Pharmacological investigation of the autonomic transmission to the rat colon
Loading...
Date
1985
Authors
Journal Title
Journal ISSN
Volume Title
Publisher
Obafemi Awolowo University, Ile Ife, Nigeria
Abstract
The automatic neurotransmission to the distal rat colon has been studied using electrical field
stimulation and actions of drugs on the isolated in vitro preparations. The minimal parameters for
eliciting contractile responses were 0.5Hz, 0.5msec, although the stimulation programme
employed were 10Hz, 1msec. for 5 seconds at 120 seconds interval under a supramaximal
voltage of 25V. This usually resulted in monophasic responses which were abolished by
tetrodotoxin(TTX).
Hexamethonium (5 x 10 -7 -5 x 10-5M) produced an inhition of ca 18.5 69% (n =6) on the
amplitude of the electrically mediated twitches (EMTs). Adrenaline (Adr.) (5 x 10-8 5 x 10-6M),
noradrenaline (NA) (8.5 x 10-7 8.5 x 10-5M) and isoprenaline (Isop) (1.3 x 10-6M) depressed the
EMTs in the rat colon. Propranolol (10-8 10-6M) and phentolamine (1.34 x 10-7 1.34 x 10-5M)
depressed the EMTs by ca 17- 38% and 7.5-15% respectively (n =7) and also potentiated the
twitch-inhibiting action of theses catecholamines. Idazoxan (2.5 x 10-7 2.5 x 10-5M) inhibited the
EMTs by ca 5- 50% (n =3). Tyramine (4 x 10-8M) profoundly inhibited the EMTs by ca 85%.
Guanethidine (8 x 10-9 8 x 10-7M), however, produced a concentration dependent twitchaugmentation
of the EMTs. Low doses of NA (5 x 10-8 - 4 x 10-7M) induced contractile
responses which were partially reduced by phentolamine (5 x 10-7 - 2 x 10 -6M). High doses of
adrenaline (10-6 8 x 10-6M), noradrenaline (10-6 8 x 10-6M) and isoprenaline (6.6 x 10-8 5.3 x
10-7M) relaxed the colon. These were partially reversed by propranolol (2 x 10-7M) and
phentolamine (5.3 x 10-7M).
Atropine (1.45 x 10-8 1.45 x 10-6M) partially reduced the EMTs by ca 10 50%, while
physostigmine neither augmented the EMTs nor enhanced responses that were resistant to
inhibition by atropine. Atropine abolished all contractile responses elicited by acethycholine,
carbachol and nicotine. ATP (3.6 x 10-6 3 x 10-4M) induced inhibition of the EMTs by ca 5
90%. Low doses of ATP (1.2 x 10-7 9.6 x 10-7M) however contracted the colon.
Thus, the functional autonomic transmission appears to be:
a) entirely neurogenic; b) partially cholinergic and motor; c) in possession of weak inhibitory and
excitatory α (α1 +α2) but inhibitory β adrenoceptors. Evidence for non-adrenergi c and noncholinergic
(NANC) contribution is also presented and may involve, e.g. purinergic receptors,
and the multiple tachykinin receptors
Description
87p
Keywords
Neurotransmission, Electrical field stimulation, Colon, Contractile, Inhibition, Adrenaline, Phentolamine, Tetrodotoxin, Electrically mediated twitches, Propranolol, Nicotine, Cholinergic, Tachykinin receptors, Rats