Rabbit Bladder Base Research Articles

In vitro and in vivo effects of endothelin-1 and YM598, a selective endothelin ETA receptor antagonist, on the lower urinary tract

We investigated the contractile response of the lower urinary tract to endothelin-1 in vitro (rabbits) and in vivo (dogs). We also assessed the effects of a selective endothelin ETA receptor antagonist, (E)-N-[6-methoxy-5-(2-methoxyphenoxy)[2, 2′-bipyrimidin]-4-yl]-2-phenylethenesulfonamide monopotassium salt (YM598), on endothelin-1-induced contractile responses. In the in vitro study, endothelin-1 induced contractile responses in isolated rabbit bladder base, urethra, and prostate tissues. YM598 (10−7–10−5 M) antagonized these endothelin-1-induced contractile responses without affecting the maximal responses. In the in vivo study, endothelin-1 induced the elevation of non-prostatic urethral pressure as well as prostatic urethral pressure even in the presence of tamsulosin (10 μg/kg, i.v.) in anesthetized male dogs. YM598 (0.1–3 mg/kg, i.v.) inhibited these endothelin-1-induced contractile responses in a dose-dependent fashion. These results suggest that endothelin ETA receptors play an important role in the lower urinary tract contraction, and that the selective endothelin ETA receptor antagonist YM598 has ameliorating effects on various urinary dysfunctions, including benign prostatic hyperplasia.

Effect of partial outlet obstruction on choline acetyltransferase activity in the rat and rabbit.

Partial outlet obstruction of the rabbit bladder induces a rapid and significant increase in bladder mass. This increase in mass is associated with a variety of specific contractile dysfunctions, characterized by a marked decrease in the response to field stimulation (acting through the release of neurogenic transmitters). There is histological evidence indicating that the decrease in the contractile response of isolated strips of rabbit urinary bladder to field stimulation is associated with a degeneration of synaptic membranes within the bladder detrusor (neuropathy). In the current experiments, the effect of partial outlet obstruction in rabbit and rat urinary bladders on choline acetyltransferase activity (ChAT) were determined and correlated with both the level of bladder hypertrophy (increase in mass) and the contractile response to field stimulation. The results can be summarized as follows: In the rabbit, partial outlet obstruction induced a rapid 5-fold increase in bladder mass over the 7 day period of study. This increase in mass was associated with a decrease in the contractile response of isolated strips of bladder body and base to field stimulation and a decrease in ChAT activity. Interestingly, the rabbit bladder base showed a significantly higher ChAT activity than the bladder body, although the contractile response to muscarinic stimulation was significantly greater in the bladder body than in the base. In the rat, partial outlet obstruction induced a mild 2-fold increase in bladder mass.(ABSTRACT TRUNCATED AT 250 WORDS)

Regional distribution of alpha-adrenoceptor subtypes in the female rabbit urethra.

The aim of the present investigation was to study the regional distribution of alpha-adrenoceptor subtypes in the female rabbit bladder base and urethra, using radioligand binding and mechanical activity studies. The binding studies performed on membranes prepared from the bladder base, and the proximal and distal part of the urethra, revealed that the number of alpha 1-adrenoceptors did not significantly differ between the three regions, whereas the number of alpha 2-adrenoceptors increased distally. The mechanical activity studies showed that noradrenaline and clonidine, but not phenylephrine, were more potent in the distal than the proximal part of the urethra. It is suggested that in the female rabbit urethra the lower EC50-value found for noradrenaline and clonidine in the distal as compared to the proximal part of the urethra, at least in part, is attributable to a higher number of postjunctional alpha 2-adrenoceptors in the distal than in the proximal urethra.

P2B0321) - Alpha adrenergic subtype in the rabbit bladder base smooth muscle

P2B0321) - Alpha adrenergic subtype in the rabbit bladder base smooth muscle

Differential effects of nifedipine, verapamil, and diltiazem on noradrenaline-induced contractions, adrenergic transmitter release, and alpha-adrenoceptor binding in the female rabbit urethra.

In order to study differences in action between "Ca2+-entry blockers" on smooth muscle and peripheral nerves, the effects of nifedipine, verapamil, and diltiazem on noradrenaline (NA)-induced contractions and electrically evoked release of 3H-NA were investigated in the female rabbit urethra. In addition, possible influences of Ca2+-entry blockers on alpha-adrenoceptors were studied with radioligand binding technique. Exposure to Ca2+-free medium completely abolished the contractile response to 1 microM NA in the rabbit urethra, indicating that the contraction was entirely dependent on influx of extracellular Ca2+. The Ca2+-entry blockers inhibited the NA-induced contractions in the following order of potency: nifedipine greater than verapamil approximately equal to diltiazem. In contrast to nifedipine and diltiazem, which produced a maximum inhibition of between 50 and 60%, verapamil was able to abolish the contractile responses to NA. The electrically evoked efflux of 3H-NA was decreased by diltiazem and increased by verapamil, whereas nifedipine failed to alter the 3H-NA efflux. Only verapamil was effective in inhibiting specific 3H-DHE binding to a crude membrane preparation of the rabbit bladder base and urethra, and the inhibition appeared to be of the competitive type. It is suggested that the effects of verapamil on electrically evoked efflux of 3H-NA and on NA-induced contractions can be partly explained by blockade of pre- and post-junctional alpha-adrenoceptors. The failure of nifedipine and diltiazem to abolish the NA-induced contraction might indicate the existence of different Ca2+-entry pathways in urethral smooth muscle.

Influence of antimuscarinics on alpha-adrenoceptors in the female rabbit urethra.

The effects of the tertiary amine atropine and its structural analogues homatropine and scopolamine, as well as the quarternary amine emeprone, were evaluated on noradrenaline (NA)-induced contractions of isolated female rabbit urethral ring preparations. In addition, the abilities of these antimuscarinics to inhibit 3H-dihydro-alpha-ergocryptine (3H-DHE) binding to alpha-adrenoceptors were studied on a crude membrane preparation from the female rabbit bladder base and urethra. Atropine and homatropine depressed the NA-induced contractions in a concentration-dependent way, whereas this was not seen with scopolamine. Emeprone 10(-5) and 10(-4) M augmented the contractions, an effect possibly attributable to a NA-uptake blocking effect. All antimuscarinics displaced specific 3H-DHE binding, the order of potency being atropine greater than homatropine greater than emeprone greater than scopolamine. In general a good correlation was seen between the binding and mechanical activity studies for atropine, homatropine and scopolamine, while this was not found for emeprone. It is concluded that alpha-adrenoceptor blockade by atropine can be observed at concentrations exceeding 10(-7) M. Scopolamine, showing alpha-adrenoceptor blocking properties only in high concentrations, may be used as an alternative for blockade of muscarinic cholinoceptors.

Characterization of the alpha-adrenoceptors in the female rabbit urethra.

A radioligand binding technique was used to evaluate the proportions of alpha 1- and alpha 2-adrenoceptors in crude membrane preparations obtained from the female rabbit bladder base and urethra. In addition, urethral rings were studied in vitro in an attempt to determine if alpha 1- and/or alpha 2-adrenoceptors are located postjunctionally in the urethral smooth muscle. Studies of the inhibition of [3H]-dihydroergocryptine binding by the selective alpha 1-adrenoceptor antagonist prazosin or the selective alpha 2-adrenoceptor antagonist rauwolscine revealed the alpha-adrenoceptor population to consist of approximately 25% alpha 1-adrenoceptors and 75% alpha 2-adrenoceptors. These proportions were confirmed in saturation studies with [3H]-prazosin and [3H]-rauwolscine. The sum of alpha 1- and alpha 2-adrenoceptors labelled by these selective alpha 1- and alpha 2-adrenoceptor antagonists was about equal to the number labelled by the non-selective alpha-adrenoceptor antagonist [3H]-dihydroergocryptine. Noradrenaline, as well as the selective alpha 1-adrenoceptor agonist phenylephrine and the selective alpha 2-adrenoceptor agonist clonidine, induced contractions of urethral ring preparations. Prazosin blocked contractions induced by phenylephrine to a greater extent than contractions induced by clonidine. The opposite was true for the inhibitory effect of rauwolscine. In addition to showing that both alpha 1- and alpha 2-adrenoceptor binding sites exist in membrane preparations of the rabbit bladder base and urethra, the results reveal the presence of both adrenoceptor subtypes postjunctionally in the rabbit urethra; and both mediate contraction of the smooth muscle.

Sensitivity to indomethacin of tetrodotoxin-resistant contractions of smooth muscle from the base of rabbit bladder.

Tetrodotoxin (TTX) reduced the contractions to field stimulation of strips of rabbit bladder base by 58% of control (at 40 Hz), and increased the spontaneous activity occurring between the evoked responses. The TTX-resistant contractions resembled the spontaneous activity in that they were of comparable size and poorly sustained; in the presence of indomethacin, TTX produced a significantly greater reduction (to 13% of control at 40 Hz), of the evoked contractions. Indomethacin abolished spontaneous activity in the presence and absence of TTX, but did not affect evoked responses in strips that were not exposed to TTX. The results imply that a prostaglandin-like substance may potentiate residual evoked responses in TTX-treated strips, but does not contribute to field stimulation-induced contractions in untreated bladder base smooth muscle.

Demonstration of alpha-adrenoceptors in the rabbit bladder base and urethra with 3H-dihydroergocryptine ligand binding.

The purpose of this work was to demonstrate the presence of alpha-adrenoceptors in a crude membrane preparation made from rabbit bladder base and urethra. This was achieved by radioligand binding studies, using 3H-dihydro-alpha-ergocryptine (3H-DHE) as the radioligand. The specific binding, i.e. the binding that could be inhibited by 10(-5) M phentolamine, was saturable with 73 fmol 3H-DHE bound per mg membrane protein. Binding was at steady state after 60 min., and reversible. Rate constants for association and dissociation were 3 X 10(7) M-1 min.-1, and 2 X 10(-2) min.-1, respectively. A number of compounds were tested for their abilities to compete with 3H-DHE for the binding sites. The relative affinity of some adrenoceptor agonists was: (-)-adrenaline greater than (-)-noradrenaline much greater than (+/-)-isoprenaline. Stereoselectivity was shown, since (-)-noradrenaline had 42 times higher affinity than (+)-noradrenaline. Adrenoceptor antagonists inhibited 3H-DHE binding in the following order of potency: DHE greater than phentolamine much greater than (+/-)-propranolol. The dissociation constant, KD, for DHE to the binding sites was estimated in three different ways. The constants were derived from saturation, competition, and kinetic studies, and gave KD values of 1.1, 1.4 and 0.7 nM, respectively. The results suggest that alpha-adrenoceptors were labelled by 3H-DHE in the tissue homogenates.