Elevated blood glucose is associated with poor outcome in the carbon-monoxide-poisoned rat

Levine-prepared, unanesthetized rats exposed to 2400 and 2700 ppm carbon monoxide (CO) for 90 min were used to examine the effect of acute CO poisoning on plasma glucose and insulin concentrations, and neurologic dysfunction. Body temperature and mean arterial blood pressure fell progressively during CO exposure. Glucose rose during initial CO exposure, then declined: glucose increased again after 2 h of room air recovery. Neurologic deficit, behaviorally-assessed after 4 h of recovery, was strongly correlated (r = 0.71, P less than 0.001) with glucose increase during the first 2 h of recovery. Recovery hyperglycemia was, in turn, correlated (r = 0.69, P less than 0.001) with the fall in glucose during the second half of CO exposure. Neurologic deficit was also correlated, but less strongly so, with hypoglycemia during CO exposure. Failure to rapidly regain body temperature during recovery was correlated with the post-CO rise in glucose concentration and with increased neurologic deficit. Plasma insulin activity was depressed immediately following CO exposure, and increased during recovery. CO-induced hypothermia was greater at 2700 than at 2400 ppm CO, as were post-CO recovery hyperglycemia, neurologic deficit and mortality, while body temperature recovery was less complete. The results provide evidence of an association between neurologic deficit and general morbidity following acute CO poisoning and the magnitude of post-CO hyperglycemia.     

Hypothermia protects brain function in acute carbon monoxide poisoning

The role of body temperature in the morbidity and mortality resulting from acute severe carbon monoxide (CO) poisoning (2400 ppm CO, 90 min) was investigated using an unanesthetized animal model. Modified Levine prepared female rats (left common carotid artery and jugular cannulated) displayed a lower rate of recovery period (4 hr) re-warming, and an increased mortality rate and behaviorally-assessed neurologic index (NI) compared to normal rats. This indicated their greater susceptibility to CO hypoxia, although the degree of CO-induced hypothermia was the same in both groups. The whole-body cooling of Levine rats to a similar extent prior to CO exposure increased somewhat the post-CO re-warming rate, and marginally decreased NI and mortality during CO exposure (in-CO). In contrast, maintenance of constant body temperature by external heating during CO exposure resulted in a negative post-CO re-warming rate and sharply increased NI and in-CO mortality. Normal euthermic rats were much less severely affected by CO. The results suggest that hypothermia, whether CO-induced or produced by prior cooling, provides measurable protection of brain function during acute severe CO poisoning, and that maintenance of body temperature increases in-CO mortality and interferes with ability to thermoregulate and increases NI in survivors.     

New treatment methods in verapamil poisoning: experimental studies

The aim of this study was to evaluate the effectiveness of the treatment with 4-aminopyridine (4-AP, potassium channel inhibitor) and Bay K 8644 (calcium channel activator) in experimentally evoked verapamil poisoning in rats and to compare the results of this treatment with the effectiveness of widely accepted methods (adrenaline, calcium compounds). The experiment was carried out on male and female Wistar rats which were divided into 4 experimental (A, B, C, D) and a control (K) groups. Rats were anesthetized and the abdominal aorta was cannulated for mean arterial pressure and heart rate measurements while caudal vein was cannulated for drug administration. All animals were infused with verapamil (150 mg/kg/h) until 50% reduction of mean arterial pressure and/or heart rate was observed. After verapamil, control animals were given 0.9% NaCl solution and the other groups received 687.5 mg/kg/h of calcium glucolactobionicum (group A), 0.3 mg/kg/h of adrenaline (group B), 2 mg/kg/h of 4-AP (group C) or 2 mg/kg/h of Bay K 8644 (group D). The mean blood pressure and heart rate was checked and ECG was recorded every 10 min. A statistically significant decrease in mortality compared with the control group was observed in animals treated with adrenaline (p < or = 0.05), Bay K 8644 (p < or = 0.01) and 4-AP (p < or = 0.005). The treatment of experimentally evoked poisoning in rats using 4-AP or Bay K 8644 resulted in fast receding of poisoning symptoms: increase in blood pressure and heart rate, receding of bradyarrhythmia and return of sinus rhythm. The results of the study suggest the usefulness of 4-AP and Bay K 8644 in the treatment of verapamil poisoning.     

Cardiovascular, metabolic and neurologic effects of carbon monoxide and cyanide in the rat.

Levine-prepared, female Sprague-Dawley rats were used to investigate the effects of carbon monoxide (CO) and cyanide (CN) on heart rate, blood pressure, hematocrit, body temperature, blood glucose, lactate, and neurologic function. Rats were exposed to either 2400 ppm CO, 1500 ppm CO, 4 mg/kg NaCN, or both 1500 ppm CO and 4 mg/kg NaCN for 90 min, followed by 4 h of room air recovery. Following exposure to 2400 ppm CO, rats exhibited a significant bradycardia which normalized by 2 h of recovery. All groups exhibited an initial hypotension which was either maintained or exaggerated during exposure in all but the rats exposed to CN, and which returned to pre-exposure values by 90 min. All groups experienced a significant hypothermia during the exposure period, with those in the 1500 ppm CO or the CN returning to initial values over the recovery period. The only significant change in hematocrit was due to 2400 ppm CO (4.1% increase). During exposure, all groups experienced an initial surge in glucose concentration which was maintained in all but rats exposed to 2400 ppm CO. The greatest hyperglycemic response resulted from the combination of CO and CN, whereas 2400 ppm CO produced the smallest. CN alone produced no significant rise in lactate concentration. However, lactate concentration in all other groups was significantly elevated during the exposure period, returning to initial values by 4 h of recovery. Lactate concentrations and neurologic deficit in rats exposed to 1500 ppm CO, when added to those rats treated with CN, closely approximated the lactate and neurologic deficit of the combination treatment. Neurologic deficit was greatest in rats exposed to 2400 ppm CO. While in most cases the responses of the rats to CO and CN differed whether the substances were administered alone or in combination, a synergistic relationship is not suggested. An additive or less than additive relationship is more likely.     

Blood lactate and catecholamine levels in the carbon monoxide-exposed rat: the response to elevated glucose.

Previous studies have shown that elevated blood glucose is detrimental to the outcome in acute carbon monoxide (CO) poisoning. The present goals were to characterize the blood lactate and catecholamine changes and to determine whether elevated blood glucose results in increases in the levels of these substances. Two groups of adult Sprague-Dawley, Levine-prepared, female rats (n = 22 each) were exposed to 2400 ppm CO for 90 min: one group received nothing (CO alone), while the other group was infused with a 50% glucose solution (4 ml/kg) (CO + glucose). The usual hypothermia, hypotension, bradycardia and hemoconcentration associated with acute severe CO poisoning were observed. Survival rates were 68% and 54% in the CO alone and CO + glucose groups, respectively. Arterial blood pressure tended to decline more in rats that died; the difference was significant in the CO + glucose group. In the CO alone group, plasma glucose concentration was significantly lower after CO exposure in rats that died than in survivors (35 +/- 15 vs. 99 +/- 16 mg/dl). In the CO + glucose group, glucose concentration was significantly higher after 45 min in rats that died (d) than in survivors (s) (447 +/- 29 vs. 324 +/- 31 mg/dl). Elevated blood glucose in the CO + glucose group failed to significantly increase blood lactate; however, lactate tended to be higher in rats that died in both groups [CO alone group: 175 +/- 17 (d) vs. 138 +/- 9 (s); CO + glucose group: 154 +/- 10 (d) vs. 143 +/- 8 (s)]. Plasma epinephrine and norepinephrine increased significantly 6-10-fold and 2-6-fold in each of the two groups, respectively; however, catecholamine levels were not related to either the administration of glucose or survival. With regard to CO poisoning in this animal model, the results do not support the hypotheses that elevated blood glucose exacerbates the increase in blood lactate, that increased catecholamine increases glucose, or that greater CO-induced hypoglycemia results from increased lactate production. The results do show that death is related to abnormally high or low blood glucose, but that it is not due to higher blood lactate or catecholamine levels.     

Levosimendan infusion improves cardiac output but not blood pressure in a rodent model of severe metoprolol toxicity

Levosimendan (Levo) is an inodilator improving cardiac output (CO) and reducing afterload in heart failure. Previously, we reported that Levo improved CO but not blood pressure (BP) in a rodent model of verapamil poisoning. We theorised that Levo-induced vasodilation should not influence BP to a similar degree in metoprolol poisoning. Aim: To assess the effect of Levo on haemodynamics in a rodent model of metoprolol poisoning. Method: Anaesthetized male Wistar rats were infused metoprolol continuously. When the BP dropped to 50% of baseline (time 0) rats received 1 of the 4 treatments: (a) control (0.9% saline bolus?+?infusion); (b) Levo-l (Levo 36?μm/kg loading dose followed by 0.6?μm/kg/min); (c) Levo-I (Levo infusion only at 0.6?μm/kg/min); and (d) Epi (epinephrine 0.5?μm/kg/min). All groups received comparable fluid volumes. Haemodynamics were recorded every 10?min for 70?min. CO, mean arterial pressure (MAP) and heart rate (HR) of each group were compared to the control. Results: All groups had comparable baseline and time 0 HR, MAP and CO. Levo-L and Levo-I rats showed significantly greater CO at t?=?10?min (p?>?0.02 and p?>?0.04, respectively). CO was higher at all other time points for both Levo groups. This was not statistically significant. Levo did not improve MAP compared to control. Adrenaline increased MAP but not CO compared to control and Levo groups. Conclusion: Levo did not improve MAP but moderately improved CO compared to control in this model of metoprolol poisoning. The response was similar to that reported previously in verapamil-poisoned rats. The improvement in MAP seen with epinephrine was most likely vasoconstriction mediated.     

Depression by morphine and levorphanol of activity in sympathetic nerve fibres in anaesthetized rats

In urethane-anesthetized rats, the effects of intravenous injections of morphine, levorphanol, dextrorphan, pentazocine and naloxone were studied studied on the activity in nerve fibres of the cervical sympathetic trunk, and on mean arterial blood pressure and heart rate. Impulse frequency in sympathetic nerve fibres was recorded with tungsten microelectrodes and proved to be more sensitive to drug action than blood pressure or heart rate. Morphine 1 and 2 mg/kg dose dependently reduced sympathetic impulse frequency, blood pressure and heart rate; morphine 0.5 mg/kg was ineffective. Levorphanol 1 and 2 mg/kg dose dependently reduced sympathetic impulse frequency and blood pressure but did not affect heart rate. Dextrorphan (the dextro-isomer of levorphanol) 2 and 4 mg/kg had no effect on the parameters tested. Pentazocine 3 and 6 mg/kg did not cause a consistent change in sympathetic impulse frequency, blood pressure and heart rate. Naloxone 0.2 mg/kg abolished the depressant effects of morphine and levorphanol and, when given alone, increased sympathetic impulse frequency. Naloxone 1 mg/kg increased blood pressure but did not affect heart rate. It is concluded that morphine can reduce blood pressure and heart rate by causing opiate-specific central sympathetic depression.     

Comparative Hemodynamic Effects of Levosimendan Alone and in Conjunction with 4-Aminopyridine or Calcium Chloride in a Rodent Model of Severe Verapamil Poisoning

Levosimendan (Levo) increases sensitivity of troponin-C to calcium, thus increasing myocardial contractility. It is also a vascular K+-ATP channel agonist producing peripheral vasodilation. Previous research with levosimendan revealed an increase in cardiac output (CO) but not blood pressure (BP) in experimental verapamil poisoning. Levosimendan’s K+-channel agonist properties may augment verapamil’s vasodilatory effects. 4-Aminopyridine (4-AP) is a K+-channel antagonist. It has successfully reversed hypotension in experimental verapamil poisoning. We hypothesized that coadministration of these agents may improve BP and CO in verapamil poisoning. Anesthetized, ventilated, and canulated male Wistar rats were poisoned with verapamil. Animals received one of six treatments, which are as follows: (1) n-saline infusion (control), (2) Levo 6.25 μg/kg loading dose and 36 μg/kg/h infusion, (3) 4-AP 2 mg/kg loading dose and infusion (4-AP), (4) Levo+4-AP, (5) CaCl₂ loading dose and infusion, and (6) Levo+CaCl₂. Hemodynamic parameters were recorded for 60 min. Outcome measures were changes in CO, BP, and heart rate (HR) compared to control. All groups had similar pretoxicity and peak toxicity CO (50% of pretoxicity value), BP (50% or pretoxicity value), and HR. Control group CO, BP, and HR progressively dropped during the verapamil infusion. Levosimendan produced a statistically significant improvement in CO (75% of pretoxicity level) but not BP in comparison to control. 4-AP produced a significant improvement in CO (110% of pretoxicity) and BP (78% of pretoxicity). Levo+4-AP and Levo+CaCl₂ groups improved CO (100% of pretoxicity) and BP (77% and 50% of pretoxicity, respectively), but there was no additive increase in CO or BP in animals compared to 4-AP or CaCl₂ alone. Levosimendan moderately improved CO but not BP in verapamil poisoning. The hypotensive effects of levosimendan were not overcome by coadministration of either 4-AP or CaCl₂. Levosimendan may not be an appropriate agent to use in the treatment of verapamil poisoning.     

Effects of esmolol on 35 GHz microwave-induced lethal heat stress

1 The purpose of this study was to examine effects of the β₁-adrenoreceptor antagonist esmolol (infused at 2 or 4 mg kg^?1 body wt min^?1) on heart rate, blood pressure, respiratory rate, localized body temperature changes, survival times, and lethal body temperatures that occur during the exposure of anesthaetized rats to 35 GHz microwaves. 2 Forty Sprague–Dawley rats, anaesthetized with ketamine, were exposed to 35 GHz microwaves at a level that resulted in heating and death. During irradiation, a continuous increase in heart rate and a biphasic response in blood pressure (initial increase followed by a decrease) were observed in all groups of animals. 3 Esmolol caused a significant dose-dependent decrease in blood pressure, relative to saline-treated animals, but only a small attenuation of the heat-induced rise in heart rate. In experiments in which esmolol was infused and microwave exposure was continued until death, drug-treated animals survived for significantly shorter periods and died at significantly lower body temperatures. The change in survival may have been related to the lower blood pressure due to esmolol treatment.     

Effect of urethane on hydralazine-induced tachycardia in rats.

1. In conscious normotensive rats, hydralazine (5-10 mg kg-1 p.o.) produced a dose-related fall in systolic blood pressure, accompanied by a pronounced increase in heart rate. 2. The tachycardia induced by hydralazine (10 mg kg-1 p.o.) in conscious normotensive rats was strongly inhibited after anaesthesia with urethane (1.26 g kg-1 i.p.). 3. In anaesthetized normotensive rats, hydralazine (1 mg kg-1 i.v.) caused a fall in mean blood pressure, accompanied by irregular effects on the heart rate that consisted in a combination of initial tachycardia followed by bradycardia. 4. In pithed rats, hydralazine (1 mg kg-1 i.v.) did not affect mean arterial blood pressure but produced a significant decrease in heart rate. 5. In rat isolated atria, hydralazine (2 mM) produced a positive inotropic/negative chronotropic effect. 6. These results suggest that urethane inhibits the cardiovascular reflex that causes the tachycardia induced by hydralazine in conscious normotensive rats. For this reason, in anaesthetized normotensive rats appear the direct effect of the drug on the heart.     

Selective versus non-selective suppression of nitric oxide synthase on regional hemodynamics in rats with or without LPS-induced endotoxemia

The late phase of severe septic shock is associated with reduced cardiac output (CO) and activation of the inducible isoform of nitric oxide synthase (NOS). This study examined the effects of 1400 W (N-3-aminomethyl-benzyl-acetamidine), a new selective inhibitor of inducible NOS (iNOS), relative to those of N(G)-nitro-L-arginine (L-NNA, non-selective inhibitor of NOS) and the vehicle, on mean arterial pressure (MAP), CO, total peripheral resistance (TPR) and tissue blood flow (BF) in thiobutabarbital-anesthetized rats with lipopolysaccharide (LPS, 10 mg/kg, i.v.) induced endotoxemia. At 2.5 as well as 4 h after injection of LPS, MAP, CO, and BF of the stomach, skeletal muscle and skin were decreased, but TPR was increased, BF to the heart and kidneys were also decreased at 4 h after injection of LPS. Treatment of endotoxemic rats with 1400 W (3 mg/kg followed by 3 mg/kg/h, i.v.) at 2.5 h after endotoxin challenge prevented the late phase fall in MAP without exacerbating the decreases in CO and tissue BF. In contrast, treatment with L-NNA (8 mg/kg followed by 3 mg/kg/h, i.v.) at 2.5 h did not prevent the decline in MAP in the LPS-treated rats. Furthermore, CO drastically decreased, TPR markedly increased, and BF to the heart, brain, intestine and skeletal muscle were decreased at 4 h relative to the readings in saline- or 1400 W-treated endotoxemic rats. Therefore, selective inhibition of iNOS by 1400 W restores MAP without compromising CO, but non-selective inhibition of NOS is detrimental at the late stage of septic shock.     

HAEMODYNAMIC AND HORMONAL EFFECTS OF N-NITRO-l-ARGININE, AN INHIBITOR OF NITRIC OXIDE BIOSYNTHESIS, IN SHEEP

1. The haemodynamic and hormonal responses to N-nitro-l-arginine (NOLA), a potent inhibitor of nitric oxide biosynthesis in endothelial cells, were investigated in conscious sheep. 2. Mean arterial blood pressure (MAP), heart rate (HR) and cardiac output by thermodilution (CO) were measured in four oophrectomized ewes. Two other ewes were surgically implanted with aortic electromagnetic flow probes and an indwelling carotid arterial line for monitoring CO and MAP over 40 h. 3. After a control period, NOLA (10 mg/kg) was injected intravenously and MAP, HR and CO monitored and blood samples taken at intervals over the following 24 h. 4. NOLA increased blood pressure within minutes, from 76 ± 4 to a maximum of 99 ± 4 mmHg (P<0.001) at 6 h after injection. It remained elevated 24 h after injection. CO and HR fell but these falls were not sustained longer than 6 h. Calculated total peripheral resistance increased to a maximum of 2 h, but had returned to control levels 24 h after injection. There were no significant changes in plasma concentrations of renin, atrial natriuretic factor, vasopressin, noradrenaline or endothelin during the first hour. 5. NOLA may be a useful tool in understanding the role of the endothelium and nitric oxide in the control of blood pressure.     

Effects of ethanol in acute carbon monoxide poisoning

The combined effects of ethyl alcohol (ETOH) intoxication and carbon monoxide (CO) poisoning were studied in the Levine-prepared rat. Infusion or injection of ETOH before and during 90 min of CO exposure to blood levels 2-4 times those considered legally drunk in humans, increased survival at 2400 ppm, and extended the tolerance time at 2400 ppm and 3000 ppm. CO exposure produced the usual hypothermia, hypotension and hemoconcentration; these responses were not altered by concurrent ETOH treatment. Blood ETOH concentration was increased in the presence of CO, and this was related to CO concentration. Although ETOH did not alter the average degree of hypoglycemia seen during the later stages of CO exposure, rats with the highest ETOH concentration tended to have the lowest blood glucose. ETOH increased the magnitude of the hyperglycemic rebound during recovery from exposure to both CO concentrations. Moreover, the magnitude of the recovery hyperglycemic rebound was directly related to the magnitude of the previous hypoglycemia, at both CO concentrations, with or without ETOH. Rats dying during exposure to both CO concentrations were severely hypoglycemic, whereas survivors maintained more or less normal blood glucose concentrations. The results suggest that the presence of ETOH during CO poisoning increases blood ETOH to higher than expected levels and provides a significant degree of survival protection.     

CARDIOVASCULAR HABITUATION TO EMOTIONAL STRESS IN LYON HYPERTENSIVE RATS

1. Intra-aortic blood pressure was recorded continuously in freely moving genetically hypertensive (LH), normotensive (LN) and low blood pressure (LL) rats of the Lyon strain during two 11 h periods (08:00-19:00 h). During the first period (control), the animals were left undisturbed and during the second period (stress), a jet of air was applied for 20 min every hour. Urine was collected simultaneously and analysed for its content in norepinephrine and epinephrine. 2. The first exposure to the stressor induced larger increases in blood pressure and heart rate in LH than in LN and LL rats. However blood pressure and heart rate responses to the 10 following stressors decreased in LH rats while they remained stable in LN and LL animals. 3. Repeated stress exposure induced significant increases in epinephrine excretion in both LN and LL but not in LH rats. 4. It is concluded that LH rats exhibit marked cardiovascular habituation to repeated stress. Taken together with the lack of stress-induced sympathoadrenal activation, this suggests a reduced level of emotional responsiveness in Lyon hypertensive rats.     

Effects of chemical sympathectomy with 6-hydroxydopamine on cardiac output and its distribution in the rat

Cardiac output and its regional distribution were determined with radioactive microspheres in pentobarbitone anaesthetised rats 16 h and 5 days after sympathectomy with 6-hydroxydopamine (150 mg/kg i.p. over 24 h). Distribution was not different at either time in sympathectomised animals compared to controls given i.p. saline/ascorbic acid. Cardiac output was 12% greater 16 h after sympathectomy than in the controls but heart rate and blood pressure were 20% lower. Stroke volume was 43% greater in animals given 6-hydroxydopamine and total peripheral resistance 29% lower than in sham-sympathectomised rats. Five days after sympathectomy, blood pressure and heart rate were still lower in sympathectomised rats, but cardiac output and total peripheral resistance were not significantly different from control. It is concluded that basal sympathetic tone does not determine the distribution of cardiac output at rest and that its primary effect on the heart is to maintain heart rate rather than contractility.     

Effect of intravenous pimobendan (UDCG 115 BS) on hemodynamics and left ventricular volumes in idiopathic dilative cardiomyopathy

Acute cardiovascular effects of 5 mg (group I, n = 6) and 10 mg (group II, n = 6) intravenous pimobendan (UDCG 115 BS) were studied by right and left heart catheterizations in patients suffering from idiopathic dilative cardiomyopathy (NYHA II and III). Before and 2.5 h after application of pimobendan, left ventricular volumes and left ventricular dP/dtmax were evaluated by left heart catheterization. Right atrial pressure (RAP), pulmonary capillary wedge pressure (PCP), cardiac output (CO), heart rate (HR), and sytemic blood pressure (BP) were assessed before and 2.5, 4, and 6 h after administration of pimobendan. PCP was reduced from 12.2 +/- 7.5 to 8.3 +/- 7.1 mm Hg (p less than 0.05) by 5 mg pimobendan, and from 18.3 +/- 6.2 to 6.2 +/- 3.4 mm Hg (p less than 0.005) by 10 mg pimobendan. Reduction of RAP was only significant in group II (6.2 +/- 3.2 to 1.2 +/- 0.9 mm Hg; p less than 0.05). In contrast to other hemodynamic parameters, the significant increase of CO exhibited no dose dependency. Only at 10 mg pimobendan induced a temporary reduction of mean arterial blood pressure (MAP). An increase in HR occurred only in group I and was merely transient. Left ventricular end-diastolic (EDVI) and end-systolic volume (ESVI) indices were clearly reduced by 5 mg, as well as by 10 mg pimobendan. However, a significant rise of left ventricular ejection fraction (EF) only occurred in group II. On the other hand, left ventricular dP/dtmax was increased significantly in both groups. No adverse effects were noted during acute administration of pimobendan.(ABSTRACT TRUNCATED AT 250 WORDS)     

Hypotensive effects of diltiazem hydrochloride in the normotensive, spontaneously hypertensive and renal hypertensive rats (author's transl)

In conscious and anesthetized normotensive rats, intravenous administration of diltiazem (0.1--3 mg/kg) produced a dose-related decrease in blood pressure. Administration of diltiazem (1--50 mg/kg) into the duodenum of anesthetized rats also reduced the blood pressure in a dose related manner. In parallel with the change in blood pressure, the heart rate increased in conscious rats and decreased in anesthetized animals. Such an increase in the heart rate was suppressed by pretreatment with propranolol. Similarly, in conscious spontaneously hypertensive rats (SHR), diltiazem dose-dependently decreased the blood pressure and increased the heart rate after intravenous administration (0.03--1 mg/kg). Oral administration of diltiazem (100 mg/kg) also reduced the blood pressure of SHR. In addition, the progressive increase in blood pressure in young SHR was significantly suppressed by chronic oral administration of diltiazem (30 mg/kg). The blood pressure in conscious renal hypertensive rats was also decreased with diltiazem (50 mg/kg p.o.). On the other hand, it was demonstrated that the pressor responses to norepinephrine and angiotensin II in the anesthetized normotensive rats were non-competitively inhibited by intravenous administration of diltiazem at a dose which had no effect on the blood pressure.     

AN ANTIHYPERTENSIVE ACTION OF PROPRANOLOL IN DOCA/SALT-TREATED RATS

SUMMARY 1. The cardiovascular effects of acute and long-term (4–7 weeks) treatment with propranolol and guanethidine were observed in conscious, DOCA/salt-treated hypertensive rats. 2. During long-term treatment with a low dose of propranolol (0.2 mg/kg, subcutaneously, twice daily), the blood pressure is reduced to normotensive levels. 3. The subcutaneous injection of 0.2 mg/kg of propranolol lowers blood pressure and heart rate for 2–4 h at the start of long-term treatment, but these acute effects become less as treatment continues. 4. Long-term treatment with a high dose of propranolol (5 mg/kg, subcutaneously, twice daily) reduces heart rate but not blood pressure. 5. The acute effects of subcutaneous injection of 5 mg/kg of propranolol are a rise in blood pressure and a fall in heart rate; these effects are maintained throughout the period of long-term treatment. 6. Guanethidine (5 mg/kg, subcutaneously, once daily) produces a gradual fall in blood pressure. The acute depressor effect becomes less as treatment continues. 7. Observations were made on the responses to noradrenaline injections and thoraco-lumbar stimulation in pithed rats, pretreated 1 h beforehand with propranolol (0.2 or 5 mg/kg) or guanethidine (5 mg/kg). 8. Pressor responses to noradrenaline are slightly increased by all three pretreatments; the tachycardia produced by noradrenaline is increased by guanethidine and reduced by propranolol. 9. The pressor response to thoraco-lumbar stimulation is abolished by guanethidine and not affected by either dose of propranolol; the tachycardia is reduced by guanethidine and the high dose of propranolol (5 mg/kg) but not by the low dose. 10. The antihypertensive action of propranolol in DOCA/salt-treated rats can not be attributed to adrenergic neurone blockade or to a non-specific depressant effect, and does not appear to be due to a dose-dependent antagonistic effect on cardiac β-receptors. It is suggested that it is due to a central impairment of sympathetic activity.     

Lipotab, a polyherbal formulation, attenuates isoprenaline-induced left ventricular remodeling and heart failure in rats

The present study was designed to evaluate the effect of Lipotab, a polyherbal formulation on isoprenaline (ISO)-induced left ventricular (LV) remodeling and heart failure (HF). HF in Wistar albino rats was produced by two consecutive injections of ISO (150 mg/kg, s.c.) at an interval of 24 h. After 15 days of 2nd ISO injection, HF was indicated by rise in left ventricular end-diastolic pressure (LVEDP), lowering of maximal rate of rise of LV pressure divided by LV systolic pressure (LVdP/dtmax/P; cardiac contractility) and maximal rate of fall of LV pressure (LVdP/dtmin), fall in cardiac output (CO), cardiac hypertrophy (heart to body weight ratio) and histopathological changes in heart. HF rats showed a significant increase in serum malondialdehyde (MDA), reduction in serum reduced glutathione (GSH) content and a significant rise in tumor necrosis factor-α (TNF-α) level. Prior treatment with Lipotab (275 mg/kg/day, p.o.) was significantly able to preserve LV functions. Post treatment with Lipotab (275 mg/kg/day, p.o.) also improved LV functions but did not prevent the fall in LVdP/ dtmin, CO and cardiac hypertrophy. Lipotab significantly prevented fall in GSH levels, rise in level of MDA and TNF-α in serum of HF rats. Histopathological examination confirmed hemodynamic and biochemical findings. Results of the present study indicate that Lipotab prevents ISO-induced LV remodeling and consequent HF in rats through its antioxidant and anti-inflammatory activity.     

Pinacidil,a new vasodilator: Pharmacokinetics and pharmacodynamics of a new retarded release tablet in essential hypertension

In an open study increasing doses of a retarded tablet formulation of pinacidil were given twice daily for four weeks to 9 patients with untreated essential hypertension (WHO I-II). In all patients a decrease in diastolic blood pressure to below 100 mmHg, or a fall exceeding 15 mmHg, was obtained 2 h after tablet intake (p less than 0.02), but in only two patients was the effect maintained after 10 hours (n.s.). At a mean serum concentration of 100 ng/ml 2 h after pinacidil 30 mg, the mean blood pressure had decreased by 14 and 12.7 mmHg in the supine and erect positions, respectively (p less than 0.05). In contrast, mean blood pressure 10 h after the same dose was unchanged, when the mean serum concentration was 47.5 ng/ml. No change in heart rate was observed. Pharmacokinetic and pharmacodynamic investigations showed a tendency towards a more gradual and longer lasting antihypertensive effect and serum concentration-time curve after the retarded tablet than the previous tablet. Pinacidil 40 mg in the retarded tablet reduced mean blood pressure and increased heart rate for at least 8 h. There was a linear correlation between the serum concentration and the change in mean blood pressure, and between the changes in mean blood pressure and in heart rate. There was no indication of tachyphylaxis. A serum level of 50 ng/ml of pinacidil appeared to be the minimal effective concentration. The side effect consisted of fluid retention, and the body weight increased by 1.0 kg (p less than 0.05); four patients complained of oedema.(ABSTRACT TRUNCATED AT 250 WORDS)