The Japanese Journal of Pharmacology
Online ISSN : 1347-3506
Print ISSN : 0021-5198
ISSN-L : 0021-5198
The Contraction Mechanisms for Norepinephrine in Single Cells Prepared from Tracheal Smooth Muscles of Guinea Pig of Different Ages
Mitsutoshi SatohIssei Takayanagi
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1992 Volume 58 Issue 4 Pages 383-389


Single cells were prepared from guinea pig tracheal smooth muscle and used in an experiment on the contraction mechanisms for norepinephrine and a study on the change of α2-adrenoceptors with age. Specific bindings of [3H]p-aminoclonidine to the single cells from the tracheal smooth muscles of 6- and 40-week-old guinea pigs were saturable and analyzed by Scatchard plot. The maximum number of [3H]p-aminoclonidine binding sites was larger in the preparation from 40-week-old guinea pigs than that from 6-week-old animals, while its dissociation constant did not change with age. The amount of prostaglandin F released from the single cells was increased by norepinephrine, not affected by phenylephrine, and reduced by an α2-antagonist such as yohimbine. The amount released by norepinephrine was significantly larger in the preparation from 6-week-old guinea pigs than that from 40-week-old animals. These results suggest that the age-related decrease in the potency of norepinephrine is due to reduction in the amount of excitable prostaglandin F released by the drug, but not to a change in the total amount of α2-adrenoceptors or the dissociation constant of the drug with respect to these adrenoceptors. Furthermore, α2-adrenoceptors in the tracheal smooth muscle cell play an important role in the release of prostaglandin F and the production of contractile responses of these muscles.

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