Cs. Venugopalan et al., NONADRENERGIC NONCHOLINERGIC (NANC) EXCITATORY RESPONSE OF THE CHANNEL CATFISH INTESTINE, Journal of autonomic pharmacology, 14(3), 1994, pp. 229-238
1 Optimal parameters for electrical field stimulation (EFS) of catfish
pyloric and middle intestinal segments were determined (15 Hz, 60 V)
from a range of frequencies (5-45 Hz) and voltages (40-120 V) using a
modified Magnus' method. Contractile responses were produced by EFS wh
ich were reproducible and showed no significant difference between the
tissues. 2 The contractile cholinergic responses of the tissues to ca
rbachol and acetylcholine (ACh) were blocked by atropine on an equimol
ar concentration, whereas, these responses were enhanced in the presen
ce of neostigmine, an acetylcholinesterase inhibitor. 3 Adrenergic res
ponses were examined with noradrenaline (NA). NA produced contraction
of the segments only, at a concentration of 10(-4) M. Among the variou
s adrenoceptors, beta-adrenoceptor stimulation produced a weak relaxat
ion whereas, both alpha(1)- and alpha(2)-adrenoceptor stimulation prod
uced contractions, of which alpha(2)-induced contraction was of greate
r magnitude. The beta, alpha(1) and alpha(2) responses were blocked by
their respective blocking agents propranolol, prazosin and yohimbine.
4 The autonomic components of the response to EFS were determined by
using selected cholinergic and adrenergic antagonists separately or co
llectively. Cholinergic blockade with atropine did not produce a signi
ficant blockade of the EFS-induced response. Similarly, blockade of be
ta-adrenoceptors with propranolol did not modulate the contractile res
ponse to EFS to any significant level. Blockade by prazosin or yohimbi
ne did not significantly change the contractile response to EFS. After
a complete blockade of the adrenergic and cholinergic divisions, the
intestinal segments still showed a contractile response to EFS which w
as not significantly different from the control response. This indicat
ed the presence of a non-adrenergic non-cholinergic (NANC) response. 5
Tetrodotoxin, at 10(-6) M, significantly blocked the EFS-induced NANC
response suggesting a neurogenic origin for the response. 6 The prese
nt study indicated that the EFS-induced response of the catfish intest
inal segments is predominantly NANC-e in nature suggesting an importan
t role for it in the regulation of intestinal motility.