angiotensin-mediated renal vascular response which must be considered in the interpretation of experiments performed under these conditions.

Ultrastructural investigation of peripheral arterial vessels in the cortex of rats with experimental hypertension

The peripheral arterial blood vessels in the cerebrum of 36 experimental animals and 9 controls were studied by electron microscopy. In 5 rats of these renal hypertension was produced (the animals were sacrificed 3 to 15 days following the second operation). 24 animals were treated with depot angiotensin (0.02 to 2.5 mg/daily) for 3 hr up to 40 days, and 7 rats were neurotized for 1 to 41/2 months. The alterations of the cerebral vessels were distinctly different within these 3 models already in the early reactions. Thus, even in the first 14 days of the experiment with renal and angiotensinogenic hypertension alterations were observed that did never occur in the neurotized rats. There were always observed disturbances in permeability of the cerebral vessels, but they were never followed by such heavy wall insudations as usually noticed in the splanchnic vessels. The less frequent occurrence of hemorrhages and malacic processes in the rat brain is ascribed aside from the physiological properties of the brain supply, to genetic factors and the absence of arteriosclerotic burden to the vascular wall in the non-dietetically pretreated experimental animals.

Effects of angiotensin II on fluid transport, transmural potential difference and blood flow by rat jejunum in vivo

A method has been described for the measurement of fluid transport by rat jejunum in vivo over two consecutive 30 min periods. 2. Subpressor infusion rates of angiotensin (0-59 ng/kg per minute) stimulate fluid transport, while high (pressor) infusion rates (590 ng/kg per minute) inhibit fluid absorption. 3. Both the inhibitory and stimulatory effects of angiotensin on fluid transport are not accompanied by any change in the transmural p.d., total blood flow to the jejunum or distribution of blood flow within the wall of the jejunum. 4. These results are discussed in relation to the mechanism of action of angiotensin on fluid transport and its role in sodium and water homoeostasis.

Uterine blood flow and uterine renin secretion

Experiments were carried out in pregnant nephrectomized rabbits to determine the relationship between uterine blood flow and uterine renin secretion. Uterine blood flow was measured by the percentage distribution of radioactive microspheres injected into the left ventricle which lodged in uterus and placenta, and cardiac output was measured by dye dilution. In 40 animals, 24 hr after nephrectomy, uterine blood flow was 4.7+/-0.4% of cardiac output and absolute flow 32.4+/-3 ml/100 g per min. Plasma renin activity (PRA) in uterine vein, 994+/-182 ng/100 ml per hr, was higher than in carotid artery, 832+/-143 (P < 0.025). With reduction of uterine blood flow from 4.7+/-0.5 to 1.95+/-0.3% of cardiac output and absolute flow from 30.8+/-4.6 to 8.8+/-2 ml/100 g per min, uterine vein PRA rose from 1434+/-234 to 4430+/-300 (P < 0.001), and carotid artery PRA from 1009+/-200 to 2300+/-350 (P < 0.01). Hemorrhagic hypotension caused uterine vein PRA to increase from 913+/-293 to 3638+/-1276 (P < 0.001) and carotid artery PRA from 774+/-252 to 1730+/-433 (P < 0.01). Uterine blood flow expressed as a percentage of cardiac output remained constant after hemorrhage, 5.5+/-0.9 and 6.3+/-0.8%, although absolute flow fell from 37+/-7.7 to 29+/-3.6 ml/100 g per min because of the large fall in cardiac output which occurred.Angiotensin, 10 ng/kg per min, caused no significant change in blood pressure or cardiac output but increased uterine blood flow from 4.1+/-0.6 to 8.4+/-1% (P < 0.005) of cardiac output with absolute flow increasing from 37.4+/-7 to 73.2+/-10 ml/100 g per min (P < 0.001). The increase in uterine blood flow during angiotensin was abolished by the prior administration of propranolol. Isoproterenol, 0.5 mu/min, increased uterine blood flow from 3.5+/-0.6 to 6.4+/-1.2% of cardiac output (P < 0.02) with absolute flow increasing from 25+/-5 to 51+/-12 ml/100 g per min (P < 0.05). Norepinephrine, 500 ng/min, caused no significant change in uterine blood flow. These findings suggest that uterine renin might be involved in regulating uterine blood flow, secretion being increased in response to a reduction in flow with the resultant rise in circulating or local angiotensin, through beta adrenergic stimulation, increasing uterine blood flow.

Intrarenal conversion of angiotensin I to angiotensin II in the dog

Effects of close intra-arterial injections of angiotensins I and II on changes in renal blood flow and renal vascular resistance were studied in dogs anesthetized with pentobarbital sodium. In the first series of experiments, angiotensin I (0.375 µg) or angiotensin II (0.13 µg) decreased renal blood flow and pressures in a small renal cortical vein and the renal vein. Although renal vascular resistance was markedly increased by angiotensins I or II, these increases did not appear to involve renal venous segments. Responses to angiotensin I occurred when the injected agonist was not allowed to reach the systemic circulation, and were virtually abolished during infusion of SQ 20475, a synthetic pentapeptide (Pyr-Lys-Try-Ala-Pro) that inhibits enzymatic conversion of angiotensin I to angiotensin II. In the second series of experiments, renal vascular responses to intra-arterial injections of angiotensin I (0.375-3.75 µg) and angiotensin II (0.13-1.00 µg) were studied. Responses to angiotensin I, but not those to angiotensin II, were significantly attenuated by SQ 20475. The results suggest that similar renal vascular segments respond to angiotensins I and II. Responses to angiotensin I are probably due to its intrarenal conversion to angiotensin II. Such conversion appears to occur to the extent of about 4%.

The relationship of the renal vascular activity of angiotensin II to the autonomic nervous system

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