ON THE MUSCARINIC RECEPTORS IN THE URINARY BLADDER AND THE PUTATIVE SUBCLASSIFICATION OF MUSCARINIC RECEPTORS

Inhibition of isolated rat and human detrusor muscle contraction by disopyramide

1. The aim of this study was to investigate the effect of in vitro and in vivo disopyramide treatment on human and rat isolated detrusor muscle contractile response. Muscle strips were suspended in an organ bath chamber containing Kreb's solution at 37 degrees C aerated with 95% oxygen and 5% carbon dioxide. 2. Disopyramide antagonized significantly the contractile response of isolated human detrusor muscle to carbachol stimulation, shifting the concentration-response curve to the right in a parallel manner. The pA2 for competitive inhibition was estimated to be 6.4 with a slope of 0.64 for disopyramide. 3. Rat detrusor muscle contractile response to electrical field stimulation (EFS) was inhibited by 28% (P < 0.01) after in vitro administration of disopyramide (7.5 x 10(-6) M). Disopyramide had no effect on the atropine-resistant component of the response to EFS or on spontaneous contractions of isolated rat detrusor muscle strips. The concentration-response curve to carbachol was competitively antagonized by disopyramide with a pA2 of 6.3 and a Schild curve a slope of 0.85. 4. Disopyramide (7.5 x 10(-6) M) had no effect on rat detrusor contractile response to low concentrations of KCl but at high concentrations contraction was reduced significantly by 16% (P < 0.01). 5. In vivo treatment of rats with disopyramide for 8 days or with a single dose had a significant inhibitory effect on the contractile response of detrusor muscle strips. 6. In conclusion, disopyramide had a significant anticholinergic effect on isolated human and rat detrusor muscle contraction.

Analysis of pressure/flow characteristics in the female rat and their pharmacologic modulation

A new in vivo urodynamic animal model was developed to analyze the micturition characteristics of the rat. This model was used to study the modulating effect of pharmacological agents on vesicourethral function, using cystometry and uroflowmetry. Pressure-flow studies were done in 25 female rats anesthetized with urethane. Filling cystometry was recorded using a physiological rate of bladder filling through transvesical infusion. Micturition characterization was done by identifying the time course and amount of voided volume. Voided volume was measured by a novel application of a mechanotransducer, which provided the data to measure flow rate and compute the voided volume-time curve. Flow rate was calculated by differentiating the curve produced by the mechanotransducer. Using this system, comparative tests of pharmacological stimulus were done using anticholinergic stimulation, alpha 1, and a new N-methyl-D aspartate (NMDA) receptor antagonist. The effects of the intravenous use of these drugs in the lower urinary tract were evaluated at various dose levels. The results showed that anticholinergic stimulation produced an increase of bladder capacity and decreases of detrusor pressure and maximum flow rate. Although the alpha 1 blocker decreased detrusor pressure, flow rate did not change significantly. By contrast, NMDA receptor antagonism produced a depressant effect on bladder reflex contraction, and increased bladder capacity in a dose-dependent way. However, maximum flow rate increased at a dose of 10 mg/kg and decreased at 30 mg/kg significantly. These results suggest that a decrease in flow resistance through the outlet region was due to the effects of NMDA receptor inhibition at lower doses. In conclusion, this model enables the evaluation of drugs regarding lower urinary tract function and provides in small animals the possibility of evaluating the relationships between pressure and flow in various experimental models.

Influence of lithium pretreatment and of cooling on the responsiveness of the rat isolated jejunum and urinary bladder to muscarinic agonists

1. The aim of the present study was to see whether contractile responses induced by muscarinic agonists in the rat jejunum and urinary bladder were differently affected by procedures that mainly influence the steps following agonist-receptor interaction. Thus, the effects of ex vivo lithium pretreatment (6.8 mmol kg-1 i.p. for 3 days) and in vitro cooling from 37 degrees C to 20 degrees C) on the contractile responses to full and partial agonists, carbachol, oxotremorine, muscarine and pilocarpine were studied. 2. Lithium pretreatment did not affect muscarinic responses on the urinary bladder. It significantly reduced responses to carbachol and oxotremorine but not to muscarine and pilocarpine on the rat jejunum. 3. A decrease of the bath temperature from 37 degrees C to 20 degrees C potentiated responses to carbachol, muscarine and oxotremorine and abolished those to pilocarpine in the urinary bladder. The same lowering of the bath temperature potentiated responses to carbachol, did not affect those to muscarine and to oxotremorine and reduced those to pilocarpine in the jejunum. 4. Together the findings indicate that differences exist in the stimulus-response coupling induced by muscarinic agonists between the two tissues and that, in a given tissue, differences exist among agonists in their ability to activate the agonist-receptor-transducer complex.

In vitro contractile responses of vasa deferentia from spontaneously diabetic BB rats

1. The effects of diabetes of 6 months' duration on autonomic function of the vas deferens were examined in spontaneously diabetic BB rats and diabetes-resistant BB rats. 2. Diabetes caused significant decreases in rat and testes weights, but had no effects on the weights of vasa deferentia compared to diabetes-resistant controls. 3. The contractile responses of vasa deferentia to nerve stimulation and to carbachol were increased compared to controls. However, the contractile responses of vasa deferentia from diabetic BB rats to ATP, phenylephrine, and 120 mM KCl were unaltered. 4. The increased responses to carbachol were associated with increases in the muscarinic receptor density, but no changes were detected in the number of dihydropyridine binding sites. 5. The data indicate that, in contrast to vasa deferentia from streptozotocin-diabetic rats which exhibit decreases in responsiveness to nerve stimulation and a non-specific supersensitivity to contractile agents, vasa deferentia from diabetic BB rats have no changes in sensitivity, and increased contractile responses to only nerve stimulation and carbachol. These differences in urogenital sensitivity to diabetes may be related to the insulin treatment which diabetic BB rats require to keep them alive.