Normorphine, methionine enkephalin methylester (MEM) and apomorphine inhibited the twitches of the isolated, field stimulated medial smooth muscle of the cat nictitating membrane without affecting the action of exogenous noradrenaline (9X10-6M). The activity of methionine and leucine enkephalin and enkephalin structure analogues was compared in the cat nictitating membrane and in the longitudinal muscle preparation of the guinea-pig ileum. In the nictitating membrane of the cat, both the morphine antagonist naloxone (2.7X10-7M) and the dopamine antagonist haloperidol (2.7X10-7M) counteracted significantly the depressant effects of normorphine (1.1x10-6M) and apomorphine (1.1X10-6M). However, the action of MEM (8.5X10-6M) could be antagonized only by naloxone (2.7X10-7M) and that of dopamine (1.6X10-5M) only by haloperidol (2.7X10-7M). Moreoever, tachyphylaxis to apomorphine and cross-tachyphylaxis between normorphine and apomorphine could be demonstrated. In the field stimulated longitudinal muscle preparation of the guinea-pig ileum, dopamine inhibited twitches only in extremely high concentrations and phentolamine (2.7X10-6M), but not haloperidol (8.1X10-7M), did antagonize the action of dopamine (1.6X10-4M). The isolated nictitating membrane of the cat seems to be a promising preparation for the analysis of the mechanism of action of opiates and opioid peptides, and morphine and dopamine receptors in this organ are similar in many respects.
|Number of pages||12|
|Journal||Polish journal of pharmacology and pharmacy|
|Publication status||Published - Dec 1 1978|
ASJC Scopus subject areas
- Pharmaceutical Science