title: Cardiac function of the naked mole-rat: ecophysiological responses to working underground.
abstract: The naked mole-rat (NMR) is a strictly subterranean rodent with a low resting metabolic rate. Nevertheless, it can greatly increase its metabolic activity to meet the high energetic demands associated with digging through compacted soils in its xeric natural habitat where food is patchily distributed. We hypothesized that the NMR heart would naturally have low basal function and exhibit a large cardiac reserve, thereby mirroring the species' low basal metabolism and large metabolic scope. Echocardiography showed that young (2-4 yr old) healthy NMRs have low fractional shortening (28 ± 2%), ejection fraction (43 ± 2%), and cardiac output (6.5 ± 0.4 ml/min), indicating low basal cardiac function. Histology revealed large NMR cardiomyocyte cross-sectional area (216 ± 10 μm(2)) and cardiac collagen deposition of 2.2 ± 0.4%. Neither of these histomorphometric traits was considered pathological, since biaxial tensile testing showed no increase in passive ventricular stiffness. NMR cardiomyocyte fibers showed a low degree of rotation, contributing to the observed low NMR cardiac contractility. Interestingly, when the exercise mimetic dobutamine (3 μg/g ip) was administered, NMRs showed pronounced increases in fractional shortening, ejection fraction, cardiac output, and stroke volume, indicating an increased cardiac reserve. The relatively low basal cardiac function and enhanced cardiac reserve of NMRs are likely to be ecophysiological adaptations to life in an energetically taxing environment.
authors.affiliation: Department of Physiology and the Sam and Ann Barshop Institute for Aging and Longevity Studies, The University of Texas Health Science Center at San Antonio, San Antonio, Texas;
authors.forename: Kelly M
authors.initials: KM
authors.lastname: Grimes
authors.forename: Andrew
authors.initials: A
authors.lastname: Voorhees
authors.forename: Ying Ann
authors.initials: YA
authors.lastname: Chiao
authors.forename: Hai-Chao
authors.initials: HC
authors.lastname: Han
authors.forename: Merry L
authors.initials: ML
authors.lastname: Lindsey
authors.forename: Rochelle
authors.initials: R
authors.lastname: Buffenstein
mesh_terms: D000222:Adaptation, Physiological; D000818:Animals; D001696:Biomechanical Phenomena; D002316:Cardiotonic Agents / Q000494:pharmacology; D003094:Collagen / Q000378:metabolism; D004280:Dobutamine / Q000494:pharmacology; D025401:Echocardiography, Stress; D017753:Ecosystem; D004734:Energy Metabolism; D005260:Female; D006321:Heart / Q000187:drug effects / Q000502:physiology*; D006339:Heart Rate; D008297:Male; D019577:Mole Rats / Q000502:physiology*; D009200:Myocardial Contraction; D032383:Myocytes, Cardiac / Q000378:metabolism; D013045:Species Specificity; D013318:Stroke Volume; D016277:Ventricular Function, Left / Q000187:drug effects
chemical_list: D002316:Cardiotonic Agents; D004280:Dobutamine; D003094:Collagen
keywords: cardiac reserve; echocardiography; ecophysiology; left ventricular function; naked mole-rat