LOSS OF [I-125] PINDOLOL BINDING TO BETA-ADRENOCEPTORS ON RAT NODOSE GANGLION AFTER CHRONIC ISOPRENALINE TREATMENT

The nodose ganglion contains the cell bodies of afferent nerves which convey predominantly sensory information from the viscera to the centr al nervous system (CNS). Autoradiographic studies show binding sites f or beta-adrenoceptor ligands are present on sections of the rat nodose ganglion and also on the corresponding inferior vagal ganglion in hum ans, indicating the presence of beta-adrenoceptors in these ganglia. S ince prolonged stimulation of beta-adrenoceptors in rats with the nons elective beta-adrenoceptor agonist isoprenaline (400 mu g kg(-1) day(- 1) s.c.) for 14 days results in desensitisation and/or down-regulation of receptors in peripheral tissues, such as heart, kidney and blood v essels, the effects of this treatment on the p-adrenoceptor population on the nodose ganglion have been examined. Using [I-125]-pindolol as a radioligand, autoradiographic studies revealed that specific binding was reduced by 74% in ganglia from isoprenaline-pretreated rats compa red to that in ganglia from vehicle-pretreated rats, demonstrating dow n-regulation of receptors by isoprenaline. [I-125]-Pindolol binding wa s sensitive to inhibition by ICI 118,551 (selective beta(2)-adrenocept or antagonist) but not to atenolol (selective beta(1)-adrenoceptor ant agonist), indicating receptors are predominantly of the beta(2)-adreno ceptor subtype. No change in binding was apparent over the vagus nerve . The nodose ganglion appears to be an additional site at which beta(2 )-adrenoceptors may be down-regulated in vivo, possibly interfering wi th normal baro-, chemo- and sensory reflexes.