Effects of atropine, pirenzepine, clonidine, and morphine on biphasic response of rat gastric fundus to field stimulation.
1. Electrically evoked contractions in isolated strips of rat gastric fundus were inhibited by atropine (IC50 = 2.5 x 10(-9) M), pirenzepine (IC50 = 2.3 x 10(-8) M), clonidine (IC50 = 3.9 x 10(-8) M) and morphine (IC50 = 3.2 x 10(-7) M) in a dose-dependent manner. 2. The inhibitory effect of morphine was antagonized by naloxone (10(-6) M). The inhibitory effect of clonidine not only was not reversed by yohimbine but also was enhanced. Yohimbine per se inhibited these contractions (IC50 = 6.4 x 10(-6) M). 3. In presence of atropine (2 x 10(-6) M) and guanethidine (5 x 10(-6) M), electrical stimulation of isolated strips of rat gastric fundus produced a non-adrenergic, non-cholinergic (NANC) inhibitory response. 4. The NANC inhibitory response was decreased by morphine (10(-8)-3 x 10(-6) M). In addition, morphine decreased the tone of the muscle. These effects of morphine was antagonized by naloxone (3 x 10(-6) M). 5. Clonidine up to 10(-6) M had no influence on the NANC inhibitory response but yohimbine per se (10(-7)-3 x 10(-5) M) blocked it (IC50 = 3 x 10(-6) M). 6. These findings indicate that electrically evoked contractions in the rat gastric fundus were mediated by muscarinic receptors. In addition, the NANC inhibitory response in the isolated 5-strips of rat gastric fundus was blocked by morphine and yohimbine.
Department of Pharmacology, School of Medicine, Tehran University of Medical Sciences, Iran.
A R
AR
Dehpour
A
A
Delfan
K
K
Mousavizadeh
S R
SR
Mortazavi
D000818:Animals; D001285:Atropine / Q000494:pharmacology*; D003000:Clonidine / Q000494:pharmacology*; D004305:Dose-Response Relationship, Drug; D004558:Electric Stimulation; D005748:Gastric Fundus / Q000187:drug effects* / Q000294:innervation / Q000502:physiology; D066298:In Vitro Techniques; D008297:Male; D009020:Morphine / Q000494:pharmacology*; D009119:Muscle Contraction / Q000187:drug effects; D010890:Pirenzepine / Q000494:pharmacology*; D051381:Rats; D017207:Rats, Sprague-Dawley
D010890:Pirenzepine; D009020:Morphine; D001285:Atropine; D003000:Clonidine