Springer Online Journal Archives 1860-2000
Summary 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 × 108 1 mol−1 min−1), reversible (k −1 = 0.47 min−1), saturable, and of high affinity (K D = 0.61.−nmol/l). Isoprenaline competed for specific [3H]-DHA binding in a stereoselective manner; IC50 values (μmol/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 β-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. 6. Adrenaline levels in the atria were 5 to 18% of total catecholamine (noradrenaline+adrenaline) content and were not significantly altered by 6-OHDA treatment.
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