摘要:

The mechanoinhibitory effect of estradiol on the myogenic activity of guinea pig urinary bladder detrusor muscles was studied. In detrusor muscles tonically contracted with 80 mmol/l KCl, 17β-estradiol and the nonestrogenic isomer 17α-estradiol at 30 µmol/l reduced the contraction by 64 ± 3 and 59 ± 1 %, respectively. In detrusor muscles maintained in Ca2+-free media and depolarized with 80 mmol/l KCl, the contractile response of muscles to the reintroduction of Ca2+ was inhibited in a dose-dependent manner by 17β-estradiol, suggesting that 17β-estradiol blocked entry of extracellular Ca2+ into bladder smooth muscle cells and reduced the rise of intracellular Ca2+ required for contraction. In detrusor muscles mildly depolarized with 15 mmol/l KC1, 17β-estradiol reduced the myogenic activity with an IC50 of 6.8 ± 1.3 µmol/l. The higher activity of 17β-estradiol in this latter test indicated that estradiol could also possess some K+ channel opening activity. Glibenclamide at 1 µmol/l did not affect the relaxant activity of 17β-estradiol in detrusor muscles stimulated with 15 mmol/l; however, this activity was diminished in a dose-dependent manner by iberiotoxin. Collectively, these results have demonstrated that in addition to the Ca2+ antagonist activity, 17β-estradiol possesses K+ channel opening activity in guinea pig urinary bladder smooth muscles, activating probably not the adenosine triphosphate sensitive, but the Ca2+-dependent large-conductance K+

ISSN:0031-7012    

DOI:10.1159/000139336

出版商:S. Karger AG    

年代:1995

数据来源: Karger

摘要:

The role of peptides in mediating the nonadrenergic, noncholinergic (NANC) response of the rat urinary bladder was studied. Electrical stimulation of muscle strips from 3-month-old female Wistar rat urinary bladders in the presence of autonomic blockers (atropine 10–6 mol/l, propanolol 10–6 mol/l, phentolamine 10–6 mol/l, and guanethidine 10–6 mol/l) showed NANC contraction accounting for 60% of the maximum contractile responses at 40 Hz. Frequency-response studies showed that in the presence of alpha-chymotrypsin (2 U/ml, 30-min incubation), the NANC contractile responses to electrical stimulation at lower frequencies (3–10 Hz) were enhanced (p < 0.05; n = 9). However, no significant differences were observed at higher frequencies (20–40 Hz). With repetitive 4-Hz stimulation, alpha chymotrypsin caused a 19% increase in the NANC contractile response (p < 0.05; n = 8). It is postulated that the NANC response of the rat bladder smooth muscle is composed of an excitatory (contractile) and an inhibitory (relaxant) component. Some peptide(s) is/are responsible for mediating the inhibito

ISSN:0031-7012    

DOI:10.1159/000139337

出版商:S. Karger AG    

年代:1995

数据来源: Karger

摘要:

To determine the existence of β3-adrenoceptors in functional assays in isolated preparations for which data are lacking, we compared the effects of SR 58611A, a selective β3-adrenoceptor agonist, and isoprenaline in the guinea pig common bile duct, distal colon and urinary bladder. SR 58611A and isoprenaline relaxed the common bile duct (EC50: 6.85 and 0.41 µmol/l, respectively). The effect of SR 58611A was resistant to CGP20712A, ICI 118551, propranolol and tetrodotoxin, but was antagonized by alprenolol (pA2 = 6.86), while the effect of isoprenaline was antagonized by CGP 20712A, ICI 118551, propranolol and alprenolol (pA2 = 7.04, in the presence of propranolol to saturate β1- and β2-adrenoceptors). In colonic preparations, SR 58611A and isoprenaline relaxed circular muscle strips (EC50: 5.48 and 0.49 µmol/l, respectively). The effect of SR 58611A was resistant to CGP 20712A, ICI 118551, propranolol and tetrodotoxin, but was antagonized by alprenolol (pA2 = 7.01). The effect of isoprenaline was resistant to CGP 20712A, but was antagonized by ICI 118551, propranolol and alprenolol (pA2 = 6.88, in the presence of propranolol). In urinary bladder strips, SR 58611A had no effect, whereas isoprenaline reduced resting tone (EC50: 0.87 µmol/l), an effect antagonized by alprenolol (pA2 = 8.14). These data provide functional evidence for the presence of β3-adrenoceptors in the guinea pig common bile duct and colon, but not in the urinary bladder. At the concentrations used, the effect of SR 58611A was probably mediated solely by activation of β3-adrenoceptors located on smooth muscle cells, whereas the effects of isoprenaline were due to β3- and also to β1- and/or β2-adrenoceptor

ISSN:0031-7012    

DOI:10.1159/000139338

出版商:S. Karger AG    

年代:1995

数据来源: Karger

摘要:

The first putative extracellular domains of both ml and ml muscarinic receptors contain a triplet of amino acid residues consisting of leucine (L), tyrosine (Y), and threonine (T). This triplet is repeated as LYTLYT in m2 receptors. However, it is repeated in a transposed fashion (LYTTYL) in the sequence of ml receptors. In this work we employed site-directed mutagenesis to investigate the possible significance of this unique sequence diversity in determining the distinct differential drug-receptor interaction at the two receptor subtypes. Mutation of the LYTTYL sequence of ml receptors to the corresponding m2 receptor LYTLYT sequence, however, did not significantly change the binding affinity of the agonist carbachol or the affinity of the majority of a series of receptor antagonists which are able to discriminate between wild-type ml and m2 receptors. The reverse mutation at the m2 receptor also did not modify agonist affinity, but altered affinity of several receptor subtype-selective antagonists. The magnitude of affinity changes, however, was small, and the direction of these changes was opposite to what would be expected if the m2 receptor LYTLYT sequence were important for determining the binding profile of m2-receptor-selective antagonists. Our data suggest that the LYTTYL-LYTLYT sequence differences between ml and m2 muscarinic receptors are not important for determining receptor pharmacology.

ISSN:0031-7012    

DOI:10.1159/000139339

出版商:S. Karger AG    

年代:1995

数据来源: Karger

摘要:

The effects of hyper- and hypothyroidism on the vasorelaxing responses to acetylcholine (ACh), sodium nitroprusside (NP), and CaCl2 were investigated in aortic strips and isolated perfused kidneys. The renal vascular reactivity to ACh and NP was increased in hyperthyroid rats, whereas the concentration-response curve to ACh in hypothyroid rats was flattened. In the renal vasculature from hypothyroid rats, NP produced a dual response: vasoconstriction at low doses and vasodilation at medium to high doses. Aortic strips from hyperthyroid rats showed an increased response to ACh without significant differences between hypothyroid and control groups. Aortic strips from all three experimental groups showed a similar relaxing response to CaCI2. These results indicate that: (1) the raised arterial pressure of hyperthyroid rats is not associated with a reduced endothelium-dependent and calcium-induced vasodilation, and (2) the changes in responsiveness to vasodilators in resistance vessels from hyper- and hypothyroid rats may play a role in the increased and decreased peripheral vascular resistances, respectively, previously reported in such animals.

ISSN:0031-7012    

DOI:10.1159/000139340

出版商:S. Karger AG    

年代:1995

数据来源: Karger

摘要:

Nitrovasodilators and β-adrenoceptor antagonists are effective in the treatment of angina pectoris and hypertension, but each has side effects that may prevent their long-term use. In the present study responses of coronary arteries and arterioles to nipradilol, a β-adrenoceptor antagonist with nitrovasodilator action, were compared to nitroglycerin in normal myocardium of the beating left ventricle in anesthetized dogs. Coronary arteries and arterioles were visualized using stroboscopic illumination of epicardial surface of the heart and intravital microscopy with fluorescence angiography. Diameters were measured under control conditions and during topical suffusion of nipradilol (10–8–10–4M) or nitroglycerin (10–8–10–4 M). Nipradilol produced dose-dependent dilation of all size arteries and arterioles however, dilation was inversely related to vessel size. Arterioles less than 100 µm in diameter dilated more than arteries greater than 200 µm in diameter. In contrast, dilation to nitroglycerin was directly related to vessel size. Arteries larger than 200 µm dilated more than arterioles less than 100 µm. In conclusion, although nipradilol and nitroglycerin are both nitrovasodilators the microvascular response to these ag

ISSN:0031-7012    

DOI:10.1159/000139341

出版商:S. Karger AG    

年代:1995

数据来源: Karger

摘要:

In male Sprague-Dawley rats, acute and chronic effects of dizocilpine (MK-801), a noncompetitive antagonist of the N-methyl-D-aspartate (NMDA) receptor, were determined on the analgesic and hypothermic actions of U-50,488H, a ĸ-opioid receptor agonist. In addition, the in vitro effects of MK-801 on the binding of [3H]ethylketocyclazocine ([3H]EKQ to ĸ-opioid receptors in brain and spinal cord of the rat were determined. A single injection of MK-801 given 10 min prior to U-50,488H or given twice a day for 4 days dose-dependently enhanced the analgesic action of U-50,488H. The enhancement of the analgesic response was much greater in rats injected chronically with MK-801 as compared with those injected acutely. Both single and multiple injections of MK-801 failed to affect the hypothermic action of U-50,488H. In vitro, MK-801 inhibited the binding of [3H]EKC to brain and spinal cord membranes with IC50 values of 9.80 ± 1.7 and 1.37 ± 0.58 µM, respectively. Chronic administration of MK-801 twice a day for 4 days increased the Bmax value of [3H]EKC binding in the brain, but had no effect on Kd. On the other hand, chronic treatment with MK-801 decreased the Kd of [3H]EKC binding in spinal cord without affecting Bmax. It is concluded that blockade of NMDA receptor enhances the analgesic response to a ĸ-opioid receptor agonist and upregulates brain and spinal cord ĸ-opioid receptors. Finally, the results suggest that the NMDA receptor may have a role in the regulation of ĸ-opioid

ISSN:0031-7012    

DOI:10.1159/000139342

出版商:S. Karger AG    

年代:1995

数据来源: Karger

摘要:

Using the same initial Fractogel (tentacle) ion-exchange chromatography to isolate murine cytochrome P-450, mouse hepatic NADPH-cytochrome P-450 reductase (EC 1.6.2.4) was simultaneously isolated from solubilized liver microsomes and purified on a DE-52 column to a single band on sodium dodecyl sulfate-polyacrylamide gel electrophoresis. The enzyme had a molecular mass of 77 kD, and its specific activity was 25.4 µmol·min–1·mg protein-1. Purified constitutive mouse liver NADPH-cytochrome P-450 reductase was successfully reconstituted in vitro with dilauroylphosphatidyl-choline and constitutive purified mouse testosterone 2α-hydroxylase (cytochrome P-4502α) with an observed activity of 13.8 nmol·min–1·nmol P-450–1. Although the partially purified reductase obtained from the Fractogel column was contaminated by significant levels of two unidentified proteins, it was as equally effective in the reconstituted system as the DE-52-derived purified reductase. Lastly, we found that rat and mouse NADPH-cytochrome P-450 reductases were similarly effective in supporting the catalytic activity of rat cytochrome P-450 2B1, but the murine reductase was 50% more effective than the rat reductase in a reconstituted system containing mouse cytochrome P-450<

ISSN:0031-7012    

DOI:10.1159/000139343

出版商:S. Karger AG    

年代:1995

数据来源: Karger