Baseline Cardiovascular and Oximetric Parameters Across the Lifespan of Male Sprague Dawley Rats

Abstract

Human populations are experiencing unprecedented growth and longevity creating an urgent need for research into the pathologies, mechanisms, and dysfunctions of senescence. Invasive measurements and long-term control conditions for longitudinal studies are infeasible in humans, necessitating surrogate animal models. Rats have short lifespans (2–3 years) with translatable cardiovascular systems, and Sprague Dawley microcirculatory preparations are key to studying the oxygen transport mechanisms critical to aging. Here we present baseline physiological data of 61 male, Sprague Dawley rats at 3, 6, 12, 18, and 24 months of age. Anesthetized animals were surgically prepared for femoral arterial and venous cannulations, tracheal intubation, and exteriorization of the spinotrapezius muscle. Measurements included cardiovascular function, blood gases, and peripheral tissue interstitial oxygen tension (PISFO2) using phosphorescence quenching microscopy. Intrinsic heart rates decreased with age without significant changes to blood pressure. Arterial oxygen tension declined 17% by 18 and 24 Months (p < 0.05) while pACO2 and PISFO2 were unchanged. Lactate was elevated at 12 and 18 Months along with an alkaline shift in blood pH. Heart rate and the decline in pAO2 without a rise in pACO2 are conserved phenomena in human aging. The continuity of resting PISFO2 despite an anaerobic shift in metabolism may be due to declining mitochondrial function and dysregulation of the vascular response to hypoxemia, which are also present in aged humans. These findings contribute to our understanding of age-related physiological changes and underscore the suitability of the Sprague Dawley rat model for aging research.