Aim: Bioassay of Oxytocin Using Rat Uterine Horn by Interpolation Method
References
1. Ghosh, M.N. (2008). Fundamentals of Experimental Pharmacology (6th ed.). Hilton & Company.
2. Rang, H.P., Dale, M.M., Ritter, J.M., & Flower, R.J. (2015). Rang & Dale’s Pharmacology (8th ed.). Churchill Livingstone.
3. Schild, H.O. (1947). The bioassay of oxytocin on the rat uterine horn. British Journal of Pharmacology, 2(3), 189-195.
Introduction
Oxytocin is a hormone that induces contractions in the uterine muscles. The rat uterine horn is a common preparation used in bioassays to measure the potency of oxytocin. The interpolation method involves comparing the response of the unknown sample to that of standard concentrations of oxytocin to determine its potency.
Objective
To determine the concentration of oxytocin in an unknown sample using the rat uterine horn by the interpolation method.
Materials and Equipment
Female rats (preferably in the estrus phase)
Dissection tools (scissors, forceps, etc.)
Physiological saline (De Jalon’s solution or Tyrode’s solution)
Oxytocin standard solutions (known concentrations)
Unknown oxytocin solution
Tissue bath setup
Aeration system (Oxygen supply)
Isometric transducer or force transducer
Recording device (kymograph or digital recorder)
Micropipettes and tips
Data analysis software (optional)
Procedure
1. Preparation of Rat Uterine Horn:
- Euthanize the rat using an appropriate method (e.g., CO2 inhalation or anesthetic overdose).
- Quickly dissect the abdomen to isolate the uterine horn.
- Remove mesenteric attachments and mount the uterine horn in a tissue bath filled with De Jalon’s solution or Tyrode’s solution, maintained at 30-37°C and continuously aerated with oxygen.
2. Equilibration:
- Allow the uterine horn to equilibrate in the tissue bath for about 30 minutes, with constant aeration.
- Apply a resting tension of 1 gram to the tissue.
3. Baseline Recording: Record the baseline muscle tension to ensure stability and viability of the preparation.
4. Standard Oxytocin Response:
- Prepare standard oxytocin solutions of known concentrations (e.g., 0.5, 1.0, 2.0, 4.0 mU/mL).
- Add the lowest concentration of oxytocin to the tissue bath and allow the uterine horn to contract.
- Record the maximum contraction.
- Wash the uterine horn with fresh De Jalon’s solution or Tyrode’s solution and allow it to return to baseline tension.
- Repeat the process for each standard concentration and plot the dose-response curve.
5. Testing Unknown Oxytocin Solution:
- Add the unknown oxytocin solution to the tissue bath and allow the uterine horn to contract.
- Record the maximum contraction.
6. Interpolation Method:
- Compare the contraction response of the unknown sample to the standard oxytocin dose-response curve.
- Interpolate the response to determine the concentration of oxytocin in the unknown sample.
Data Analysis
1. Plotting Standard Dose-Response Curve: Plot the maximum contraction (response) on the y-axis against the concentration of oxytocin on the x-axis for the standard solutions.
2. Determining Unknown Concentration:
- Locate the response produced by the unknown oxytocin solution on the y-axis.
- Draw a horizontal line from this point to intersect the standard dose-response curve.
- From the intersection point, draw a vertical line down to the x-axis to determine the concentration of oxytocin in the unknown sample.
Sample Data Table
| Oxytocin Concentration (mU/mL) | Maximum Contraction (g) |
| 0.5 | 0.4 |
| 1.0 | 0.8 |
| 2.0 | 1.5 |
| 4.0 | 2.5 |
| Unknown | 1.2 |
Sample Plot
To visualize the data, plot the dose-response curve using the sample data provided. The unknown concentration can be identified by interpolating the response.
The blue line represents the response of the tissue to known concentrations of oxytocin. The red dashed line indicates the unknown response (1.2 g), which can be interpolated on the standard curve to determine the concentration of oxytocin in the unknown sample. ​