CARDIOVASCULAR-RESPONSES OF SEMIARBOREAL SNAKES TO CHRONIC, INTERMITTENT HYPERGRAVITY

Cardiovascular functions were studied in semi-arboreal rat snakes (Ela phe obsoleta) following long-term, intermittent exposure to + 1.5 G(z) (head-to-tail acceleration) on a centrifuge. Snakes were held in a ne arly straight position within horizontal plastic tubes during periods of centrifugation. Centrifugal acceleration, therefore, subjected snak es to a linear force gradient with the maximal force being experienced at the tail. Compared to non-centrifuged controls, G(z)-acclimated sn akes showed greater increases of heart rate during head-up tilt or acc eleration, greater sensitivity of arterial pressure to circulating cat echolamines, higher blood levels of corticosterone, and higher blood r atios of prostaglandin F-2 alpha/prostaglandin E(2). Cardiovascular to lerance to increased gravity during graded G(z) acceleration was measu red as the maximum (caudal) acceleration force at which carotid arteri al blood flow became null. When such tolerances were adjusted for effe cts of body size and other continuous variables incorporated into an a nalysis of covariance, the difference between the adjusted mean values of control and acclimated snakes (2.37 and 2.84 G(z), respectively) c orresponded closely to the 0.5 G difference between the acclimation G (1.5) and Earth gravity (1.0). As in other vertebrates, cardiovascular tolerance to G(z) stress tended to be increased by acclimation, short body length, high arterial pressure, and comparatively large blood vo lume. Voluntary body movements were important for promoting carotid bl ood how at the higher levels of G(z) stress.