The histology of the respiratory system in Sprague Dawley Rats after chronic heat exposure

Abstract

Over the past years, the Earth has experienced rapid climate changes as a result of anthropogenic influences. The forthcoming environmental conditions may place homeotherms under heat stress, which is the rise in core body temperature beyond the individual’s upper critical temperatures. Exposure to acute heat stress causes progressive tissue injury, and this damage can be reversed upon cooling. Few studies have completed a comprehensive analysis of the respiratory responses to chronic heat stress. As such, this study aimed to assess how the respiratory system was altered as a result of chronic heat stress. The experiment took place over two weeks (Group I) and four weeks (Group II) in which Sprague Dawley rats were exposed to either 25 oC (control – treatmentA), 33 o C (treatment B), or 34 o C (treatment C) temperatures continuously. The respiratory system was analysed using gross morphology which revealed non-diseased lungs in the control treatments for groups I and II; darker, more indented lungs in the experimental treatments for group I; and non-diseased lungs in treatment B while treatment C was lighter in colour and smaller for group II. Light microscopy revealed no abnormalities in the control treatment and tissue injury in the experimental treatments. In group I, there was an active inflammatory response and heat shock response (recognised with the means of hemotoxylin and eosin and Mallroy trichrome stains), in the form of leukocytes, inducible bronchus-associated lymphoid tissue and pneumocyte hyperplasia (all of which were identified with the use of the New Pentachrome stain). In group II, tissue injury had been eradicated from the 33 o C treatment, indicating a sufficient acclimation response, while the 34 o C treatment presented with progressive pulmonary oedema and pulmonary alveolar proteinosis (identified using the Periodic-Acid Schiff stain), indicating an insufficient heat shock and acclimatory response. Rats exposed to 33 o C were able to alleviate damage associated with heat stress over a longer period of time, while those exposed to 34 o C could not sufficiently overcome heat stress in the respiratory system.