Circadian rhythm of circulating corticosterone and prolactin levels in spontaneously hypertensive rats

Immune system of the spontaneously hypertensive rat: II. Morphology and function

The spontaneously hypertensive rat (SHR) is a stress-sensitive animal which exhibits moderate immune dysfunction that has been implicated in the onset of hypertension. In this study, we examined the morphology of SHR thymus and spleen and further characterized the immune deficiency using Wistar-Kyoto (WKY) and Fisher 344 (F-344) rats for comparison. The adult SHR thymus does not display the increase in medullary volume typically noted with aging and the volume density of the marginal zone is decreased in the spleen. In vivo tritiated-thymidine incorporation is also decreased in the spleen of unstimulated SHR. In mixed lymphocyte reactions (MLR), the proliferative response of SHR splenocytes is significantly decreased relative to controls, WKY and F-344. Addition of interleukin-1 (IL-1), interleukin-2 (IL-2), or indomethacin to the MLR cultures does not increase proliferation. The proliferative response to T cell receptor monoclonal antibody (mAb-TCR) or interleukin-2 (IL-2) are similarly impaired in the SHR. The depressed proliferative T cell response is reversed by prolactin. It is suggested that the SHR is a valuable model for the study of immune deficiency.

Spontaneous hypertensive rats: behavioral and corticosterone response depend on circadian phase

Baseline and reactive motor activity and corticosterone levels of spontaneous hypertensive rats (SHR) and their normotensive controls (WKY) were compared with respect to circadian rhythmicity. In the open field, SHR showed higher ambulation and rearing and less defecation than WKY in both light and dark phases. There were significant interactions between strain and time of day in the rate of habituation. SHR showed elevated baseline motor activity, increased motor response and enhanced corticosterone response to "mild" stress only in the light phase. There may be a disorder of temporal organisation in SHR characterised by increased sensitivity to external stimuli during the sleeping state.