Adrenoceptor changes in spontaneous hypertensive rats: a circadian approach

Circadian adrenoceptor rhythms were measured in the cortex, hypothalamus, cerebellum and pons-medulla of WKY and SHR rats. The 24-h mean binding to alpha 1-, and beta-adrenoceptors was higher in SHR than WKY in all regions:greatest differences were found at the end of the dark phase. The most consistent and large amplitude circadian rhythms in adrenoceptor binding occurred in the hypothalamus; strain differences in wave form of the rhythm were the most noticeable phenomenon. In the pons-medulla SHR rats showed decreased rhythm amplitudes. In the cerebellum, beta-adrenoceptor binding was higher in SHR rats at all time points, with an identical rhythm to that in WKY rats. Thus regional differences between SHR and WKY rats were expressed in changes in many circadian rhythm parameters. There were no differences between SHR and WKY in the ratios of pre-synaptic: post-synaptic receptors. High affinity binding to alpha-adrenoceptors showed similar circadian rhythms to total specific binding, indicating that the short-term fluctuations cannot be attributed to change in affinity state. Whether these modifications in circadian rhythm characteristics are related to the development or maintenance of hypertension in the SHR strain remains to be investigated.