Sympathetic fiber sprouting in inflamed joints and adjacent skin contributes to pain-related behavior in arthritis.

Although chronic pain is the most common symptom of arthritis, relatively little is known about the mechanisms driving it. Recently, a sprouting of autonomic sympathetic fibers into the upper dermis of the skin, an area that is normally devoid of them, was found in the skin following chronic inflammation of the rat hindpaw. While this sprouting only occurred when signs of joint and bone damage were present, it remained to be clarified whether it was a consequence of the chronic inflammation of the skin or of the arthritis and whether it also occurred in the joint. In the present study, we used a model of arthritis in which complete Freund's adjuvant (CFA) was injected into the rat ankle joint. At 4 weeks following CFA treatment, there was an increase in sympathetic and peptidergic fiber density in the ankle joint synovium. We also observed a sympathetic, but not peptidergic, fiber sprouting in the skin over the joint, which may be a consequence of the increased levels of mature nerve growth factor levels in skin, as revealed by Western blot analysis. The pharmacological suppression of sympathetic fiber function with systemic guanethidine significantly decreased the pain-related behavior associated with arthritis. Guanethidine completely suppressed the heat hyperalgesia and attenuated mechanical and cold hypersensitivity. These results suggest that transmitters released from the sprouted sympathetic fibers in the synovial membrane and upper dermis contribute to the pain-related behavior associated with arthritis. Blocking the sympathetic fiber sprouting may provide a novel therapeutic approach to alleviate pain in arthritis.

Gender- and age-related differences in muscular and nerve-mediated responses in human colon.

BACKGROUND: Gender- and age-related differences in muscular and nerve-mediated responses in human colon are poorly characterized. We studied carbachol-induced motor responses and electrically evoked contractions in sigmoid circular muscle from adult and elderly patients of different gender. METHODS: Sigmoid colon segments were obtained from 24 men and 16 women undergoing left hemicolectomy for colon cancer. Isometric tension was measured on muscle strips exposed to increasing carbachol concentrations. The effects of atropine, guanethidine, L-nitro arginine methyl ester (L-NAME), and tetrodotoxin on electrically evoked contractions were also studied. RESULTS: Female patients showed higher maximal response to carbachol than male patients, elderly females being the most sensitive to carbachol among all patient groups. Electrically evoked contractions were linearly related to stimulation frequency and abolished by tetrodotoxin. Electrically evoked contractions were significantly more pronounced in elderly male patients; they were reduced by atropine and guanethidine and increased by L-nitro arginine methyl ester in the presence of atropine and guanethidine (P < 0.05). The effect of L-NAME was most marked in elderly male patients and least pronounced in elderly females. CONCLUSIONS: The response to carbachol and the role of nitrergic pathways differ according to age and gender; this may depend on muscarinic receptor upregulation or humoral factors affecting nitric oxide release, respectively.

Parasympathetic, but not sympathetic denervation, suppressed colorectal cancer progression.

Disruption in the nerve-tumor interaction is now considered as a possible anticancer strategy for treating various cancer types, particularly colorectal cancer. However, the underlying mechanisms are not still fully understood. Therefore, the present study aimed to evaluate the effects of sympathetic and parasympathetic denervation on the inhibition of colorectal cancer progression in early and late phases and assess the involvement of nerve growth factor in denervation mediated anticancer effects. One-hundred and fifty male Wistar rats were assigned into 15 groups. Seven groups comprising the control group, 1,2-dimethylhydrazine (DMH) group, sympathetic denervation group (celiac-mesenteric ganglionectomy and guanethidine sulphate administration), parasympathetic denervation group (vagotomy and atropine administration), and combination group were used in the early-stage protocol. For the late-stage protocol, eight groups comprising the control, DMH, surgical and pharmacological sympathetic and parasympathetic denervation groups, combination group, and 5-flourouracil group were considered. After 8 weeks, sympathetic and parasympathetic denervation significantly reduced ACF numbers in rats receiving DMH. On the other hand, in the late stages, parasympathetic but not sympathetic denervation resulted in significant reductions in tumor incidence, tumor volume and weight, cell proliferation (indicated by reduced immunostaining of PCNA and ki-67), and angiogenesis (indicated by reduced immunostaining of CD31 and VEGF expression levels), and downregulated NGF, ß2 adrenergic, and M3 receptors. It can be concluded that parasympathetic denervation may be of high importance in colon carcinogenesis and suggested as a possible therapeutic modality in late stages of colorectal cancer.

Nitric oxide and carbon monoxide act as inhibitory neurotransmitters in the longitudinal muscle of C57BL/6J mouse distal colon.

The present study was designed to identify the inhibitory neurotransmitters mediating nonadrenergic noncholinergic relaxation in the longitudinal muscle of C57/BL mouse distal colon. Relaxation induced by electrical field stimulation (EFS) was recorded isotonically in the presence of atropine and guanethidine. Cyclic guanosine-3',5'-monophosphate (cyclic GMP) content was measured by radioimmunoassay. EFS-induced relaxation was inhibited by nitro-L-arginine (L-NNA) and Sn (IV) protoporphyrin dichloride IX (SnPP-IX), a nitric oxide (NO) and carbon monoxide (CO) synthase inhibitor, respectively. A combination of both inhibitors produced an additive effect. ODQ, a soluble guanylate cyclase inhibitor, inhibited EFS-induced relaxation. NOR-1, a NO donor, and carbon monoxide-releasing molecule-2 (CORM-2), a CO donor, treatment relaxed the distal colon and increased cyclic GMP content. The effects of NOR-1 and CORM-2 were inhibited by ODQ. KT5823, a cyclic GMP-dependent protein kinase inhibitor, inhibited EFS-induced relaxation. EFS-induced relaxation in the presence of KT5823 was further inhibited by L-NNA, but not by SnPP-IX. In addition, KT5823 inhibited CORM-2-induced relaxation, but not NOR-1-induced relaxation. H89, a cyclic AMP-dependent protein kinase inhibitor, inhibited EFS-induced relaxation, and EFS-induced relaxation in the presence of H89 was further inhibited by L-NNA. These results suggested that NO and CO function as inhibitory neurotransmitters in the longitudinal muscle of C57BL mouse distal colon.

Functional characterization of nonadrenergic noncholinergic neurotransmitter release via endocannabinoids: an in vitro study in rabbit corpus cavernosum.

INTRODUCTION: Corporal smooth muscle relaxation is mediated mainly but not completely by nitric oxide. Endocannabinoids modulate the various neurotransmitter systems. AIM: In the present study, a possible role of endocannabinoids on non-nitrergic nonadrenergic noncholinergic (NANC)-mediated relaxations was investigated. METHODS: In precontracted tissues, control electrical field stimulation (EFS)-induced NANC relaxation responses were obtained using varying frequencies of stimulation in the presence of L-arginine methyl ester (L-NAME), guanethidine, and atropine. To investigate the effects of cannabinoids on EFS-evoked non-nitrergic NANC relaxation responses, a similar experimental procedure was applied in the presence of cannabinoid receptor antagonists AM251 or AM630; vanilloid receptor antagonist capsazepine; or cannabinoid receptor agonists anandamide, arachidonyl-2-chloroethylamide (ACEA), or JHW015. MAIN OUTCOME MEASURES: Effects of cannabinoid receptor antagonists and agonists on EFS-evoked non-nitrergic NANC relaxation responses. RESULTS: L-NAME abolished EFS-induced relaxation responses at lower frequencies (2-4 Hz) and inhibited the relaxation responses at higher frequencies (8-32 Hz). AM251 and AM630 either together or separately inhibited, whereas anandamide, ACEA, and JHW015 enhanced non-nitrergic NANC relaxation responses. Anandamide did not alter EFS-induced non-nitrergic NANC relaxations in the presence of AM251 and AM630. Capsazepine enhanced non-nitrergic NANC relaxation responses. CONCLUSION: These results suggest that non-nitrergic NANC relaxations may be mediated partially by cannabinoid-like neuronal factors acting at both cannabinoid CB(1) and cannabinoid CB(2) receptors.

Sympathectomy alters bone architecture in adult growing rats.

Sympathetic nervous system (SNS) fibres and alpha- and beta-receptors are present in bone, indicating that the SNS may participate in bone metabolism. The importance of these observations is controversial because stimulation or inhibition of the SNS has had various effects upon both anabolic and catabolic activity in this tissue. In this study we evaluated the effects of pharmacological sympathectomy, using chronic treatment of maturing male rats with 40 mg of guanethidine/kg i.p., upon various parameters in bone. Double labelling with tetracycline injection was also performed 20 and 2 days before sacrifice. Bone mass, mineral content, density and histomorphometric characteristics in different skeletal regions were determined. Bone metabolic markers included urinary deoxypyridinoline and serum osteocalcin measurements. Guanethidine significantly reduced the accretion of lumbar vertebral bone and of mineral content and density, compared to controls. Femoral bone mineral content and density were also significantly reduced, compared to controls. Histomorphometric analyses indicated these effects were related to a reduction of cortical bone and mineral apposition rate at femoral diaphysials level. Both markers of bone metabolism were reduced in controls as they approached maturity. Guanethidine significantly decreased serum osteocalcin compared to controls, while urinary deoxypyridinoline was unchanged. These data indicate that guanethidine-induced sympathectomy caused a negative balance of bone metabolism, leading to decreased mass by regulating deposition rather than resorption during modeling and remodeling of bone.

[Use of ilio-inguinal iliohypogastric nerve block for herniorraphy: a prospective study in a 35-case series at the Lome University Hospital Center in Togo]. / Pratique du bloc ilio-inguinal ilio-hypogastrique pour cure herniaire: étude prospective à propos de 35 cas colligés au CHU de Lomé, Togo.

The purpose of this prospective-descriptive study was to evaluate the quality of anaesthesia and analgesic effect achieved by ilio-inguinal iliohypogastric nerve block (IINB) in patients undergoing herniorraphy. Study was carried out over a 6-month period in the Anaesthesia Intensive Care Department of the Lomé University Hospital Centre in Togo. All patients indicated for unilateral herniorraphy were enrolled. A total of 35 patients underwent herniorraphy with IINB. Mean patient age was 32 years. Farmers accounted for 57% of the population. Men accounted for 86.7%. The anaesthesia classification was ASA I or II in 88.6% of cases. Complete sensory block was obtained within 15 minutes after induction in 71.43% of cases. Additional sedation using ketamine and/or fentanyl was used in 51.43% of cases. Conversion from IINB to general anaesthesia was necessary in three cases including 2 due to extension of the surgical incision and one for the surgeon's convenience. The mean duration of the procedure was 70 minutes. Intraoperative complications included nausea in one case, dizziness in 2 cases, and bitterness in mouth in 3 cases. Postoperatively, extension to the femoral nerve was observed in 2 cases. Five patients presented a visual analogue pain scale (VAS) > or = 4 within 18 hours after the procedure. This study shows that IINB is a useful alternative to general anaesthesia for herniorraphy. Specific training is necessary to allow more widespread use.

Delayed sympathetic dependence in the spared nerve injury (SNI) model of neuropathic pain.

BACKGROUND: Clinical and experimental studies of neuropathic pain support the hypothesis that a functional coupling between postganglionic sympathetic efferent and sensory afferent fibers contributes to the pain. We investigated whether neuropathic pain-related behavior in the spared nerve injury (SNI) rat model is dependent on the sympathetic nervous system. RESULTS: Permanent chemical sympathectomy was achieved by daily injection of guanethidine (50 mg/kg s.c.) from age P8 to P21. SNI was performed at adulthood followed by 11 weeks of mechanical and thermal hypersensitivity testing. A significant but limited effect of the sympathectomy on SNI-induced pain sensitivity was observed. The effect was delayed and restricted to cold allodynia-like behavior: SNI-related cold scores were lower in the sympathectomized group compared to the control group at 8 and 11 weeks after the nerve injury but not before. Mechanical hypersensitivity tests (pinprick and von Frey hair threshold tests) showed no difference between groups during the study period. Concomitantly, pericellular tyrosine-hydroxylase immunoreactive basket structures were observed around dorsal root ganglia (DRG) neurons 8 weeks after SNI, but were absent at earlier time points after SNI and in sham operated controls. CONCLUSION: These results suggest that the early establishment of neuropathic pain-related behavior after distal nerve injury such as in the SNI model is mechanistically independent of the sympathetic system, whereas the system contributes to the maintenance, albeit after a delay of many weeks, of response to cold-related stimuli.

Renal denervation by CT-guided periarterial injection of hyperosmolar saline, vincristine, paclitaxel and guanethidine in a pig model.

AIMS: The aim of the study was to evaluate the feasibility, safety and efficacy of renal sympathetic denervation with CT-guided periarterial injection of potentially neurolytic agents in pigs. METHODS AND RESULTS: Unilateral injection of formulations containing either 5M hyperosmolar saline, vincristine, paclitaxel or guanethidine around the renal artery was performed in 24 normotensive pigs with six animals per group. Needle placement and injections were performed under CT fluoroscopy guidance. Blood pressure measurements and CT scans were performed immediately before and after the intervention and four weeks after treatment. After euthanasia, norepinephrine (NE) concentrations of both kidneys were determined. The renal arteries and surrounding tissue were examined histologically to evaluate nerve fibre degeneration. Procedures were technically successful with good periarterial distribution of the injectant in all but one pig in the guanethidine group. No major adverse events or post-interventional complications occurred. In the vincristine group, NE concentrations of the renal parenchyma were lower on the treated side in all pigs with a mean decrease of 53% (38%-62%, p<0.01) compared to the contralateral control. Correspondingly, histological examination revealed neural degeneration in all animals treated with vincristine. In the other groups, no significant drop of NE values, or histological signs of nerve fibre degeneration were found. CONCLUSIONS: CT-guided periarterial injection of the different substances was feasible and safe. Renal sympathetic denervation was achieved with vincristine. In contrast, hyperosmolar saline, paclitaxel and guanethidine do not seem to be appropriate for renal denervation in a pig model at the dosage used.

5-HT4 receptors facilitate cholinergic neurotransmission throughout the murine gastrointestinal tract.

BACKGROUND: In the gastrointestinal tract of several species, facilitating 5-HT4 receptors were proposed on myenteric cholinergic neurons innervating smooth muscle by in vitro study of the effect of the selective 5-HT4 receptor agonist prucalopride on submaximal cholinergic contractions. This was not yet established in the murine gastrointestinal tract. METHODS: In circular smooth muscle strips from murine fundus, jejunum and colon, contractions were induced by electrical field stimulation in the presence of guanethidine, L-NAME and for colon also MRS 2500. Submaximal contractions were induced to study the influence of prucalopride. KEY RESULTS: Electrical field stimulation at reduced voltage induced reproducible submaximal neurogenic and cholinergic contractions as the contractions were abolished by tetrodotoxin and atropine. Hexamethonium had no systematic inhibitory effect but mecamylamine reduced the responses, suggesting that part of the cholinergic response is due to activation of preganglionic neurons. Prucalopride concentration-dependently increased the submaximal cholinergic contractions in the three tissue types, reaching maximum from 0.03 µmol/L onwards. The facilitation in the different series with 0.03 µmol/L prucalopride ranged from 41% to 104%, 30% to 76% and 24% to 74% in fundus, jejunum, and colon, respectively. The effect of 0.03 µmol/L prucalopride was concentration-dependently inhibited by GR 113808. CONCLUSIONS & INFERENCES: In the murine gastrointestinal tract, activation of 5-HT4 receptors with prucalopride enhances cholinergic contractions, illustrating facilitation of myenteric cholinergic neurotransmission. The degree of enhancement with prucalopride is of similar magnitude as previously reported in other species, but the effective concentrations are lower than those needed in the gastrointestinal tract of other species.

Long-term treatment with low-dose, but not high-dose, guanethidine improves ventricular function and survival of rats with heart failure after myocardial infarction.

OBJECTIVES: We sought to evaluate the effects of various doses of guanethidine, a sympathoinhibitory drug, on ventricular function and survival in chronic heart failure (CHF) after myocardial infarction (MI) in rats. BACKGROUND: Direct inhibition of sympathetic outflow by a sympathoinhibitory drug might be an effective approach to therapy of CHF. However, recent clinical trials suggest that excessive suppression of sympathetic activity has an adverse effect on outcome. It remains unclear whether the beneficial effects of the sympathoinhibitory drug would be modified by its dosage. METHODS: Three doses of guanethidine (low-dose [LG], 1 mg/kg/day; medium-dose, 3 mg/kg/day; high-dose, 10 mg/kg/day) were administered via an osmotic mini-pump for 4 weeks. Hemodynamics, left ventricular (LV) diameters, plasma and myocardial norepinephrine (NE) levels, and survival were determined for four weeks after MI. RESULTS: As compared with MI rats receiving vehicle, LG suppressed LV dilation (9.2 +/- 0.9 mm vs. 11.0 +/- 0.8 mm, p < 0.05) and improved LV fractional shortening (25.0 +/- 4.5% vs. 16.4 +/- 4.7%, p < 0.05) in association with a reduction of plasma NE levels (520 +/- 250 pg/ml vs. 1,000 +/- 570 pg/ml, p < 0.05), but not with a significant reduction of noninfarcted myocardial NE levels (154 +/- 71 ng/g vs. 207 +/- 71 ng/g). Low-dose guanethidine reduced 24-h (6%) and 28-day mortality (6%), as compared with untreated MI rats (36% and 52%, respectively). High-dose guanethidine also reduced 24-h mortality (12%) but increased 28-day mortality (91%), in association with a depletion of myocardial NE. Medium-dose guanethidine had no beneficial effects on LV hemodynamics or long-term survival. CONCLUSIONS: These results indicate that the dosage of the sympathoinhibitory drug might be quite important for the treatment of CHF.

Safety of single large oral doses of guanethidine.

The cardiovascular effects of single 100-mg doses of guanethidine were assessed in hypertensive patients by measurement of arterial pressure, heart rate, and systolic time intervals. In the 3-hr period following a dose there was no evidence of an inotropic effect. Therefore, large doses of guanethidine as required for the guanethidine loading regimen would seem to be safe even in patients in whom inotropic effects of released catecholamines would be contraindicated.

The use of topical guanethidine in the relief of dentine hypersensitivity: a controlled study.

After a pilot study had indicated that the topical application of guanethidine might be of value in the treatment of tooth dentine hypersensitivity, a double-blind study was undertaken to investigate whether guanethidine was more effective than a distilled water control in alleviating dentinal pain. In 39 adult subjects, who had complained of dentine hypersensitivity, a 1 sec blast of air from a dental 3-in-1 syringe was directed onto sensitive root dentine at an angle of 90 degrees from a distance of 1 cm. The severity of the resulting pain was indicated by the subject on a 10 cm visual analogue scale (VAS). One droplet of either 1% guanethidine monosulphate (Ismelin, Ciba-Geigy) or distilled water, allocated at random, was applied to the dentine for 1 min. The tooth was re-tested with the standardised air blast and a second VAS was marked by the subject. In total, 19 patients received guanethidine and 20 received water. VAS scores before treatment in the 2 groups treated with either guanethidine or water (means: 6.5 +/- 2.2 and 6.0 +/- 2.5, respectively) were not significantly different (Mann-Whitney, P = 0.48) whereas the VAS scores in the 2 groups after treatment with guanethidine or water (means: 2.7 +/- 2.4 and 4.8 +/- 2.9, respectively) were significantly different (Mann-Whitney, P < 0.02). It was concluded that guanethidine reduced dentinal hypersensitivity more effectively than distilled water.(ABSTRACT TRUNCATED AT 250 WORDS)

Regional intravenous guanethidine vs. stellate ganglion block in reflex sympathetic dystrophies: a randomized trial.

Regional intravenous guanethidine blocks and stellate ganglion blocks have been compared in a randomized trial. Nineteen patients, randomly allocated to two groups of therapy and exhibiting severe reflex sympathetic dystrophy following peripheral nerve lesions, have been treated. The performance of the intravenous guanethidine block is of longer duration and superior to stellate ganglion block, as regards some early pharmacological effects (skin temperatures and amplitude of plethysmographic waves recorded before blockade and 15 min, 60 min, 24 h, 48 h after institution of the block). In fact the intravenous guanethidine group shows a persistent and significant increase of the skin temperature and of the plethysmographic traces in the blocked side 24 h and 48 h after blockade in comparison with the patients treated with stellate ganglion block. Concerning the therapeutic effects (changes in pain scores and clinical signs--hyperpathia, allodynia, vasomotor disturbances, trophic changes, oedema and limited motion), recorded at the end of treatment and 1 month and 3 months follow-up, an intravenous guanethidine block carried out every 4 days up to a total of 4 blocks is comparable with a stellate ganglion block every day up to a total of 8 blocks. The results of this study show that regional sympathetic block with guanethidine is a good therapeutic tool in the treatment of reflex dystrophies, especially on account of its negligible risks and contraindications.

Sympathetically maintained pain of the digits in porphyria cutanea tarda relieved by i.v. regional guanethidine.

A case of a sympathetically maintained pain of the tips of the fingers in a 39-year-old man with porphyria cutanea tarda is presented. Occupational vibrating trauma is the presumed cause. The successful treatment with intravenous regional guanethidine is reported.

Effects of regional intravenous guanethidine in patients with neuralgia in the hand; a follow-up study over a decade.

A study on the effect of regional intravenous (i.v.) guanethidine blockade (RGB) was done over a 10 years period in patients with post-traumatic neuralgia. Seven patients, investigated with quantitative sensory testing (QST) before and after RGB between 1979 and 1982, were reinvestigated in the period 1990-1992. In addition to the RGB, 6 patients were subjected to a placebo procedure with tourniquet inflation and i.v. injection of saline at follow-up. All patients had ongoing pain and stimulus-induced pain (hyperalgesia) in one hand. The QST was done by an independent observer who was blind with regard to the different treatments. Three patients with long-lasting relief of ongoing pain and significant reduction of stimulus-induced pain after RGB, were classified as having sympathetically maintained pain (SMP) both at 1st examination and at follow-up 10 years later. In 2 patients, classified as having sympathetically independent pain (SIP), neither the ongoing pain nor the hyperalgesia improved at any occasion. Two patients, classified as SMP in 1979-1982, changed to SIP at follow-up. Placebo had no significant effect on the hyperalgesia to heat, cold or vibration in the 6 SMP/SIP patients tested. In conclusion, some patients with neuralgia, diagnosed 17-26 years ago, still had long-lasting pain relief from an i.v. RGB, whereas others consistently had no such effect. None obtained long-lasting pain relief from placebo. This supports the notion that different pathophysiological mechanisms are involved in post-traumatic neuralgia.

Intravenous phentolamine test: diagnostic and prognostic use in reflex sympathetic dystrophy.

In some patients, ongoing and evoked neurogenic pain is relieved by pharmacological or destructive block of the sympathetic innervation of the affected part. In others, sympatholysis is ineffective. The present report shows that these two groups of patients can be distinguished by a safe and simple diagnostic test. Individuals in whom the pain was transiently relieved by intravenous phentolamine (Regitine) were very likely to respond favourably to subsequent sympatholytic treatment with i.v. regional guanethidine. Individuals in whom the phentolamine test was negative did not enjoy pain relief from this type of sympatholysis.

Effect of long-term treatment with high doses of guanethidine on sperm transport and fertility of rats.

1. Male rats treated with guanethidine 25 mg/kg daily for eight weeks had no demonstrable ejaculatory function immediately after cessation of treatment. Four weeks later, ejaculatory function had returned in two-thirds of the males, and after eight weeks, all males were able to deposit sperm in the vagina. However, fertility had returned at that time in only two of the nine males. On the basis of these findings it might be expected that fertility would return in the other males after a more prolonged observation period.2. At autopsy, 66 days after cessation of treatment, the vasa deferentia were congested and filled with viscous material, and along their course dilated regions and pseudocysts containing sperm debris and spermatozoa were found.3. The isolated ducts of the guanethidine-treated males showed a markedly increased response to noradrenaline if compared with ducts from control rats. Response to tyramine was similar in both treated and untreated rats. In view of the increased response to noradrenaline it may be concluded that the noradrenaline stores, which are sensitive to tyramine, were still reduced 66 days after guanethidine treatment had been stopped.

Effects of clonidine and guanethidine on peripheral sympathetic nerve function in the pithed rat.

Clonidine, in low intravenous doses, inhibited the increased heart rate of pithed rats caused by peripheral sympathetic nerve stimulation. The magnitude of this effect was greatest at low frequencies of nerve stimulation, responses to high frequencies being little affected by the drug. In contrast, guanethidine reduced cardiac responses to both low and high rates of nerve stimulation. The difference between the depressant effects of the two drugs on responses to various frequencies of sympathetic nerve traffic may contribute to the differences known to occur between their properties as hypotensive agents.

Characterization of the receptors and mechanisms involved in the cardiovascular actions of sCCK-8 in the pithed rat.

1. The cardiovascular actions of cholecystokinin and related peptides were investigated in the pithed rat. The receptors and the mechanisms involved in these experiments were characterized. 2. Sulphated cholecystokinin octapeptide (sCCK-8, 0.1-100 nmol kg-1, i.v.) elicited a dose-dependent bradycardia and increase in mean arterial blood pressure. Neither gastrin-17 nor pentagastrin had any effect at concentrations up to 100 nmol kg-1. 3. Both the pressor response and bradycardia elicited by sCCK-8 were reduced by the selective CCKA receptor antagonists, devazepide (0.5-50 nmol kg-1) and lorglumide (1-7 mumol kg-1). The selective CCKB receptor antagonists, CI-988 (1 mumol kg-1) and L-365,260 (15 mumol kg-1) did not inhibit the effects of sCCK-8. 4. The pressor response induced with sCCK-8 was reduced by treatment with either phentolamine (3 mumol kg-1) or guanethidine (2 mumol kg-1) and was unaffected by treatment with propranolol, atropine or hexamethonium. The pressor response also persisted following bilateral adrenalectomy. 5. The bradycardia induced with sCCK-8 was unaffected by treatment with phentolamine, propranolol, guanethidine, atropine, hexamethonium or bilateral adrenalectomy. 6. The tetrapeptide of cholecystokinin (CCK-4) elicited a dose-dependent pressor response but did not induce bradycardia. The pressor response was unaffected by devazepide (50 nmol kg-1), L-365260 (15 mumol kg-1) or phentolamine (3 mumol kg-1). 7. In the pithed rat, sCCK-8 acted via CCKA receptors to increase arterial blood pressure indirectly, at least in part, through activation of alpha-adrenoceptors. The observed bradycardia was also mediated byCCKA receptors but possibly through a direct action on the heart.