Abstract
1. 1. Methoxamine 0.5 μm induced an extremely regular rhythmic activity in isolated rabbit anococcygeus muscle. 2. 2. Prazosin had an inhibitory effect on methoxamine-induced rhythmic contractions. IC 50 of prazosin was 7.94 nM. 3. 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 (IC 50 = 0.11 μM) or nifedipine (IC 50 = 0.21 μM). 4. 4. Application of reserpine made the preparations 40-fold more sensitive to methoxamine. 5. 5. It can be concluded that rhythmic contractions produced by methoxamine are mediated through stimulatory action of methoxamine on α-1 adrenoceptors and depend on extracellular calcium. 6. 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 × 10 −7 M, 5 × 10 −8 M and 1.5 × 10 −8 M of methoxamine, respectively.
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