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Effects of raised intracranial pressure on regional cerebral blood flow: a comparison of effects of naloxone and TRH on the microcirculation in partial cerebral ischaemia

1 The effects on regional cerebral blood flow (rCBF) of raised intracranial pressure (ICP) and of naloxone and thryrotropin releasing hormome (TRH) during this condition were studied in anaesthetized rabbits. 2 The ICP was elevated until a central ischaemic response was observed. The regional blood flow was determined with the microsphere technique before and during elevation of the ICP (ICPc) and after drug treatment. 3 Total CBF was reduced by about 70% during ICPc while the uveal blood flow increased slightly and some other peripheral tissue blood flows remained unaffected. 4 The administration of TRH caused an increase in mean arterial blood pressure (MAP) from 11.9 ± 0.6 to 14.6 ± 0.7 kPa and a normalization of the rCBF. In some peripheral tissues, e.g. gastric mucosa and spleen, TRH reduced the blood flow by 53% and 76%, respectively. In blood pressure stabilized animals no effect on rCBF was seen after TRH. 5 Naloxone had no consistent effect on MAP or local blood flow. 6 It was concluded that in the range of cerebral perfusion pressure studied there was a passive relationship between cerebral blood flow and perfusion pressure. The lack of effect of naloxone and the marked effect of TRH during cerebral ischaemia are consistent with a mechanism of action of TRH not related to a ‘physiological’ antagonism of opioids.