Endocrine Abstracts

The aim of this study was to compare the effects of prostaglandin E₂ (PGE₂) and a PGE analogue, sulprostone with isoprenaline (β₁/β₂ agonist) on mouse uterine tissue taken during labour.

Uterine tissue was taken and set up for superfusion (Krebs’ solution at 2 ml/min and 37°C) as previously described by Senior et al (1991). After allowing the tissue to equilibrate for approximately 20 minutes agonists were added as bolus doses and the responses measured as area under the curve using a Powerlab and Chart software.

All samples exhibited significant and sustained myogenic activity, this activity was constant along the length of the uterine horn. Isoprenaline (which was chosen to represent the β-mimetics used to attempt to delay preterm labour in women) evoked a dose related (0.1–100 nmol) inhibition of myometrial activity. PGE₂ (0.1–100 nmol) evoked an excitatory response which was dose related no inhibitory response was seen. The response to PGE₂ was significantly greater in tissue samples taken from the upper and middle segments of the uterine horn compared with samples taken from the cervical section. The response (0.1–100 nmol) to the EP₃ receptor agonist, sulprostone, was similar to that observed with PGE₂.

These data suggest that excitatory prostaglandin EP-receptors are present on mouse tissue taken at labour and the results obtained with sulprostone suggest that this receptor is the EP₃ subtype. The lack of inhibitory response to PGE₂ may suggest that the EP-receptors that mediate inhibition, namely the EP₂ and EP₄-receptors, may not be present on this tissue and this is currently being investigated further using selective agonists for these receptors. The results obtained with isoprenaline suggest that the β₂ adrenergic receptor is present and this response is qualitatively similar to that found on isolated human tissue taken at term (but not in labour).