NEUROTRANSMITTERS INVOLVED IN THE MECHANICAL RESPONSE OF GUINEA-PIG GALLBLADDER TO ELECTRICAL-FIELD STIMULATION

The type of neurotransmitters released from neural plexuses in the gal lbladder was investigated using transmural electrical field stimulatio n (EFS). EFS produced a frequency and intensity-dependent contraction whose main component was neurogenic since treatment with tetrodotoxin (TTX) reduced the response to 18.92 +/- 6.06 % compared to the respons e in the absence of TTX. In order to elucidate the mechanism involved in the EFS-induced contraction we studied the effects of several neuro transmitter antagonists on this response. The presence of atropine (10 (-9) M - 10(-6) M) reduced contractions in a concentration-dependent f ashion, but atropine was unable to abolish the EFS-induced contraction s. Treatment with guanethidine also decreased the response to EFS (28. 48 +/- 5.40 % compared to control) whereas the b-blocking agent propra nolol (10(-6) M) induced increases in the measured response. Loxiglumi de was able to reduce the contractile response in a concentration-depe ndent manner and addition of increasing concentrations L-NAME, to the bath resulted in a enhancement of the EFS-response. The data clearly d emonstrated that EFS induces a contractile gallbladder response which is the result of stimulation of cholinergic, adrenergic, CCK-ergic and nitrergic fibers.