Muscular and Neuronal a and ß Adrenercig Receptor Mechanisms in Rat Ileal Longitudinal Muscle Contractility.
Abstracts
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BACKGROUND: Adrenergic Inhibition modulates gut motility. AIM: To study receptor specific adrenergic contractile mechanisms in normal rat ileum. HYPOTHESIS: Muscular (1 and (2 receptors mediate inhibition in rat. METHODS: We harvested proximal ileum from normal male Wistar rats (n=8). Full thickness muscle strips were suspended parallel to longitudinal muscle direction in a temperature-controlled tissue chamber with modified Krebs solution and stretched to optimal length. Spontaneous contractile activity (area under the curve) and dose responses (six doses, 10-7-3?10-5M) to norepinephrine (NE, nonspecific), phenylephrine (PH,(1), clonidine (C,(2), prenalterol (PR,(1), ritodrine (RI,(2) and ZD7714 (ZD,(3) were evaluated with and without TTX (nerve blocker). RESULTS (Table): NE(3?10-5M)inhibited 65(6% (mean(SEM) of spontaneous contractile activity. This was the maximum effect. The same dose of RI((2), PH((1) or ZD ((3) resulted in an inhibition of only 46(7%, 31(5%, 39(3% ,respectively. The calculated concentration to induce 50% inhibition (EC50) of ZD ((3) was similar to NE, whereas higher concentrations of PH((1) or RI((2) were required. C((2) and PR((1) had no effect at any dose. TTX affected exclusively RI at the doses of 3?10-6, 10-5, 3?10-5M by 14(4%, 14(3%, 10(2%, resp. SUMMARY: Contractile activity was inhibited by NE (nonspecific), PH((1), RI((2) and ZD ((3) mimic the effect of NE. TTX reduced the effect of RI up to 14( 1% (but not EC50).CONCLUSIONS: Our results suggest that adrenergic inhibition of contractile activity in the rat ileum are mediated mainly by muscular (1, (3 and (2 receptor mechanisms. The latter involves presynaptic receptors as well. |
