I 2 Imidazoline binding sites have been shown to exist on cardiac myocytes of human beings and rat. Both of I 1 and I 2 imidazoline binding sites have been identified on vascular smooth muscle cells of various species. Vascular I 2 imidazoline binding sites may participate in vascular smooth muscle proliferation. The sympathetic nerves supplying the cardiovascular system are endowed with presynaptic inhibitory imidazoline receptors. Being different from most of the imidazolines, moxonidine does not activate presynaptic imidazoline receptors, but SR141716A, which is considered as a selective antagonist at cannabinoid receptors, antagonizes presynaptic imidazoline receptors. It has been shown that imidazolines exhibit antiarrhythmic action. Agamatine, which is endogenous ligand at imidazoline receptors, not only decreases the rate of pacemaker firing in sinoatrial node of animal, prolongs action potential duration on cardiac myocytes of human beings and animal, but also inhibits afterdepolarizations induced by isoproterenol. On the other hand, imidazolines and guanidines inhibit the cardiovascular K ATP channel in a noncompetitive manner, those effects might interfere with the cardioprotective effects of K ATP channel.

0.05). Phenylephrine induced contractile responses in a concentration-dependent manner in the dorsal detrusor strips, but not in the ventral detrusor strips. S-doxazosin, R-doxazosin and rac-doxazosin at 1 ?mol?L-1 antagonized the phenylephrine-induced contractile responses competitively in the dorsal detrusor strips, and their pKB values were 7.44?0.19, 7.39?0.14 and 7.38?0.30, respectively. Three pKB values of doxazosin and its enantiomers were not significantly different from each other. Electric field stimulation produced a steady contractile response that was completely inhibited by tetrodotoxin at 0.3 ?mol?L-1. S-doxazosin, R-doxazosin and rac-doxazosin significantly inhibited the contractile responses to electric field stimulation in the dorsal detrusor strips of the rabbit urinary bladder(P0.05). However, S-doxazosin, R-doxazosin and rac-doxazosin did not affect the responses to electric field stimulation in the ventral detrusor strips. Conclusion The pKB value of S-doxazosin against phenylephrine-induced contraction via-adrenoceptors is same to R-doxazosin and rac-doxazosin, and the three agents are able to inhibit the adrenergic contraction induced by electric field stimulation in dorsal detrusor strips of the rabbit urinary bladder.

Aim To observe the modulation of adenosine triphosphate (ATP) on motility of isolated gastric smooth muscle from rat.Methods Longitudinal and circular muscle strips of rat gastric body and antrum were prepared, and the effects of ATP (0.1, 1,10,100 ?mol?L~-1 and 1 mmol?L~-1 ) on the motility of the strips were investigated. Results ATP induced a small relaxation followed by an obvious spasm in longi- tudinal muscle strips of the gastric body; when tone was raised by KCl, ATP induced a larger relaxation followed by a smaller spasm.ATP only produced contraction in circular muscle strips of the gastric body.Low concentration of ATP inhibited the contractile amplitude of the antral longitudinal strips, at the same time increased the frequency of the contraction apparently; when tone was raised by KCl, ATP produced a concentration-related relaxation.Low concentration of ATP firstly enhanced and then inhibited contractile amplitude of antral circular musle strips, while high concentration of ATP fully inhibited the motility. Conclusion We firstly reported the obvious effects of ATP on longitudinal and circular strips of rat gastric body and antrum. The effects of ATP on the four preparations were different from each other, suggesting that ATP plays an important modulatory role on motility of gastric smooth muscle of rats.

Aim To analyze the blocking effect of ( ± ) doxazosin [ ( ± ) DOX ] , ( -) doxazosin [ ( -) DOX] and ( +) doxazosin [( +) DOX] on the vaso-constriction of rat isolated mesenteric arterioles media-ted by α1-adrenoceptors. Methods The vasoconstric-tion induced by phenylephrine ( Phe) in the rat isola-ted mesenteric arterioles ( the second- and third-order branches) was recorded using DMT wire myograph sys-tem 620M, and theα1-adrenoceptor antagonistic activ-ity of ( ± ) DOX and its enantiomers was analyzed. Results The inner diameter of second- and third-or-der branches of the rat mesenteric artery was (162. 5 ± 5. 3) μm (n=11) and (103. 1 ± 2. 3) μm (n=23), respectively. The values of normalized preload of the second-and third-order branches, which were calculat-ed by the LabChart software, were (2. 93 ± 0. 51) mN ( n =11 ) and ( 2. 64 ± 0. 50 ) mN ( n =23 ) ( P >0. 05 ) . Vasoconstrictive responses to Phe in the sec-ond-order branche of rat mesenteric artery under nor-malized preloads were not significantly different from those under 5 mN preload;however, the Emax values of the Phe-induced vasoconstriction under 10 mN, 15 mN and 20 mN preloads were decreased by 12%, 29%and 43% ( P<0. 01 ) respectively compared with those under normalized preload. The concentration-response curves for Phe were shifted to right in a concentration dependent manner by ( -) DOX or ( +) DOX at 0. 001 , 0. 01 and 0. 1 μmol · L-1 without significant change in their Emax values in the second-and third-or-der branches of rat mesenteric artery. Schild plot anal-ysis indicated that ( -) DOX, ( +) DOX and ( ± ) DOX non-competitively inhibited the vasoconstrictive responses to Phe in the second-order branches, and the rank order of pKB values was ( +) DOX ( 8. 67 ± 0. 10 ) , ( ± ) DOX ( 8. 53 ± 0. 090 ) , ( -) DOX (7. 85 ± 0. 09). However, schild plot analysis indica-ted that ( -) DOX and ( +) DOX competitively inhibi-ted the vasoconstrictive responses for Phe in the third-order branch, and the rank order of their pKB values was ( ± ) DOX ( 8. 68 ± 0. 17 ) , ( +) DOX ( 8. 48 ± 0. 10 ) , ( -) DOX ( 7. 48 ± 0. 140 ) . Conclusion The α1-adrenoceptor blocking activity of ( -) DOX is much weaker than that of ( +) DOX or ( ± ) DOX in the rat isolated mesenteric arterioles, and there is a tendency to enhance the activity of ( ± ) DOX in third-order branches of the rat mesenteric artery though theα1-adrenoceptor blockade effect of ( ± ) DOX is not significantly different from ( +) DOX.

P-glycoprotein (P-gp) is an ATP-dependent multidrug efflux pump that acts as a major obstacle for oral drug delivery and cancer therapy. Recent reports have provided evidence that excipients often used in pharmaceutical formulations, such as Pluronic and TPGS, also have inhibitory effects on P-glycoprotein. Because inhibition of efflux transporters by polymeric inhibitors may dramatically increase the bioavailability of P-gp substrates with negligible side effects, identification of the mechanism and their structure activity relationship is therefore of significant importance for pharmaceutical development. Other than competitive inhibition for traditional inhibitors, polymeric inhibitors may modify P-gp function through alterations on membrane fluidity, inhibition of P-gp ATPase, depletion of intracellular ATP and down-regulating of P-gp expression. In the present review, the inhibition mechanism of potential polymeric inhibitors and their structure activity relationship will be discussed along with a brief introduction to the established methodologies.

The study is to establish an HPLC method using fluorescence detector for the determination of doxazosin enantiomers and investigate their chiral inversion in vitro and in vivo. Ultron ES-OVM was taken as the chiral chromatographic column, and the column temperature was 30 degrees C. Isocratic elution using a mobile phase of phosphate buffer-acetonitrile (85 : 15, v/v) at a flow rate of 0.8 mL x min(-1) was done. The fluorescence detection was set at lambda(Ex) = 255 nm and lambda(Em) = 385 nm. Prazosin was used as the internal standard. (-) Doxazosin or (+) doxazosin added into rat plasma in vitro was determined after incubating in 37 degrees C water bath for 2, 5 and 10 days. (-) Doxazosin or (+) doxazosin was administered orally to the rats for one months. Plasma samples were taken at 8 h after the last administration. A good linear relationship was achieved when the concentration of doxazosin enantiomers was within the range of 4 - 2 000 ng x mL(-1). The average recovery for (-) doxazosin was 99.5% with RSD 3.6%, and for (+) doxazosin was 99.3% with RSD 4.3%. Chiral inversion was observed neither in vitro nor in vivo studies. The method is selective, accurate and reproducible, which is suitable for the detection of doxazosin enantiomers in rat plasma. The in vitro and in vivo studies indicate that chiral inversion occurs uneasily between (-) doxazosin and (+) doxazosin in the rat.

AIM: To study the effects of urocortin(Ucn) on the isolated heart tissues of spontaneously hypertensive rat(SHR).METHODS: Effects of Ucn on contractile force and heart rate were observed in the SHR and Wistar rat right atrium,left atrium and right ventricle strip.RESULTS: Ucn(1-10 nmol/L) concentration-dependently increased the contractile force in the SHR and Wistar rat isolated right atrium.Ucn increased the contractile force in the SHR by(31.1?14.9)% at 3 nmol/L and by(65.7?22.4)% at 10 nmol/L,and its inotropic effect was significantly greater than that in Wistar rat(P

Aim To study effects of intraduodenal administration of S-doxazosin, R-doxazosin and rac-doxazosin on the carotid blood pressure and urinary bladder function in anesthetized rats. Methods The various parameters of carotid blood pressure, heart rate, vesical micturition pressure, intercontraction interval in anesthetized rats were recorded with an ADInstruments PowerLab/8s data recording and analysis system, and the vesical micturition volume was measured simultaneously. Results S-Doxazosin, R-doxazosin and rac-doxazosin administered intraduodenally decreased the systolic blood pressure, diastolic blood pressure and mean arterial blood pressure significantly in anesthetized rats in a dose-dependent manner. The inhibition of mean arterial pressure by S-doxazosin, R-doxazosin and rac-doxazosin at 1.0 mg?kg-1 was 23.5%?4.6%, 38.5%?8.9% and 42.6%?7.5%, respectively. The ED30 values of decreasing mean arterial blood pressure by S-doxazosin, R-doxazosin and rac-doxazosin were (2.0?0.8),(0.6?0.7) and (0.6?0.5) mg?kg-1,respectively. S-Doxazosin had a weaker inhibitory effect on the carotid blood pressure compared with R-doxazosin and rac-doxazosin, but no significantly different effect was observed between R-doxazosin and rac-doxazosin on the carotid blood pressure. rac-Doxazosin produced a significant inhibition on the heart rate at the dosage from 0.1 mg?kg-1 to 3.0 mg?kg-1 in a dose-dependent manner, but S-doxazosin and R-doxazosin reduced the heart rate only at 3.0 mg?kg-1. S-Doxazosin, R-doxazosin and rac-doxazosin administered intraduodenally decreased the vesical micturition pressure dose-dependently in anesthetized rats. The maximal inhibition of vesical micturition pressure by S-doxazosin, R-doxazosin and rac-doxazosin was 13.4%?5.7%, 14.5%?11.0% and 10.9%?7.6%, and their inhibitory potency on the vesical micturition pressure was not significantly different each other. R-Doxazosin, however, decreased the intercontraction interval and vesical micturition volume significantly compared with S-doxazosin, but S-doxazosin and rac-doxazosin did not significantly affect the intercontraction interval and vesical micturition volume. Conclusion In comparison with R-doxazosin and rac-doxazosin, S-doxazosin administered intraduodenally remains the beneficial action on vesical micturition pressure and relieves the adverse effects on blood pressure, heart rate and intercontraction interval in anesthetized rats.

In industrial application of NAD(P)H-dependent dehydrogenases, NAD(H) has the advantages over NADP(H) in higher stability, lower price and wider recycling system. Recently, a meso-2,6-diaminopimelate dehydrogenase from Symbiobacterium thermophilum (StDAPDH) has been found to be a useful biocatalyst for the production of D-amino acids, but it requires NADP(H) as co-enzyme. To switch the co-enzyme specificity from NADP(H) to NAD(H), we studied the effect of Y76 on the co-enzyme specificity of StDAPDH, because the crystal structural analysis indicated that residue Y76 is near the adenine ring. The mutation of Y76 exerted significant effect on the co-enzyme specificity. Furthermore, the double mutant R35S/R36V significantly lowered the specific activity toward NADP+, and the combination of R35S/R36V with some of the Y76 mutants resulted in mutant enzymes favorable NAD+ over NADP+. This study should provide useful guidance for the further development of highly active NAD(+)-dependent StDAPDH by enzyme engineering.
Amino Acid Oxidoreductases ; chemistry ; Amino Acids ; Clostridiales ; enzymology ; Mutation ; NAD ; NADP ; Substrate Specificity

Objective To explore the functional mechanism of a Chinese medicine compound “Qiangzhizufang”on rat model of Tourette syndrome ( TS) combined with fear.Methods The rat model of TS combined with fear was established by intraperitoneal injection of 3,3’-iminodipropionitrile (IDPN) combined with acoustic stimulation.After giving different drug lavage treatment, the changes of behavior of the rat models were assessed by field test and behavior test.The content of DA, TH and TH mRNA in the brain tissue was detected by HPLC, immunohistochemistry and RT-PCR, separately.Results Compared with the normal control group, stereotyped behavior and exercise behavior were increased, freezing time prolonged, but the content of DA, TH and TH mRNA in the brain tissue were not obviously changed in the model control group.Compared with the model control group, the stereotyped behavior and exercise behavior were decreased, content of DA, TH and TH mRNA in the brain tissue was decreased in the “Qiangzhizufang” group. Conclusions The Chinese medicine compound“Qiangzhizufang” can improve the behavior in rat models of TS combined with fear.This effect may be realized through down-regurating TH mRNA expression, reducing the content of TH, and reducing the dopamine synthesis.