Mechanisms mediating cholinergic antral circular smooth muscle contraction in rats

AIM:To investigate the pathway(s)mediating rat antral circular smooth muscle contractile responses to the cholinomimetic agent,bethanechol and the subtypes of muscarinic receptors mediating the cholinergic contraction. METHODS:Circular smooth muscle strips from the antrum of Sprague-Dawley rats were mounted in muscle baths in Krebs buffer.Isometric tension was recorded.Cumulative concentration-response curves were obtained for(+)-cis- dioxolane(cD),a nonspecific muscarinic agonist,at 10^(-8)- 10^(-4)mol/L,in the presence of tetrodotoxin(TTX,10^(-7)mol/L). Results were normalized to cross sectional area.A repeat concentration-response curve was obtained after incubation of the muscle for 90 min with antagonists for M1(pirenzepine), M2(methoctramine)and M3(darifenadn)muscarinic receptor subtypes.The sensitivity to PTX was tested by the ip injection of 100 mg/kg of PTX 5 d before the experiment.The antral circular smooth muscles were removed from PTX-treated and non-treated rats as strips and dispersed smooth muscle cells to identify whether PTX-linked pathway mediated the contractility to bethanechol. RESULTS:A dose-dependent contractile response observed with bethanechol,was not affected by TTx.The pretreatment of rats with pertussis toxin decreased the contraction induced by bethanechol.Lack of calcium as well as the presence of the L-type calcium channel blocker,nifedipine,also inhibited the cholinergic contraction,with a reduction in response from 2.5±0.4 g/mm^2 to 1.2±0.4 g/mm^2(P<0.05).The dose- response curves were shifted to the right by muscarinic antagonists in the following order of affinity:darifenacin (M_3)>methocramine(M_2)>pirenzepine(M_1). CONCLUSION:The muscarinic receptors-dependent contraction of rat antral circular smooth muscles was linked to the signal transduction pathway(s)involving pertussis-toxin sensitive GTP-binding proteins and to extracellular calcium via L-type voltage gated calcium channels.The presence of the residual contractile response after the treatment with nifedipine,suggests that an additional pathway could mediate the cholinergic contraction.The involvement of more than one muscarinic receptor(functionally predominant type 3 over type 2)also suggests more than one pathway mediating the cholinergic contraction in rat antrum.

Ethanol inhibits the motility of rabbit sphincter of Oddi in vitro

AIM:The rote of the sphincter of Oddi(SO)in ethanol (ETOH)-induced pancreatitis is controversial.Our aim was to characterise the effect of E-I-OH on basal and stimulated SO motility. METHODS:SOs removed from white rabbits were placed in an organ bath(Krebs solution,pH7.4,37℃).The effects of 2 mL/L,4 mL/L,6 mL/L and 8 mL/L of ETOH on the contractile responses of the sphincter were determined. SOs were stimulated with either 0.1 μmol/L carbachol,1 μmol/L erythromycin or 0.1 μmol/L cholecystokinin(CCK). RESULTS:ETOH at a dose of 4 mL/L significantly decreased the baseline contractile amplitude from 11.98±0.05 mN to 11.19±0.07 mN.However,no significant changes in the contractile frequency were observed.ETOH(0.6%) significantly decreased both the baseline amplitude and the frequency compared to the control group(10.50±0.01 mN, 12.13±0.10 mN and 3.53±0.13 c/min,5.5±0.13 cycles(c)/min, respectively).Moreover,0.8% of ETOH resulted in complete relaxation of the SO.Carbachol(0.1 μmol/L)or erythromycin (1 μmol/L)stimulated the baseline amplitudes(by 82% and 75%,respectively)and the contractile frequencies (by 150% and 106%,respectively).In the carbachol or erythromydn-stimulated groups 2-6 mL/L of E-IOH significantly inhibited both the amplitude and the frequency.Interestingly, a 4-5 min administration of 6 mL/L ETOH suddenly and completely relaxed the SO.CCK(0.1 μmol/L)stimulated the baseline amplitude from 12.37±0.05 mN to 27.40±1.82 mN within 1.60±0.24 min.After this peak,the amplitude decreased to 17.17±0.22 mN and remained constant during the experiment.The frequency peaked at 12.8±0.2 c/min, after which the constant frequency was 9.43±0.24 c/min throughout the rest of the experiment.ETOH at a dose of 4 mL/L significantly decreased the amplitude from 16.13±0.23 mN to 14.93±0.19 mN.However,no significant changes in the contractile frequency were observed.ETOH at a dose of 6 mL/L inhibited both the amplitudes and the frequencies in the CCK-stimulated group,while 8 mL/L of ETOH completely relaxed the SO. CONCLUSION:ETOH strongly inhibits the basal,carbachol, erythromycin,and CCK-stimulated rabbit SO motility. Therefore,it is possible that during alcohol-intake the relaxed SO opens the way for pancreatic fluid to flow out into the duodenum in rabbits.This relaxation of the SO may protect the pancreas against alcohol-induced damage.

Effect of Varenicline on Detrusor Overactivity in Rat Model of Parkinson’s Disease Induced by Intranigral 6-Hydroxydopamine

Background: Parkinson disease (PD) is a progressive neurodegenerative disorder characterized by both motor and non-motor symptoms. Bladder dysfunction is the common non-motor symptom of PD, most often presenting with detrusor overactivity (DO). Treatment of DO is currently limited, poorly tolerated and sometimes ineffective. Bladder responses are not only mediated by muscarinic cholinergic receptors (mAChR) but also by nicotinic cholinergic receptors (nAChR). However, nicotinic receptor subtypes and functions in the bladder are not clearly identified. Purpose: This study aimed at investigating the effect of varenicline, an alpha7 full agonist and alpha4beta2/alpha3 partial agonist, on detrusor strips in rat PD model induced by substantia nigra injection of 6-hydroxydopamine. Method: The detrusor activity was studied in an isolated organ bath system. Results: In PD group, the detrusor activity was increased, whereas varenicline decreased the DO. Conclusion: Alpha7 nAChR agonists may have therapeutic potential in treatment of bladder overactivity in PD.