A Rat Model of Mild Intrauterine Hypoperfusion with Microcoil Stenosis

Summary

Mild intrauterine hypoperfusion was produced by artery stenosis with metal microcoils wrapped around the uterine and ovarian arteries in rats at embryonic day 17. This procedure produced prenatal hypoperfusion and intrauterine growth restriction.

Abstract

Intrauterine hypoperfusion/ischemia is one of the major causes of intrauterine/fetal growth restriction, preterm birth, and low birth weight. Most studies of this phenomenon have been performed in either models with severe intrauterine ischemia or models with gradient degree of intrauterine hypoperfusion. No study has been performed in a model on uniform mild intrauterine hypoperfusion (MIUH). Two models have been used for studies of MIUH: a model based on suture ligation of either side of the arterial arcade formed with the uterine and ovarian arteries, and a transient model based on clipping the bilateral ovarian arteries and aorta having patency. Those two rodent models of MIUH have some limitations, e.g., not all fetuses are subjected to MIUH, depending on their position in the uterine horn. In our MIUH model, all fetuses are subjected to a comparable level of intrauterine hypoperfusion. MIUH was achieved by mild stenosis of all four arteries feeding the uterus, i.e., the bilateral uterine and ovarian arteries.

Arterial stenosis was induced by metal microcoils wrapped around the feeding arteries. Producing arterial stenosis with microcoils allowed us to control, optimize, and reproduce decreased blood flow with very little inter-animal variability and a low mortality rate, thus enabling accurate evaluation. When microcoils with an inner diameter of 0.24 mm were used, the blood flow in both the placenta and fetus was mildly decreased (approximately 30% from the pre-stenosis level in the placenta). The offspring of our MIUH model clearly demonstrates long-lasting alterations in neurological, neuroanatomical and behavioral test results.

Introduction

Infants with intrauterine growth restriction (IUGR) (also known as fetal growth restriction) (birth weight <10^th percentile for gestational age), preterm birth (born at < 37 weeks of gestation), and/or low birth weight (< 2500 g) account for nearly 10% of all newborns ^2,3. Many of these infants present with neurological problems such as cerebral palsy and developmental disorders (e.g., attention-deficit/hyperactivity disorder (ADHD) and learning disorders) ^3,4,5. Those conditions have similariti....

Protocol

All experiments were performed in accordance with protocols approved by the Experimental Animal Care and Use Committee of the National Cerebral and Cardiovascular Center, Suita, Japan.

1. Prepare the following animals and materials for MIUH surgery

1. Prepare timed pregnant Sprague-Dawley rats at gestational day 17, i.e., embryonic day 17 (E17). The dams' average body weights are 307.0 ± 40.7 g (mean ± SD, n = 9).
2. Prepare metal microcoils; inner diameter 0.24 mm, made from gold-coated steel.
3. Prepare all the materials as per the Table of Materials.

2. Prepar....

Results

After applying microcoils to all of the arteries feeding the uterus, i.e., the bilateral uterine and ovarian arteries, all fetuses are subjected to comparable levels of hypoperfusion. The application of microcoils with an inner diameter of 0.24 mm causes mild stenosis of those arteries, thereby causing a mild decrease in blood flow to the placentas and fetuses (Figure 3; approximately 30% from the pre-stenosis level in the placenta, see reference 1 for detail.......

Discussion

The microcoil stenosis of both ovarian and uterine arteries in both uterine horns produces consistent and reproducible intrauterine hypoperfusion in all placentas and fetuses. The level of hypoperfusion can be modified by using microcoils with different inner diameters. Rat pups born from a dam on which artery stenosis has been performed with microcoils 0.24 mm in inner diameter demonstrate IUGR and premature birth (see reference 1 for details). The pups exhibit neuroanatomical and behavioral alterations that resemble th.......

Materials

List of materials used in this article

Name	Company	Catalog Number	Comments
Stereomicroscope
Isoflurane anesthesia machine
Anesthesia induction box
Heating pad
Diaper 30x40 cm
Depilatory foam or shaver
Iodine disinfectant solution
Gauze 10x20 cm
Surgical drape 45x45 cm with a round opening 5 cm in diameter
Spray bottle with ethanol for disinfection
Cotton swab
Forceps with large blunt tips
Forceps with angled fine tips
Scissors
Surgical scalpel, blade size is 27mm long (no.10, Axel, AS ONE Corporation, Osaka, Japan)
Surgical suture needle
Metal microcoils; inner diameter 0.24 mm, made from gold-coated steel (SAMINI Co. Ltd., Shizuoka, Japan)
Silk suture 4-0
Sterile saline (0.9% sodium chloride)
Heating water bath
Plastic syringes (50ml) and needles (18G)