Effect of folic acid on isoprenaline-induced myocardial injury in rats

Background

Isoprenaline (ISO), a synthetic catecholamine and a β-adrenoceptor agonist, is widely used to develop an experimental model of myocardial injury (MI) in rats. The leading hypothesis for ISO-induced MI in rats is that it results from catecholamine overstimulation, oxidative stress, inflammatory responses, and development of cardiomyopathy during ISO administration. Folic acid (FA) reduces oxidative stress, improves endothelial function and prevents apoptosis, thereby contributing to cardiovascular protection. This study aimed to investigate the potentially protective effect of FA pretreatment on ISO-induced MI in rats.

Methods

For 7 days, adult male Wistar albino rats were pretreated with 5 mg/kg/day of FA. On the sixth and seventh days, MI in rats was induced by administering 85 mg/kg/day of ISO. Prooxidant markers in plasma samples, antioxidant capacity in erythrocyte lysates, cardiac damage markers, lipid profile, electrocardiography (ECG) and histopathological analysis were evaluated.

Results

FA pretreatment significantly alleviated changes induced by ISO; it decreased the homocysteine and high-sensitivity troponin I level. FA moderately decreased the reactive oxygen species (ROS) levels (superoxide anion radical, hydrogen peroxide and thiobarbituric acid reactive substances) and improved the antioxidant activities of catalase, superoxide dismutase and reduced glutathione. ISO reduced the nitrite level and FA significantly alleviated this change.

Conclusion

It can be concluded that FA, as a mild antioxidant, could be an appropriate cardioprotective substance in the rat model of ISO-induced MI.

Comparative Efficacy of High-Dose Dexamethasone Versus Methylprednisolone in Coronavirus Disease 2019 (COVID-19)-Associated Acute Respiratory Distress Syndrome

OBJECTIVE

This retrospective (matched paired) clinical trial aimed to compare the efficacy of dexamethasone vs. methylprednisolone at equipotent (high) doses in patients with coronavirus disease 2019 (COVID-19)-associated acute respiratory distress syndrome (ARDS).

METHODS

A total of 347 patients with moderate and severe COVID-19-associated ARDS were administered either a high (equipotent) dose of dexamethasone (32 mg) or methylprednisolone (180 mg) for a duration of up to 10 days. All participants received the standard of care for critically ill COVID-19 patients.

RESULTS

The primary outcomes included length of stay in the ICU, ICU mortality, and discharge from the hospital. Based on the obtained results, a tendency towards more favorable clinical outcomes concerning the length of stay in the ICU (in the group of patients treated with non-invasive mechanical ventilation (NIV), p<0.05), ICU mortality, and discharge from the hospital (in the group of patients who were intubated, p<0.05) in patients receiving the high dose of dexamethasone compared to those receiving methylprednisolone was observed.

CONCLUSION

It appears that severe cases of COVID-19, especially intubated ones, treated with high doses of dexamethasone have a more favorable clinical outcome than the use of equipotent doses of methylprednisolone. However, larger multicenter studies are needed to validate our observations.

Analysis of redox status and HDL subclasses in patients with lymphoma and the associations with FDG-PET/CT findings

Newer research points to alterations in the plasma redox status and the HDL subclass distributions in cancer. We aimed to assess the redox status and the HDL subclass distributions, lipids, and inflammatory markers in lymphoma patients in order to determine whether they were correlated with changes in FDG-PET/CT scans. At the beginning of this study, redox status, HDL subclasses, lipids, and inflammation biomarkers were determined in 58 patients with lymphoma (Hodgkin lymphoma, n=11 and non-Hodgkin lymphoma, n=47), and these same measurements were reassessed during their ensuing treatment (in 25 patients). Initially, the total oxidation status (TOS), the prooxidant-antioxidant balance (PAB), the OS index (OSI), the total protein sulfhydryl groups (SH-groups), and the advanced oxidation protein products (AOPP) were significantly higher in lymphoma patients as compared to healthy subjects, but the total antioxidant status (TAS) was significantly reduced. The PAB had a strong correlation with the CRP and interleukin-6 (rho=0.726, p<0.001; rho=0.386, p=0.003). The correlations between these parameters and the maximum standardized uptake values (SUVmax) were: PAB, rho=0.335 and p=0.010; SH-groups, rho=0.265 and p=0.044; CRP, rho=0.391 and p=0.002; HDL3b, rho=0.283 and p=0.031; HDL2b, rho= -0.294 and p=0.025; and HDL size, rho= -0.295 and p=0.024. The reductions in SUVmax between two follow-up points were associated with increases in the OSI, TOS, and SH-groups, as well as a reduction in the PAB and TAS. In conclusion, the redox parameters in patients with lymphoma were consistent with FDG-PET/CT findings. Targeting the redox status parameters and the HDL subclasses could be potential strategies in the molecular fight against lymphoma.

GPX3 rs8177412 Polymorphism Modifies Risk of Upper Urothelial Tumors in Patients with Balkan Endemic Nephropathy

Current data suggest that aristolochic acid (AA) exposure is a putative cause of Balkan endemic nephropathy (BEN), a chronic kidney disease strongly associated with upper tract urothelial carcinoma. The cellular metabolism of AA is associated with the production of reactive oxygen species, resulting in oxidative distress. Purpose: Therefore, the aim of this study was to analyze individual, combined and cumulative effect of antioxidant gene polymorphisms (Nrf2 rs6721961, KEAP1 rs1048290, GSTP1AB rs1695, GSTP1CD rs1138272, GPX3 rs8177412 and MDR1 rs1045642), as well as GSTP1ABCD haplotypes with the risk for BEN development and associated urothelial cell carcinoma in 209 BEN patients and 140 controls from endemic areas. Experimental method: Genotyping was performed using polymerase chain reaction (PCR) and PCR with confronting two-pair primers (PCR-CTTP) methods. Results: We found that female patients carrying both variant GPX3 rs8177412 and MDR1 rs1045642 genotypes in combination exhibited significant risk towards BEN (OR 1 = 3.34, 95% CI = 1.16-9.60, p = 0.025; OR 2 = 3.79, 95% CI = 1.27-11.24, p = 0.016). Moreover, significant association was determined between GPX3rs8174412 polymorphism and risk for urothelial carcinoma. Carriers of variant GPX3*TC + CC genotype were at eight-fold increased risk of BEN-associated urothelial tumors development. There was no individual or combined impact on BEN development and BEN-associated tumors among all examined polymorphisms. The haplotype consisting of variant alleles for both polymorphisms G and T was associated with 1.6-fold increased risk although statistically insignificant (OR = 1.64; 95% CI = 0.75-3.58; p = 0.21). Conclusions: Regarding GPX3 rs8177412 polymorphism, the gene variant that confers lower expression is associated with significant increase in upper urothelial carcinoma risk. Therefore, BEN patients carrying variant GPX3 genotype should be more frequently monitored for possible upper tract urothelial carcinoma development.

Boosting ICU capacity during the COVID-19 pandemic in the western Balkan region, The Republic of Srpska experience

Background

Response to the outbreak of poliomyelitis in mid-1950 led to recognition and consequent development of critical care. Seventy years later the humankind was struck by COVID-19, another major challenge for critical care medicine which was especially big in Low-Resources-Settings where more than two thirds of the world population live, including the population of the Republic of Srpska (RS).

Design and methods

The main aim was to show an overview of all interventions in order to boost hospitals' capacities to the level which is sufficient to manage high amount of critically ill COVID-19 patients in the RS. A before-after cohort study design was conducted to evaluate the effects of interventions for increase in preparedness and capacity of ICUs for admission and treatment of COVID-19 critically ill patients in nine hospitals in the RS. Results: Following interventions, the biggest and university affiliated hospital in the RS has increased ICU capacities: total number of ICU beds increased by 38% and number of ventilators by 114%. Availability of machines for veno-venous extracorporeal membrane oxygenation (vvECMO) increased by 100%. Number of doctors who were involved in treatment of critically ill patients increased by 47% and nurse/patient's ratio reached 1:2.5. Similarly, all other hospitals experienced boosting of ICU beds by 189% and ventilators by 373% while number of doctors increased by 108% and nurse/patient's ratio reached 1:4.

Conclusion

All interventions implemented during COVID-19 pandemic outbreak in the RS resulted in increasing capacity for treatment of critically ill patients, but the education of health care professionals was identified as the most important conducted intervention.

Dynamic changes in coagulation, hematological and biochemical parameters as predictors of mortality in critically ill COVID-19 patients: A prospective observational study

INTRODUCTION

This study was created to analyze dynamic alterations in coagulation, hematological and biochemical parameters and their association with mortality of COVID-19 patients. To identify the most sensitive biomarkers as predictors of mortality more research is required.

METHODS

The present study was a prospective, one-year-long observational study conducted on all critically ill, COVID-19 patients with respiratory failure. The following data were collected: demographic and clinical characteristics of the study population, comorbidities, coagulation, biochemical and hematological parameters. The primary outcome was the proportion of patients who died.

RESULTS

91 patients with median age 60 (50-67), 76.9% male, met the acute respiratory distress syndrome criteria. It was tested whether dynamic change (delta-Δ) of parameters that were found to be predictors of mortality is independently associated with poor outcome. Adjusted (multivariate) analysis was used, where tested parameters were corrected for basic and clinical patients characteristics. The only inflammatory parameter which dynamic change had statistically significant odds ratio was ΔCRP (p < 0.005), while among coagulation parameters statistically significant OR was found for Δ fibrinogen (p < 0.005) in predicting mortality.

CONCLUSION

Monitoring of coagulation, hematological and biochemical parameters abnormalities and their dynamical changes can potentially improve management and predict mortality in critically ill COVID -19 patients.

The role of high-income countries in the establishment and development of modern critical care in low resource settings: A Slovenian model

BACKGROUND

Critical care medicine is a young branch of medicine, of which the development was much faster in High Income Countries (HICs) than in Low Resources Settings (LRS). Slovenia, as one of the successor states of former Yugoslavia, passed the process of transition and joined the European Union successfully. On the contrary, Bosnia and Herzegovina (B&H) went through the extremely difficult process of transition (four years of civil war), which left a deep scar to the healthcare system, including critical care medicine.

OBJECTIVE

To examine the impact of HICs on the development of critical care in LRS.

METHOD

This review examined the process of growing up the first modern Medical Intensive Care Unit (MICU) in the Republic of Srpska.

RESULTS

The five-year process of transferring critical care knowledge from Slovenia to the health care system of Republic of Srpska has contributed to the existence of modern and state of the art MICU with tremendous social effects.

CONCLUSION

The model of using the impact of HICs for improving critical care in LRS can be extrapolated to other similar settings.

Characteristics and Outcomes of Critically Ill Pregnant/Postpartum Women with COVID-19 Pneumonia in Western Balkans, The Republic of Srpska Report

Background and Objectives: Coronavirus disease 2019 (COVID-19) is a novel infectious disease that has spread worldwide. As of 5 March 2020, the COVID-19 pandemic has resulted in approximately 111,767 cases and 6338 deaths in the Republic of Srpska and 375,554 cases and 15,718 deaths in Bosnia and Herzegovina. Our objective in the present study was to determine the characteristics and outcomes of critically ill pregnant/postpartum women with COVID-19 in the Republic of Srpska. Materials and Methods: The retrospective observational study of prospectively collected data included all critically ill pregnant/postpartum women with COVID-19 in a university-affiliated hospital between 1 April 2020 and 1 April 2022. Infection was confirmed by real-time reverse transcriptase polymerase chain reaction (RT-PCR) from nasopharyngeal swab specimens and respiratory secretions. Patients' demographics, clinical and laboratory data, pharmacotherapy, and neonatal outcomes were analysed. Results: Out of the 153 registered pregnant women with COVID-19 treated at the gynaecology department of the University Clinical Centre of the Republic of Srpska, 19 (12.41%) critically ill pregnant/postpartum women (median age of 36 (IQR, 29-38) years) were admitted to the medical intensive care unit (MICU). The mortality rate was 21.05% (four patients) during the study period. Of all patients (19), 14 gave birth (73.68%), and 4 (21.05%) were treated with veno-venous extracorporeal membrane oxygenation (vvECMO). Conclusions: Fourteen infants were born prematurely and none of them died during hospitalisation. A high mortality rate was detected among the critically ill pregnant/postpartum patients treated with mechanical ventilation and vvECMO in the MICU. The preterm birth rate was high in patients who required a higher level of life support (vvECMO and ventilatory support).

Homocysteine, Vitamins B6 and Folic Acid in Experimental Models of Myocardial Infarction and Heart Failure—How Strong Is That Link?

Cardiovascular diseases are the leading cause of death and the main cause of disability. In the last decade, homocysteine has been found to be a risk factor or a marker for cardiovascular diseases, including myocardial infarction (MI) and heart failure (HF). There are indications that vitamin B6 plays a significant role in the process of transsulfuration in homocysteine metabolism, specifically, in a part of the reaction in which homocysteine transfers a sulfhydryl group to serine to form α-ketobutyrate and cysteine. Therefore, an elevated homocysteine concentration (hyperhomocysteinemia) could be a consequence of vitamin B6 and/or folate deficiency. Hyperhomocysteinemia in turn could damage the endothelium and the blood vessel wall and induce worsening of atherosclerotic process, having a negative impact on the mechanisms underlying MI and HF, such as oxidative stress, inflammation, and altered function of gasotransmitters. Given the importance of the vitamin B6 in homocysteine metabolism, in this paper, we review its role in reducing oxidative stress and inflammation, influencing the functions of gasotransmitters, and improving vasodilatation and coronary flow in animal models of MI and HF.

Mechanism and Clinical Importance of Respiratory Failure Induced by Anticholinesterases

Respiratory failure is the predominant cause of death in humans and animals poisoned with anticholinesterases. Organophosphorus and carbamate anticholinesterases inhibit acetylcholinesterase irreversibly and reversibly, respectively. Some of them contain a quaternary atom that makes them lipophobic, limiting their action at the periphery, i.e. outside the central nervous system. They impair respiratory function primarily by inducing a desensitization block of nicotinic receptors in the neuromuscular synapse. Lipophilic anticholinesterases inhibit the acetylcholinesterase both in the brain and in other tissues, including respiratory muscles. Their doses needed for cessation of central respiratory drive are significantly less than doses needed for paralysis of the neuromuscular transmission. Antagonist of muscarinic receptors atropine blocks both the central and peripheral muscarinic receptors and effectively antagonizes the central respiratory depression produced by anticholinesterases. To manage the peripheral nicotinic receptor hyperstimulation phenomena, oximes as acetylcholinesterase reactivators are used. Addition of diazepam is useful for treatment of seizures, since they are cholinergic only in their initial phase and can contribute to the occurrence of central respiratory depression. Possible involvement of central nicotinic receptors as well as the other neurotransmitter systems – glutamatergic, opioidergic – necessitates further research of additional antidotes.

Risk factor control and adherence to treatment in patients with coronary heart disease in the Republic of Srpska, Bosnia and Herzegovina in 2005-2006

INTRODUCTION

European treatment guidelines in persons with known coronary heart disease (CHD) focus on adherence to antiplatelet therapy, β-blockers, ACE/ARBs, and lipid-lowering agents, with goals for blood pressure (BP) of < 140/90 mm Hg and LDL cholesterol of < 3.0 mmol/l. Data on adherence to these measures in Eastern Europe are limited.

MATERIAL AND METHODS

The Third Republic of Srpska, Bosnia and Herzegovina, Coronary Prevention Study (ROSCOPS III) was conducted in 2005-2006 at 10 primary heath care centres in 601 patients (36% female, mean age 55 years) with CHD including acute myocardial infarction or ischaemia, coronary artery bypass graft, or angioplasty who were examined and interviewed at least 6 months after the event. We examined the proportion of subjects on recommended treatments and at goal for BP, LDL-C, and non-smoking.

RESULTS

The proportion of subjects on recommended treatments included 61% for β-blockers, 79% for ACE/ARBs, 63% for lipid-lowering agents and 74% for antiplatelet therapy. Only 30% of subjects were on all four of these treatments. 59% of subjects had BP at goal of < 140/90 mm Hg and 33% were controlled to < 130/80 mm Hg, 41% for LDL-C, and 88% were non-smokers. Improvements were seen in lipid-lowering and ACE/ARB drug use and non-smoking status from an earlier survey (ROSCOPS II) in 2002-2003.

CONCLUSIONS

Our data show, despite improvement over recent years, that many persons with CHD in the Republic of Srpska, Bosnia and Herzegovina are neither on recommended treatments nor at target for BP and/or LDL-C. Improved efforts targeted at both physicians and patients to address these issues are needed.

Hydrogen peroxide affects contractile activity and anti-oxidant enzymes in rat uterus

BACKGROUND AND PURPOSE

The effects of hydrogen peroxide (H(2)O(2)) on uterine smooth muscle are not well studied. We have investigated the effect and the mechanism of action of exogenous hydrogen peroxide on rat uteri contractile activity [spontaneous and calcium ion (Ca(2+))-induced] and the effect of such treatment on anti-oxidative enzyme activities.

EXPERIMENTAL APPROACH

Uteri were isolated from virgin Wistar rats and suspended in an organ bath. Uteri were allowed to contract spontaneously or in the presence of Ca(2+) (6 mM) and treated with H(2)O(2) (2 microM-3 mM) over 2 h. Anti-oxidative enzyme activities (manganese superoxide dismutase-MnSOD, copper-zinc superoxide dismutase-CuZnSOD, catalase-CAT, glutathione peroxidase-GSHPx and glutathione reductase-GR) in H(2)O(2)-treated uteri were compared with those in uteri immediately frozen after isolation or undergoing spontaneous or Ca(2+)-induced contractions, without treatment with H(2)O(2). The effect of inhibitors (propranolol, methylene blue, L-NAME, tetraethylamonium, glibenclamide and 4-aminopyridine) on H(2)O(2)-mediated relaxation was explored.

KEY RESULTS

H(2)O(2) caused concentration-dependent relaxation of both spontaneous and Ca(2+)-induced uterine contractions. After H(2)O(2) treatment, GSHPx and MnSOD activities were increased, while CuZnSOD and GR (In Ca(2+)-induced rat uteri) were decreased. N(omega)-nitro-L-arginine methyl ester antagonized the effect of H(2)O(2) on Ca(2+)-induced contractions. H(2)O(2)-induced relaxation was not affected by propranolol, potentiated by methylene blue and antagonized by tetraethylamonium, 4-aminopyridine and glibenclamide, with the last compound being the least effective.

CONCLUSIONS AND IMPLICATIONS

H(2)O(2) induced dose-dependent relaxation of isolated rat uteri mainly via changes in voltage-dependent potassium channels. Decreasing generation of reactive oxygen species by stimulation of anti-oxidative pathways may lead to new approaches to the management of dysfunctional uteri.

Seven decades of angiotensin (1939-2009)

Two research groups in both North and South America independently discovered that renin released a novel vasopressor agent. The Argentine group named it hypertensin, and called its plasma protein substrate hypertensinogen. The group from the United States named it angiotonin. In 1958, Braun Menendez and Irvine Page suggested that the peptide should be named angiotensin. The combined name eventually became commonly used to avoid linguistic confusion. Research scientists and physicians today acknowledge that studies of the renin-angiotensin system (RAS) have greatly improved our understanding of several diseases. Certainly, medical practice profited significantly from the synthesis and application of numerous pharmacological agents that antagonize either the biosynthesis or pharmacological responses of endogenously generated angiotensin II. Ultimately, discovery of the renin-angiotensin system led to many studies that resulted in therapies for vascular disease. This article briefly reviews research related to the discovery of angiotensin and indicates the importance of additional studies related to the RAS.

Probiotic Pre-treatment Reduces Gliclazide Permeation (ex vivo) in Healthy Rats but Increases It in Diabetic Rats to the Level Seen in Untreated Healthy Rats

Aim

To investigate the influence of probiotic pre-treatment on the permeation of the antidiabetic drug gliclazide in healthy and diabetic rats.

Methods

Wistar rats (age 2–3 months, weight 350 ± 50 g) were randomly allocated into one of 4 groups (N = 16 each group): healthy control, healthy probiotic, diabetic control, and diabetic probiotic. Probiotics (75 mg/kg, equal quantities of Lactobacillus acidophilus, Bifidobacterium lactis, and Lactobacillus rhamnosus) were administered twice a day for three days to the appropriate groups after diabetes had been induced with alloxan i.v. 30 mg/kg. Rats were sacrificed, ileal tissues mounted in Ussing chambers and gliclazide (200 µg/mL) was administered for the measurement of the mucosal to serosal absorption Jss^(MtoS) and serosal to mucosal secretion Jss^(StoM) of gliclazide.

Results

Treatment of healthy rats with probiotics reduced Jss^(MtoS) of gliclazide from 1.2 ± 0.3 to 0.3 ± 0.1 µg/min/cm² (P < 0.01) and increased Jss^(StoM)from 0.6 ± 0.1 to 1.4 ± 0.3 (P < 0.01) resulting in net secretion while, in diabetic tissues, treatment with probiotics increased both Jss^(MtoS) and Jss^(StoM)fluxes of gliclazide to the comparable levels of healthy tissues resulting in net absorption.

Discussion

In healthy rats, the reduction in Jss^(MtoS) after probiotics administration could be explained by the production of bacterial metabolites that upregulate the mucosal efflux drug transporters Mrp2 that control gliclazide transport. In diabetic rats, the restored fluxes of gliclazide after probiotic treatment, suggests the normalization of the functionality of the drug transporters resulting in a net absorption.

Conclusion

Probiotics may alter gliclazide transport across rat ileal tissue studied ex vivo.

Dominant antagonistic action of alpha 2-adrenoceptor agonists on alpha 1-agonist-induced vasoconstriction

The action of clonidine and xylazine to suppress constrictor responses to norepinephrine (NE) and phenylephrine was analysed in isolated, perfused dog and monkey lingual arteries. In both kinds of arteries, alpha 1-adrenoceptor agonists, NE and phenylephrine induced strong vasoconstrictor responses, whereas alpha 2-adrenoceptor agonists, clonidine and xylazine, produced only a slight but long-lasting increase in perfusion pressure. Pretreatment with bolus injections of 300 micrograms clonidine or 1000 micrograms xylazine caused a significant inhibition of vasoconstrictor responses to NE and phenylephrine and shifted the dose-responses curves to the right. Clonidine induced a more potent inhibition than did xylazine. However, neither clonidine nor xylazine pretreatment inhibited 5-HT- and KCl-induced vasoconstriction. In preparations preconstricted with phenylephrine, clonidine and xylazine induced vasodilatation dose relatedly, but in preparations preconstricted with prostaglandin F2 alpha (PGF2 alpha), clonidine and xylazine never induced vasodilatation but only vasoconstriction. The vasoconstrictor effect of clonidine was readily blocked by bunazosin (an alpha 1-adrenoceptor antagonist), but was not affected by midaglizole (an alpha 2-antagonist). It was now demonstrated that alpha 2-agonists act as partial agonists on alpha 1-adrenoceptors when added alone but antagonized alpha 1 activation by alpha 1-agonists, suggesting that alpha 2-agonists have a high affinity for alpha 1-adrenoceptors in isolated lingual arteries.

Pharmacological properties of α1-adrenoceptor-mediated vasoconstrictions in dog and monkey lingual arteries: Evidence for subtypes of α1-adrenoceptors

We examined whether alpha 1-adrenoceptor-mediated vasoconstrictions were due to extra- or intracellular Ca2+ movements, and whether they were subdivided into alpha 1-adrenoceptor subtypes in dog and monkey lingual arteries. The NE-induced vasoconstriction in dog lingual arteries was mostly dependent on Ca2+ influx from the extracellular space, since it was readily blocked by a Ca2+ entry blocker, diltiazem, and the NE-induced response was attenuated approximately 90% in Ca(2+)-free solution. On the other hand, in monkey lingual arteries, diltiazem failed to depress the NE-induced dose-response curve, and the response was attenuated only about 60% in Ca(2+)-free solution. The vasoconstrictor response to 10mg caffeine in normal KHS was almost the same as that to 1 micrograms NE in Ca(2+)-free solution in both kinds of arteries, suggesting that alpha 1-adrenoceptor-mediating vasoconstrictions require a different number of sources of Ca2+ in different blood vessels. Pretreatment of preparations with CEC (an alpha 1B-antagonist) significantly suppressed and shifted the dose-response curve for NE to the right in monkey lingual arteries, but it had no significant effect in dog lingual arteries. However, WB4101 (an alpha 1A-antagonist) showed almost the same potency in blocking vasoconstrictor responses as bunazosin in both kinds of arteries (the pA2 values were not significantly different). Moreover, responses to ME (an alpha 1A-agonist) were blocked by diltiazem as well as by bunazosin and WB4101, while CEC had no blocking effect on ME-induced responses.(ABSTRACT TRUNCATED AT 250 WORDS)

Pharmacological features of vascular responses of isolated dog and monkey lingual arteries to vasoactive substances

Using a perfusion technique of isolated vessels, vasoconstrictor responses to alpha-adrenoceptor agonists (norepinephrine [NE], phenylephrine [PE], clonidine, xylazine and tyramine) and KCl were investigated in isolated, perfused dog and monkey lingual arteries. A stainless steel cannula was inserted into the lingual artery segment and perfused with Krebs-Henseleit solution at a constant flow rate. In dog lingual arteries, the agonists induced vasoconstrictions with the following order of potency: NE greater than PE greater than tyramine much greater than clonidine greater than xylazine greater than KCl. In monkey preparations, the order was NE greater than PE much greater than clonidine greater than or equal to tyramine greater than xylazine greater than KCl. In both preparations, NE- and PE-induced constrictions were blocked by bunazosin (an alpha-1 adrenoceptor antagonist), but not influenced by midaglizole (a potent alpha-2 antagonist). Diltiazem (a Ca entry blocker) significantly attenuated NE-induced vasoconstrictions in dog lingual arteries, but did not significantly influence these in monkey preparations. These results suggest that: [1] these arteries contain mostly alpha-1 but scarcely any alpha-2 adrenoceptors; [2] in dog preparations, tyramine induced a marked vasoconstriction which may contribute to investigation on the mechanisms of catecholamine releases from sympathetic nerve terminals; and [3] different blocking effects of diltiazem may indicate that extracellular Ca++ influx may have varying degrees of importance in alpha-1 adrenoreceptor-mediated constrictions in different species, although participation of an intracellular mechanism might not be ruled out.