On receptor changes in cerebral arteries after subarachnoid haemorrhage
Abstract: Overall the aim has been to characterise the in vitro upregulation of the 5-hydroxytryptamine 1B/1D (5-HT(1B/1D)) and endothelin (ET) receptors in the cerebral circulation as well as demonstrating phenotypic changes in a pathophysiological model mimicking subarachnoid haemorrhage. The first part describes receptor upregulation using organ culture of whole vessel segments from both rat and man. The upregulation is dependent on gene transcription and translation; thus, an active signalling pathway is involved. Further analysis of this pathway revealed that protein kinase C is especially important in the upregulation process of the ET(B) receptor. The second part attempts to take the concept of receptor upregulation into the pathophysiological realm, especially focusing on experimental subarachnoid haemorrhage. Changes similar to those observed using the in vitro organ culture technique were observed in vivo. Especially the ET(B) receptor upregulates and perhaps more importantly, this appears to be associated with a generally increased sensitivity towards ET-1. Now, even at physiological concentrations of ET-1 were appreciable contraction observed. Similar results were obtained when studying the upregulation of the 5-HT(1B) receptor; the upregulation imparts increased sensitivity of the cerebral arteries towards serotonin. The increased functional responses represent a significant contribution towards the understanding of cerebral vasospasm after subarachnoid haemorrhage. Finally, it is revealed that the ET(B) receptor is more frequently present in human arteries from patients with cerebrovascular disease thus substantiating the idea of receptor upregulation as part of human cerebrovascular pathology.
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