Polytocus focus: Uterine position effect is dependent upon horn size

Abstract

Understanding the variability caused by uterine position effects in polytocus species, such as rats, may enhance prenatal animal models for the study of drug and environmental agents. The primiparous litters of 42 intact female Sprague-Dawley rats were studied. Uterine position, fetal body weight, and fetal brain (wet) weight were recorded on gestation day (GD) 20 (GD 0 = sperm positive). Uterine position effect for brain and body weight varied depending upon horn size. Furthermore, an inverse relationship between horn size (and, to a lesser extent, litter size) and fetal weight applied to both body and brain weight measures. There were no statistical differences in brain and body weights between the left and right uterine horns. The position of the uterine horn (left vs. right) and litter size did not influence the uterine position effect in the rat. Collectively, the present data suggest the presence of a significant uterine position effect. Prenatal differences based on uterine position provide an untapped opportunity to increase our understanding of developmental neurotoxicological and teratological studies that employ a polytocus species as an animal model.

Considering Intrauterine Location in a Model of Fetal Growth Restriction After Maternal Titanium Dioxide Nanoparticle Inhalation

“…In theory, there should be no change to blood quality or oxygenation between the ovarian, middle, or vaginal segments of the uterine horn (Burbank, 2012). However, as evidenced by human placental position studies and control animal data, balanced perfusion throughout the uterus may not be the case (Garris et al, 1983;Kalanithi et al, 2007;Zia, 2013;Jang et al, 2014;McLaurin and Mactutus, 2015). Raz et al suggested feti at extreme ends of a uterine horn receive more nutrient-and volume-rich blood conveying a growth advantage over the middle positions in a normal pregnancy (Raz et al, 2012).…”

“…Existing literature has shown that maternal horn size and litter size can influence the intrauterine position effect in the Sprague Dawley rat (Raz et al, 2012;McLaurin and Mactutus, 2015). To correct for differences in maternal weight and litter size, each fetal weight was normalized to the number of feti within that horn by the following equation:…”

“…The number of feti in a litter is negatively correlated with birth weight (Romero et al, 1992;Ishikawa et al, 2006;McLaurin and Mactutus, 2015). Romero and colleagues reported an inverse relationship between fetal weight and litter size in Sprague Dawley (SD) rats, and emphasized that if this relationship is not taken into account when toxicity on fetal weight is analyzed there is a potential to mask a decrease in fetal weight due to litter size reduction (Romero et al, 1992).…”

“…Romero and colleagues reported an inverse relationship between fetal weight and litter size in Sprague Dawley (SD) rats, and emphasized that if this relationship is not taken into account when toxicity on fetal weight is analyzed there is a potential to mask a decrease in fetal weight due to litter size reduction (Romero et al, 1992). Importantly, the number of feti deposited within the right and left uterine horns, respectively, not total litter size, determines the influence of the intrauterine position effect; therefore, experimental outcomes should be evaluated on a per-horn basis (Raz et al, 2012;McLaurin and Mactutus, 2015). Lastly, maternal weight may be an important consideration, as smaller dams may have less energy reserve per fetus to produce feti of a similar weight compared to a larger female (Thame et al, 2015).…”

Thyroid hormone signaling and consequences for cardiac development

“…These differences may influence the fetal nutritional, hemodynamic and hormonal milieu in which the heart develops (Jonker et al 2007a, Barry & Anthony 2008, Mu et al 2008. Rodents have litters of up to ten pups or more and their location in the uterine horn influences nutrient delivery and their ultimate size (McLaurin & Mactutus 2015, Rennie et al 2015. In contrast, sheep and humans have few offspring with each pregnancy.…”