The influence of muscarinic and prostaglandic mechanisms on regional cerebral and peripheral blood flows and on the vascular effects of thyrotropin releasing hormone (TRH).

TRH has pronounced vascular effects. The final transmitter mechanisms of these effects are not fully understood. The present study was conducted in order to elucidate whether these effects are mediated by prostaglandic or muscarinic mechanisms. Muscarinic blockade augmented the vasoconstricting- and pressor effect of TRH; vasodilation in the brain was attenuated only in the caudate nucleus. Indomethacin provoked a decrease in regional cerebral blood flow and in the gastric mucosal blood flow. No effect of indomethacin was observed on the vascular effects of TRH. It is concluded that the cerebral vasodilating and peripheral vasoconstricting effects of TRH are not mediated by prostaglandins. Muscarinic mechanisms are involved in the vasodilating effect of TRH only in the caudate nucleus.