61.6 Friday, Jan. 6 Cardiac hypertrophy in response to pressure overload and exercise training in the American alligator OWERKOWICZ, T*; CAMPBELL, C; EME, J; BLANK, JM; HICKS, JW; California State Uni, San Bernardino; Uni California, Irvine; Uni North Texas, Denton; California Polytechnic State Uni, San Luis Obispo; Uni California, Irvine email@example.com
In mammals, cardiac hypertrophy is often categorized as physiologic or pathologic based on the degree of interstitial fibrosis in the ventricular myocardium. Physiologic (muscular) hypertrophy is an expected response to regular exercise, and pathologic (fibrotic) hypertrophy is seen in mammals faced with chronic pressure overload (e.g., aortic banding). We investigated whether these stressors can drive similar cardiac phenotypes in a non-mammalian model with a four-chambered heart, the American alligator. In earlier studies, surgical ablation of the left aorta (LAo), which exits the right ventricle and allows for potential pulmonary bypass (R-L shunt), resulted in chronic pressure overload, with doubled peak systolic pressures in both ventricles. Juvenile alligators, which had undergone LAo ablation as hatchlings, had greater wet ventricular mass (+65%) and higher DNA content (1.5-3 fold) than sham-operated controls. In order to characterize the histologic nature of this impressive hypertrophy, we compared ventricular cross-sections (stained with Masson’s trichrome) from alligators with and without the LAo. Animals were either sedentary or exercised to exhaustion (treadmill, flume) every other day. As expected, no significant differences existed in myocardial composition between three exercise groups. Surprisingly, the proportion of myocardial fibrosis was significantly lower in alligators without the R-L shunt, which suggests that their hypertrophy was based on myocyte growth. Whether other vertebrate taxa are capable of similar cardiac plasticity in response to pressure overload remains to be investigated. Funded by NSF IOB 00445680 to JWH.