Alterations in beta-adrenoceptor number and catecholamine content of chick atria after reversible sympathetic denervation with 6-hydroxydopamine.

1. The characteristics of [3H]-dihydroalprenolol (DHA) binding were determined in atria from untreated chicks. [3H]-DHA binding to atrium homogenates was rapid (k1 = 8.52 X 10(8) l mol-1 min-1), reversible (k-1 = 0.47 min-1), saturable, and of high affinity (KD = 0.6-1.0 nmol/l). Isoprenaline competed for specific [3H]-DHA binding in a stereoselective manner; IC50 values (mumol/l) were: (-)isoprenaline 0.12, (+)isoprenaline 4.7. 2. The number of [3H]-DHA binding sites and catecholamine content of left and right atria were examined after injection of chicks with a single dose of 6-hydroxydopamine hydrobromide (100 mg/kg). There were transient increases in the number of [3H]-DHA binding sites in both the left and the right atrium after 6-OHDA treatment. These increases were quicker in onset and in offset in the right atrium than in the left atrium. [3H]-DHA binding was significantly increased in the left atrium at 5 and 7 days, and in the right atrium at 3 and 5 days after 6-OHDA injection. 3. Saturation binding isotherms indicated that the increase in [3H]-DHA binding was due to an increase in beta-adrenoceptor number with no change in affinity for [3H]-DHA. 4. Twenty four hours after 6-OHDA treatment there was a significant (80%) decrease in noradrenaline content of left and of right atria. 5. The decrease in noradrenaline content was reversible, noradrenaline levels returning to 55% of control in left atrium and to 71% of control in right atrium by 21 days after 6-OHDA treatment. These changes are consistent with reversible sympathetic denervation of the atria.(ABSTRACT TRUNCATED AT 250 WORDS)