Four motor effects of capsaicin on guinea‐pig distal colon

Abstract

1The motor effects of capsaicin on the guinea-pig distal colon have been investigated in vivo and in vitro. 2 Capsaicin (0.1-10 Ig kg-' i.v.) produced a transient relaxation which was reduced by pretreatment with capsaicin itself, atropine, hexamethonium, phentolamine or guanethidine and almost abolished by tetrodotoxin (TTX). Topically applied capsaicin produced a transient inhibition of tone and spontaneous activity prevented by topically applied TTX. 3 In isolated preparations of distal colon, capsaicin produced a transient, TTX-and atropinesensitive contraction which was followed by a depression of the contractile activity. The depressant effect was unaffected by atropine plus guanethidine but was greatly reduced by TTX, indicating activation of intramural non-adrenergic, non-cholinergic (NANC) mechanisms. The depressant effect on the first exposure to capsaicin (1 jiM) was greater than that produced by a second, third or fourth exposure.4 In preparations excised from capsaicin-pretreated animals, capsaicin (1 jM) only produced an inhibitory effect on spontaneous contractions. Desensitization did not occur to this inhibitory effect. 6 It is concluded that, in vivo, capsaicin activates inhibitory reflexes, presumably due to stimulation of primary afferent fibres. This effect involves, at least in part, activation of sympathetic nerves to this organ. The contractile effect of capsaicin on the isolated colon involves activation of intramural cholinergic neurones, whereas the TTX-sensitive component of the inhibitory effect involves either release of an inhibitory transmitter through an axon reflex arrangement or activation of NANC neurones. In addition, at high concentrations capsaicin produces a direct depression of smooth muscle contraction.

Enteric Glia Are Targets of the Sympathetic Innervation of the Myenteric Plexus in the Guinea Pig Distal Colon

“…Although we did not observe glial Ca 2ϩ elevations in response to capsaicin in the present study, this discrepancy is likely attributable to capsaicin stimulating a colo-colonic reflex in vivo through the inferior mesenteric ganglion (IMG) (Maggi et al, 1987;Lomax et al, 2010). Axon collaterals from colonic TRPV1-positive primary afferent fibers make excitatory synapses in the guinea pig IMG (Crowcroft et al, 1971).…”

Multiple mechanisms in the motor responses of the guinea‐pig isolated urinary bladder to bradykinin

“…In vitro capsaicin desensitization was achieved by prolonged (30min) exposure of the strips to 10pM capsaicin, followed by washing and re-equilibration, as described previously (Maggi et al, 1987b;1989).…”

A comparison of bradykinin‐ and capsaicin‐induced myocardial and coronary effects in isolated perfused heart of guinea‐pig: involvement of substance P and calcitonin gene‐related peptide release

“…Some experiments were performed in capsaicinpretreated animals in which capsaicin desensitization was achieved by giving a total dose of 55mgkg-1 s.c. over two days according to Maggi et al (1987a); the experiments were carried out five days after the last injection of capsaicin.…”