Alteration in cardiac uncoupling proteins and eNOS gene expression following high-intensity interval training in favor of increasing mechanical efficiency

OBJECTIVES

High-intensity interval training (HIIT) increases energy expenditure and mechanical energy efficiency. Although both uncoupling proteins (UCPs) and endothelial nitric oxide synthase (eNOS) affect the mechanical efficiency and antioxidant capacity, their effects are inverse. The aim of this study was to determine whether the alterations of cardiac UCP2, UCP3, and eNOS mRNA expression following HIIT are in favor of increased mechanical efficiency or decreased oxidative stress.

MATERIALS AND METHODS

Wistar rats were divided into five groups: control group (n=12), HIIT for an acute bout (AT1), short term HIIT for 3 and 5 sessions (ST3 and ST5), long-term training for 8 weeks (LT) (6 in each group). The rats of the training groups were made to run on a treadmill for 60 min in three stages: 6 min running for warm-up, 7 intervals of 7 min running on treadmill with a slope of 5° to 20° (4 min with an intensity of 80-110% VO2max and 3 min at 50-60% VO2max), and 5-min running for cool-down. The control group did not participate in any exercise program. Rats were sacrificed and the hearts were extracted to analyze the levels of UCP2, UCP3 and eNOS mRNA by RT-PCR.

RESULTS

UCP3 expression was increased significantly following an acute training bout. Repeated HIIT for 8 weeks resulted in a significant decrease in UCPs mRNA and a significant increase in eNOS expression in cardiac muscle.

CONCLUSION

This study indicates that Long term HIIT through decreasing UCPs mRNA and increasing eNOS mRNA expression may enhance energy efficiency and physical performance.

The effect of high intensity interval training on cardioprotection against ischemia-reperfusion injury in wistar rats

The aims of the present study were to determine whether short term high intensity interval training (HIIT) could protect the heart against ischemia reperfusion (IR) injury; and if so, to evaluate how long the exercise-associated protection can be lasted. Sixty-three rats were randomly assigned into sedentary (n = 15), sham (n = 7), and exercise groups (n = 41). Rats in the exercise groups performed 5 consecutive days of HIIT on treadmill: 5 min warm up with 50 % VO₂max, 6×2 min with 95-105 % VO₂max (about 40 to 45 m/min), 5×2 min recovery with 65-75 % VO₂max (about 28 to 32 m/min), and 3 min cool down with 50 % VO₂max, all at 0 % grade. Animals exposed to an in vivo cardiac IR surgery, performed at days 1, 7, and 14 following the final exercise session. Ischemia-induced arrhythmias, myocardial infarct size (IS), plasma lactate dehydrogenase (LDH) and creatine kinase (CK) activities were measured in all animals. Compared to sedentary rats, exercised animals sustained less IR injury as evidenced by a lower size of infarction and lower levels of LDH and CK at day one and day 7 post exercise. In comparison of sedentary group, IS significantly decreased in EX-IR1 and EX-IR7 groups (50 and 35 %, respectively), but not in EX-IR14 group (19 %). The exercise-induced cardioprotection disappeared 14 days following exercise cessation. There were no significant changes in ischemia-induced arrhythmia between exercised and sedentary rats. The results clearly demonstrate that HIIT protects the heart against myocardial IR injury. This protective effect can be sustained for at least one week following the cessation of the training.

Influence of ramiprilat and losartan on ischemia reperfusion injury in rat hearts

Hypothesis/introduction: Our aim was to investigate whether a non-hypotensive dose of ramiprilat and losartan has myocardial protective effects during myocardial ischemia/reperfusion in vivo.

Materials and methods: Three groups of rats were given 10 mg/kg per day of losartan for one (L-1W), four (L-4W) or 10 (L-10W) weeks. Another three groups were given 50 µg/kg per day of ramiprilat for one (R-1W), four (R-4W) or 10 (R-10W) weeks. The animals underwent 30 min of left anterior descending artery occlusion and subsequent reperfusion for 120 min.

Results: Myocardial infarct size (IS) was reduced in R-1W (28.4 ± 6.3%, p < 0.001), R-4W (27.8 ± 7.4, p < 0.001), L-4W (31.8 ± 6%, p < 0.05) and L-10W (25.3 ± 5.7, p < 0.001) groups compared with a saline group (48.3 ± 7.8%). A significant reduction in the number of ventricular ectopic beats (VEBs) was noted in groups R-1W (209 ± 41, p < 0.01), R-4W (176 ± 39, p < 0.01), L-4W (215 ± 52, p < 0.05) and L-10W (191 ± 61, p < 0.01 vs. saline 329 ± 48). The incidence of irreversible ventricular fibrillation (VF) and mortality were decreased significantly only in L-10W group.

There were no significant decreases in episodes of VT, the incidence of irreversible VF and mortality in all of the groups treated with ramiprilat.

Conclusion: These data indicate that losartan and ramiprilat protect the heart against ischemia/reperfusion injury independently of their hemodynamic effects but in a time-dependent manner.

Dietary virgin olive oil reduces blood brain barrier permeability, brain edema, and brain injury in rats subjected to ischemia-reperfusion

Recent studies suggest that dietary virgin olive oil (VOO) reduces hypoxia-reoxygenation injury in rat brain slices. We sought to extend these observations in an in vivo study of rat cerebral ischemia-reperfusion injury. Four groups, each consisting of 18 Wistar rats, were studied. One group (control) received saline, while three treatment groups received oral VOO (0.25, 0.5, and 0.75 mL/kg/day, respectively). After 30 days, blood lipid profiles were determined, before a 60-min period of middle cerebral artery occlusion (MCAO). After 24-h reperfusion, neurological deficit scores, infarct volume, brain edema, and blood brain barrier permeability were each assessed in subgroups of six animals drawn from each main group. VOO reduced the LDL/HDL ratio in doses of 0.25, 0.5, and 0.75 mL/kg/day in comparison to the control group (p < 0.05), and offered cerebroprotection from ischemia-reperfusion. For controls vs. doses of 0.25 vs. 0.5 vs. 0.75 mL/kg/day, attenuated corrected infarct volumes were 207.82 ± 34.29 vs. 206.41 ± 26.23 vs. 124.21 ± 14.73 vs. 108.46 ± 31.63 mm³; brain water content of the infarcted hemisphere was 82 ±± 0.25 vs. 81.5 ± 0.56 vs. 80.5 ± 0.22 vs. 80.5 ± 0.34%; and blood brain barrier permeability of the infarcted hemisphere was 11.31 ± 2.67 vs. 9.21 ± 2.28 vs. 5.83 ± 1.6 vs. 4.43 ± 0.93 µg/g tissue (p < 0.05 for measures in doses 0.5 and 0.75 mL/kg/day vs. controls). Oral administration of VOO reduces infarct volume, brain edema, blood brain barrier permeability, and improves neurologic deficit scores after transient MCAO in rats.

Hyperoxia-induced protection against rat's renal ischemic damage: relation to oxygen exposure time

BACKGROUND

Pre-exposure to hyperoxic gas (>or= 95%) has been shown to protect the heart and central nervous system from ischemia-reperfusion injury. In the present study, we investigated whether oxygen pretreatment induces delayed renal protection in rats. The possible role of some renal antioxidant agents was also investigated.

MATERIALS AND METHODS

Adult male Wistar rats were kept in a hyperoxic (HO) (>or= 95% O(2)) environment for 0.5 h, 1 h, 2 h, 3 h, 6 h, and 2 h/day for three consecutive days and 4 h/day for six consecutive days, and control group (IR) animals were kept in the cage with no HO, one day before subjecting their kidney to 40 minutes of ischemia and 24h of reperfusion. Renal function was assessed by comparing plasma creatinine (Cr), blood urea nitrogen (BUN), creatinine clearance (CLCr), and fractional excretion of sodium (FENa%). Histopathological injury score was also determined according to the Jablonski method. To examine the antioxidant system induction by hyperoxia, we measured renal catalase and superoxide dismutase activity, and renal glutathione and malondialdehyde content.

RESULTS

Our data demonstrated that only in 4 h/day HO for six consecutive days, the renal function tests (Cr, CLCr, BUN, and FENa%) and Jablonski histological injury were better than control group (p < 0.05). The beneficial effect of oxygen pretreatment in this group was associated with increased renal catalase activity compared with those obtained from control group (p < 0.05).

CONCLUSION

The present study demonstrates that repeated exposure to hyperoxic (>or= 95% O(2)) environment can reduce subsequent rat's renal ischemia-reperfusion damage. Induction of endogenous antioxidant system may partially explain this beneficial effect of hyperoxic preconditioning.

Type of cell death and the role of acetylcholinesterase activity in neurotoxicity induced by paraoxon in cultured rat hippocampal neurons

Organophosphate (Ops) neurotoxicity is attributed both to its well-known cholinergic and non-cholinergic effects. In the present study we compared enzymatic and morphologic changes in neurons exposed to paraoxon during one day and one week. The effect of exposure time is important in neurotoxicity of Ops. The longer the exposure time is the more damage is observed in neurons, although there are few investigations about the effect in the post-exposure period. Hippocampal cells were obtained from rat neonates and cultured in Neurobasal/B27. Paraoxon at 50 and 100 microM were added. Inverted microscope and electron microscope were used to study cell morphology and Neutral Red staining was used to measure viability. We also assayed caspase-3 and (acetylcholinesterase) AChE activity. Hoechst staining was utilized to determine the type of cell death. Culture medium was replaced after 24 h in one-day group, however, tests were all carried out at the end of the first week in both group. The results indicate that paraoxon reduced the viability in a dose-dependent manner. Our results do not confirm apoptosis in either group; it seems that the cell death in one-day exposure group was not AChE dependent. In conclusion, present data imply that the toxicity of paraoxon is both dose and duration dependent, which may even remain after the cessation of exposure.

Delayed cardioprotective effects of hyperoxia preconditioning prolonged by intermittent exposure

BACKGROUND

In our previous study, it was indicated that pre-exposing rats to normobaric hyperoxia could induce a late preconditioning against infarction and arrhythmia. In this study, attempts were made to know whether the intermittent pre-exposure to the same environment could prolong the late phase of hyperoxia preconditioning.

METHODS

In the first series of experiments, rats were divided into five groups; group 1 was pre-exposed to normal air (NOR) and the other groups to hyperoxic air (O(2)>95%, 120 min once a d) 12, 24, 48, and 72 h (H12, H24, H48, and H72 groups) before 30 min ischemia. In the second series of experiments, rats were pre-exposed to intermittent hyperoxic air (1, 2, or 3 consecutive d) at different times before being subjected to ischemia (H48, H2-48, H2-72, H3-72, and H3-96 groups). The infarct size was measured by triphenyltetrazolium chloride staining, and lead II of electrocardiogram recorded to monitor ischemic-induced arrhythmia.

RESULTS

Compared with NOR group, the infarct size and incidence of arrhythmia were reduced significantly in H24 and H48 groups. When the exposure periods were enhanced to 2 d, the infarct size did not decrease significantly, but the incidence of arrhythmia reduced. When the pre-exposure times were enhanced to 3 d, both the infarct size and incidence of arrhythmia decreased significantly in H3-72 group, but not in H3-96 group.

CONCLUSION

These results show that the late phase of hyperoxia preconditioning may last for more than 48 h and prolong by intermittent per-exposure to the same environment.

Angiotensin-converting enzyme genotype and late respiratory complications of mustard gas exposure

BACKGROUND

Exposure to mustard gas frequently results in long-term respiratory complications. However the factors which drive the development and progression of these complications remain unclear. The Renin Angiotensin System (RAS) has been implicated in lung inflammatory and fibrotic responses. Genetic variation within the gene coding for the Angiotensin Converting Enzyme (ACE), specifically the Insertion/Deletion polymorphism (I/D), is associated with variable levels of ACE and with the severity of several acute and chronic respiratory diseases. We hypothesized that the ACE genotype might influence the severity of late respiratory complications of mustard gas exposure.

METHODS

208 Kurdish patients who had suffered high exposure to mustard gas, as defined by cutaneous lesions at initial assessment, in Sardasht, Iran on June 29 1987, underwent clinical examination, spirometric evaluation and ACE Insertion/Deletion genotyping in September 2005.

RESULTS

ACE genotype was determined in 207 subjects. As a continuous variable, FEV1 % predicted tended to be higher in association with the D allele 68.03 +/- 20.5%, 69.4 +/- 21.4% and 74.8 +/- 20.1% for II, ID and DD genotypes respectively. Median FEV1 % predicted was 73 and this was taken as a cut off between groups defined as having better or worse lung function. The ACE DD genotype was overrepresented in the better spirometry group (Chi2 4.9 p = 0.03). Increasing age at the time of exposure was associated with reduced FEV1 %predicted (p = 0.001), whereas gender was not (p = 0.43).

CONCLUSION

The ACE D allele is associated with higher FEV1 % predicted when assessed 18 years after high exposure to mustard gas.

Normobaric hyperoxia induces ischemic tolerance and upregulation of glutamate transporters in the rat brain and serum TNF-alpha level

Recent studies suggest that intermittent and prolonged normobaric hyperoxia (HO) results in ischemic tolerance to reduce ischemic brain injury. In this research, we attempted to see changes in excitatory amino acid transporters (EAATs) and TNF-alpha levels following prolonged and intermittent hyperoxia preconditioning. Rats were divided into four experimental groups, each of 21 animals. The first two were exposed to 95% inspired HO for 4 h/day for 6 consecutive days (intermittent HO, InHO) or for 24 continuous hours (prolonged HO, PrHO). The second two groups acted as controls, and were exposed to 21% oxygen in the same chamber. Each main group was subdivided to middle cerebral artery occlusion (MCAO-operated), sham-operated (without MCAO), and intact (without any surgery) subgroups. After 24 h from pretreatment, MCAO-operated subgroups were subjected to 60 min of right MCAO. After 24 h reperfusion, neurologic deficit score (NDS) and infarct volume were measured in MCAO-operated subgroups. EAATs expression and serum TNF-alpha levels were assessed in sham-operated and intact subgroups. Preconditioning with prolonged and intermittent HO decreased NDS and upregulated EAAT1, EAAT2, and EAAT3 and increased serum TNF-alpha levels significantly. Although further studies are needed to clarify the mechanisms of ischemic tolerance, the intermittent and prolonged HO seems to partly exert their effects via increase serum TNF-alpha levels and upregulation of EAATs.

In vivo preconditioning with normobaric hyperoxia induces ischemic tolerance partly by triggering tumor necrosis factor-alpha converting enzyme/tumor necrosis factor-alpha/nuclear factor-kappaB

Recent studies suggest that intermittent and prolonged normobaric hyperoxia (HO) results in brain ischemic tolerance (BIT), reducing ischemic brain injury. We have attempted to determine the time course of HO-induced BIT, and to explore the putative roles of tumor necrosis factor-alpha (TNF-alpha) converting enzyme (TACE), TNF-alpha, and nuclear factor-kappaB (NF-kappaB) activation in mediating this effect. Two core experimental protocols were applied to rats (experiments 1 [E1] and 2 [E2] respectively). E1 rodents comprised six subgroups, breathing room air (RA; O(2)=21%), or 95% oxygen (HO) for 4, 8, 16 h (4RA, 8RA, 16RA and 4HO, 8HO, 16HO respectively). E2 rodents were divided into subgroups, exposed to 95% inspired HO for 4 h/day for six consecutive days (intermittent hyperoxia, InHO) or for 24 continuous hours (prolonged hyperoxia, PrHO). Each of these had a control group exposed to 21% oxygen in the same chamber. Twenty-four hours after pretreatment, each group was randomly divided to receive 60 min right middle cerebral artery occlusion (MCAO-operated), sham-operation (without MCAO), or no operation (intact). After 24 h reperfusion, neurologic deficit score (NDS), brain water content, Evans Blue extravasation (as a marker of blood-brain barrier permeability), TACE expression, serum TNF-alpha, and phosphor- kappaBalpha levels were assessed in all animals, and infarct volume in the MCAO-operated subgroups. E1: Compared with the control (RA) group, infarct volume was reduced by 58.6% and 64.4% in 16 h and 24 h respectively. NDS and Evans Blue extravasation was also reduced in 16 h and 24 h. There was no statistical difference among 4 h and 8 h. E2: Preconditioning with prolonged and intermittent HO decreased NDS, infarct volume and upregulated TACE and increased phosphor-kappaBalpha and serum TNF-alpha level significantly. Although further studies are needed to clarify the mechanisms of brain ischemic tolerance, InHO and PrHO may partly exert their effects via triggering TACE/TNF-alpha/NF-kappaB.

Synaptosomal GABA uptake decreases in paraoxon-treated rat brain

A synaptosomal model was used to evaluate in vivo effects of paraoxon on the uptake of [(3)H]GABA in rat cerebral cortex and hippocampus. Male Wistar rats were given a single intraperitoneal injection of one of three doses of paraoxon (0.1, 0.3, or 0.7 mg/kg) and acetylcholinesterase (AChE) activity in the plasma, cerebral cortex, and hippocampus was measured at 30 min, 4h, and 18 h after exposure. [(3)H]GABA uptake in synaptosomes was also studied in another series of animals. Paraoxon administration (0.3 and 0.7 mg/kg) caused significant inhibition of AChE activity in the plasma and both brain areas at all time points. 0.1 mg/kg paraoxon significantly inhibited AChE activity but only in the plasma for 4h, the activity was completely recovered at 18 h. GABA uptake was significantly (p<0.001) reduced in both cerebral cortex (18-32%) and hippocampal (16-23%) synaptosomes at all three time points after administering 0.7 mg/kg of paraoxon, a dose that seems to be sufficient to induce seizure activity. L-DABA, an inhibitor of neuronal GABA transporter, allowed us to conclude that the uptake was mediated primarily by neuronal GABA transporter GAT-1. In conclusion, present data suggests that GABA uptake by synaptosomes decreases probably secondary to paraoxon-induced seizure activity.

The effect of paraoxon on GABA uptake in rat cerebellar synaptosomes

BACKGROUND

The compounds used to treat organophosphate (OP) poisoning are not able to fully alleviate long-lasting effects. They are mainly used to antagonize the cholinergic effects of OPs; however, non-cholinergic effects such as interference with different neurotransmitter systems, especially GABA release and uptake, are now attracting more attention.

MATERIAL/METHODS

Cerebellar synaptosomes were used to investigate any potential interaction between paraoxon and GABA uptake. The cerebella of 250- to 280-g Wistar rats were rapidly dissected out, homogenized, centrifuged, and incubated with 0.004 microM [(3)H]GABA in the presence of different doses of paraoxon for 15 minutes at 37 degrees C. At the end of the incubation period, the synaptosomes were layered in chambers of a superfusion system (UGO). To assay the amount of [(3)H]GABA uptake, radioactivity was measured using a beta-counter (Winspectrul).

RESULTS

Mean GABA uptake was 111, 95, 71, 73, and 75 percent of the control values in the presence of paraoxon concentrations of 0.01, 0.1, 1, 10, and 100 microM, respectively. Accordingly, GABA uptake was significantly reduced at doses 1, 10, and 100 microM of paraoxon (P<0.05).

CONCLUSIONS

Paraoxon may interfere with GABA uptake by cerebellar synaptosomes at micromolar concentrations or higher.

Paraoxon inhibits GABA uptake in brain synaptosomes

To investigate possible effect of paraoxon (10(-9)-10(-3)M) on GABA uptake, we used rat cerebral cortex synaptosomes. K(m) and V(max) of GABA uptake were determined in presence of paraoxon (10(-3)M). Acetylcholine and its antagonists (atropine and mecamylamine) were used for evaluating cholinergic-dependency of uptake. Type of transporter involved was determined by using glial (beta-alanine) and neuronal (DABA) GABA uptake inhibitors. The results of the study showed that paraoxon at low doses (10(-9)-10(-6)M) increased and at high doses (10(-5)-10(-3)M) decreased GABA uptake. One millimolar paraoxon significantly decreased V(max) (175.2+/-4.23 vs. 80.4+/-2.03, P<0.001) of GABA uptake while had no effect on its K(m). DABA significantly decreased GABA uptake (P<0.001) while beta-alanine had no effect. In conclusion, present data suggests that paraoxon probably acts as non-competitive antagonist of GABA uptake.

Prolonged and intermittent normobaric hyperoxia induce different degrees of ischemic tolerance in rat brain tissue

Prior prolonged oxygen exposure is associated with some protection against ischemia-reperfusion (IR) injury to rat brain tissue, but also with toxic effects. We sought to compare the magnitude of protection offered by prolonged and intermittent oxygen pretreatments against IR injury to the rat brain. Rats were divided into four experimental groups, each of 21 animals. The first two were exposed to 95% inspired (normobaric hyperoxia, NBHO) for 4 h/day for 6 consecutive days (intermittent NBHO) or for 24 continuous hours (prolonged NBHO). The second two groups acted as controls were exposed to 21% oxygen. After 24 h, they were subjected to 60 min of right middle cerebral artery occlusion (MCAO) followed by 24 h of reperfusion. The animals were sacrificed for assessment of infarct volume, brain edema, and blood-brain barrier (BBB) permeability, respectively. Prolonged and intermittent NBHO pretreatment reduced infarct volume by 63.3% and 73.7%, respectively, when compared to the respective NBNO groups. Intermittent NBHO (when compared to intermittent NBNO) also reduced the post-ischemic increment of brain water content significantly (81.53+/-0.8%, vs. 80.12+/-0.79%) and Evans Blue extravasation (7.49+/-2.89+/-g/g tissue vs. 3.9+/-0.79 microg/g tissue, P<0.001), while prolonged NBHO had no significant effect on brain water content (81.69+/-1.16% vs. 80.74+/-0.94%) and EB extravasations (6.48+/-2.42 microg/g tissue vs. 4.31+/-1.07 microg/g tissue). Intermittent hyperoxia had relatively more significant effects on brain edema and BBB protection. Although preconditioning with both prolonged and intermittent oxygen exposure protects rat brain tissue against IR injury, the intermittent hyperoxia could have relatively more protective effects in this regard.

The role of nitric oxide within the nucleus accumbens on the acquisition and expression of morphine-induced place preference in morphine sensitized rats

In the present study, the effects of intra-accumbal administration of L-arginine, a nitric oxide precursor, and N(G)-nitro-L-arginine methyl-ester (L-NAME), a nitric oxide synthase inhibitor, on the acquisition and expression of morphine-induced place conditioning in morphine-sensitized rats were studied. Subcutaneous (s.c.) administration of morphine (2.5, 5 and 7.5 mg/kg) induced conditioned place preference. Repeated pretreatment of morphine (5 mg/kg, i.p.) followed by 5 days without drug treatment, increased conditioning response induced by morphine (0.25, 0.5 and 0.75 mg/kg). Intra-accumbal (intra-nucleus accumbens; 1 microg/rat) administration of L-arginine (0.3, 1 and 3 microg/rat) significantly increased or reduced the acquisition of morphine place conditioning in non-sensitized and sensitized rats respectively. However, the drug reduced expression of place conditioning by morphine in sensitized animals. Intra-nucleus accumbens injections of L-NAME (0.3, 1 and 3 microg/rat) reduced the acquisition and expression of morphine place conditioning in the sensitized animals. The results indicate that nitric oxide (NO) within the nucleus accumbens is involved in the acquisition and expression of morphine place conditioning in morphine-sensitized rats.

Effects of short-term and subchronic lead poisoning on nitric oxide methabolites and vascular responsiveness in rat

Chronic exposure to low levels of lead results in sustained hypertension in humans and experimental animals. The mechanism of lead-induced hypertension remains unclear. We investigated the short-term (4 and 8 weeks) and subchronic (12 weeks) effects of lead treatment on responsiveness of vascular adrenergic system and level of nitric oxide metabolites, that is, total nitrates and nitrites (NOx). Male Sprague-Dawley rats were treated with lead acetate (100 ppm in drinking water) for 12 weeks. Short-term lead administration resulted in marked elevation of blood pressure accompanied by significant reduction in serum NOx levels. In contrast, after subchronic lead administration the trend of decrease in NOx levels somehow reversed despite further increase in blood pressure. Both short-term and subchronic lead administration resulted in significant differences in vascular reactivity with respect to either vasoconstrictor (phenylephrine and clonidine) or vasodilator (isoproterenol) agents. We conclude that vascular adrenergic system and nitric oxide pathway change in short-term and subchronic phases of lead poisoning.

Acute lead exposure and contraction of rat isolated aorta induced by D1-dopaminergic and alpha-adrenergic drugs

BACKGROUND/OBJECTIVE

In the present study, the effect of acute lead exposure in the presence and absence of dopamine or alpha (alpha)-adrenoceptor agents on contractile response of rat isolated thoracic aorta was studied.

METHODS

Male Wistar rats were used in all experiments. Thoracic aorta was carefully removed, cleaned, and cut into 2-mm thick rings. The rings were mounted for measurement of isometric contractions in a tissue bath containing 10 mL of Kreb's solution at 37 - 38 degrees C. The following drugs were used: lead chloride, dopamine, phenylephrine, prazosin, clonidine, yohimbine, and SCH23390. One-way analysis of variance (ANOVA) and Student's t-test were used for statistical analyses. P < 0.05 was considered significant.

RESULTS

The alpha1-adrenoceptor antagonist (prazosin), alpha2-adrenoceptor antagonist (yohimbine), or dopamine D1 receptor antagonist (SCH23390), did not elicit any response. Combination of lead with dopamine, phenylephrine, or clonidine did not show any potentiation. SCH23390, prazosin, and yohimbine decreased the contraction induced by lead. SCH23390 decreased the contraction induced by dopamine, or lead plus dopamine. Prazosin reduced the contraction induced by phenylephrine or lead plus phenylephrine. Yohimbine attenuated the response induced by clonidine or lead plus clonidine.

CONCLUSION

alpha1, alpha2, and D1 dopamine receptor mechanisms could have a role in lead-induced contraction.

Paraoxon-induced ultrastructural growth changes of rat cultured hippocampal cells in neurobasal/B27

Organophosphates (OPs) neurotoxicity is attributed both to their well-known cholinergic and recently attended non-cholinergic effects. Since parathion has been observed to be responsible for more cases of poisoning than any other OP insecticides, it is vitally important to investigate other mechanisms, besides cholinesterase inhibition, which can potentially contribute to the neurotoxicity of parathion (or its metabolite, paraoxon). In present study, hippocampal cells obtained from Wistar rat neonates were cultured in neurobasal medium supplemented with B27 serum where different doses of paraoxon were also introduced. The neuronal growth in the control group and those exposed to paraoxon was compared. Phase contrast microscopy, cell staining (Neutral Red) and computer assessment morphometric study (Motic) were used to study cell morphology, viability and type of cell death. Statistical analysis was carried out using one-way ANOVA. There was no clear morphologic differences between neurons in the control group and those exposed to 10 microM paraoxon; however, deformity of the soma was clear in pellets containing higher concentration of paraoxon. Ultrastructure of cells was markedly altered at 50 microM dose of paraoxon as evidenced by gradual discontinuation of cytoplasm, appearing of numerous vacuoles and intracytoplasmic myelin figure. The processes (neurites) did not grow in media containing 100 microM paraoxon or more. Viability decreased with increasing paraoxon especially above 100 microM. In conclusion, the present data reveal that paraoxon, in 30 microM or higher concentrations, induces a decrease in cell growth, followed by cell swelling and neuronal death (possibly necrosis).

Involvement of nucleus accumbens in L-arginine-induced conditioned place preference in rats

In the present study, the effects of intraperitoneal, intra-accumbal and intra-ventral tegmental area administration of L-arginine and N(G)-nitro-L-arginine methyl-ester (L-NAME) on conditioned place preference behavior were studied. Intraperitoneal (i.p.; 0.5, 1 and 5 mg/kg) and intra-accumbal (intra-NAc; 0.3, 1 and 3 microg/rat), but not intra-ventral tegmental area (intra-VTA; 0.3, 1 and 3 microg/rat) administrations of L-arginine produced a significant place conditioning. Similar injections of L-NAME did not produce any response. However, intraperitoneal pretreatment of the animals with L-NAME (5, 10 and 20 mg/kg), 30 min before L-arginine administration, significantly abolished the acquisition of place conditioning induced by either intraperitoneal or intra-accumbal injection of L-arginine. Moreover, injection of L-NAME (5, 10 and 20 mg/kg) on the test day did not alter the L-arginine response. The results may indicate that L-arginine induces conditioned place preference via an increase in nitric oxide (NO) in the nucleus accumbens.

Investigation of circulatory and tissue ACE activity during development of lead-induced hypertension

Prolonged exposure to low levels of lead causes systemic hypertension. Several mechanisms have been proposed to explain lead-induced hypertension. Recently, the etiological role of the renin-angiotensin system (RAS) has been investigated in this context. This study assessed the alterations of circulatory and tissue angiotensin converting enzyme (ACE) activity during development of lead induced hypertension. Male rats were divided to two main groups: lead-treated animals which received lead acetate, 100 ppm, in drinking water for 2, 4, 6, and 8 weeks and a control group given distilled water. The ACE activity in serum and tissues was analyzed by HPLC. The blood pressure gradually increased in correlation with lead exposure with time. The study also revealed significant elevation of local and serum ACE activity in the early phase of lead treatment; however, chronic lead exposure suppressed ACE activity in serum and tissues. These results emphasize the etiological role of ACE activity in the early phase of lead-induced hypertension.

Effects of nitric oxide on morphine self-administration in rat

Previous studies have reported that morphine exerts its effects in part through the release of nitric oxide (NO). In the present study, the effects of acute and chronic administration of the NO precursor, L-arginine and NO synthase (NOS) inhibitor, L-nitro-amino-methyl-ester (L-NAME) on morphine self-administration in rats were investigated. The animals were initially trained to press a lever using food as reinforcer. Rats were surgically prepared with a chronic Silastic catheter implanted in the external jugular vein. Five days after surgery, they were trained to press a lever for drug self-administration. The present data indicate that L-arginine (0.05, 0.1, and 0.15 mg/kg/injection) but not L-NAME (0.05, 0.1, and 0.15 mg/kg/injection) induced self-administration behavior and increased locomotion. The response induced by L-arginine (0.1 mg/kg/injection) was reduced by pretreatment with L-NAME (5, 10, and 15 mg/kg ip). Both the acute (5, 10, and 15 mg/kg ip) and the chronic (200 mg/kg ip; twice daily for 4 days) administration of L-arginine reduced morphine self-administration. However, acute (5, 10, and 20 mg/kg ip) and chronic (50 mg/kg ip; twice daily for 4 days) administration of L-NAME increased morphine self-administration significantly. It can be concluded that NO may have a role in morphine self-administration.

Effects of subacute lead acetate administration on nitric oxide and cyclooxygenase pathways in rat isolated aortic ring

Low level exposure to lead increases blood pressure in human and rats. In this study, we investigated the contribution of the nitric oxide (NO) and cyclooxygenase pathways of aortic rings of 28-day lead-treated and control rats, to the responsiveness to phenylephrine and acetylcholine. There were no differences in phenylephrine contractions between the two groups. N(omega)-nitro-L-Arginine-methyl ester (L-NAME), a NO synthase inhibitor, caused attenuation in contraction response to phenylephrine in the aortic rings of the lead-treated rats, while endothelium-denudation caused attenuation in those of controls. This may be due to either endothelium-derived vasoconstrictor(s) (such as reactive oxygen species or endothelins) or a source of NO in smooth muscle cells. There is a left-shift in acetylcholine relaxation response. Indomethacin incubation caused a left-shift in relaxation response to acetylcholine in controls but without any effect on lead-treated ones. Indomethacin incubation caused attenuation in contraction to phenylephrine in both groups. The relaxation response to sodium nitroprusside is not different between the two groups, suggesting that smooth muscle relaxation component is intact. However, the relaxation response to glyceryl trinitrate is impaired in aortic rings of lead-treated rats. It can be concluded that NO and cyclooxygenase pathways are altered in aortic rings of lead-treated rats, with possible involvement of endothelium-derived vasoconstrictors.

The physiological and pathophysiological modulation of the endocrine function of the heart

Under physiological conditions, the endocrine heart contributes to the maintenance of cardiovascular homeostasis through the polypeptide hormones ANF and BNP, which are members of the natriuretic peptide (NP) family. Given that NPs are of interest from the basic and clinical points of view, the genetic expression and secretion of ANF and BNP as well as the nature of the interaction of these hormones with their receptors has been the subject of extensive studies since the discovery of ANF in 1980. Following hemodynamic overload, increased secretion of NPs by the heart can be seen. This change may occur without an increase in gene expression as observed for atrial NPs following acute volume expansion, or it can occur with an increase in both ANF and BNP gene expression in atria only as seen in mineralocorticoid escape during which it is obvious that a critical decrease in hormone stores must be reached before transcriptional activation occurs. Chronic hemodynamic pressure or volume overload results in increased expression of NPs in atria and ventricles. Under these circumstances, the increased production of BNP by hypertrophic ventricles changes the normal plasma concentration ratio of ANF to BNP, a fact that has clinical diagnostic and prognostic implications. There are exceptions to this rule: chronic, severe L-NAME hypertension, which may occur without left ventricular hypertrophy, does not cause this effect and increased ventricular NP gene expression can occur in mineralocorticoid hypertension before detectable ventricular hypertrophy. Atrial and ventricular NP gene expression appears to be under different transcriptional control because pharmacological treatments such as chronic ACE inhibition or ET(A) receptor blockade can reverse the increased ventricular NP expression but has no detectable effect on atrial NP gene expression. This is not unlike the myosin heavy chain switch that is observed in certain pathologies, and can be pharmacologically reversed in a manner similar to NPs in the ventricles but it does not occur in atrial muscle. These observations made in vivo or using isolated adult atria often differ strikingly from results obtained using the mixed phenotype afforded by cardiocytes in culture, indicating that the kinds of questions addressed by each approach must be judiciously chosen. G-protein coupled receptor-mediated actions of neurohumors such as endothelin and phenylephrine are normally used to stimulate NP gene expression and release in different in vitro models. The main physiological stimulus for increased ANF release, atrial muscle stretch, also appears to rely on G-protein-coupled mechanisms. Alternative agonists and receptor types at play are suggested by the finding that circulating levels of BNP are selectively increased before and during overt cardiac allograft rejection episodes in human patients. The data suggest that enhanced BNP plasma levels could form a basis for a noninvasive test for cardiac allograft rejection. However, the molecular mechanism by which expression of NPs are regulated in the transplanted heart is not well understood. Conditioned medium from mixed lymphocyte reaction cultures, considered an in vitro model of transplantation immunity, induces specific upregulation of BNP as do individual pro-inflammatory cytokines. Findings such as these suggest that the study of NPs will continue to produce a wealth of information relevant to basic and clinical scientists.

The physiological and pathophysiological modulation of the endocrine function of the heart

Under physiological conditions, the endocrine heart contributes to the maintenance of cardiovascular homeostasis through the polypeptide hormones ANF and BNP, which are members of the natriuretic peptide (NP) family. Given that NPs are of interest from the basic and clinical points of view, the genetic expression and secretion of ANF and BNP as well as the nature of the interaction of these hormones with their receptors has been the subject of extensive studies since the discovery of ANF in 1980. Following hemodynamic overload, increased secretion of NPs by the heart can be seen. This change may occur without an increase in gene expression as observed for atrial NPs following acute volume expansion, or it can occur with an increase in both ANF and BNP gene expression in atria only as seen in mineralocorticoid escape during which it is obvious that a critical decrease in hormone stores must be reached before transcriptional activation occurs. Chronic hemodynamic pressure or volume overload results in increased expression of NPs in atria and ventricles. Under these circumstances, the increased production of BNP by hypertrophic ventricles changes the normal plasma concentration ratio of ANF to BNP, a fact that has clinical diagnostic and prognostic implications. There are exceptions to this rule: chronic, severe L-NAME hypertension, which may occur without left ventricular hypertrophy, does not cause this effect and increased ventricular NP gene expression can occur in mineralocorticoid hypertension before detectable ventricular hypertrophy. Atrial and ventricular NP gene expression appears to be under different transcriptional control because pharmacological treatments such as chronic ACE inhibition or ETA receptor blockade can reverse the increased ventricular NP expression but has no detectable effect on atrial NP gene expression. This is not unlike the myosin heavy chain switch that is observed in certain pathologies, and can be pharmacologically reversed in a manner similar to NPs in the ventricles but it does not occur in atrial muscle. These observations made in vivo or using isolated adult atria often differ strikingly from results obtained using the mixed phenotype afforded by cardiocytes in culture, indicating that the kinds of questions addressed by each approach must be judiciously chosen. G-protein coupled receptor-mediated actions of neurohumors such as endothelin and phenylephrine are normally used to stimulate NP gene expression and release in different in vitro models. The main physiological stimulus for increased ANF release, atrial muscle stretch, also appears to rely on G-protein-coupled mechanisms. Alternative agonists and receptor types at play are suggested by the finding that circulating levels of BNP are selectively increased before and during overt cardiac allograft rejection episodes in human patients. The data suggest that enhanced BNP plasma levels could form a basis for a noninvasive test for cardiac allograft rejection. However, the molecular mechanism by which expression of NPs are regulated in the transplanted heart is not well understood. Conditioned medium from mixed lymphocyte reaction cultures, considered an in vitro model of transplantation immunity, induces specific upregulation of BNP as do individual pro-inflammatory cytokines. Findings such as these suggest that the study of NPs will continue to produce a wealth of information relevant to basic and clinical scientists.Key words: atrial natriuretic factor, hypertension, hypertrophy, heart failure, cytokines.

Decreased response of rat knee joint blood vessels to phenylephrine in chronic inflammation: involvement of nitric oxide

The effect of chronic inflammation induced by Freund's Complete Adjuvant (FCA) on rat articular blood vessels and knee joint diameter was investigated. Blood flow changes in response to phenylephrine (an 1-adrenoceptor agonist) in FCA-treated and contralateral knee joints were studied over a 40 day period, using the laser Doppler flowmetery (LDF) technique. Unilateral injection of FCA (0.2 ml) increased the injected knee diameter on all days examined post-injection (P < 0.001) and its maximum increase (53 +/- 2 %) was reached on day 3. After this, the diameter decreased gradually but did not return to its initial value. In control animals, topical application of 10-13-10- 7 mol phenylephrine onto the exposed joint capsule decreased blood flow dose dependently (11. 1 +/- 4.4 to 58.2 +/- 4.5 %, respectively, P < 0.001). Unilateral injection with FCA attenuated the phenylephrine response in both ipsilateral and contralateral knees compared with the response of control animals (5.2 +/- 1.6 to 48.3 +/- 6.1 % and 1.9 +/- 2.2 to 45. 3 +/- 5.6 %, respectively, P < 0.05). The reduction persisted for 3 weeks after FCA injection (ipsilateral for 21 days; contralateral for 30 days, P < 0.001). Subsequently the response returned towards normal. To avoid the influence of 2-adrenoceptors, yohimbine (an 2-adrenoceptor antagonist) was injected (0.5 mg kg-1, I.P.) 30 min before phenylephrine application. Yohimbine blocked the vasoconstrictor effect of 10-10-10-7 mol clonidine (an 2-adrenoceptor agonist, topical application) by 44-67.7 % inhibition, respectively (P < 0.001). Prazosin (an 1-adrenoceptor antagonist, 0.1 mg kg-1, I.P.) blocked the vasoconstrictor effect of phenylephrine (10-10-10-7 mol, topical application) effectively (42 to 69.8 % inhibition, respectively, P < 0.001). To assess the role of nitric oxide (NO) on the observed responses, N G-nitro-L-arginine methyl ester (L-NAME, NO synthase inhibitor) was applied topically (0.2 micromol) 5 min before phenylephrine application. L-NAME application at 7 and 14 days after FCA injection potentiated the vasoconstrictor response in the FCA-treated knee (P < 0.001) but had no significant effect on the contralateral knee. Blood pressure monitoring during phenylephrine, clonidine and L-NAME administration indicated that topical application of the drugs had no significant effect on the systemic blood pressure. These findings indicate that the vasoconstrictor response to phenylephrine was decreased in chronic inflammation and increased NO production could be involved.

Adenosine A(2) receptors inhibit morphine self-administration in rats

In the present study, the effect of adenosine receptor agonists and antagonists on morphine self-administration was investigated. Intravenous administration of morphine (0.3-3 mg/kg/injection) induced dose-dependent self-administration. The adenosine receptor antagonists, theophylline (2.5, 5, 10 mg/kg) and 3, 7-Dimethyl-1-propargylxanthine (DMPX; 0.25, 0.5, 1 mg/kg), when injected 1 h before the start of the test, reduced the number of self-administered morphine infusions. The adenosine receptor antagonists when administered in the training period (11 days) greatly increased the number of morphine infusions, however, they did not induce any response by themselves. 5'-N-ethylcarboxamido-adenosine (NECA; 0.5, 1 mg/kg) and 4-[2-[[6-Amino-9-(N-ethyl-beta-D-ribofuranuronamidosyl)-9H-purin-2 -yl ]amino] ethyl]benzenepropanoic acid (CGS21680; 0.001, 0.01, 0.025, 0. 05 mg/kg), given 1 h before the start of the test, increased morphine self-administration. Although the adenosine agonists, when injected during training period (11 days), reduced morphine self-administration. Furthermore, NECA, but not CGS21680, induced significant self-administration. The adenosine A(1) receptor agonist, N(6)-cyclohexyladenosine (CHA; 0.01, 0.1, 0.25, 0.5 and 1 mg/kg), and the adenosine A(1) receptor antagonist, 8-phenyletheophylline (2, 4, 6, 8 mg/kg), themselves neither altered morphine infusion nor induced any response. These results indicate a role for adenosine A(2) receptors in the expression and/or development of morphine self-administration.

Nerve-mediated responses of blood vessels in the rabbit knee joint

Blood vessels in the anterior region of the knee joint of anaesthetised rabbits showed a biphasic response to the electrical stimulation (10 Hz, 1 ms width, 10 V amplitude) of nerve fibres supplying the knee, as measured by laser Doppler flowmetry. The response consisted of vasoconstriction during nerve stimulation followed by a prolonged dilatation. The vasoconstrictor response was mediated by noradrenaline acting mainly via alpha 1-adrenoceptors as it was substantially reduced by close intra-arterial injection of the alpha-adrenergic antagonist phentolamine (approximately 50% reduction) and the selective alpha 1-adrenergic antagonist prazosin (approximately 50% reduction) but not by the alpha 2-antagonist rauwolscine. Further studies involving prolonged (2-hour) close intra-arterial infusion of prazosin gave a approximately 50% reduction of the constrictor response with a concentration of 10(-5) M and approximately 95% reduction when the concentration was raised to 10(-4) M. At the higher prazosin concentration responses to close intra-arterial injection of the alpha 1-agonist phenylephrine were substantially reduced but responses to the alpha 2-agonists clonidine and UK-14304 were not significantly influenced. Infusions of the alpha 2 antagonist CH 38083 failed to inhibit nerve-mediated vasoconstriction at 10(-5) or 10(-4) M. There did not appear to be a purinergic component, as the constrictor response was unaffected by the P2X desensitiser alpha,beta-methylene adenosine 5'-triphosphate. The dilator response appeared to be mediated principally by substance P (presumably released from sensory C fibers) as it was substantially reduced by intraarticular injection of substance P antagonist D-Pro4D-Trp7,9,10-SP(4-11).(ABSTRACT TRUNCATED AT 250 WORDS)

Localized neural control of blood flow in the posterior region of the knee joint in anaesthetized rabbits

Radiolabelled microspheres were used to measure blood flow of structures in and around the rabbit knee joint and to determine the effect of electrical stimulation of the posterior articular nerve (PAN) supplying the knee. Surgical exposure of the posterior aspect of the knee joint 'capsule' and section of PAN resulted in an increase in flow restricted to this region. Electrical stimulation produced frequency-dependent reductions of blood flow in the posterior region, but no alterations occurred in the anterior region or in any other surrounding structures, suggesting that the neural supply is specific to the posterior joint capsule.

Responses of bone and joint blood vessels in cats and rabbits to electrical stimulation of nerves supplying the knee

1. Experiments were performed to assess the extent to which knee joint blood flow in cats and rabbits is affected by electrical stimulation of the nerve supply to the knee. 2. Absolute changes in blood flow were measured using the radiolabelled microsphere (approximately 15 microns) technique whilst relative changes in blood flow were assessed using laser Doppler flowmetry. 3. Despite deep general anaesthesia, sympathetic nerve fibres innervating cat knee joint blood vessels showed marked 'tone'. 4. Blood flow to the joint capsule (synovium and overlying fibrous and areolar tissues) was substantially reduced (by approximately 90% in the cat and approximately 45% in the rabbit) during electrical stimulation of the articular nerve supply. 5. The percentage change in the laser Doppler flowmeter signal did not differ significantly from the percentage change in blood flow measured by microsphere technique. 6. Blood vessels in the cancellous bone of the distal femur (condyles) and proximal tibia (plateau) appear to be innervated by vasoconstrictor fibres which reach their effectors via the articular nerves. However, the cortical bone and red marrow of the diaphysis of the femur do not receive such innervation. 7. The potency of the vasoconstrictor influences acting on joint blood vessels could be of relevance in the pathogenesis of inflammatory joint diseases.

Alterations in cat knee joint blood flow induced by electrical stimulation of articular afferents and efferents

1. Experiments were performed in cats anaesthetized with pentobarbitone. Laser Doppler flowmetry was used to assess the responses of knee joint blood vessels to nerve stimulation under control conditions and in the presence of different adrenoceptor antagonists in order to establish the nature of neurotransmitters released from articular nerve fibres. 2. The posterior articular nerve (PAN) supplying the knee was stimulated at different intensities, and frequency-response curves were obtained. In fourteen animals electrical stimulation of PAN produced an initial vasoconstriction during stimulation which in eight of these was followed by a prolonged dilatation on cessation of stimulation. The constrictor response was increased as a function of frequency but was little altered with increasing intensity beyond a threshold level. 3. The constrictor response to electrical stimulation of PAN was markedly reduced by the alpha-adrenergic antagonist phentolamine (10(-5) M, the alpha 1-blocker prazosin (10(-5) M), and guanethidine (10(-5) M) which inhibits the release of noradrenaline, ATP, and neuropeptide Y from sympathetic nerve endings. 4. The constrictor response to PAN stimulation was unaffected by the alpha 2-blocker rauwolscine and the P2-purinoceptor desensitizer alpha,beta-methylene ATP. 5. The dilator response was due to activation of afferent fibres as it could also be produced by direct electrical stimulation of the L7 dorsal roots. 6. The dilator response to stimulation of PAN or the L7 dorsal root was reduced by prior intra-articular injection of 100 micrograms of the substance P antagonist D-Pro4-D-Trp7,9,10-SP4-11. 7. These results suggest that the vasoconstrictor response to electrical stimulation of PAN is most likely to be mediated via noradrenaline acting mainly upon alpha 1-adrenoceptors. As the dilator response to articular nerve stimulation is reduced by a substance P antagonist, the mediator inducing this response may be substance P or a related neurokinin.

Responses of blood vessels in the rabbit knee to acute joint inflammation

These experiments examined the responses of articular blood vessels in the rabbit knee to induction of acute joint inflammation by intraarticular injection of 4% kaolin suspension. This produced an inflammatory response, which became evident about four hours after injection. Electrical stimulation of the nerve supply to the knee joint before induction of inflammation produced a biphasic response--an initial vasoconstriction during the stimulation phase followed by dilatation after stimulation stopped. These responses were followed up for eight hours and it was noted that the constrictor response became progressively greater, producing a further 19% decrease in blood flow during nerve stimulation about three hours after the injection of kaolin. The sensitivity of postjunctional alpha adrenoceptors, however, showed still greater increase in the inflamed joint as close intraarterial injection of 10(-6) M adrenaline produced an additional 30% reduction in blood flow four hours after kaolin injection compared with the control response. Possibly, the smaller enhancement of the constrictor response to nerve stimulation in the inflamed joint may reflect sensitisation of prejunctional alpha adrenoceptors in addition to the effects exerted on postjunctional alpha adrenoceptors by the inflammatory process. The dilator response also increased over eight hours, though this rise was less marked. These findings indicate that even over the limited time span of the experiments, significant alterations occurred in factors which influence the calibre of articular blood vessels.

Responses of blood vessels in the rabbit knee to electrical stimulation of the joint capsule

1. An in vitro preparation of the rabbit knee joint, perfused with oxygenated Locke's solution, was used to study the response of articular blood vessels to electrical stimulation of the joint capsule. 2. Using trains of stimulus pulses of different durations, frequency-response curves were obtained. Electrical stimulation always produced vasoconstriction of joint blood vessels, which increased as a function of both frequency and pulse width. 3. This vasoconstrictor response was neurally mediated as it was markedly inhibited after addition to both bath and perfusate of tetrodotoxin. In addition, the response to field stimulation of the capsule was virtually abolished in animals pretreated with reserpine which depletes sympathetic nerve endings of noradrenaline. 4. The response to electrical stimulation was substantially reduced by the alpha-adrenergic antagonist phenoxybenzamine (10(-5) M), the alpha 1-blocker prazosin (10(-6) M), and by guanethidine (10(-5) M) which inhibits the release of noradrenaline, ATP and neuropeptide Y from sympathetic nerve endings. 5. The attenuation of the vasoconstrictor response to field stimulation by prazosin (10(-6) M) was little altered by addition of the alpha 2-adrenoceptor blocker rauwolscine (10(-6) M) to the perfusate. 6. alpha, beta-Methylene ATP (10(-6) M), a P2-purinoceptor desensitizer, had no effect on the vasoconstrictor response to electrical stimulation. 7. These results indicate that the vasoconstrictor response to electrical stimulation of the rabbit knee joint capsule is mediated via noradrenaline acting upon alpha 1-adrenoceptors.

The role of the endothelium in mediating the actions of ATP, adenosine and acetylcholine on flow through blood vessels in the rabbit knee joint

1. An in vitro preparation of the rabbit knee joint, perfused with oxygenated Locke solution, was used to investigate the presence of purinoceptors and the role of endothelium within articular blood vessels. 2. The basal tone of the blood vessels was not affected by adenosine or acetylcholine. Adenosine 5'-triphosphate (ATP) injection produced vasoconstriction which was unaffected by removal of the endothelial layer, but diminished by alpha, beta methylene ATP, a compound which desensitizes P2-purinoceptors. 3. When knee joint blood vessel tone was raised by perfusion with vasopressin (10(-8) M) or 5-hydroxytryptamine (10(-5) M), acetylcholine, ATP and adenosine were all found to induce concentration-dependent relaxation of these vessels. ATP was found to have a dual effect of transient constriction followed by longer-lasting dilatation. 4. 3-Methylxanthine, a P1-purinoceptor antagonist significantly reduced the relaxation response to adenosine but had no effect on the vasodilator effect of ATP. 5. Removal of the endothelial layer virtually abolished the vasodilator effects of acetylcholine and ATP but not adenosine. 6. These results demonstrate that articular blood vessels supplying the rabbit knee contain P1-purinoceptors located on the vascular smooth muscle which mediate vasodilatation. P2-purinoceptors mediating a constrictor effect are also present on this smooth muscle. It is likely that the vasodilator effect of ATP is mediated via P2-purinoceptors located on the endothelial layer.

Adrenoceptor profile of blood vessels in the knee joint of the rabbit

1. An in vitro preparation of the rabbit knee joint, perfused with oxygenated Locke solution, was used to assess the nature of adrenoceptors within articular blood vessels. 2. Dose/response relationships were obtained to intra-arterial injection of alpha- and beta-adrenoceptor agonists. 3. Adrenaline and noradrenaline produced a similar pattern of increasing constriction of articular vessels with increasing dose of drug. 4. The alpha 1-agonist, phenylephrine, also produced dose-dependent constrictor responses, but the alpha 2-agonist; clonidine, had no effect. The alpha 2-agonist UK-14304 did, however, produce modest vasoconstriction which was not greatly altered by the alpha 1-blocker prazosin. The constrictor effect of noradrenaline was abolished by both the alpha 1,2-blocker phenoxybenzamine and by prazosin but not by the alpha 2-blocker rauwalscine. 5. The beta-adrenoceptor agonist, isoprenaline, had little effect at a dose of 10(-6) M or lower, but gave rise to a constrictor effect at higher concentrations. This response was blocked by phenoxybenzamine but not by the beta 1,2-blocker propranolol, suggesting that the constrictor effect was mediated via alpha-adrenoceptors. 6. The results suggest that alpha 1- and alpha 2-adrenoceptors are present within articular blood vessels, but that beta-receptors are absent. The effects of noradrenaline appear to be mediated principally via alpha 1-adrenoceptors.