To assess the regional changes in cerebral blood flow, 10 healthy volunteers were given 400 μg thyrotropin-releasing hormone iv in a double-blind, randomized, cross-over study. Regional cerebral blood flow was determined simultaneously in two slices of the brain, using a single photon emission computerized tomograph and inhalation of 133Xe. Thyrotropin-releasing hormone caused a significant mean increase of 3.7% (range −8.8–22.7) in blood flow in a region consistent with the left thalamus compared to placebo (3.2% decrease). In 25 other regions no significant change was detected. The thalamic region has previously been shown to be a region especially affected by thyrotropin-releasing hormone in animal studies. The thyrotropin-releasing hormone injection was followed by a minor rise in systemic blood pressure, but not a rise that could affect the cerebral blood flow. The effect of thyrotropin-releasing hormone on the regional cerebral blood flow in the thalamic region was much lower compared to changes found in sedated animals given a hundredfold higher dose of thyrotropin-releasing hormone.
