The Relaxant Effect of Nitroglycerin on Oxytocin Desensitized Human Myometrium

The Relaxant Effect of Nitroglycerin on Oxytocin Desensitized Human Myometrium and the Return of Contractility on Re-exposure to Oxytocin- an in Vitro Study

Oxytocin causes myometrial contraction via the oxytocin receptor (OTR). Desensitization of the OTR after exposure to oxytocin has been demonstrated in previous studies. The resultant need for a higher oxytocin dose to cause adequate uterine contraction in vivo has also been demonstrated in laboring women having received oxytocin for labor augmentation.

Achieving rapid uterine relaxation can be invaluable for maternal and fetal wellbeing in some acute obstetric emergency settings. Nitroglycerin has become a commonly used agent for achieving rapid uterine relaxation amongst obstetric anesthesiologists.

Previous studies have concluded that oxytocin can be used to re-establish uterine tone following nitroglycerin mediated relaxation. However, no studies to date have looked at the effects of nitroglycerin mediated relaxation of uterine muscle that has undergone oxytocin receptor desensitization. Nor has the response to oxytocin re-exposure and return of contractility in desensitized myometrium (following nitroglycerin) been examined.

The investigators hypothesize that nitroglycerin will reduce and inhibit uterine contractions in both oxytocin pre-treated myometrium, as well as untreated myometrium in a dose dependent fashion, but that myometrium that has undergone OTR desensitization will require less nitroglycerin for contractions to abate.

The investigators also expect that the dose of oxytocin required to re-establish equivalent contractions will be higher in the myometrial samples which have undergone nitroglycerin mediated relaxation.

Study Overview

• Status: Completed
• Conditions: Postpartum Hemorrhage
• Intervention / Treatment: Drug: Oxytocin; Drug: Nitroglycerin

Detailed Description

Oxytocin and nitroglycerin have opposing actions on the myometrium. The pharmacological properties of quick onset and offset of action of nitroglycerin have made this the preferred drug to be used in acute scenarios where uterine relaxation is necessary.

As nitroglycerin causes changes to intracellular calcium levels and the ability uterine muscle to engage in effective contraction, it is plausible that the effects of nitroglycerin may interfere with subsequent uterine contractility and action of oxytocin.

The situation where a difficult fetal extraction is encountered at cesarean section may be in two broad groups of patients. Those pre-exposed to oxytocin and those with an oxytocin naïve myometrium. Given the large observational variation in dosages of nitroglycerin usage seen in the literature we feel it is vital to investigate whether pre-exposure to oxytocin impacts on the ability of nitroglycerin to relax uterine smooth muscle. Furthermore, once the uterus has relaxed following nitroglycerin exposure, is there a need for higher doses of oxytocin to be administered in order to re-engage the uterus in effective contraction? And is this requirement further exacerbated by the phenomenon of oxytocin receptor desensitization? These clinically important questions will be addressed by the design of this in vitro myometrial study.

• Study Type: Interventional
• Enrollment (Actual): 17
• Phase: Not Applicable

Contacts and Locations

Study Locations

• Canada
  • Ontario
    • Toronto, Ontario, Canada, M5G1X5
      • Mount Sinai Hospital

Participation Criteria

Eligibility Criteria

• Ages Eligible for Study: 14 years to 38 years (Child, Adult)
• Accepts Healthy Volunteers: No
• Genders Eligible for Study: Female

Description

Inclusion Criteria:

• Patients who give written consent to participate in this study
• Patients with gestational age 37-41 weeks
• Non-laboring patients, not exposed to exogenous oxytocin
• Patients requiring primary Cesarean delivery or first repeat Cesarean delivery under spinal anesthesia

Exclusion Criteria:

• Patients who refuse to give written informed consent
• Patients who require general anesthesia
• Patients who had previous uterine surgery or more than one previous Cesarean delivery
• Patients with any condition predisposing to uterine atony and postpartum hemorrhage, such as abnormal placentation, multiple gestation, preeclampsia, macrosomia, polyhydramnios, uterine fibroids, bleeding diathesis, chorioamnionitis, or a previous history of postpartum bleeding
• Emergency Cesarean section in labor
• Patients with medical/pregnancy related conditions, such as diabetes, preeclampsia and essential hypertension

Study Plan

How is the study designed?

Design Details

• Primary Purpose: Treatment
• Allocation: Non-Randomized
• Interventional Model: Parallel Assignment
• Masking: None (Open Label)

Number of Arms

4

Arms and Interventions

Participant Group / Arm	Intervention / Treatment
No Intervention: Control group; No oxytocin desensitization (pretreatment), no nitroglycerin
Active Comparator: Oxytocin desensitized - no nitroglycerin; Pretreated with oxytocin, no nitroglycerin exposure	Drug: Oxytocin; Oxytocin 10-5M solution; Other Names: Duratocin, pitocin
Active Comparator: Oxytocin desensitized - plus nitroglycerin; Pretreated with oxytocin followed by nitroglycerin exposure	Drug: Oxytocin; Oxytocin 10-5M solution; Other Names: Duratocin, pitocin; Drug: Nitroglycerin; Nitroglycerin 25-1000mcg
Active Comparator: Non oxytocin desensitized - plus nitroglycerin; No oxytocin pretreatment, followed by nitroglycerin exposure	Drug: Nitroglycerin; Nitroglycerin 25-1000mcg

What is the study measuring?

Primary Outcome Measures

Outcome Measure	Measure Description	Time Frame
Motility Index	Motility index (MI) takes into account both the amplitude and frequency of the myometrial contraction. It is a calculated outcome, based on the formula: frequency/(10 x amplitude). The analysis is undertaken by attaching myometrial strips between an isometric force transducer and the base of an organ bath chamber.	8 hours

Secondary Outcome Measures

Outcome Measure	Measure Description	Time Frame
Amplitude of contraction	The maximum extent of uterine muscle contraction, measured in grams (g). The analysis is undertaken by attaching myometrial strips between an isometric force transducer and the base of an organ bath chamber.	8 hours
Frequency of contraction	The number of contractions in uterine muscle (myometrium) over 10 minutes, spontaneously and in response to an agonist. The analysis is undertaken by attaching myometrial strips between an isometric force transducer and the base of an organ bath chamber.	8 hours
Integrated area under response curve (AUC)		8 hours

Collaborators and Investigators

• Sponsor: Samuel Lunenfeld Research Institute, Mount Sinai Hospital

Publications and helpful links

General Publications

• Jayasooriya GS, Carvalho JCA, Luca A, Balki M. The Effects of Nitroglycerin on the Oxytocin Dose-Response Profile in Oxytocin-Desensitized and Naive Human Myometrium: An In Vitro Study. Anesth Analg. 2021 Jan;132(1):231-239. doi: 10.1213/ANE.0000000000005055.

Study record dates

Study Major Dates

• Study Start (Actual): January 3, 2018
• Primary Completion (Actual): April 13, 2018
• Study Completion (Actual): April 13, 2018

Study Registration Dates

• First Submitted: January 17, 2018
• First Submitted That Met QC Criteria: January 17, 2018
• First Posted (Actual): January 23, 2018

Study Record Updates

• Last Update Posted (Actual): February 22, 2019
• Last Update Submitted That Met QC Criteria: February 21, 2019
• Last Verified: February 1, 2019

More Information

Terms related to this study

• Keywords: Oxytocin; Nitroglycerin; Uterine contraction
• Additional Relevant MeSH Terms: Pathologic Processes; Pregnancy Complications; Obstetric Labor Complications; Puerperal Disorders; Uterine Hemorrhage; Hemorrhage; Postpartum Hemorrhage; Physiological Effects of Drugs; Vasodilator Agents; Reproductive Control Agents; Oxytocics; Oxytocin; Nitroglycerin
• Other Study ID Numbers: 18-01 (National Center for Advancing Translational Sciences (NCATS))

Drug and device information, study documents

• Studies a U.S. FDA-regulated drug product: No
• Studies a U.S. FDA-regulated device product: No