Objective: Inspired by organ culture-induced changes in the vascular endothelin (ET) receptor population, we investigated whether such changes occur in cerebral arteries in a rat subarachnoid hemorrhage (SAH) model.
Methods: SAH was induced with injection of 250 microl of blood into the prechiasmatic cistern. After 2 days, the middle cerebral artery, basilar artery, and posterior communicating artery were harvested. Pharmacological studies were performed in vitro, and levels of messenger ribonucleic acid (mRNA) were quantified in real-time reverse transcriptase-polymerase chain reaction assays.
Results: In the middle cerebral artery and basilar artery from rats with induced SAH, enhanced biphasic responses to ET-1 were observed. The -log(50% effective concentration) value for the high-affinity phase was approximately 12, compared with approximately 8.5 for sham-operated animals. At a concentration of ET-1 of 10(-9) mmol/L (approximately equal to the physiological concentration of ET-1 in the plasma), submaximal contractions of 50 to 75% of the contraction obtained through stimulation with 60 mmol/L K(+) were now observed. Quantitative mRNA studies with the same arteries demonstrated significant increases in the number of copies of ET(B) receptor mRNA but not ET(A) receptor mRNA. Evidence of functional ET(B) receptors was provided in antagonist studies. The posterior communicating artery did not exhibit significant changes.
Conclusion: The altered receptor profile observed may represent the final stage in the series of events leading from SAH to actual spasm of the artery. The pharmacological data for the ET(B) receptor suggest complex interactions between normally present ET(A) receptors and up-regulated ET(B) receptors.