Introduction: We aimed to investigate factors contributing to ureteral responses and establish a reliable porcine model for studying ureteral contractility. Methods: Isolated ureteral strips from young (6-month old) and older (3-year old) pigs were mounted in organ baths and subjected to phenylephrine, 5-HT, carbachol and histamine.Ureteral strips developed bursts of contractile activity which was measured as area under the curve (AUC) and frequency. Phenylephrine and 5-HT-induced responses of proximal and distal ureters were obtained, in the presence and absence of indomethacin (10μM) and L-NNA (100μM), and the influence of an intact mucosa was examined.Results: Phenylephrine and 5-HT-induced contractile responses were greater than those to carbachol in the porcine ureter. In fact, responses to carbachol were only present in ureters from older animals. Ureters suspended longitudinally had increased phenylephrine-induced contractions compared to those suspended circularly (p<0.05). A greater amount of tissue strips developed spontaneous contractions from the proximal region compared to distal (83% vs 25%). There was an increase in maximum phenylephrine-induced responses in the distal ureter when compared to the proximal ureter (p<0.05). In the presence of indomethacin, only 5-HT-induced contractions in the young animals were depressed (p<0.05) while L-NNA did not affect any ureteral responses. The intact mucosa significantly decreased contractile responses to phenylephrine and 5-HT in the porcine ureter.Discussion: The complexity of ureteral contractions depicting bursts of phasic activity requires AUC assessment. Porcine ureteral contractile properties, such as regional differences, influence of mucosa and lack of response to carbachol, are similar to those reported in the literature for human ureter.

The primary goals of medical expulsive therapy are to increase the rate of stone expulsion along the ureter to avoid ureteral obstruction and reduce ureteral colic and thus avoid the need for surgical and more invasive interventions. This review focussed on the findings from in vivo and in vitro animal and human studies that have investigated the pharmacological mechanisms controlling ureteral motility and their translation to current and potentially new clinically used drugs for increasing the rate of stone expulsion along the ureter. The complicated contractility profile of the ureter, which alters with age, tissue segment region, orientation and species contributes to the difficulty of interpreting studies on ureteral pharmacology, which translates to the complexity of discovering ideal drug targets for medical expulsive therapy. Nevertheless, the current drug classes clinically used for patients with stone lodgement include α1‐adrenoceptor antagonists, calcium channel blockers and NSAIDS, whilst there are promising targets for drug development that require further clinical investigations including the phosphodiesterase type 5 enzyme, β‐adrenoceptors and 5‐HT receptors.

This study investigated the role of calcium sensitisation in the regulation of ureteral contractility with ageing. Isolated ureteral strips from young (6-month old) and older (3-year old) pigs were mounted in Krebs bicarbonate solution and contractility induced by the α1-adrenoceptor agonist phenylephrine (30 and 300 μM) and 5-HT (10 and 100 μM), recorded in the absence and presence of the rho-kinase inhibitors Y-27632 (10 μM) and fasudil (30 μM). Ureteral strips developed bursts of contractile activity which was measured as area under the curve (AUC) and frequency. Maximum contraction to phenylephrine was significantly enhanced in tissues from older animals compared to younger animals (p < 0.001) while maximum contraction to 5-HT was greater in tissues from younger animals (p < 0.001). Both inhibitors significantly depressed AUC and frequency responses to both agonists in ureters from both age groups (p < 0.05). Inhibition by Y-27632 of phenylephrine (300 μM)- and 5-HT(100 μM)-induced contractions was greater in tissues from older animals than young (p < 0.05). Rho-kinase activity was also assayed in ureteral tissues, and basal activity was similar in ureters from both age groups. Neither phenylephrine nor 5-HT increased rho-kinase activity over basal levels. These data demonstrate the significant role rho-kinase plays in ureteral contractility and possible alterations with age.

Isolated ureteral strips develop spontaneous phasic contractile activity which is enhanced by 5-hydroytryptamine (5-HT). The aim of this study was to identify the receptor subtype mediating these responses and to determine whether responses to 5-HT change with age. The frequency of contractions and the overall contractile activity (measured as the area under the curve, AUC) were recorded in strips of porcine distal ureter isolated from young (3 months) and old (2 years) pigs. Responses to 5-HT were examined in the absence and presence of selective 5-HT receptor subtype antagonists. Tissues from the younger animals elicited larger contractile responses to 5-HT (5885 ± 335g s) than tissues from the older animals (2787 ± 317g s, P < 0.001). The 5-HT receptor antagonist ketanserin (10-100nM) elicited rightward shifts of 5-HT concentration-response curves, antagonising AUC and frequency responses with high affinity in tissues from both age groups (pK values 8.4-8.8). The slopes of the corresponding Schild plots were not significantly different from unity, suggesting a competitive antagonism at a single receptor, except for frequency responses to 5-HT in the older animals. Antagonists selective for other 5-HT receptor subtypes: methiothepin (non-selective), RS-10221 (5-HT), ondansetron (5-HT), GR-113808 (5-HT), SB699551 (5-HT), SB39988 (5-HT), SB269970 (5-HT)) had no effect on 5-HT-induced responses. The results suggest that the 5-HT receptor subtype is the predominant receptor mediating 5-HT responses in ureteral tissues, being the sole mediator of responses in tissues from young animals, but with another receptor subtype also playing a minor role in the older animals.

To explore contractile actions of angiotensin II (ATII) on the muscularis mucosae (MM) of the bladder, ATII-induced contractions were compared between MM and the detrusor smooth muscle (DSM) of the pig bladder by isometric tension recordings. Effects of ATII on spontaneous Ca 2+ transients in MM were visualized using Cal-520 fluorescence. ATII receptor type 1 (ATR1) expression in MM and DSM was also examined by immunohistochemistry. ATII (1 nM-1 μM) caused phasic contractions of MM in a concentration-dependent manner, while ATII (10 nM-10 μM) had no or marginal effects on DSM contractility. ATII (100 nM)-induced MM contractions had an amplitude of approximately 70% of carbachol (1 μM)-induced or 90% of U46619 (100 nM)-induced contractions. Candesartan (10 nM), an ATR1 blocker, prevented the contractile effects of ATII (1 nM) in MM, while ATR1 immunofluorescence was greater in MM than DSM. ATII (10-100 pM) increased the frequency but not the amplitude of spontaneous Ca 2+ transients in MM. Both urothelium-intact and-denuded MM strips developed comparable spontaneous phasic contractions, but ATII, carbachol and U46619-induced contractions were significantly larger in urothelium-denuded than urothelium-intact MM strips. In conclusion, the MM appears to have a much greater sensitivity to ATII compared with DSM that could well sense circulating ATII, suggesting that MM may be the predominant target of contractile actions induced by ATII in the bladder while the urothelium appears to inhibit MM contractility.