Prolonged Head-Down Posture of Bats Induces Remodeling of the Aorta

Inversion is the regular position for bats at rest, but continuous inversion was expected to reverse the gravity vector exposure from feet-ward to head-ward and present hemodynamic challenges that induce remodeling of the aorta. There is paucity of information regarding the cardiovascular structural adaptations in bats engaged in regulating cranial or caudal blood redistribution in prolonged inversion. The aim of this study was to determine aortic adaptations in bats during prolonged inversion. Forty (40) bats were captured at Iwo, Osun State, Nigeria and randomly allocated into a normal control group and three test groups (n=10/group). The inversion period was not extended in control group A, but was maintained 8 days in B, 15 days in C, and 22 days in D. At the end of each inversion period, the bats were euthanized using intramuscular injection, and tissues were processed for Haematoxylin and Eosin, Orcein, and Van Gieson staining. Histological changes in the tunica media and adventitia were quantified, and the results were analyzed statistically. The ascending aorta exhibited thickening of the media and adventitia, whereas the abdominal aorta showed thinning of these regions. The changes increased in magnitude with longer periods of inversion. The histological stains indicated alterations in smooth muscle cells, collagen, and elastin content, consistent with predicted elevated pressure in the ascending and decreased pressure in the abdominal aortae. The vascular adaptation in bats may provide insights into suspected cardiovascular changes in astronauts during long-term spaceflight.