EFFECT OF CENTRAL ADENOSINE ON BRAIN-STEM BLOOD-FLOW IN FETAL SHEEP

The effect of the adenosine analogue R-N-6-(phenylisopropyl)adenosine (R-PIA) on blood flow to the medulla and pens was examined in unanaest hetized fetal sheep. Micropheres labelled with isotopes were used to d etermine blood flow before and after instillation of 0.2 or 0.5 mu g R -PIA into the cerebrospinal fluid of the fourth ventricle. Blood flow to the medulla, which had a mean value (+/- S.E.M.) of 285 +/- 41 ml m in(-1) (100 g)(-1) during the control period, was not changed by the c entral instillation of R-PIA. Blood flow to the pens was also nor affe cted. These data indicate that central adenosine, which depresses resp iratory drive in fetal sheep, acts by mechanisms independent of remova l of carbon dioxide from the brainstem.