Lcal administration of 1 per cent Ubretid in the handling of glaucoma, myasthenia gravis and esotropia

[Mechanism of the Long-lasting Potentiating Effect of Distigmine on Urinary Bladder Motility]

Distigmine bromide (distigmine) is a carbamate cholinesterase (ChE) inhibitor, which is mainly used for the treatment of myasthenia gravis. Distigmine is also used in Japan for the treatment for underactive bladder and glaucoma. The effectiveness of distigmine for underactive bladder treatment has been confirmed by many clinical reports, and this effect is thought to be caused by potentiating urinary bladder smooth muscle contraction due to inhibition of acetylcholine degradation during micturition. However, the pharmacological effects of distigmine on urinary bladder smooth muscle have not been well studied. The most distinctive pharmacological feature of distigmine is that it shows long-lasting effects than other ChE inhibitors; however, few studies have investigated the persistence of the enhancing effect of distigmine on the contractile function of urinary bladder smooth muscle. Moreover, this mechanism remains unclear. In this review, we present our findings on the mechanism of the potentiating effect of distigmine on isolated guinea pig urinary bladder smooth muscle contraction. We also discuss the long-lasting potentiating effect of distigmine on urinary bladder motility and the mechanism of these effects using guinea pig urinary bladder smooth muscle in vivo and in vitro. In addition, we present our investigations on the long-lasting mechanism of distigmine using recombinant human acetylcholinesterase.

Effects of Distigmine on the Mechanical Activity of Urinary Bladder Smooth Muscle

Distigmine bromide (distigmine) is a reversible carbamate cholinesterase (ChE) inhibitor. Its principle clinical application is in the treatment of myasthenia gravis. Distigmine is also used as a remedy for dysuria and glaucoma. Its effectiveness in the management of dysuria has been demonstrated in several clinical reports. Distigmine may improve (enhance) urinary bladder smooth muscle (UBSM) contraction during micturition by inhibiting acetylcholine (ACh) decomposition. However, the pharmacological effects of distigmine on UBSM have not been adequately studied so far. In this review article, we summarize the reported effects of distigmine on the contractile responses elicited by exogenous and endogenous ACh in isolated UBSM preparations. We also discuss the effects of distigmine on the UBSM basal tone and the contractile response of UBSM to ATP, which is co-released with ACh from parasympathetic nerve terminals.

The Long-Lasting Enhancing Effect of Distigmine on Acetylcholine-Induced Contraction of Guinea Pig Detrusor Smooth Muscle Correlates with Its Anticholinesterase Activity

Distigmine bromide (distigmine), a reversible, long-lasting cholinesterase (ChE) inhibitor, is used for the treatment of underactive bladder in Japan and has been shown to potentiate urinary bladder (UB) contractility. We studied the duration of distigmine's potentiating effects on acetylcholine (ACh)-induced UB contraction and its inhibitory effects on ChE activity, and compared that with those of other ChE inhibitors (neostigmine, pyridostigmine, and ambenonium). The duration of potentiating/inhibitory effects of ChE inhibitors, including distigmine, on ACh-induced guinea pig UB contraction/ChE activity was evaluated for 12 h following washout. Dissociation rate constants (k) of the inhibitors were also tentatively calculated based on the time courses of their ChE inhibitory effects. The potentiating effect of distigmine (10^-6 M) on ACh-induced UB contraction and its inhibitory effect on ChE activity were significantly sustained 12 h after washout. The potentiating effect of other ChE inhibitors on ACh-induced UB contraction, however, was sustained only until 3 h after washout. The ChE inhibitory effects of these inhibitors dissipated in a time-dependent manner after washout, with more than 75% of ChE activity restored by 4 h after washout. The k values of ChE inhibitors approached 0.50 h^-1, except for distigmine, where k could not be determined. Compared with that of other ChE inhibitors, the potentiating effect of distigmine on UB contractile function was significantly more sustainable following washout, which was likely associated with its corresponding long-lasting ChE inhibitory effect. Distigmine may associate more strongly with UB ChE than other ChE inhibitors, which would partly explain its sustained effects.

Long-Lasting Inhibitory Effects of Distigmine on Recombinant Human Acetylcholinesterase Activity

To elucidate the mechanism whereby distigmine, an underactive bladder remedy, potentiates urinary bladder contractions long-lastingly, the inhibition of recombinant human acetylcholinesterase (rhAChE) by distigmine was investigated. A centrifugal ultrafiltration device, Nanosep^® 10K, was used to separate rhAChE and a bound inhibitor from an unbound inhibitor, reaction substrate, and reaction product. This allowed the same aliquot of rhAChE to be repeatedly assayed for up to 48 h to confirm the long-lasting binding of an inhibitor. Cholinesterase (ChE) inhibitors, distigmine, pyridostigmine, neostigmine, and ambenonium, were tested. The dissociation rate constant (k_diss) and dissociation half-life (t_1/2) of each inhibitor were determined based on the changes in rhAChE activity. Within 2-4 h after removing pyridostigmine, neostigmine, or ambenonium, the rhAChE activity was restored to the control levels. The k_diss values for pyridostigmine, neostigmine, and ambenonium were calculated to be 0.51±0.05, 0.66±0.03, and 1.41±0.08 h^-1, and the t_1/2 values were calculated to be 1.36, 1.05, and 0.49 h, respectively. With distigmine, the rhAChE activity initially dropped to 17% of that in the control and then slowly recovered to only 50% by 48 h after drug removal. The k_diss and t_1/2 values of distigmine were calculated to be 0.012±0.001 h^-1 and 57.8 h, respectively. Based on the t_1/2 values, distigmine was judged to dissociate from acetylcholinesterase (AChE) 40-120-fold slower than the other ChE inhibitors did. This may explain the long-lasting potentiation of urinary bladder contractions and motility by distigmine as a treatment for an underactive bladder.

Effect of distigmine on the contractile response of guinea pig urinary bladder to electrical field stimulation

Distigmine bromide (distigmine) is a reversible carbamate group cholinesterase (ChE) inhibitor. Although mainly used clinically for the treatment of myasthenia gravis, distigmine is also indicated for detrusor underactivity in Japan. According to the pharmacological classification of distigmine, its therapeutic effect against detrusor underactivity appears to be produced by enhanced urinary bladder smooth muscle (UBSM) contractility due to an increased concentration of acetylcholine between parasympathetic nerve endings and UBSM cells. However, ATP as well as acetylcholine is also released from parasympathetic nerve endings that dominate UBSM. The present study was thus carried out to investigate the potentiating effects of distigmine on the two UBSM contractile components in response to parasympathetic nerve stimulation induced by electrical field stimulation (EFS). In isolated guinea pig UBSM tissues, EFS (1-16Hz) produced tetrodotoxin-sensitive, frequency-dependent contractions. The contractile responses to EFS were largely diminished by atropine (10^-6M), and the remaining contractile components in the presence of atropine were virtually abolished by α,β-methylene adenosine triphosphate (α,β-mATP) (10^-4M). Distigmine (10^-6M) significantly potentiated EFS-induced contractile components generated in the presence of α,β-mATP (10^-4M), but did not potentiate EFS-induced contractile components generated in the presence of atropine (10^-6M). These findings clearly indicate that distigmine strongly potentiates UBSM contraction selectively induced by parasympathetic nerve-derived acetylcholine, suggesting a potential mechanism by which distigmine restores detrusor underactivity.

Effects of TAK-802, a novel acetylcholinesterase inhibitor, on distension-induced rhythmic bladder contractions in rats and guinea pigs

In the present study, we investigated the effects of 8-[3-[1-[(3-fluorophenyl)methyl]-4-piperidinyl]-1-oxopropyl]-1,2,5,6-tetrahydro-4H-pyrrolo[3,2,1-ij]quinolin-4-one (TAK-802), a novel acetylcholinesterase inhibitor, on distension-induced rhythmic bladder contractions in urethane-anesthetized rats and guinea pigs. TAK-802 potently inhibited human-erythrocyte-derived acetylcholinesterase activity with an IC(50) value of 1.5 nM, which represented a potency 30 and 250 times greater than that of the two carbamate acetylcholinesterase inhibitors, neostigimine and distigmine, respectively. Unlike the carbamate acetylcholinesterase inhibitors, TAK-802 exhibits high selectivity for acetylcholinesterase inhibition over butyrylcholinesterase inhibition. In an assay conducted to measure the muscarinic and nicotinic actions, TAK-802 was found to exhibit higher selectivity for muscarinic actions over nicotinic actions in comparison to distigmine. Both TAK-802 and distigmine increased isovolumetric bladder contractions in rats and guinea pigs in a dose-dependent manner, with a minimum effective dose (MED) of 0.01 and 0.03 mg/kg i.v., respectively, in rats, and 0.01 and 0.1 mg/kg i.v., respectively, in guinea pigs. The effects of both the drugs were completely abolished by atropine. These results suggest that TAK-802 and other acetylcholinesterase inhibitors can effectively increase reflex bladder contractions by increasing the efficacy of acetylcholine released by nerve impulses. On the other hand, bethanechol, a muscarinic agonist, markedly changed the pattern of distension-induced bladder contractions when administered at the dose of 1 mg/kg i.v., and it did not necessarily augment well-coordinated bladder contractions. Thus, considering that it has some selectivity for muscarinic action, TAK-802 might be expected to be useful in the treatment of voiding dysfunction caused by impaired detrusor contractility.