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 RESEARCH PAPER
Year : 1989  |  Volume : 21  |  Issue : 4  |  Page : 120-128

Pre-synaptic dopamine receptors in the rat anococcygeus muscle



Correspondence Address:
A Subramaniam


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1. Dopamine (1.3 x l0-7M to 7.7 x 10-5M) and noradrenaline (NE) (1.9x l0-7 M to 1.9 x l0-4M) produced dose dependent contractions of rat anococcygeus muscle. 2. Bromocriptine (5 x IO-6M) and dopamine (1 x 10-10M) inhibited the contractions evoked by field stimulation. These inhibitions were prevented by metoclopramide (9.8 x IO-6M). 3. Bromocriptine also significantly inhibited the dopamine evoked contractions but did not alter the responses to NE. The inhibition induced by bromocriptine was prevented by metoclopramide. 4. SKF 38393 (4.1 x IO-6M), a selective dopamine D1 receptor agonist potentiated the contractions elicited by dopamine and NE. Pimozide (7.0 x 10-7 M) prevented the potentiation produced by SKF 38393. 5. SKF 38393 (4.1 x lO-6M) failed to potentiate the dopamine and NE induced contractions in the reserpinized preparations. 6. Further, nialamide (2.2 x 10-6 M), pyrogallol (2.6 x 10-5 M) and cocaine (3.3 x 10-6M) potentiated the responses to dopamine (2.2 x I0-6M) and NE (1.7x 10-6 M). SKF 38393 (4. I x lO-6M) caused further potentiation of dopamine and NE evoked contractions in presence of nialamide and pyrogallol. 7. However, in the presence of cocaine, SKF 38393 failed to potentiate further the responses to dopamine and NE. 8. The results suggest that the rat anococcygeus muscle consists of excitatory as well as inhibitory dopamine receptors. The inhibitory dopamine receptors appear to be located pre-synaptically and are of D2 type.The dopamine D1 receptors also appear to be located pre-synaptically and they are linked to the catecholamine uptake blocking mechanism.






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