Methoxamine-induced rhythmic activity in rabbit anococcygeus muscle.
1. Methoxamine 0.5 microns induced an extremely regular rhythmic activity in isolated rabbit anococcygeus muscle. 2. Prazosin had an inhibitory effect on methoxamine-induced rhythmic contractions. IC50 of prazosin was 7.94 nM. 3. The methoxamine-induced contractions are dependent on extracellular calcium and can be inhibited by the omission of calcium from media or the introduction of verapamil (IC50 = 0.11 microM) or nifedipine (IC50 = 0.21 microM). 4. Application of reserpine made the preparations 40-fold more sensitive to methoxamine. 5. It can be concluded that rhythmic contractions produced by methoxamine are mediated through stimulatory action of methoxamine on alpha-I adrenoceptors and depend on extracellular calcium. 6. Lithium made the muscle more sensitive to methoxamine action. In preincubated muscles with 1, 3 and 5 mM lithium the initiation of contractions occurred at 1.5 x 10(-7), M, 5 x 10(-8) M and 1.5 x 10(-8) M of methoxamine, respectively.
Dehpour
A R
AR
Department of Pharmacology, Faculty of Medicine, Tehran University of Medical Sciences, Iran.
Tajkhorshid
E
E
Radjaee-Behbahani
N
N
Kheirollahi
K
K
D000316:Adrenergic alpha-Agonists / Q000494:pharmacology; D000818:Animals; D002118:Calcium / Q000172:deficiency / Q000502:physiology; D002121:Calcium Channel Blockers / Q000494:pharmacology; D005260:Female; D066298:In Vitro Techniques; D008094:Lithium / Q000494:pharmacology; D008297:Male; D008729:Methoxamine / Q000494:pharmacology*; D009119:Muscle Contraction / Q000187:drug effects; D009130:Muscle, Smooth / Q000187:drug effects* / Q000294:innervation / Q000378:metabolism; D010716:Phosphatidylinositols / Q000378:metabolism; D011224:Prazosin / Q000494:pharmacology; D011817:Rabbits; D018340:Receptors, Adrenergic, alpha-1 / Q000187:drug effects; D012110:Reserpine / Q000494:pharmacology
D000316:Adrenergic alpha-Agonists; D002121:Calcium Channel Blockers; D010716:Phosphatidylinositols; D018340:Receptors, Adrenergic, alpha-1; D012110:Reserpine; D008094:Lithium; D008729:Methoxamine; D002118:Calcium; D011224:Prazosin