The influence of beta-agonists on normal and clonidine-decelerated noradrenaline turnover in the rat brain.

The effect of some beta-adrenoceptor agonists, such as clenbuterol, salbutamol, isoprenaline and formoterol on the NA turnover (estimated on the basis of NA disappearance after inhibition of its synthesis by FLA-63) in various regions of the rat brain was examined. All the used beta-agonists (given ip) accelerated the FLA-63 induced disappearance of NA in the cortex, limbic system and brain stem. That effect of the beta-agonists was antagonized by propranolol. The obtained results indicate that beta-adrenoceptors are involved in regulation of the NA turnover. After chronic treatment with salbutamol (5 mg/kg, twice a day for 10 days, the last dose--10 mg/kg), tolerance to acute affects of that substance developed. In turn, salbutamol given chronically prevented the clonidine-induced deceleration of NA disappearance. The effects observed after chronic salbutamol treatment may be due to developed adaptive changes in beta-, as well as in alpha 2-adrenoceptors.