RESUMEN
When infused into the third ventricle of the brain of the conscious cat, the phosphodiesterase inhibitors, papaverine and aminophylline, increased blood pressure and heart rate whilst the phosphodiesterase stimulator, imidazole-4'-acetic acid, decreased blood pressure. Administered intravenously, these compounds caused the opposite effects indicating that the responses after third-ventricular administration were centrally mediated. Infused of dibutyryl cyclic 3',5'-AMP into the third ventricle increased blood pressure and heart rate, whereas dibutyryl cyclic 3',5'-GMP had little effect and antagonised and pressor response to dibutyryl cyclic 3',5'-AMP. ATP, 5'-AMP and adenosine induced similar changes to dibutyryl cyclic 3',5'-AMP, although the pressor responses to these compounds were of different onset and/or duration. When administered into the third ventricle both alpha- and beta-adrenoceptor blocking agents reduced the pressor response caused caused by the phosphodiesterase inhibitor, papaverine, given by the same route. These results demonstrate a central effect of adenosine and adenosine nucleotides to raise blood pressure. The possibility of a specific role for cyclic 3',5'-AMP in the central control of blood pressure is discussed.