P3.19 Friday, Jan. 6 Determining the existence of a sphincter in the caval region of Stenella spp. HENRY, A.F.**; DEAROLF, J.L.; Hendrix College, Conway, AR email@example.com
Sphincters of the vena cava have been found in the diaphragms of deep diving seals and some cetaceans (whales, dolphins, and porpoises). These sphincters produce safe, elastic aneurysms that help maintain diastolic blood pressure and prevent fluid accumulation during deep dives. Sphincters are characterized by large percentages of slow-twitch fibers, which provide prolonged contractions and do not fatigue quickly, aspects that sphincter muscles must have in order to function properly. Thus, the purpose of this experiment is to determine if striped and spotted dolphins, Stenella spp., possess a sphincter in the caval region of their diaphragms. To determine if there is a sphincter present, the percentage of slow-twitch fibers in the costal region of the diaphragm was compared to the percentage in the caval region, by cutting sections from these regions of striped and spotted dolphin diaphragms in a cryostat and staining them for their myosin ATPase activity. The stained sections were then imaged, and slow- and fast-twitch fibers were identified in each image and counted. Slow-twitch fibers are also known to contain more myoglobin than fast-twitch fibers. Thus, if the caval region has a larger proportion of slow-twitch fibers than the costal region, it should also have a higher myoglobin concentration. To test this hypothesis, myoglobin analyses were also performed on samples from the costal and caval regions of Stenella spp. diaphragms, and the average myoglobin concentrations in these regions were compared. If the diaphragms of striped and spotted dolphins are found to have a sphincter, then these findings will demonstrate that caval sphincters are common adaptations for deep diving in marine mammals.