ALPHA-1-ADRENOCEPTOR SUBTYPES MEDIATING THE NOREPINEPHRINE-INDUCED CONTRACTILE RESPONSE IN THE RAT VAS-DEFERENS

1. The effects of chlorethylclonidine (CEC), 5-methyl-urapidil (5-MU), ryanodine and prolonged exposition to norepinephrine (NE) on the conc entration-response curves (CRC) to this agonist on the bisected rat va s deferens (RVD) were investigated. 2. CEC did not affect the 50% effe ctive concentration (EC50) of NE in either the prostatic (PP) or the e pididymal (EP) portions of the RVD. 3. 5-MU did not alter the EC50 of NE in the PP but caused a significant and concentration-dependent righ tward shift of the CRC to NE in the EP. 4. Ryanodine caused a shift to the right of the CRC to NE in the PP associated to a decrease in maxi mal response, but did not affect the CRC to NE in the EP. 5. Incubatio n of the EP with NE for 6 hr elicited a significant decrease in the ma ximal response with no changes in the EC50. Similar treatment of the P P was associated with a significant shift to the right of the CRC to N E without modifications in the maximal response. 6. These results sugg est that in the RVD, NE interacts with two different alpha1-adrenocept ors subtypes which are disposed in a selective manner along the RVD: t he alpha1a subtype in the EP, and a non-alpha1b-non-alpha1a adrenocept or subtype mainly located at the PP.