Core temperature circadian rhythm across aging in Spontaneously Hypertensive Rats

• Published in: Journal of thermal biology Vol. 97; p. 102807
• Main Authors: de Rezende, Leonardo M.T., Brito, Leandro C., Moura, Anselmo G., Costa, Alexandre J.L.D., Leal, Tiago F., Favarato, Evandro S., Favarato, Lukiya S.C., Natali, Antônio J., Coimbra, Cândido C., Prímola-Gomes, Thales N.
• Format: Journal Article
• Language: English
• Published: England Elsevier Ltd 01.04.2021; Elsevier BV
• Subjects: Aging; Aging - physiology; Animals; Blood pressure; Body core temperature; Body mass; Body Temperature; Circadian rhythm; Circadian Rhythm - physiology; Circadian rhythms; Experimental strains; Hypertension; Hypertension - physiopathology; Models, Animal; Rats; Rats, Inbred SHR; Rats, Inbred WKY; Rats, Wistar; Rodents; Telemetry; Hypertension; Body core temperature; Circadian rhythm; Experimental strains
• ISSN: 0306-4565; 1879-0992
• DOI: 10.1016/j.jtherbio.2020.102807

The purpose of this study was to evaluate the circadian rhythm of core temperature (Tcore) across aging in Spontaneously Hypertensive Rats (SHR) with comparison to the two rat strains often used as their normotensive control animals, namely, Wistar (WIS) and Wistar Kyoto (WKY). WIS, WKY and SHR rats were subdivided into three different groups according their age: WIS16, WIS48, WIS72, WKY16, WKY48, WKY72, SHR16, SHR48 and SHR72 weeks-old. Body mass and blood pressure were periodically measured along the experiments. All animal group had their circadian rhythm of Tcore evaluated over three consecutive days (72 h) by telemetry using an implanted temperature sensor. The Tcore circadian rhythm was averaged in 1-h blocks and analyzed using the cosinor method. Sixteen-week-old SHR (SHR16) presented higher Tcore than WIS16 (from 06am to 06pm) and WKY16 (from 07am to 06pm). Both normotensive groups exhibited increases in Tcore during circadian rhythm with aging. The cosinor analysis showed no differences between strains and ages for the acrophase. An age effect on the SHR strain (SHR16 < SHR72) was observed regarding the amplitude. SHR16 had higher values regarding MESOR compared to WIS16 and WKY16. In addition, WIS72 and WKY72 showed higher values than WIS16 and WKY16, respectively. Finally, no differences were observed in the strength rhythm analysis. SHR presented impaired thermoregulatory control at only 16 weeks of age when showing a higher body temperature during the activity phase, while other circadian rhythm parameters showed no differences across aging. Therefore, in taking our results as a whole we can conclude that WIS and WKY are appropriate Wistar strains to be used as normotensive controls for SHR. •Aging does not affect Tcore circadian rhythm in SHR.•Aging affects Tcore circadian rhythm in normotensive WIS and WKY strains.•Hypertension affects Tcore circadian rhythm in young but not in old SHR.•Both WIS and WKY may be used as normotensive controls for SHR.