ELECTRICAL STIMULATION-INDUCED ALPHA(1)-ADRENOCEPTORS-MEDIATED AND ALPHA(2)-ADRENOCEPTORS-MEDIATED CONTRACTION IN ISOLATED DOG THORACIC DUCTS

The electrical stimulation-induced responses of isolated dog thoracic ducts were investigated using an organ bath technique. Electrical stim ulation (0.7 ms in pulse width, 25 V in nominal voltage, 10 s in durat ion time, 1-32 Hz at frequency) produced frequency-related contraction s in the lymphatic preparations. The contractions were abolished by pr etreatment with tetrodotoxin (10(-7) M), guanethidine (10(-7), 10(-6) M), and bretylium (10(-7), 10(-6) M). Cocaine (10(-6) M) significantly potentiated the electrical stimulation - induced contractions. Phento lamine (10(-8)-10(-5) M), prazosin (10(-8)-10(-5) M), bunazosin (10(-6 ), 10(-5) M), yohimbine (10(-8)-10(-6) M) and rauwolscine (10(-8)-10(- 6) M) also dose - dependently reduced the contractions. On the other h and, propranolol (10(-8)-10(-6) M), atropine (10(-6) M), hexamethonium (10(-6) M), aspirin (3 x 10(-5) M), N omega-nitro-L-arginine methyl e ster (L-NAME) (3 x 10(-5) M) and L-NAME (3 x 10(-5) M)+ L-arginine (10 (-4) M) caused no significant effect on electrical stimulation-induced contractions. No significant difference in the electrical stimulation -induced responses was observed between the lymphatic preparations wit h and without an intact endothelium. The electrical stimulation caused only a small contraction with no relaxation in the thoracic duct prep aration precontracted with 10(-8) M U46619. The small contraction was abolished by 10(-5) M phentolamine. These findings suggest that then e xists alpha(1)- and alpha(2)-adrenoceptors-mediated excitatory innerva tion, but no NO-ergic inhibitory nerve fiber in dog thoracic ducts. (C ) 1998 Elsevier Science B.V. All rights reserved.