Contraction in human urethra (Adrenoceptor – Phenylephrine)

Drug Discovery Assay – reference number: B072

Overview

Assay Description

This assay assesses whether test articles cause contraction in isolated human urethra, with phenylephrine as a reference compound.

The urethra is essential for the passage of urine and semen (males). Any changes to the urethra, such as prostate hypertrophy, can affect the passage of these substances.

Figure 1: Cumulative concentration response curve to phenylephrine on isolated longitudinal and circular smooth muscle in the human urethra tensioned to 0.5g, demonstrating a concentration dependent constriction response. Longitudinal muscle has a Log EC₅₀ = −5.66 ± 0.33M (2.2µM) (mean ± S.E.M) with a maximum constriction of 0.59 ± 0.09 g at 3 x 10-⁵M, compared to a Log EC₅₀ = −4.88 ± 0.33M (48.7µM), with a maximum constriction of 0.17 ± 0.03g at 1 × 10⁻⁴M in circular smooth muscle.

Testing Information

Introduction

The specific results that will be provided are the effects of increasing concentrations of test articles on the contractile state of isolated human urethra muscle.

Test Article Requirements

Test article(s) to be provided by the Sponsor in storable aliquots at required test concentrations with information on diluent vehicle used. Stock solutions are prepared in distilled water unless otherwise requested. Bath volumes are 25mL; sponsor to provide sufficient test article to run the entire study.

Suggested Testing

In duplicate at 6 concentrations.

Figure 2: A diagram showing organ bath set-up

Study Outline

Rationale and Experimental Design

This assay assesses whether test articles cause contraction in isolated human urethra, with phenylephrine as a reference compound.

Exclusion Criteria

No specific exclusion criteria are in place other than to reject macroscopically diseased/necrotic tissue. Furthermore, tissues which do not respond to the standard pharmacology checks will be excluded.

Standardisation and Qualification

All individual muscle strips are initially processed through standardisation and qualification procedures to ensure functionality, prior to starting the study protocol.

Muscle strips are processed through a standardisation procedure to reduce signal variability prior to pharmacological intervention. This ensures that muscle strips are maintained under appropriate physiological tension throughout the experiments.

Following standardisation, the muscle strips are challenged with an appropriate agent to ensure robust contractile responses. Test tissues are then washed, and the responses allowed to return to baseline.

Muscle strips that pass the standardisation and qualification pass/fail criteria will then progress to the study protocol.

Smooth Muscle Contractility Assay

Agonist Contraction Assay

To assess the test articles ability to elicit smooth muscle contraction, 6 point cumulative concentration response curves will be performed for each test article. These concentration response curves (CCRC’s) will be performed from resting baseline tension. A positive control compound and representative test article vehicle CCRC will also be run to allow direct comparison with test articles.

An example of the conditions assessed for 3 test articles are detailed below (each condition will be run in duplicate muscle strips):

• Representative test article vehicle CCRC

• Positive control CCRC

• Test article 1 CCRC

• Test article 2 CCRC

• Test article 3 CCRC

Supplementary Option

To assess the involvement of a specific receptor subtype in any observed responses, the concentration of test article eliciting the largest response can subsequently (following a wash out and recovery period) be tested in the presence of a specific antagonist. This supplementary option will incur an extra charge.

Antagonist Contraction Assay

Option 1 − IC₅₀ Determination

To assess the ability of each test article to antagonise an agonist mediated contraction response, 6 point cumulative concentration response curves will be performed for each test article. These concentration response curves (CCRC’s) will be performed following pre-constriction with an appropriate reference agonist. A positive control compound and representative test article vehicle CCRC will also be run to allow direct comparison with test articles.

An example of the conditions assessed for 3 test articles are detailed below (each condition will be run in duplicate muscle strips):

• Representative test article vehicle CCRC

• Test article 1 CCRC

• Test article 2 CCRC

• Test article 3 CCRC

• Positive control CCRC

Option 2 − pA₂ Determination

To assess the ability of a test article to antagonise an agonist mediated contraction response; 6 point cumulative concentration response curves (CCRC’s) will firstly be performed for the reference agonist. Following a wash out and recovery period, muscle strips will be incubated with the test item (3 different concentrations of test article will be assessed), positive control or test article vehicle before the same 6 point cumulative concentration response curve will be repeated for the reference agonist.

An example of the conditions assessed for 3 test articles are detailed below (each condition will be run in duplicate vessels):

• Representative test article vehicle

• Test article 1 concentration 1

• Test article 1 concentration 2

• Test article 1 concentration 3

• Test article 2 concentration 1

• Test article 2 concentration 2

• Test article 2 concentration 3

• Test article 3 concentration 1

• Test article 3 concentration 2

• Test article 3 concentration 3

• Positive control

Analysis

Responses shall be expressed either in milligrams or grams tension, or as a % of the maximal contractile response (e.g. KPSS). Statistical analysis will be performed using Graphpad Prism, with the results being shown in graphical form in the final report.