Contrasting circadian rhythms of blood pressure among inbred rat strains: recognition of dipper and non-dipper patterns.
OBJECTIVE
The non-dipper pattern, i.e. the lack of nocturnal blood pressure (BP) fall, carries a high risk of cardiovascular complications, both in hypertensive and normotensive subjects. Without genetic engineering, experimental demonstration of the non-dipper phenomenon is lacking. The purpose of this study was to assess the haemodynamic and behavioural daily parameters among various strains of rats - spontaneously hypertensive rats (SHR), Wistar-Kyoto (WKY) and Fischer 344 (F344) - in order to characterize their circadian patterns and to detect a non-dipper animal model.


METHODS
Changes in BP, heart rate (HR), and spontaneous locomotor activity (SLA) were recorded continuously for 11 days using telemetry in freely moving 10-week-old male SHR, WKY and F344 rats, in standardized laboratory conditions. Variations in haemodynamic and behavioural parameters were assessed in terms of day/night differences and spectral power corresponding with the 24-h period.


RESULTS
All rats exhibited clear circadian variations in HR and in SLA, in synchrony with the light cycle. Light/dark differences in BP were significantly lower in F344 compared with those of SHR and WKY. The smaller circadian changes in BP observed in F344 were also demonstrated using spectral analysis: the peak detected at 24-h was reduced in F344 compared with SHR and WKY.


CONCLUSIONS
The inbred F344 strain lacks the typical circadian BP rhythm while oscillations of HR and SLA are maintained, suggesting different regulatory mechanisms. The F344 strain may represent a useful animal model for studying the effects of drugs aimed at restoring the dipper status.
Basset
Alexandra
A
INSERM EMI 0107, Laboratoire de Biomécanique et Pharmacologie de la Paroi Artérielle, Paris, France. abasset@bhdc.jussieu.fr
Laude
Dominique
D
Laurent
Stéphane
S
Elghozi
Jean-Luc
JL
D000818:Animals; D001522:Behavior, Animal; D001794:Blood Pressure / Q000502:physiology*; D002940:Circadian Rhythm / Q000502:physiology*; D006339:Heart Rate; D006439:Hemodynamics; D008124:Locomotion; D008297:Male; D051381:Rats; D011916:Rats, Inbred F344; D011918:Rats, Inbred SHR; D011921:Rats, Inbred WKY; D013686:Telemetry; D013997:Time Factors