Effect of Nω-nitro-l-arginine methyl ester on cardiac haemodynamic responses to adenosine infusion in conscious rats

• 1.1. The aim of the present study was to evaluate the role of NO in the cardiovascular effects of adenosine in conscious rats.
• 2.2. Cardiac index was determinated by thermodilution. In a group of rats, three doses of adenosine were infused (i.v.) at a rate of 150, 300 and 450 μg/kg/min in the absence and in the presence of l-NAME (10 mg/kg). In a second group of rats, the experimental protocol was the same as that of the first group, except an infusion of methoxamine (50 μg/kg/min) was given during the second adenosine administration, instead of L-NAME.
• 3.3. In the absence of l-NAME or methoxamine, adenosine induced a dose-dependent decrease in mean arterial pressure and an increase in vascular conductance although adenosine did not affect cardiac index.
• 4.4. l-NAME administration attenuated the decreasing effect on the mean arterial pressure in response to the two lower doses of adenosine. In the presence of L-NAME, adenosine induced a significant increase in cardiac index from 18.7 ± 1.5 to 29.1 ± 1.9 and 26.2 ± 1.4 ml/min/100 g. Administration of l-NAME significantly attenuated the adenosine-induced increase in vascular conductance.
• 5.5. Methoxamine infusion induced an enhanced response to adenosine infusion. In the presence of methoxamine, adenosine induced a significant greater decrease in mean arterial pressure, and increase in cardiac index and vascular conductance.
• 6.6. These results indicate that part of the cardiovascular effects of adenosine can be mediated by NO, since L-NAME administration partially blocked the adenosine-induced vasodilatation.

     

Preferential antagonism by diltiazem of α2-adrenoceptor mediated vasoconstrictor responses in perfused tail arteries of spontaneous hypertensive rats

Summary Vasoconstrictor responses mediated by the ₂-adrenoceptor agonist TL99, were particularly sensitive to blockade by the calcium antagonist drug diltiazem in isolated perfused tail arteries of spontaneously hypertensive rats (SHR). In contrast, the vasoconstrictor responses induced by the ₁-adrenoceptor agonist methoxamine were significantly more resistant to antagonism by diltiazem. At higher concentrations (>300 nmol/l) diltiazem became an effective antagonist of all -adrenoceptor mediated responses. In normotensive Wistar Kyoto (WKY) or Sprague-Dawley (SD) rats diltiazem was significantly less potent againts vasoconstrictor responses to TL99 than in SHR. The blockade of ₁-adrenoceptor mediated vasoconstriction by diltiazem was not significantly different when normotensive rats and SHR were compared. The vasoconstrictor responses evoked by 5HT in the perfused tail arteries were particularly resistant to blockade by diltiazem in SHR arteries.The responses to endogenously released noradrenaline, evoked by electrical field stimulation, were significantly antagonised by diltiazem (30 nmol/l–3 mol/l) in SHR-tail arteries, while they were not modified in WKY-tail arteries. At the concentrations of diltiazem which blocked end organ responses to field stimulation, there was no modification of total tritium overflow SHR-tail arteries after labelling the tissue with³H-noradrenaline, indicating that diltiazem does not inhibit transmitter release at these concentrations.The tail artery preparation of SHR contains a population of postsynaptic ₂-adrenoceptors which mediate contraction in this blood vessel and the calcium entry blocker diltiazem is a potent antagonist of vasoconstrictor responses mediated by vascular ₂-adrenoceptors in hypertensive rats. These findings may be relevant to the antihypertensive action of diltiazem.     

Investigation of α1-adrenoceptor subtypes mediating vasoconstriction in rabbit cutaneous resistance arteries

1. Cutaneous resistance arteries (c.r.a.) (internal diameter=240.94±5.42 μm, n=67/25 (number arteries/number animals)) from New Zealand white rabbits were mounted in wire myographs and a normalization procedure followed.
2. Cumulative concentration-response curves (CCRCs) were constructed for the α-adrenoceptor agonists noradrenaline (NA), (R)A61603 and phenylephrine (PE) in the presence of cocaine (3 μM), propranolol (1 μM) and corticosterone (10 μM). The effects of competitive α₁-adrenoceptor antagonists, prazosin, WB4101, 5-methyl-urapidil, HV723, BMY7378 and the irreversible α_1B selective compound chloroethylclonidine (CEC) were examined versus the potency and maximum response of the c.r.a.s to noradrenaline.
3. The high potency of A-61603 relative to PE has been shown to differentiate both functional and binding site α_1A- or α_1B-adrenoceptors from α_1D-adrenoceptors: A-61603 was 944 times more potent than phenylephrine (at EC₅₀) suggesting the presence of a functional α_1A or α_1B as opposed to an α_1D-subtype.
4. Exposure to chloroethylclonidine (CEC; 100 μM) decreased the maximum response to noradrenaline but did not significantly change noradrenaline sensitivity indicating that a substantial part of noradrenaline-induced vasoconstriction in rabbit cutaneous arteries is CEC-insensitive.
5. The potencies of prazosin (pA₂=9.14) and WB4101 (pA₂=9.30) indicate the involvement of prazosin-sensitive functional α₁-adrenoceptors. The slopes of corresponding Schild plots for prazosin and WB4101 did not include negative unity which implies the possible involvement of more than one functional α₁-adrenoceptor subtype in noradrenaline-induced vasoconstriction in rabbit cutaneous resistance arteries. In contrast to this, in the case of 5-methyl-urapidil and HV723, the Schild plot slope parameters were not significantly different from negative unity over the range of concentrations used; the low pA₂ value for 5-methylurapidil (7.27) suggests the non-involvement of an α_1A- or an α_1D-adrenoceptor; the low pA₂ value for HV723 (8.47) was similar to that against responses postulated as α_1L.
6. We conclude that rabbit cutaneous resistance arteries express a prazosin-sensitive functional α₁-adrenoceptor resembling the α_1B and another low affinity site for prazosin which on the basis of the functional antagonism produced by HV723 most closely resembles the α_1L-adrenoceptor; the low pA2 value for HV723 (8.47) is similar to that against responses postulated as α_1L.

     

Modulation of L-type Ca current by denopamine, a nonparenteral partial β1 stimulant, in rabbit ventricular cells

The effects of denopamine, a nonparenteral partial agonist which is used clinically in Japan, on the L-type Ca²⁺ current (I _Ca) were examined in rabbit ventricular cells. Denopamine stimulated basal I _Ca with a maximum response of +33.2% and a concentration for half-maximal response (EC₅₀) of 0.039 M. The maximun response of I _Ca was only a quarter of that induced by isoprenaline (ISO), while 10 M denopamine elicited 70–75% of the maximum inotropic response in the papillary muscle preparations. The denopamine stimulation of I _Ca was abolished by selective ₁ antagonists (atenolol or bisoprolol). Pretreatment with forskolin or dialysis with cAMP also abolished the stimulation. Denopamine, in turn, inhibited ISO-stimulated I _Ca. This inhibition was not affected by pretreatment with pertussis toxin or prazosin. The presence of denopamine at various concentrations caused a rightward shift in the concentration/response curve for ISO stimulation of I _Ca. The Schild plot for this effect had a slope of 0.99 and K _p of 0.20 M. In the presence of guanosine-5-O-(3-thiotriphosphate) (GTPS) (0.5 mM) in the pipette, denopamine (10 M) stimulated the I _Ca to 86±5% of the maximum response induced by ISO. These findings indicate that denopamine modulates I _Ca exclusively through the ₁ adrenoceptor-adenylate cyclase pathway, that the stimulatory GTP-binding protein regulates the agonistic potency of denopamine, and that the signal from the ₁ adrenoceptors is amplified between I _Ca and the tension development, which would contribute to the spare capacity of adrenoceptors.     

Enhancement of ADP-induced aggregation by 5-HT in rabbit platelets

目的：研究５ＨＴ对ＡＤＰ介导的血小板聚集反应的增强作用．方法：以透光法、图像法和受体结合法评价聚集反应、单细胞内钙和三磷酸肌醇的含量．结果：５ＨＴ（００３－３μｍｏｌ·Ｌ－１）浓度依赖性地引起ＰＲＰ的透光度降低（ＤＬＴ），电镜结果显示血小板变形的同时伴有颗粒中心化，无聚集和释放反应．Ｆｕｒａ２负载后，５ＨＴ升高［Ｃａ２＋］ｉ，９０秒达峰值，ＩＰ３一过性升高．ＡＤＰ同样引起ＤＬＴ，但可被５ＨＴ消除，呈浓度依赖性．ＡＤＰ的聚集反应和［Ｃａ２＋］ｉ动员则由于５ＨＴ预处理而升高．结论：５ＨＴ增强ＡＤＰ的聚集反应与５ＨＴ的细胞内钙动员及ＡＤＰ的外钙内流两者的叠加作用有关．     

Stimulation of central cholinergic neurons by(-)clausenamide in vitro

Ｓｔｉｍｕｌａｔｉｏｎｏｆｃｅｎｔｒａｌｃｈｏｌｉｎｅｒｇｉｃｎｅｕｒｏｎｓｂｙ（－）ｃｌａｕｓｅｎａｍｉｄｅｉｎｖｉｔｒｏ１ＤＵＡＮＷｅｎＺｈｅｎ，ＺＨＡＮＧＪｕｎＴｉａｎ２（ＤｅｐａｒｔｍｅｎｔｏｆＰｈａｒｍａｃｏｌｏｇｙ，Ｉｎｓｔｉｔｕｔｅ...     

Modulation of multidrug resistance by three bisbenzyl-isoquinolines in comparison with verapamil

比较轮环藤碱（Ｃｙｃ）、海岛轮环藤碱（Ｉｎｓｒ）和海岛轮环藤酚碱（Ｉｎｓｎ）与维拉帕米（Ｖｅｒ）体外调节多药耐药性（ＭＤＲ）的作用．方法：细胞毒试验采用ＭＴＴ法，细胞内阿霉素（Ｄｏｘ）积累采用荧光分光光度法测定．结果：Ｃｙｃ，Ｉｎｓｒ，Ｉｎｓｎ和Ｖｅｒ在ＭＤＲ细胞系ＭＣＦ７／Ａｄｒ和ＫＢｖ２００能显著调节Ｄｏｘ和长春新碱的耐药性，且其作用呈剂量依赖性．Ｃｙｃ，Ｉｎｓｒ，Ｉｎｓｎ和Ｖｅｒ均能增加ＭＣＦ７／Ａｄｒ细胞内Ｄｏｘ的积累．Ｃｙｃ和Ｉｎｓｒ调节ＭＤＲ作用明显优于Ｖｅｒ，而Ｉｎｓｎ的作用类似于Ｖｅｒ．结论：Ｃｙｃ，Ｉｎｓｒ和Ｉｎｓｎ能通过增加ＭＤＲ细胞内Ｄｏｘ的积累而调节ＭＤＲ．     

Modulation of Δ9-tetrahydrocannabinol-induced hypothermia by fluoxetine in the rat

1. It has been suggested that the dose of Δ⁹-tetrahydrocannabinol (Δ⁹-THC) that induces hypothermia in the rat increases the release of brain 5-hydroxytryptamine (5-HT). In light of this, we investigated the hypothermia produced by Δ⁹-THC, and the effect the selective serotonin reuptake inhibitor fluoxetine has on this response.
2. A significant dose-dependent decrease in body temperature occurred after i.v. administration of 0.5 to 5 mg kg⁻¹ Δ⁹-THC; maximum decreases being 0.8±0.2°C to 2.9±0.3°C. This hypothermic response was attenuated by the cannabinoid CB₁ receptor antagonist SR 141716.
3. Fluoxetine (10 mg kg⁻¹ i.p.) alone caused a decrease in body temperature of 0.6±0.1°C (n=32, P<0.05) after 40 min. However, pretreatment with fluoxetine (10 mg kg⁻¹ i.p.) 40 min before Δ⁹-THC significantly reduced the Δ⁹-THC-induced hypothermia (n=7–8, P<0.05). Contrary to this antagonist-like effect, fluoxetine administered 40 min after Δ⁹-THC significantly potentiated the Δ⁹-THC-induced hypothermia, producing a maximum decrease of 3.2±0.3°C.
4. It is suggested that the effect of fluoxetine on the Δ⁹-THC-induced hypothermic response is dependent on the time of its administration relative to that of Δ⁹-THC. Pretreatment with fluoxetine increases extracellular 5-HT due to reuptake inhibition. Increased extracellular 5-HT can activate autoreceptors which may decrease serotonergic activity, thereby reducing the Δ⁹-THC-induced hypothermia. Conversely, when fluoxetine is adminstered after Δ⁹-THC, the reuptake block is thought to potentiate the already activated serotonegic system, hence potentiating the Δ⁹-THC-induced hypothermia.

     

Relaxation of human pulmonary arteries by PPARγ agonists

It has been suggested that activation of nuclear peroxisome proliferator-activated receptors γ (PPARγ) may represent a new strategy for the treatment of pulmonary arterial hypertension. It has been demonstrated that PPARγ activation relaxed the isolated mouse pulmonary artery. The aims of the present study were to examine whether and to which extent the two PPARγ agonists rosiglitazone and pioglitazone relax the isolated human pulmonary artery and to investigate the underlying mechanism(s). Isolated human pulmonary arteries were obtained from patients without clinical evidence of pulmonary hypertension during resection of lung carcinoma. Vasodilatory effects of PPARγ agonists were examined on endothelium-intact or endothelium-denuded vessels preconstricted with the thromboxane prostanoid receptor agonist U-46619. Rosiglitazone and pioglitazone (0.01–100 μM) caused a concentration- and/or time-dependent full relaxation of U-46619-preconstricted vessels. The rosiglitazone-induced relaxation was attenuated by the PPARγ antagonist GW9662 1 μM, endothelium denudation, the nitric oxide synthase inhibitor L-NAME 300 μM, the cyclooxygenase inhibitor indomethacin 10 μM, and the K_ATP channel blocker glibenclamide 10 μM. The prostacyclin IP receptor antagonist RO1138452 1 μM shifted the concentration–response curve for rosiglitazone to the right. The PPARγ agonists pioglitazone and rosiglitazone relax human pulmonary arteries. The rosiglitazone-induced vasorelaxation is partially endothelium-dependent and involves PPARγ receptors, arachidonic acid degradation products, nitric oxide, and K_ATP channels. Thus, the relaxant effect of PPARγ agonists in human pulmonary arteries may represent a new therapeutic target in pulmonary arterial hypertension.     

Modulation of motor activity by α1 and α2 stimulation in mice

Summary The influence of two -adrenoceptor agonists, clonidine and B-HT 920, on motor activity was tested in mice. Both, clonidine and B-HT 920 (2-amino-6-allyl-5,6,7,8-tetrahydro-4H-thiazolo-[4,5-d]-azepine) in the dose range 30–300 g/kg s.c. equieffectively inhibited exploratory activity. On the other hand only clonidine, which stimulates ₂- and ₂-adrenoceptors increased locomotor activity in mice treated with reserpine (5 mg/kg) and apomorphine (3 mg/kg) in the doses of 0.3 and 1 mg/kg i.p. The highly selective ₂-agonist B-HT 920 was ineffective under these conditions up to 30 mg/kg i.p. It is concluded, that in mice sedative -adrenoceptors are of the ₂- and excitatory of the ₁-type.     

Modulation of ammonium perfluorooctanoate-induced hepatic damage by genetically different PPARα in mice

Perfluorooctanoic acid is a ligand for peroxisome proliferator-activated receptor (PPAR??). Ammonium perfluorooctanoate (APFO) at 0.1 and 0.3?mg/kg doses activated mouse PPAR??, but not human PPAR??. This study aimed to clarify whether milligram-order APFO can activate human PPAR??, and the receptor is involved in APFO-induced chronic hepatic damage. Male Sv/129 wild-type (mPPAR??), Ppar??-null, and humanized PPAR?? (hPPAR??) mice (8 weeks old) were divided into three groups. The first was treated with water and the other two with 1.0 and 5.0?mg/kg APFO for 6?weeks, orally, respectively. Both doses activated mouse and human PPAR?? to a similar or lower degree in the latter. APFO dose dependently increased hepatic triglyceride levels in Ppar??-null and hPPAR?? mice, but conversely decreased those in mPPAR?? ones. APFO-induced hepatic damage differed markedly among the three genotyped groups: single-cell necrosis was observed in all genotyped mice; inflammatory cells and macrovesicular steatosis only in Ppar??-null mice; and microvesicular steatosis and hydropic degenerations in hPPAR?? and Ppar??-null mice. The molecular mechanism underlying these differences may be attributable to those of gene expressions involved in lipid homeostasis (PPAR??, ??- and ??-oxidation enzymes, and diacylglycerol acyltransferases) and uncoupling protein 2. Thus, milligram-order APFO activated both mouse and human PPAR?? in a different manner, which may reflect histopathologically different types of hepatic damage.     

Contractile responses and calcium movements induced by α1-adrenoceptor stimulant,norepinephrine, in rabbit iris dilator muscle

• 1.1. The mechanisms involved in contraction of rabbit iris dilator muscle induced by norepinephrine (NE) were studied.
• 2.2. The concentration-response curve of NE was not influenced by Ca²⁺ blockers in the normal physiological saline solution (PSS) and removal of Ca²⁺ from PSS.
• 3.3. In 0.01 mM EGTA containing Ca²⁺-free PSS, the NE-induced contraction was phasic, which was suppressed by TMB-8, cyclopiazonic acid, ionomycin and A23187 but still partly remained.
• 4.4. In 2 mM EGTA containing Ca²⁺-free PSS, NE increased the intracellular Ca²⁺ ([Ca²⁺]_i) and muscle tension. Ryanodine abolished the increase in [Ca²⁺]_i induced by NE but slightly inhibited the tension.
• 5.5. These results suggest that the NE-induced contraction of rabbit iris dilator in normal PSS is mainly due to the increase in the release of intracellularly sequestered Ca²⁺ and partly due to the Ca²⁺-independent processes.

     

Modulation of κ-opioid receptor mediated tolerance in the guinea-pig ileum by chronic co-administration of dihydropyridines

The influence of the L-type Ca²⁺ channel modulators nimodipine (a Ca²⁺ blocker) and BAY K 8644 (a Ca²⁺ activator) on the expression of tolerance to the inhibitory effects of - and µ-opioid agonists in the guinea-pig ileum from guinea-pigs rendered tolerant to the -opioid receptor agonist U-50,488H was investigated. Tolerance to U-50,488H was induced by its administration (15 mg/kg twice a day) for 4 days. Control groups received saline at the same time schedule. Chronic infusion of guinea-pigs with nimodipine (2 /l/h for 7 days) or BAY K 8644 (0.5 /l/h for 7 days), did not cause any modification of the height of contractions induced by electrical stimulation of the myenteric plexus-longitudinal muscle (MPLM) preparation from naive guinea-pigs. The Ca²⁺ antagonist nimodipine increases the potency of U-50,488H (selective agonist) to reduce the amplitude of neurogenic contractions of the MPLM strip in naïve animals, whereas the Ca²⁺ activator BAY K 8644 induced the opposite effect. However, the effect of DAMGO (selective µ agonist) was not modified in guinea-pigs infused with nimodipine or BAY K 8644. Tolerance to the inhibitory effects of both U-50,488H and DAMGO was observed following administration of U-50,488H for 4 days and was revealed as a rightward shift of the concentration-response curves for the two agonists. Chronic infusion of guinea-pigs with nimodipine concurrently with chronic U-50,488H, markedly attenuated the expression of selective tolerance to U-50,488H as well as the cross-tolerance between U-50,488H and DAMGO. By the contrary, the magnitude of tolerance to U-50,488H and to DAMGO was enhanced by concomitant infusion of BAY K 8644. The results suggest that, in the GPI, -opioid receptor may be functionally linked to the dihydropyridine-sensitive Ca²⁺ channel: The blockade of the channel increased whereas its activation reduced the potency of U-50,488H. In chronic experiments, nimodipine prevented the expression of tolerance to U-50,488H and the cross-tolerance between U-50,488H and DAMGO, whereas BAY K 8644 produced the opposite effect. These results suggest that, in the GPI, selective tolerance to -agonist as well as cross-tolerance between - and µ-opioid agonists would involve activation of L-type Ca²⁺ channels, which could indicate that intracellular Ca²⁺ may be the final common pathway through which myenteric neurons adapt to the chronic opioid exposure.     

Modulation of cytosolic free calcium concentration by α1-adrenoceptors in rat atrial cells

Summary The effects of ₁-adrenoceptor stimulation by phenylephrine (PE) and -adrenoceptor stimulation by isoprenaline (ISO) on Ca²⁺ current (I_Ca) and free intracellular Ca²⁺ concentration ([Ca²⁺]_i) were studied in isolated atrial myocytes from rat hearts. PE did not significantly affect the magnitude of I_Ca, whereas large increases of peak I_Ca were observed in response to ISO. In electrically driven cells, PE evoked a concentration-dependent, gradual increase in diastolic [Ca²⁺]_i and, initially, an increase in the height of peak [Ca²⁺]_i transients. When the diastolic [Ca²⁺]_i was increased to a greater extent, the amplitude of [Ca²⁺]_i transients was decreased. Simultaneous measurements of [Ca²⁺]_i and membrane potential showed that the increase in diastolic [Ca²⁺]_i was associated with a depolarization of the membrane, and the greater amplitude of [Ca²⁺]_i transients with a prolongation of the action potential (AP). The PE-induced increase in diastolic [Ca²⁺]_i was eliminated when the cells were voltage-clamped at the original resting membrane potential (RP); under these conditions, an increase in [Ca²⁺]_i transients was observed in response to PE. ISO usually caused larger increases in the amplitude of [Ca²⁺]_i transients with only minor changes in diastolic [Ca²⁺]_i. These results suggest that PE and ISO increase the amplitude of [Ca²⁺]_i transients in rat atrium in different ways. The increase in [Ca²⁺]_i transients in response to -adrenoceptor stimulation is commonly thought to be mediated by a greater conductance of voltage-dependent Ca²⁺ channels causing a greater Ca²⁺ influx and a release of more Ca²⁺ from the sarcoplasmic reticulum during the AP. The increase in diastolic [Ca²⁺]_i in response to PE is probably a consequence of the depolarization of the membrane, possibly involving the voltage-dependent Na⁺-Ca²⁺ exchange mechanism. The increase in the amplitude of the [Ca²⁺]_i transients in response to PE may be ascribed both to the initial increase in diastolic [Ca²⁺]_i and the prolongation of the AP. Send offprint requests to H. Nawrath at the above address     

Modulation of cytotoxicity of chemotherapeutic drugs by activated H-γas

Cells from a single MCF-7 clone were transfected with an isopropyl-1-thio-β-D-galactopyranoside (IPTG)-inducible construct containing activated human H-γas with a Gly¹² → Val¹² mutation. Expression of H-γas was induced by the presence of IPTG with low background. MCF-7-ras clones were examined for sensitivity to a wide variety of drugs under both induced and non-induced conditions. When expression of the activated γas was induced, these clones showed markedly increased resistance to cisplatin and mitomycin C, moderately increased resistance to methotrexate and trimetrexate, and no increased resistance to other drugs including taxol, doxorubicin, and etoposide. A DNA fragmentation assay revealed that DNA in MCF-7-γas cells treated with cisplatin under induced conditions was intact, whereas extensive degradation of DNA occurred in similarly treated cells under non-induced conditions. This result, along with the fact that MCF-7-γas cells, upon induction of the activated H-γas, showed increased resistance to drugs that bind DNA, indicates that the activated H-γas may play a role in the DNA repair process.     

Dopamine inhibits prostaglandin F2α-induced depolarization of rabbit jejunal arteries via activation of DA1-receptors

Summary In rabbit jejunal arteries, the membrane potential of single smooth muscle cells decreased on the application of noradrenaline 3 mol/1. LY 171555 1 mol/1 did not change, whereas SKF 38393 10 mol/1 reversed the effect of noradrenaline. When prostaglandin F₂ (PGF₂) was used to evoke depolarization in the presence of prazosin 0.1 mol/1, rauwolscine 1 mol/1 and propranolol 1 mol/1, both SKF 38393 10 mol/1 and dopamine 10 mol/1 repolarized the membrane. SCH 23390 1 mol/1 antagonized the effects of SKF 38393 10 mol/1 and dopamine 10 mol/1. Thus, the change in membrane potential is mediated by a DA₁-recep-tor.     

Differential effects of α-β-methylene ATP on responses to nerve stimulation in SHR and WKY tail arteries

Summary The effects of ,-methylene-adenosine triphosphate, (,-methylene ATP, a P₂-receptor desensitising agent) have been evaluated on vasoconstrictor responses elicited by exogenous agonists or electrical field stimulation in isolated perfused SHR or WKY tail arteries and on tritium release elicited by electrical field stimulation in SHR-tail arteries pre-labeled with ³H-noradrenaline.Exposure to ,-methylene ATP (0.1 mol/l) significantly inhibited vasoconstrictor responses to electrical field stimulation in SHR tail arteries. These inhibitory effects were not further increased at a higher concentration of ,-methylene ATP (1 mol/l). In WKY tail arteries, ,-methylene ATP (1 mol/l) failed to significantly inhibit vasoconstrictor responses to electrical stimulation.In SHR tail arteries prelabelled with ³H-noradrenaline, ,-methyleneATP (1 mol/l) did not inhibit the stimulation evoked release of tritium. However, at this concentration, ,-methylene ATP significantly antagonized the vasoconstrictor responses of SHR tail arteries induced by exogenous ATP (1 mol/l), ,-methylene ATP (30 mol/l), a stable agonist at P₂-receptors, or 60 mmol/l KCl. These effects of ,-methylene ATP on contractile responses to KCl were not observed in WKY-tail arteries.In tail arteries obtained from reserpine pretreated SHR, despite a 85–95% decrease in endogenous noradrenaline tissue content, the vasoconstrictor responses induced by periarterial field stimulation were greatly diminished, but not abolished. These residual responses to periarterial field stimulation were not antagonized by prazosin (0.1 mol/l), but were practically abolished by the addition of ,-methylene ATP (1 mol/l).In tail arteries from WKY rats pretreated with reserpine, exposure to prazosin (0.1 mol/l) further reduced the residual responses elicited by electrical field stimulation. In these WKY-tail arteries, addition of ,-methylene ATP (1 mol/l) did not further inhibit the remaining vasoconstrictor response obtained in the presence of prazosin.While our results suggest a significantly greater cotransmitter role for ATP with noradrenaline in tail arteries of SHR compared with control normotensive WKY rats, additional effects of ,-methylene ATP not involving P₂ receptors cannot be entirely excluded.     

Modulation of serum concentrations and hepatic metabolism of 17β-estradiol and testosterone by amitraz in rats

The present study has investigated the ability of amitraz, a widely used formamidine pesticide, to modulate serum concentrations and liver microsomal metabolism of 17β-estradiol (E2) and testosterone in rats. Amitraz was administered intraperitoneally to male rats for 4 days and to intact female rats or ovariectomized (OVX) and 0.5 mg/kg E2-supplemented female rats for 7 days. E2 and metabolites were analyzed by gas chromatography-electron capture detection and testosterone and metabolites were analyzed by high-pressure liquid chromatography. In OVX and E2-supplemented females, 50 mg/kg amitraz caused an 85% decrease of serum E2 concentration and a marked increase of 2-OH-E2 concentration. Amitraz at 25 and 50 mg/kg produced 9.0-fold or greater increases of serum testosterone and 2β-OH-testosterone levels in males. Amitraz at 25 mg/kg resulted in no or minimal increases of liver microsomal formation of E2 or testosterone metabolites. Amitraz at 50 mg/kg produced 1.4- to 3.6-fold increases of 2-OH-E2; estrone; 2β-, 6β-, and 16α-OH-testosterone; and androstenedione formation in males and intact females. Amitraz at 50 mg/kg preferentially increased intact female 16β-OH-testosterone production by 8.6-fold. In OVX females, E2 supplement alone or cotreatment with E2 and 50 mg/kg amitraz produced 1.3- to several-fold increases of 2- and 4-OH-E2 formation and 2β- and 16α-OH-testosterone production. The cotreatment increased 6β- and 16β-OH-testosterone formation by 1.8- and 1.6-fold, respectively. The present findings show that amitraz induces hepatic E2 and testosterone metabolism in male and female rats, decreases serum E2 concentration in OVX and E2-supplemented females, but increases serum testosterone in males.