Age-related changes in the reactivity of the XXXX jejunum to cholinoceptor agonists.

@entity4833 @entity3897 @entity972 @entity35 @entity9666 @entity2710 @entity934
The contractile effects of @entity9666 , @entity972 , @entity934 and @entity2710 were studied in jejunum of 4, 12 and 20 month-old @entity35 . The effects of age on the sensitivity and responsiveness of the jejunum to the agonists were examined using cumulative dose administration and measuring the pD2. The maximum contraction produced by the agonists and the sensitivity to barium and @entity972 were not modified by aging. In the middle-aged animals, the jejunum sensitivity to @entity934 decreased while the sensitivity to @entity2710 was not statistically different from that of 4 month-old @entity35 . Since at this age (12 months) the @entity4833 activity increased, the reduction in the sensitivity to @entity934 could have been due to the increase in the activity of the metabolizing enzyme. Otherwise, in the jejunum from the older animals the sensitivity for both cholinoceptor agonists, @entity934 and @entity2710 , increased 5-fold when compared with the middle-aged animals. However, compared with the jejunum of 4 month-old @entity35 the sensitivity to @entity934 , to 20 month-old animals, was not altered while the sensitivity to @entity2710 was increased. At this age (20 months), the jejunum @entity4833 activity was increased when compared with that of 4 month-old @entity35 and was not modified when compared with that of 12 month-old @entity35 . The change in supersensitivity to cholinoceptor agonists could not have been due to an alteration in muscarinic receptor affinity, since the pA2 for @entity3897 was not modified with increasing age. These results suggest that after an increase in @entity4833 activity around month 12, the jejunum develops an adaptative supersensitivity to cholinoceptor agonists.
