Subtypes of muscarinic receptors regulating gallbladder cholinergic contractions. (1/50)

The aim of this study was to determine the functional role of muscarinic receptor subtypes regulating gallbladder cholinergic contractions. Electrical field stimulation (EFS; 16 Hz) produced contractile responses of guinea pig gallbladder muscle strips in vitro that were inhibited by 1 microM tetrodotoxin (2 +/- 2% of control) and 1 microM atropine (1 +/- 1% of control), indicating activation of intrinsic cholinergic nerves. Exogenous ACh (5 microM)-induced contractions were inhibited by atropine (1 +/- 1% of control) but not tetrodotoxin (102 +/- 1% of control), indicating a direct effect on smooth muscle. The M1 receptor antagonist pirenzepine (10 nM) had no effect on ACh-induced contractions but inhibited EFS-induced contractions by 11 +/- 3%. The M2 antagonist methoctramine (10 nM) had no effect on ACh-induced contractions but augmented EFS-induced contractions by 5 +/- 2%. The M3 antagonist 4-DAMP (10 nM) inhibited ACh-induced contractions by 14 +/- 4% and EFS-induced contractions by 22 +/- 5%. In conclusion, specific M1, M2, and M3 receptors modulate gallbladder muscle contractions by regulating ACh release from cholinergic nerves and mediating the contraction. Cholinergic contractions are mediated by M3 receptors directly on the smooth muscle. M2 receptors are on cholinergic nerves and function as prejunctional inhibitory autoreceptors. M1 receptors are on cholinergic nerves and function as prejunctional facilitatory autoreceptors.  (+info)

Muscarinic receptor heterogeneity in follicle-enclosed Xenopus oocytes. (2/50)

1. Ionic current responses elicited by acetylcholine (ACh) in follicle-enclosed Xenopus oocytes (follicles) were studied using the two-electrode voltage-clamp technique. ACh generated a fast chloride current (Fin) and inhibited K+ currents gated by cAMP (IK,cAMP) following receptor activation by adenosine, follicle-stimulating hormone or noradrenaline. These previously described cholinergic responses were confirmed to be of the muscarinic type, and were independently generated among follicles from different frogs. 2. Inhibition of IK,cAMP was about 100 times more sensitive to ACh than Fin activation; the half-maximal effective concentrations (EC50) were 6.6 +/- 0.4 and 784 +/- 4 nM, respectively. 3. Both responses were blocked by several muscarinic receptor antagonists. Using the respective EC50 concentrations of ACh as standard, the antagonist 4-diphenylacetoxy-N-methylpiperidine methiodide blocked the two effects with very different potencies. Fin was blocked with a half-maximal inhibitory concentration (IC50) of 2.4 +/- 0.07 nM, whilst the IC50 for IK,cAMP inhibition was 5.9 +/- 0.2 microM. 4. Oxotremorine, a muscarinic agonist, preferentially stimulated IK, cAMP inhibition (EC50 = 15.8 +/- 1.4 microM), whilst Fin was only weakly activated. In contrast, oxotremorine inhibited Fin generated by ACh with an IC50 of 2.3 +/- 0.7 microM. 5. Fin elicited via purinergic receptor stimulation was not affected by oxotremorine, indicating that the inhibition produced was specific to the muscarinic receptor, and suggesting that muscarinic actions do not exert a strong effect on follicular cell-oocyte coupling. 6. Using reverse transcription-PCR, transcripts of a previously cloned muscarinic receptor from Xenopus (XlmR) were amplified from the RNA of both the isolated follicular cells and the oocyte. The pharmacological and molecular characteristics suggest that XlmR is involved in IK,cAMP inhibition. 7. In conclusion, follicular cells possess two different muscarinic receptors, one resembling the M2 (or M4) subtype and the other the M3 subtype. These receptors are coupled to distinct membrane mechanisms leading to independent regulation of two membrane conductances.  (+info)

Probing peripheral and central cholinergic system responses. (3/50)

OBJECTIVE: The pharmacological response to drugs that act on the cholinergic system of the iris has been used to predict deficits in central cholinergic functioning due to diseases such as Alzheimer's disease, yet correlations between central and peripheral responses have not been properly studied. This study assessed the effect of normal aging on (1) the tropicamide-induced increase in pupil diameter, and (2) the reversal of this effect with pilocarpine. Scopolamine was used as a positive control to detect age-dependent changes in central cholinergic functioning in the elderly. DESIGN: Randomized double-blind controlled trial. PARTICIPANTS: Ten healthy elderly (mean age 70) and 9 young (mean age 33) volunteers. INTERVENTIONS: Pupil diameter was monitored using a computerized infrared pupillometer over 4 hours. The study involved 4 sessions. In 1 session, tropicamide (20 microL, 0.01%) was administered to one eye and placebo to the other. In another session, tropicamide (20 microL, 0.01%) was administered to both eyes, followed 23 minutes later by the application of pilocarpine (20 microL, 0.1%) to one eye and placebo to the other. All eye drops were given in a randomized order. In 2 separate sessions, a single dose of scopolamine (0.5 mg, intravenously) or placebo was administered, and the effects on word recall were measured using the Buschke Selective Reminding Test over 2 hours. OUTCOME MEASURES: Pupil size at time points after administration of tropicamide and pilocarpine; scopolamine-induced impairment in word recall. RESULTS: There was no significant difference between elderly and young volunteers in pupillary response to tropicamide at any time point (p > 0.05). The elderly group had a significantly greater pilocarpine-induced net decrease in pupil size 85, 125, 165 and 215 minutes after administration, compared with the young group (p < 0.05). Compared with the young group, the elderly group had greater scopolamine-induced impairment in word recall 60, 90 and 120 minutes after administration (p < 0.05). CONCLUSION: There is an age-related pupillary response to pilocarpine that is not found with tropicamide. Thus, pilocarpine may be useful to assess variations in central cholinergic function in elderly patients.  (+info)

Mechanisms of acetylcholine-induced vasorelaxation in high K+-stimulated rabbit renal arteries. (4/50)

To characterize the mechanisms of acetylcholine (ACh)-induced vasorelaxation in rabbit renal arteries precontracted with high K+ (100 mM), muscle tension and cytosolic free Ca2+ concentration ([Ca2+]i) were measured simultaneously in the fura-2-loaded arterial strips. In the artery with endothelium, high K+ increased both [Ca2+]i and muscle tension. Addition of ACh (10 microM) during high-K+ induced contraction significantly relaxed the muscle and induced additional increase in [Ca2+]i. In the presence of NG-nitro-L-arginine (L-NAME, 0.1 mM). ACh increased [Ca2+]i without relaxing the muscle. In the artery without endothelium, high K+ increased both [Ca2+]i and muscle tension although ACh was ineffective, suggesting that ACh acts selectively on endothelium to increase [Ca2+]i. 4-DAMP (10 nM) or atropine (0.1 microM) abolished the ACh-induced increase in [Ca2+]i and relaxation. However, pirenzepine (0.1 microM), AF-DX 116 (1 microM) and tropicamide (1 microM) were ineffective. The ACh-induced increase of [Ca2+li and vasorelaxation was significantly reduced by 3 microM gadolinium, 10 microM lanthanum or 10 microM SKF 96365. These results suggest that, in rabbit renal artery, ACh-evoked relaxation of 100 mM K+-induced contractions is mediated by the release of endothelial NO. ACh may stimulates the M3 subtype of muscarinic receptor in the endothelial cells, resulting in the opening of the nonselective cation channels followed by an increase of [Ca2+]i and stimulation of NO synthase.  (+info)

Evaluation of potentiating effect of a drop of lignocaine on tropicamide-induced mydriasis. (5/50)

PURPOSE: To analyze whether preinstillation of lignocaine potentiates mydriasis by tropicamide in dark eyes and to determine possible mechanisms for this effect. METHODS: This investigation was conducted in two phases, the first being a double-masked, placebo-controlled, randomized clinical trial, enrolling 60 healthy dark brown eyes in 30 subjects aged 7 to 58 years. The control eye received a drop of (nonlignocaine) placebo before tropicamide 1%, and the contralateral study eye received a 4% lignocaine drop 3-minutes before the 1 drop of tropicamide was administered. A ruled pupillometer recorded pupil diameters every 10 minutes for 50 minutes. In phase II, to elucidate pathomechanisms after lignocaine, corneal and tear parameters were compared with baseline records in a further 60 such eyes. RESULTS: Pupillary diameters in the study eyes increased by 3.62 +/- 0.75 mm, significantly more than in the placebo (control) group (P = 0.000). Ninety percent of study eyes attained the clinically significant 6-mm size with preinstillation of lignocaine-many more than the 67% of control eyes (P = 0.016). The median time to achieve this critical 6-mm size was significantly faster in the study group (P = 0.005). In phase II, the 1 drop 4% lignocaine did not show corneal changes with slit lamp or fluorescein staining and did not reduce media clarity or induce a significant change in tear pH. It markedly decreased Schirmer values (P = 0.000), reduced tear break-up time (P = 0.003), and increased corneal thickness measured by optical pachymetry (P = 0.010). CONCLUSIONS: The phase II findings indicate corneal microepithelial damage and reduced tearing. Both may enhance intraocular penetration and hence potentiation of tropicamide. This remarkable phenomenon could find use with many other important topical medications.  (+info)

Tropicamide (1%): an effective cycloplegic agent for myopic children. (6/50)

PURPOSE: To evaluate the cycloplegic effect of 1% tropicamide in myopic children and to determine whether its efficacy is associated with age, gender, iris color, ethnicity, magnitude of the refractive error, or latent error. METHODS: Four hundred sixty-nine children enrolled in the Correction of Myopia Evaluation Trial (COMET; a multicenter, randomized, double-masked clinical trial evaluating the rate of progression of juvenile-onset myopia in children wearing progressive-addition versus single-vision lenses) were given 1 drop of proparacaine in each eye followed 1 minute later by 1 drop of 1% tropicamide and then a second drop of 1% tropicamide 4 to 6 minutes later. Five accommodative responses to 20/100 letters located at 4 m and 33 cm were obtained in each eye with an autorefractor, 20 minutes after the second drop. Residual accommodation was calculated as the difference between the mean spherical equivalent responses obtained at the two distances. An examiner graded iris color, and ethnicity was reported by the children's parents or guardians. RESULTS: The mean residual accommodation was small: 0.38 +/- 0.41 diopters (D) in the right eye and 0.30 +/- 0.41 D in the left eye. Small but statistically significant differences in residual accommodation were associated with ethnicity, but not with any of the other factors. CONCLUSIONS: Tropicamide (1%) is an effective cycloplegic agent in myopic children.  (+info)

Myopia: attempts to arrest progression. (7/50)

Previous studies have evaluated the efficacy of several interventions to decrease the progression of myopia. These include devices that alter the perception of the visual environment and pharmacological treatments. There is no conclusive evidence thus far that alteration of the pattern of spectacle wear, bifocals, ocular hypotensives, or contact lenses retards the progression of myopia. Several randomised clinical trials have demonstrated that the rate of progression of myopia is lower in children given atropine eye drops than those given placebo. However, atropine is associated with short term side effects such as photophobia and possible long term adverse events including light induced retinal damage and cataract formation. Other more selective antimuscarinic agents such as pirenzipine are presently being evaluated. Further well conducted randomised clinical trials with large sample sizes and adequate follow up designed to evaluate treatments to retard the progression of myopia should be conducted, since the identification of an effective intervention may have a greater public health impact on the burden and morbidity from myopia than the few treatments currently available.  (+info)

Comparative study of the effects of 2% ibopamine, 10% phenylephrine, and 1% tropicamide on the anterior segment. (8/50)

PURPOSE: To assess in normal and glaucomatous eyes the effect of the dopaminergic drug 2% ibopamine on visual acuity, IOP, pupil size and anterior segment geometry, compared with 10% phenylephrine and 1% tropicamide. METHODS: Fifteen healthy subjects and 15 patients with primary open-angle glaucoma, aged from 40 to 70 years (mean age: 54.8 +/- 9.6), were recruited into this open prospective study. After instillation of 2% ibopamine, refraction, visual acuity, pupil diameter, IOP, five A-scan ultrasonographic parameters, and 15 ultrasound biomicroscopy parameters were evaluated. The study was repeated with assessment of the same parameters 20 to 30 days later in 10 subjects (5 normal and 5 with glaucoma), using first 10% phenylephrine and then 1% tropicamide. A second group of 15 healthy subjects, aged from 45 to 70 years (mean age: 53.5 +/- 8.6) was examined to evaluate the dose-response effect and time course on pupil diameter, of ibopamine, phenylephrine, and tropicamide. RESULTS: After 40 minutes 2% ibopamine induced a marked mydriatic effect (from 5 to 9.1 mm; P < 0.0001) greater than that produced by 10% phenylephrine (from 4.7 to 7.9 mm; P < 0.0001) or 1% tropicamide (from 4.6 to 6.9 mm; P < 0.0001), with no changes in refraction or visual acuity. IOP was significantly increased only in patients with glaucoma after instillation of either 2% ibopamine (from 22.2 to 24.8 mm Hg; P < 0.0001) or 1% tropicamide (from 21.2 to 23.6 mm Hg; P = 0.004), whereas 10% phenylephrine induced no statistically significant changes. Ibopamine (2%) caused a significant increase in iris thickness with a reduction of the sulcus ciliaris and posterior chamber depth. The anterior chamber angle (ACA) showed a mean 5 degrees widening with an increase in scleral-iris angle (SIA) and sclera-ciliary process angle. In 11 (37%) of 30 cases, separation of the pupil border and lens surface occurred, whereas contact was maintained only with the zonule in the other 19 (63%) of 30. The changes after 10% phenylephrine instillation were similar, although only the increase in iris thickness and SIA was statistically significant. Tropicamide (1%) induced a slight but significant increase in SIA. CONCLUSIONS: The results confirm the potent mydriatic effect of 2% ibopamine, which is greater than that of either 10% phenylephrine or 1% tropicamide, as well as its ability to induce an increase in intraocular pressure when used in patients with glaucoma alone. These data support the hypothesis that the widening of the ACA induced by 2% ibopamine is due to posterior rotation of the iris plane and ciliary processes. These changes are quantitatively greater than those induced by 10% phenylephrine and 1% tropicamide and are related to the greater mydriatic effect of the drug.  (+info)