Abstract
1. Presynaptic α 2-adrenoceptor mechanisms in electrically stimulated longitudinal muscles of ilea isolated from 3, 10, 20 and 47 week-old guinea pigs were studied by analysis of the concentration-response curves of noradrenaline, a full agonist, and clonidine, a partial agonist, and the Scatchard plot of specific binding of [ 3H]- p-aminoelonidine to synaptosomal fractions from the longitudinal muscle of guinea pig ileum. 2. The pD 2 value of noradrenaline and the maximum contraction induced by clonidine increased with age from 3 to 20 weeks and there after decreased to 47 weeks, while the pA 2 value of yohimbine against noradrenaline did not alter with age. 3. The capacity of the maximum binding sites of [ 3H]- p-aminoclonidine increased with increasing age (3–20 weeks), while the dissociation constant ( K d) of [ 3H]- p-aminoclonidine did not change during the same period. 4. The changes in the presynaptic α 2-adrenoeeptor mechanisms with age are considered to be due to the change in the total concentration of presynaptie α 2-adrenoceptors.
Published Version
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