Circadian rhythms of heart rate and blood pressure in four strains of rat: Differences due to, and separate from, locomotor activity

Abstract

Five or six rats from four rat strains (two normotensive, two hypertensive) have been studied for seven consecutive days. All four strains were entrained to a 12:12 L:D cycle. While freely mobile, the blood pressure, heart rate and locomotor activity have been measured throughout and mean values obtained over 15‐min intervals have been analysed. In all strains there was a marked circadian rhythm of locomotor activity peaking in the dark phase. In both normotensive strains (Wistar‐Kyoto and Sprague‐Dawley) the circadian rhythms of heart rate, systolic and diastolic blood pressures paralleled those of activity. In spontaneously hypertensive rats the mean heart rate was lower than in the normotensive strains, but its circadian rhythm was similarly phased; blood pressures were higher and, though the values were higher in the active (dark) phase, the profiles did not closely parallel that of heart rate. In a hypertensive, transgenic strain, heart rate showed an altered circadian profile, though still showing higher values in the active phase. By contrast, the circadian profiles of blood pressure were almost the inverse of those in the other strains and of the profile of heart rate in the transgenic strain.

>Purification of the heart rate and blood pressure data showed that these differences could not be ascribed to masking effects caused by locomotor activity; that is, they are endogenous in origin.

>These results are discussed in terms of whether the two hypertensive strains can be considered to act as models for contributing to our understanding of primary and secondary hypertension.

Abstracting keywords:

• Blood pressure
• heart rate
• locomotor activity
• hypertension
• purification
• transgenic animals

Notes

Correspondence to: Professor Dr. med. B. Lemmer, Institute of Pharmacology and Toxicology, Faculty of Clinical Medicine, Ruprecht‐Karls‐University of Heidelberg, Maybachstr. 14–16, D‐68169 Mannheim, Germany

Institute of Pharmacology and Toxicology, Ruprecht‐Karls‐University of Heidelberg, Germany.

School of Biological Sciences, University of Manchester, Manchester, UK.