Role of histamine in the hypotensive action of d-tubocurarine in humans

The administration of d-tubocurarine (dTc) to animals and humans has been reported to produce hypotension. Experiments in animals suggest that the hypotension is a result of both ganglionic blockade and histamine release. In order to determine the role of histamine release in dTc-induced hypotension in humans, the authors developed a sensitive radioenzymatic assay for plasma histamine and measured plasma histamine following dTc administration (0.25-0.75 mg/kg) to 21 surgical patients. While neither fentanyl (3 microgram/kg) nor thiopental (6 mg/kg) produced a significant change in plasma histamine, dTc caused a dose-dependent increase in plasma [dose dTc vs. log (plasma histamine), r = 0.62 P less than 0.003]. The log (plasma histamine) correlated with the dTc-induced hypotension (r= 0.61, P less than 0.005). The data suggest that histamine release is an important factor in the hypotension accompanying dTc administration in humans.

Cardiovascular changes during the calcium carbimide-ethanol interaction

Potentially serious cardiovascular changes occur in alcoholics as a results of carbimide-ethanol reactions (CERs). Hypotension and tachycardia often occur when blood acetaldehyde levels increase. Hypotension with bradycardia can also occur secondary to vagal stimulation, the results of retching or vomiting. Conservative procedures (e.g., modified Trendelenburg's position) are usually effective in reversing the hypotension but in severe reactions active treatment (intravenous fluids, O2, and drugs) may be indicated. Three case reports are presented to illustrate cardiovascular responses during CERs; for comparison, changes for one subject during a disulfiram reaction are also presented. Caution is recommended in screening alcoholics before treatment with carbimide or disulfiram so as to rule out cardiovascular, hepatic, or renal diseases.

[High concentration of erythrocytes in blood circulating in the brain]

In experiments on rabbits the red cell count was determined in venous blood from the brain and hind limbs. It appeared that under normotensive conditions the red cell concentration in blood from the brain is by ca. 20% higher than in the peripheral blood of the same animals. The differences increased (by ca. 34%) under hypotensive conditions. These results are considered as new evidence for the phenomenon of specific distribution of red cells in the arterial ramifications of the organs where the blood flow rate and metabolic demands are the highest.

Blood levels of 6-oxo-prostaglandin F 1 alpha during endotoxin-induced hypotension in rabbits

Levels of 6-oxo-prostaglandin F1 alpha (6-oxo-PGF1 alpha), the non-enzymic degradation product of prostacyclin, were measured in arterial blood from anaesthetized rabbits, before and after intravenous (i.v.) administration of endotoxin (Lipopolysaccharine W E. coli 0111:B4, 5 mg/kg). 6-Oxo-PGF1 alpha was assessed by radioimmunoassay after extraction and separation by thin-layer chromatography. The basal concentration of 6-oxo-PGF1 alpha in blood was less than 100 mg/ml in 19 out of 20 rabbits. This indicates that the level of circulating prostacyclin is generally below 100 pg/ml. The administration of endotoxin induced a biphasic hypotension, and increased levels of 6-oxo-PGF1 alpha were found in all endotoxin-treated animals during the secondary hypotension after 60 and 120 min. Pretreatment with indomethacin (2.5 mg/kg) prevented the secondary fall in arterial blood pressure and significantly suppressed the rise in 6-oxo-PGF1 alpha. However, indomethacin failed to alter the endotoxin-induced thrombocytopenia and did not modify the endotoxin-induced platelet aggregation in vitro. It is concluded that prostacyclin contributed to the secondary hypotension which accompanied the i.v. administration of endotoxin. Thromboxane A2 seems not to be of primary importance in the endotoxin-platelet interaction.

Effect of priming volume on serum catecholamines during cardiopulmonary bypass

Several theories have been proposed to explain the transient hypotension which occurs upon the initiation of cardiopulmonary bypass. The present study investigated the possibility that addition of the lactated Ringer's solution pump priming volume to the circulation causes dilution of circulating catecholamines leading to the hypotension. Circulating epinephrine and norepinephrine levels were measured during cardiopulmonary bypass in patients anaesthetized with halothane. The results demonstrate dilution of circulating catecholamines at the start of bypass in conjunction with the observed hypotension. During the bypass period, mean blood pressure graudally recovered to normotensive levels even though circulating catecholamine levels remained significantly lowered, indicating a mechanism for the recovery of blood press which is not sympathoadrenal. The results obtained from this study demonstrate a temporal relationship between catecholamine dilution by the pump priming volume and the observed hypotension. Whether catecholamine dilution is the sole factor causing the hypotension remains to be determined.

Effect of propranolol on plasma norepinephrine during sodium nitroprusside-induced hypotension

The possibility of an action of propranolol which reduces traffic in the sympathetic nervous system and/or reduces release of norepinephrine at sympathetic nerve endings has been investigated in normal subjects. Plasma norephinephrine was measured in resting supine subjects before and during infusions of sodium nitroprusside which reduced the systolic blood pressure by approximately 10 and later by 20 mm Hg. In 5 subjects these observations were repeated 2 hr after a single 200-mg oral dose of propranolol and in 3 they were repeated after 2 to 8 wk of propranolol 320 mg twice daily. In the control experiments, plasma norepinephrine increased from 0.22 up to 0.74 ng/ml when the blood pressure was reduced by 17/15 mm Hg. Corresponding figures 2 hr after 200 mg propranolol were an increase of plasma norepinephrine from 0.30 or 0.79 ng/ml with a reduction of blood pressure of 19/15 mm Hg. After long-term treatment with 640 mg propranolol daily, a similar reduction of pressure with sodium nitroprusside increased plasma norepinephrine from 0.24 to 0.68 ng/ml. There was no significant alteration in the elevation of plasma norepinephrine following blood pressure reduction with nitroprusside after either short- or long-term treatment with propranolol. These experiments do not suggest a significant role for a nervous system effect of propranolol in modifying sympathetic activity.

Effects of converting enzyme inhibitor (SQ 20881) on changes in blood pressure and plasma aldosterone induced by angiotensin I or acute hemorrhage in rabbits

The effects of angiotensin converting enzyme inhibitor (CEI) upon blood pressure and plasma aldosterone (PA) were studied in rabbits with a simultaneous infusion of angiotensin I (ANG I) or with hemorrhagic hypotension. Pretreatment with CEI (SQ 20881), 1.0 mg/Kg, inhibited the effects of infused ANG I, 30 ng/Kg/min, upon PA and blood pressure at 30 min of the infusion, but the inhibition on PA was not significant at 60 min of the infusion. The same dose of CEI was ineffective in blocking the effect of 100 ng/Kg/min of ANG I on PA and blood pressure even at 30 min of the infusion. In rabbits with hemorrhagic hypotension, injection of CEI resulted in the decrement in blood pressure, whereas no decrement in blood pressure was observed in normal control rabbits. This study suggests that CEI exerts it's effect in part by inhibiting conversion of ANG I to angiotensin II (ANG II), but this can't exclude other mechanisms.

Effects of acute hypotension and hypertension on serum TSH concentrations in male rats

The effect of acute hypertension and hypotension on serum TSH concentration was studied in anesthetized male rats. I.v. infusions (10 and 30 min) of Na-nitroprusside and dihydralazine induced a profound hypotension, and angiotensin amide and noradrenaline increased blood pressure, but none of the treatments significantly modified serum TSH concentrations. Also clonidine and noradrenaline, when given i.p., caused hypertension, but again the increase of serum TSH levels was not consistent. When the whole material was analysed, there was a scarcely significant correlation between the change of blood pressure and the change of serum TSH level. It is inferred that the drugs affecting TSH secretion, do not exert their action solely by changing the blood pressure.

Renin response to hemorrhage and hypotension in the aglomerular toadfish Opsanus tau

Renal renin and the juxtaglomerular cells evolved in primitive bony fishes, whereas the macula densa emerged later in vertebrate phylogeny. We attempted to determine whether a renal arteriolar baroreceptor exists in the toadfish Opsanus tau, which possess renin and granulated cells in the kidneys, but lack glomeruli and macula densa. Cumulative hemorrhage of 1.5, 3, 6, 12, and 18 ml/kg, or a single massive bleeding from unanesthetized toadfish, kept in 50% seawater, caused an immediate and significant decrease in mean aortic pressure and stepwise increases (5-20 times) of plasma renin activity (PRA). Papaverine (10 mg/kg) caused hypotension and increased PRA. Minoxidil (6-12 mg/kg) neither decreased blood pressure nor increased PRA. The results suggest that toadfish respond to hemorrhage and acute hypotension with renin release despite the absence of a macula densa. It remains to be determined whether decreased renal perfusion pressure due to decreased dorsal aortic pressure stimulated the receptor in the granulated cells or whether the renal nerves may be involved.

Plasma corticosterone values in genetic hypertensive and hypotensive strains of turkeys

Plasma corticosterone levels of hypertensive and hypostensive turkeys were 2.50 and 2.19 micrograms/dl, respectively. Male turkeys of both strains had a mean plasma levels of 2.47 micrograms/dl and female turkeys had a mean level of 2.21 micrograms/gl. The average plasma corticosterone level for all turkeys was 2.35 micrograms/dl. Although the plasma corticosterone levels were higher at 1200 hr than at either 0800 or 1600 hr, the differences were not statistically significant. It was condluded that blood pressure selection had no significant effect on plasma corticosterone levels.

Transcutaneous oxygen tension in sick infants

The clinical usefulness of the transcutaneous O2 electrode was investigated in 30 sick infants; 159 simultaneous measurements of arterial PO2 and transcutaneous PO2 were made. During the comparisons, arterial blood pressure, heart rate, and thoracic impedance were continuously recorded, and skin axillary and environmental temperatures and hematocrit were noted. Despite a wide range of arterial blood pressure and hematocrits, arterial PO2 and transcutaneous PO2 were similar (slope, 0.963), except for 2 groups of sick infants. Some infants with severe, persistent pulmonary hypertension who were receiving an intravascular infusion of tolazoline and infants with mean arterial blood pressures more than 2.5 SD less than the predicted average had values for transcutaneous PO2 that were lower than PO2. The surface O2 electrode is safe and relatively easy to use and provides data that can help in the management of most sick infants.

Blood plasma constituents in 14-week old hypertensive and hypotensive strains of turkeys

Plasma inorganic phosphorous, glucose, uric acid, total cholesterol, total protein, albumin, alkaline phosphatase, lactic dehydrogenase (LDH), and serum glutamic oxaloacetic transaminase (SGOT) were determined in 14-week old turkeys from lines genetically determined for high and low blood pressure. The turkeys received a commercial grower diet (control), control + 10% animal fat, or control + 10% animal fat and 1% cholesterol. Concentrations of uric acid in plasma were higher (P less than or equal to .05) in the control-diet group than in the other dietary groups, and the high blood pressure line had significantly higher (P less than or equal to .05) concentrations of uric acid in plasma than the low blood pressure line. Turkeys fed the diet containing added cholesterol had higher levels (P less than or equal to .05) of total plasma cholesterol than those receiving the other diets. Alkaline phosphatase levels of plasma were significantly lower (P less than or equal to .05) in the control-diet group than the other dietary groups. There were no other effects within either of the genetic blood pressure lines that indicated blood pressure had any influence on blood plasma constituents other than uric acid, nor was there any indication that dietary treatment had any effect within either blood pressure group. Blood pressure and plasma constituents were not correlated.