Meeting Abstract

P1-69   -   Effects of pregnancy and lactation on the gastrocnemius muscle of female rats Barretto, J*; Danos , N; Patrick, M; University of San Diego ; University of San Diego ; University of San Diego jbarretto@sandiego.edu

The proportion of Type I oxidative to Type II glycolytic muscle fibers within a muscle, contributes to the muscle’s overall contractile properties. Although percent muscle fiber type within a muscle is mostly genetically determined, there are various instances in an individual’s lifetime, such as during aging, where muscle fiber composition can change. In our project, we examined how pregnancy and lactation induce muscle remodeling in the gastrocnemius muscle of rats using immunohistochemistry on muscle samples from virgin non-pregnant, primiparous pregnant and postpartum lactating rats. The gastrocnemius is a part of the hindlimb muscles that power the animal’s movement of the rat; therefore, muscle remodeling during these critical life stages can have potentially large effects on the animal’s fitness. Here we show that over the course of pregnancy, there is a significant shift of muscle fiber composition in the gastrocnemius from Type I to Type II. Over the three stages that we measured, we found that during pregnancy the number of Type IIa and Type IIb fibers significantly increased compared to non-pregnant animals, but then decreased slightly during lactation. For Type IIb fibers, the average cross sectional fiber area increased significantly during pregnancy but decreased postpartum. Our results demonstrate that pregnancy and lactation lead to muscle induced remodeling in the gastrocnemius. We hope that our experiments will lead to future research into how reproduction induced changes contribute to locomotor performance and survival in mammals.