production by Lewis [1942] who reviewed a large amount of evidence obtained

Transcription

1 Quarterly Journal of Experimental Physiology (1977) 62, THE EFFECTS OF BRADYKININ ON AFFERENT UNITS IN INTRA- ABDOMINAL SYMPATHETIC NERVE TRUNKS. By K. FLOYD, VERITY E. HICK, JUTHIKA KOLEY and J. F. B. MORRISON. From the Department of Physiology, University of Leeds, Leeds LS2 9JT. (Receivedfor publication 15th April 1976) The effects of intra-arterial injections of bradykinin on afferent discharges in the splanchnic and hypogastric nerves have been studied. All units which were excited by the peptide were mechanosensitive. Following i.a. bradykinin, the slowly adapting mechanoreceptors associated with the bladder showed increased discharge rates which appear to be related to changes in intravesical pressure. When the effects of bradykinin on the bladder were blocked by cord cooling, the afferents were not excited. It is concluded that bradykinin causes discharges in the slowly adapting mechanoreceptors around the bladder because it causes bladder contractions, and not because of any chemosensitivity of the nerve ending. The afferent fibres in the two main intra-abdominal sympathetic nerve trunks include slowly adapting mechanoreceptors which are activated by tension on mesenteries and visceral peritoneum, by smooth muscle contractions and by visceral distension [Morrison, 1973, Floyd and Morrison, 1974, Floyd, Hick and Morrison, 1976]. These stimuli have been associated with visceral pain production by Lewis [1942] who reviewed a large amount of evidence obtained from intra-abdominal operations performed on man under local anaesthesia, and from experiments in which these stimuli evoked pseudo-affective reflexes in anaesthetized animals. The afferent fibre populations referred to above probably include some fibres which mediate pain and associated sensations. It was therefore of interest to investigate their responses to the pain producing peptide bradykinin. Lim, Guzman, Rodgers, Goto, Braun, Dickerson and Engle [1964] and Lim, Miller, Guzman, Rodgers, Rogers, Wang, Chao and Shih [1967] have shown that intra-peritoneal injection of the peptide in man produces pain, and in animals intra-arterial injection of the drug results in pseudo-affective responses. They also recorded an increase in 'activity' of the whole splanchnic nerves of dogs and cats after injection of the peptide into the splenic artery. Armstrong [1970] has reviewed this work and concluded that the visceral pain afferents are specific chemoreceptors for bradykinin. It was, therefore, of interest to see whether any afferents could be found which were sensitive to bradykinin but not to mechanical stimuli. A preliminary account of some of these experiments has already been published [Floyd, Hick and Morrison, 1975]. METHODS Experiments were performed on 16 cats (1-8 to 6-0 kg) of either sex which were anaesthetized and maintained as described previously [Floyd, Hick, Koley and Morrison, 1977]. Recordings were made from afferent fibres in the splanchnic, hypogastric and lumbar splanchnic 19 D.

2 Pelv'Nerves \ :\?L6 1\ 20 Floyd, Hick, Koley and Morrison nerves. In some animals the lumbar (L5-6) spinal cord was either tied, transected or cooled to abolish spontaneous bladder contractions and the reflex pathway involving pelvic nerve afferents, efferents and supra-spinal centres [Edvardsen, 1968]. Fig. 1 is an illustration of this recording arrangement. For details see Floyd et al. [1977]. RESULTS Hypogastric nerve afferents Forty one mechanosensitive hypogastric afferents from the bladder (25), uterus (9) and connective tissue, prostate, ureter or colon (7) were tested with intra-arterial doses of bradykinin (1-10 jg). The conduction velocities of these units ranged from I 0 to 24 m.s.1. The units associated with the bladder all responded to distension and contractions of the bladder, and by varying the a Inferior Mesenteric _ P i ~~~~~~~Hypogastr'ic Ganglion Intravesica N rve Pressure 71 cord Cooling Thermode FIG. 1. The diagram illustrates the preparation used in the most complex of the experiments described. Recordings made from single afferent units in the hypogastric nerve at R, intravesical pressure changes were monitored, and the responses of units to intra-arterial injection of bradykinin were studied before, during and after cord cooling at L6. bladder volume the spontaneous contractions and afferent discharges could be controlled sufficiently to produce a suitable baseline. When 1-2 pg bradykinin were injected intra-arterially either a small change in bladder tone or one or a few small contractions resulted. The responses of the afferent units corresponded approximately to the changes in intravesical pressure in that the changes in bladder tone either did not affect the afferent discharge rates or resulted in small increases. The occurrence and duration of the afferent discharges were temporally related to the associated bladder contractions. The discharges did not follow exponential washout curves as might be expected if the receptors were responding directly to concentrations of the peptide in the circulation. With larger doses of the peptide (4-10 pg) the afferent discharges were also temporally related to bladder contractions. In addition, the sizes of the responses depended on the magnitudes of the intravesical pressure changes. Fig. 2 shows the response of one unit shortly after the start of a bladder con-

3 Bradykinin effects on visceral afferents 21 FIG. 2. Top: Discharge from a hypogastric nerve afferent from the bladder following the injection of 10 pg bradykinin i.a. 6 sec before the start of the trace. Bottom: Intravesical pressure. FIG. 3. The left panel shows the responses to 10 pg bradykinin i.a. when the bladder contains 32ml, and the right panel shows the effects of the same dose when the bladder is empty. Top: Arterial pressure. Middle: Intravesical pressure. Bottom: Average impulse rate in a mechanosensitive afferent associated with the bladder base.

4 22 Floyd, Hick, Koley and Morrison traction induced by bradykinin, and Fig. 3 shows that the discharge to a constant dose could be modified by changing the mechanical conditions, i.e. by lowering the bladder volume the response of the afferent to the same dose of the peptide was diminished considerably. In 11 units, attempts were made to dissociate any direct chemical effect of the peptide on the nerve endings from concomitant mechanical changes induced in the bladder, using the techniques described by Floyd et a!. [1976]. During cord cooling both the mechanical and the afferent responses to 10 4g bradykinin were negligible, which contrasted with the large responses in the pre- and Fio. 4. The three panels show the responses to 10 pg bradykinin i.a. before, during and after cord cooling. Top: Arterial pressure. Middle: Intravesical pressure. Bottom: Average spike rate in a slowly adapting mechanoreceptor associated with the bladder. post-control tests when the cord was warm. Fig. 4 shows the responses of one unit, which is representative of 8 others which responded similarly. In two other units a similar effect was obtained when cord conduction was abolished by local application of lignocaine. The response to the peptide was recovered when the return of the spontaneous bladder contractions indicated that the lignocaine block had ceased to be effective. Thirteen units from the uterus, pelvic fat pads and prostate were also tested with 10 pg bradykinin i.a. These units did not give consistent responses but this may relate to an uncontrolled mechanical situation. These units behaved in a manner similar to the splanchnic slowly adapting mechanoreceptors described

5 Bradykinin effects on visceral afferents 23 in the next section. Three units from the colon, mesocolon and ureter gave responses related to local movement of smooth muscle. Splanchnic nerve afferents Thirty-five mechanosensitive units were tested with intra-arterial injections of 1-10 pg bradykinin. Eleven were initially identified as mechanosensitive single units, of which 2 were Pacinian corpuscle afferents and 9 were slowly adapting mechanoreceptors. A further group of 24 were from strands in which fibres which had responded to bradykinin were then traced and identified as mechanoreceptors. Eighteen of this latter group were shown to be slowly adapting with receptive fields similar to those described by Morrison [1973], and were distributed in the spleen (8), small intestine (4), pancreas (2) and ileocolic junction or colon (4). Their conduction velocities ranged from 0 7 to 40 m.s -'. The remainder were mechanosensitive but their receptive fields could not be examined in detail. No response was obtained from 4 of the 8 Pacinian corpuscles tested with bradykinin or from 3 of the 27 slowly-adapting mechanoreceptors. The other 4 Pacinian corpuscles discharged in time with the increased cardiovascular pulsations in the mesentery but the responses of the remaining slowly-adapting receptors were not always reproducible. When they occurred they had a variable time course which seemed to depend on the local movement of the associated smooth muscle or viscus. In 7 units a solution of bradykinin (10 ug/ml) was applied directly to mechanosensitive sites in the mesentery, pancreas or splenic hilum. Two of these units developed cardiovascular rhythms but the other 5 did not respond to this stimulus. DISCUSSION The results show that (a) at low (threshold) doses of intra-arterial bradykinin, the afferents from the bladder may or may not show a response; when a response occurs it is associated temporally with a bladder contraction, (b) when the response of the bladder to a suprathreshold dose of the peptide is modified by altering the bladder volume there is a relationship between the magnitude of the afferent discharge and the changes in intravesical pressure, and (c) when the mechanical changes in the bladder are abolished by cord cooling or transections, bradykinin does not cause an afferent discharge. All of these results indicate that bradykinin excites these afferents by causing contractions of the vesical muscle. Slowly adapting mechanoreceptors in the other viscera and peritoneum did not show such consistent responses to bradykinin as occurred in the bladder, the responses varying from zero to an irregular discharge. Because the effects of bradykinin on gastrointestinal smooth muscles have been shown to include both relaxation and contraction [Feniuk and Large, 1973; Fasth, Hulten, Jahnberg and Matinson, 1975] depending on the site within the gastrointestinal tract as well as on other variables, the responses of these mechanoreceptors might be attributed to concomitant changes in smooth muscle tone induced in the vicinity of the nerve endings. Direct application of bradykinin in concen-

6 24 Floyd, Hick, Koley and Morrison trations of 10 pg.ml-' could excite some of the afferents. It seems likely that the slowly adapting mechanoreceptors in the splanchnic nerve are not directly chemosensitive but that the peptide activates them by causing local muscular contractions. However, it was not possible to dissociate the chemical and mechanical effects in the other viscera as it was in the bladder. In skin and muscle, afferent nerves which respond to bradykinin have also been found to be either mechanosensitive [Fjallbrant and Iggo, 1962; Burgess and Perl, 1972; Mense and Schmidt, 1974] or sensitive to noxious heat [Beck and Handwerker, 1975]. The finding, however, that some Pacinian corpuscle afferents in the mesentery were not excited when bradykinin was administered is in agreement with the results of Lim et al. [1964]. Other Pacinian corpuscles, however, did develop cardiac rhythms which suggested that they were responding to concomitant changes in the vessels of the mesentery. Lewis [1942] concluded that visceral pain could be elicited by distension and contractions of viscera, and tension on mesenteries. Afferents in the vagi and pelvic nerves are able to respond to visceral distension and contraction [Iggo, 1955, 1957; Leek, 1972] and the slowly adapting mechanoreceptors found in intra-abdominal sympathetic pathways respond to these stimuli and to tension on mesenteries and visceral peritoneum [Morrison, 1973; Floyd, Hick and Morrison, 1975, 1976]. The more recent pharmacological studies on pain production by chemicals such as bradykinin have incorporated the view that specific chemoreceptors for this peptide may be present in the afferent innervation of viscera [Armstrong, 1970]. In the present study, no evidence has been found for this hypothesis. Indeed the present experiments indicate that there is no need to postulate separate groups of mechanoreceptors and chemoreceptors in visceral pain mediation. The afferent fibres which respond to the mechanical stimuli implicated by Lewis [1942] are also able to respond to bradykinin. In one intra-abdominal site (bladder) where control of the mechanical and chemical stimuli is easiest, bradykinin has little or no direct effect on the nerve endings, and its effect can be attributed to the mechanical changes which it induces in their receptive fields. ACKNOWLEDGMENTS We wish to thank Mr E. G. Tate for technical assistance, Mrs E. R. Baister, Sandoz Ltd., for a generous gift of synthetic bradykinin, and the Medical Research Council for financial support. REFERENCES ARMSTRONG, DESIRSE A. J. (1970). Pain. In: Handbook of Experimental Pharmacology Vol. XXV: Bradykinin, Kallidin and Kallikrein. Springer Verlag, Berlin, pp BECK, P. W. and HANDWERKER, H. 0. (1974). Bradykinin and serotonin effects on various types of cutaneous nerve fibres. Pflugers Archives, 347, BuRGEss, P. R. and PERL, E. R. (1973). Cutaneous mechanoreceptors and nociceptors. In: Handbook of Sensory Physiology Vol. II Somatosensory System. Ed. A. Iggo, Springer Verlag, Berlin.

7 Bradykinin effects on visceral afferents 25 EDVARDSEN, P. (1968). Nervous control of urinary bladder in cats. Acta physiologica scandinavica, 72, FJALLBRANT, N. and IGGo, A. (1961). The effect of histamine, 5-hydroxy-tryptamine and acetylcholine on cutaneous afferent fibres. Journal ofphysiology, 156, FASTH, S., HULTEN, L., JAHNBERG, T. and MARTINSON, J. (1975). Comparative studies on the effects of bradykinin and vagal stimulation on motility in the stomach and colon. Acta physiologica scandinavica, 93, FENIUK, W. and LARGE, B. J. (1973). Some actions of bradykinin on mouse isolated colon. British Journal ofpharmacology, 49, P. FLOYD, K. and MoRRISON, J. F. B. (1974). Splanchnic mechanoreceptors in the dog. Quarterly Journal of Experimental Physiology, 59, FLOYD, K., HICK, VERITY E., KOLEY, JUTHIKA and MORRIsoN, J. F. B. (1977). Effects of bradykinin mediated by autonomic efferent nerves. Quarterly Journal of Experimental Physiology, 62, FLOYD, K., HICK, VERITY E. and MORRISON, J. F. B. (1975). The response of visceral afferent nerves to bradykinin. Journal ofphysiology, 247, 53-54P. FLOYD, K., HICK, VERrrY E. and MORRISON, J. F. B. (1976). Mechanosensitive afferent units in the hypogastric nerve of the cat. Journal ofphysiology, 259, IbGo, A. (1955). Tension receptors in the stomach and the urinary bladder. Journal of Physiology, 128, IGGo, A. (1957). Gastro-intestinal tension receptors with unmyelinated afferent fibres in the vagus of the cat. Quarterly Journal of Experimental Physiology, 42, LEEK, B. F. (1972). Abdominal Visceral Receptors. In Handbook of Sensory Physiology Vol. III, I Enteroceptors. Ed. E. Neil. Springer Verlag, Berlin, pp LEWIS, T. (1942). Pain. pp. 192, Macmillan, New York. LiM, R. K. S., GUZMAN, F., ROGERS, V. W., GoTo, K., BRAUN, C., DICKERSON, G. D. and ENGEL, R. J. (1964). Site of action of narcotic and non-narcotic analgesics determined by blocking bradykinin evoked visceral pain. Archives internationales de pharmacodynamie (et de therapie), 153, LiM, R. K. S., MILLER, D. G., GUZMAN, F., RODGERS, D. W., ROGERS, R. W., WANG, S. K., CHAO, P. Y. and SHm, T. Y. (1967). Pain and analgesia evaluated by the intraperitoneal bradykinin-evoked pain method in man. Clinical Pharmacology and Therapeutics, 8, MENSE, S. and SCHMIDT, R. F. (1974). Activation of group IV afferent units from muscle by algesic agents. Brain Research, 72, MORRISON, J. F. B. (1973). Splanchnic slowly adapting mechanoreceptors with punctate receptive fields in the mesentery and gastrointestinal tract ofthe cat. Journal ofphysiology, 233,