RESPONSES OF REGIONAL CEREBRAL BLOOD-FLOW TO INTRAVENOUS ADMINISTRATION OF THYROTROPIN-RELEASING-HORMONE IN AGED RATS

The effects of i.v. administration of thyrotropin releasing hormone (TRH) on regional cerebral blood flow (rCBF) were examined in both healthy adult (3-5 months old) and healthy aged (24-25 months old) male Wistar rats under halothane anesthesia. The rCBFs in 9 different brain regions - cerebral cortex, caudate putamen, hippocampus, thalamus+hypothalamus, superior colliculus, inferior colliculus, cerebellum, pons, and medulla - were measured by [C-14]iodoantipyrine method. In the adult rats, i.v. administration of TRH (300-mu-g/kg) produced significant increases in rCBFs in cerebral cortex, caudate putamen, hippocampus, thalamus+hypothalamus and superior colliculus. In the aged rats, the rCBFs in all brain regions measured did not change significantly by TRH administration, From these results, it is suggested that the system involved in TRH-induced vasodilatation of cerebral blood vessels was impaired with aging.