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Pharmacological identification of ?-adrenoceptor subtypes mediating isoprenaline-induced relaxation of guinea pig colonic longitudinal smooth muscle.

ABSTRACT: Object We aimed to identify the ?-adrenoceptor (?-AR) subtypes involved in isoprenaline-induced relaxation of guinea pig colonic longitudinal smooth muscle using pharmacological and biochemical approaches. Methods Longitudinal smooth muscle was prepared from the male guinea pig ascending colon and contracted with histamine prior to comparing the relaxant responses to three catecholamines (isoprenaline, adrenaline, and noradrenaline). The inhibitory effects of subtype-selective ?-AR antagonists on isoprenaline-induced relaxation were then investigated. Results The relaxant potencies of the catecholamines were ranked as: isoprenaline > noradrenaline ? adrenaline, whereas the rank order was isoprenaline > noradrenaline > adrenaline in the presence of propranolol (a non-selective ?-AR antagonist; 3 × 10-7 M). Atenolol (a selective ?1-AR antagonist; 3 × 10-7-10-6?M) acted as a competitive antagonist of isoprenaline-induced relaxation, and the pA2 value was calculated to be 6.49 (95% confidence interval: 6.34-6.83). The relaxation to isoprenaline was not affected by ICI-118,551 (a selective ?2-AR antagonist) at 10-9-10-8?M, but was competitively antagonized by 10-7-3 × 10-7?M, with a pA2 value of 7.41 (95% confidence interval: 7.18-8.02). In the presence of propranolol (3 × 10-7 M), the relaxant effect of isoprenaline was competitively antagonized by bupranolol (a non-selective ?-AR antagonist), with a pA2 value of 5.90 (95% confidence interval: 5.73-6.35). Conclusion These findings indicated that the ?-AR subtypes involved in isoprenaline-induced relaxation of colonic longitudinal guinea pig muscles are ?1-AR and ?3-AR.

SUBMITTER: Chino D

PROVIDER: S-EPMC5863046 | biostudies-literature | 2018

REPOSITORIES: biostudies-literature

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Pharmacological identification of β-adrenoceptor subtypes mediating isoprenaline-induced relaxation of guinea pig colonic longitudinal smooth muscle.

Chino Daisuke D Sone Tomoyo T Yamazaki Kumi K Tsuruoka Yuri Y Yamagishi Risa R Shiina Shunsuke S Obara Keisuke K Yamaki Fumiko F Higai Koji K Tanaka Yoshio Y

Journal of smooth muscle research = Nihon Heikatsukin Gakkai kikanshi 20180101 0

Object We aimed to identify the β-adrenoceptor (β-AR) subtypes involved in isoprenaline-induced relaxation of guinea pig colonic longitudinal smooth muscle using pharmacological and biochemical approaches. Methods Longitudinal smooth muscle was prepared from the male guinea pig ascending colon and contracted with histamine prior to comparing the relaxant responses to three catecholamines (isoprenaline, adrenaline, and noradrenaline). The inhibitory effects of subtype-selective β-AR antagonists o ...[more]

PMID: 29540623

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Project description:The muscularis mucosae, a type of smooth muscle located between the urothelium and the urinary bladder detrusor, has been described, although its properties and role in bladder function have not been characterized. Here, using mucosal tissue strips isolated from guinea pig urinary bladders, we identified spontaneous phasic contractions (SPCs) that appear to originate in the muscularis mucosae. This smooth muscle layer exhibited Ca(2+) waves and flashes, but localized Ca(2+) events (Ca(2+) sparks, purinergic receptor-mediated transients) were not detected. Ca(2+) flashes, often in bursts, occurred with a frequency (?5.7/min) similar to that of SPCs (?4/min), suggesting that SPCs are triggered by bursts of Ca(2+) flashes. The force generated by a single mucosal SPC represented the maximal force of the strip, whereas a single detrusor SPC was ?3% of maximal force of the detrusor strip. Electrical field stimulation (0.5-50 Hz) evoked force transients in isolated detrusor and mucosal strips. Inhibition of cholinergic receptors significantly decreased force in detrusor and mucosal strips (at higher frequencies). Concurrent inhibition of purinergic and cholinergic receptors nearly abolished evoked responses in detrusor and mucosae. Mucosal SPCs were unaffected by blocking small-conductance Ca(2+)-activated K(+) (SK) channels with apamin and were unchanged by blocking large-conductance Ca(2+)-activated K(+) (BK) channels with iberiotoxin (IbTX), indicating that SK and BK channels play a much smaller role in regulating muscularis mucosae SPCs than they do in regulating detrusor SPCs. Consistent with this, BK channel current density in myocytes from muscularis mucosae was ?20% of that in detrusor myocytes. These findings indicate that the muscularis mucosae in guinea pig represents a second smooth muscle compartment that is physiologically and pharmacologically distinct from the detrusor and may contribute to the overall contractile properties of the urinary bladder.

Project description:Newborns exposed to prenatal opioids often experience intense postnatal withdrawal after cessation of the opioid, called neonatal opioid withdrawal syndrome (NOWS), with limited pre- and postnatal therapeutic options available. In a prior study in pregnant mice we demonstrated that the peripherally selective opioid antagonist, 6β-naltrexol (6BN), is a promising drug candidate for preventive prenatal treatment of NOWS, and a therapeutic mechanism was proposed based on preferential delivery of 6BN to fetal brain with relative exclusion from maternal brain. Here, we have developed methadone (MTD) treated pregnant guinea pigs as a physiologically more suitable model, enabling detection of robust spontaneous neonatal withdrawal. Prenatal MTD significantly aggravates two classic maternal separation stress behaviors in newborn guinea pigs: calling (vocalizing) and searching (locomotion) - natural attachment behaviors thought to be controlled by the endogenous opioid system. In addition, prenatal MTD significantly increases the levels of plasma cortisol in newborns, showing that cessation of MTD at birth engages the hypothalamic-pituitary-adrenal (HPA) axis. We find that co-administration of 6BN with MTD prevents these withdrawal symptoms in newborn pups with extreme potency (ID50 ∼0.02 mg/kg), at doses unlikely to induce maternal or fetal withdrawal or to interfere with opioid antinociception based on many prior studies in rodents and non-human primates. Furthermore, we demonstrate a similarly high potency of 6BN in preventing opioid withdrawal in adult guinea pigs (ID50 = 0.01 mg/kg). This high potency appears to run counter to our pharmacokinetic studies showing slow 6BN transit of both the placenta and maternal blood brain barrier in guinea pigs, and calls into question the preferential delivery mechanism. Rather, it suggests a novel receptor mechanism to account for the selectively high potency of 6BN to suppress opioid dependence at all developmental stages, even in adults, as compared to its well-established low potency as a classical opioid antagonist. In conclusion, 6BN is an attractive compound for development of a preventive therapy for NOWS.

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Dataset Information

Pharmacological identification of ?-adrenoceptor subtypes mediating isoprenaline-induced relaxation of guinea pig colonic longitudinal smooth muscle.

Publications

Pharmacological identification of β-adrenoceptor subtypes mediating isoprenaline-induced relaxation of guinea pig colonic longitudinal smooth muscle.

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