The mechanisms of enhancement and inhibition of field stimulation responses of guinea-pig vas deferens by prostacyclin analogues.

1. In the guinea-pig isolated vas deferens preparation bathed in Tyrode's solution, the prostacyclin analogues, cicaprost, TEI-9063, iloprost, taprostene and benzodioxane-prostacyclin, enhanced twitch responses to submaximal electrical field stimulation (20%-EFS). The high potency of cicaprost (EC150 = 1.3 nM) and the relative potencies of the analogues (equi-effective molar ratios = 1.0, 0.85, 1.6, 17 and 82, respectively) suggest the involvement of a prostacyclin (IP-) receptor. 2. Maximum enhancement induced by cicaprost in 2.5 mM K+ Krebs-Henseleit solution was similar to that in Tyrode solution (2.7 mM K+), but was progressively reduced as the K+ concentration was increased to 3.9, 5.9 and 11.9 mM. There was also a greater tendency for the other prostacyclin analogues to inhibit EFS responses in 5.9 mM standard K+ Krebs-Henseleit solution; this may be attributed to their agonist actions on presynaptic EP3-receptors resulting in inhibition of transmitter release. 3. The EFS enhancing action of cicaprost was not affected by the alpha1-adrenoceptor antagonist prazosin (100 and 1000 nM). Cicaprost (20 and 200 nM) did not affect contractile responses of the vas deferens to either ATP (5 microM) or alpha,beta-methylene ATP (1 microM) in the presence of tetrodotoxin (TTX, 100 nM). In addition, enhancement by cicaprost of responses to higher concentrations of ATP (30 and 300 microM) in the absence of TTX, as shown previously by others, was not seen. Prostaglandin E2 (PGE2, 10 nM) and another prostacyclin analogue TEI-3356 (20 nM) enhanced purinoceptor agonist responses. Unexpectedly, TTX (0.1 and 1 microM) partially inhibited contractions elicited by 10-1000 microM ATP; contractions elicited by 1-3 microM ATP were unaffected. Further studies are required to establish whether a pre- or post-synaptic mechanism is involved. 4. In a separate series of experiments, cicaprost (5-250 nM), TEI-9063 (3-300 nM), 4-aminopyridine (10-100 microM) and tetraethylammonium (100-1000 microM) enhanced both 20%-EFS responses and the accompanying overflow of noradrenaline to a similar extent. In further experiments with the EP1-receptor antagonist AH 6809, TEI-3356 (1.0-100 nM) and the EP3-receptor agonist, sulprostone (0.1-1.0 nM) inhibited both maximal EFS responses and noradrenaline overflow, thus confirming previous reports of the high activity of TEI-3356 at the EP3-receptor. Cicaprost had no significant effect on noradrenaline overflow at 10 and 100 nM, but produced a modest inhibition at 640 nM. 5. In conclusion, our studies show that prostacyclin analogues (particularly TEI-3356) can inhibit EFS responses of the guinea-pig vas deferens by acting as agonists at presynaptic EP3-receptors. Prostacyclin analogues (particularly cicaprost and TEI-9063) can also enhance EFS responses through activation of IP-receptors. The mechanism of the enhancement has not been rigorously established but from our results we favour a presynaptic action to increase transmitter release.

Differences in response to 5-HT4 receptor agonists and antagonists of the 5-HT4-like receptor in human colon circular smooth muscle.

1. In isolated circular smooth muscle strips of human colon 5-hydroxytryptamine (5-HT) produced a concentration-related inhibition of spontaneous motility. 2. The azabicycloalkyl benzimidazolones, BIMU 8 and BIMU 1, which have 5-HT4 receptor stimulant properties, inhibited motility with EC50 values of 0.76 microM and 3.19 microM respectively and their Emax values were not significantly different from 5-HT (EC50, 0.13 microM). 3. The 5-HT4 receptor antagonist, DAU 6285 (1-10 microM), displaced the 5-HT concentration-response curve to the right in a parallel concentration-dependent manner without depressing the maximum. The Schild plot was linear and the slope did not differ significantly from unity giving a pA2 value of 6.32. 4. The high affinity selective 5-HT4 receptor antagonist, GR 113808, at a concentration of 3 nM displaced the 5-HT concentration-response curve in a parallel manner giving an apparent pKB estimate of 8.9 +/- 0.24. However, higher concentrations of 10-100 nM GR 113808 did not result in a further significant displacement of the 5-HT concentration-response curve and there was no suppression of Emax. 5. GR 113808 (10 nM) also caused a parallel displacement of the concentration-response curve to the 5-HT4 receptor agonist, 5-methoxytryptamine (5-MeOT) giving apparent pKB values ranging from 8.3-9.3. 6. GR 113808 (3-100 nM) failed to displace 5-HT or 5-MeOT concentration-response curves in tissue strips from 3 patients out of a total of 10 patients studied in whom the response to 5-HT and 5-MeOT was normal. 7. The 5-HT4 receptor antagonist, SDZ 205-557 (0.3-10 microM), had no significant effect on 5-HT-induced inhibition of spontaneous motility.8. The present results are discussed in the light of variability of response to GR 113808 and SDZ205-557 in other tissues.9. Overall, our data indicate that human colon circular smooth muscle can be regarded as a site in which 5-HT4-like receptors are present but it is as yet unclear whether these results are also an indication of receptor variation.

Characterization of the 5-hydroxytryptamine receptor type involved in inhibition of spontaneous activity of human isolated colonic circular muscle.

1. Experiments were carried out to characterize pharmacologically the 5-hydroxytryptamine (5-HT) receptor types which mediate inhibition of spontaneous contractions of the intertaenial circular muscle in human isolated colon. 2. 5-HT caused a reproducible concentration-dependent inhibition of spontaneous contractions of the circular muscle of human colon in vitro with a mean EC50 value of 0.2 microM and 95% confidence limits of 0.1-0.5 microM. No evidence for a contractile action of 5-HT was found. Tetrodotoxin (TTX, 1.5 microM) caused a rightward shift of the concentration-response curve of 5-HT with a concentration-ratio of 2.9. 3. The inhibitory response to 5-HT was mimicked by several indoles with the rank order of potency 5-HT > 5-methoxytryptamine = alpha-methyl-5-HT > 5-carboxamidotryptamine >> 2-methyl-5-HT. 5-Hydroxyindalpine was inactive. 4. The substituted benzamides were agonists with the following rank order of potency, 5-HT > renzapride > zacopride > metoclopramide > cisapride. 5. The inhibitory responses to 5-HT were not inhibited by methysergide (10 microM) or methiothepin (1 microM), which are antagonists selective for 5-HT1-like and 5-HT2 receptors, nor by ondansetron (10 microM) which is an antagonist at 5-HT3 receptors. 6. The inhibitory responses induced by 5-HT and 5-methoxytryptamine were competitively antagonized by a weak 5-HT4 receptor antagonist, tropisetron, with pKB values of approximately 6. Tropisetron had no significant effect on the inhibitory response curve produced by isoprenaline (0.01-100 microM). 7. The pharmacological profile of the 5-HT-evoked relaxations of human colon circular muscle are consistent with activation of a 5-HT4-like receptor.

Effects of social interaction on distress and recovery from minor surgery in elective paediatric patients.

Thirty-six children aged 2-10 years, the majority of whom were males admitted for urogenital surgery, were observed for level and frequency of distress and type of social interaction over the duration of hospitalization. The results indicate that high levels of observed distress were associated with longer post-operative hospital stays. Staff interactions were associated with higher levels of distress while peer caretaking interactions were associated with lower levels of distress. We tested the hypothesis that social interaction lowered distress, leading to a briefer hospital stay. Using path analysis, we found peer caretaking interactions accounted for a small but significant percentage of the observed variance in duration of post-operative hospital stay. These data illustrate the potential importance of social environments in the maintenance of reduction of distress before and after paediatric surgery. This raises the expectation that certain types of social environments could facilitate recovery from surgery.

The role of nitric oxide in mediating non-adrenergic non-cholinergic relaxation in longitudinal muscle of human taenia coli.

Electrical field stimulation (EFS) of isolated longitudinal muscle of human taenia coli at 4Hz produced relaxation which was abolished by tetrodotoxin but not adrenergic and cholinergic blockade (NANC-relaxation). NG-nitro L-arginine (L-NOARG; 1-100 microM), an NO synthesis inhibitor, produced a concentration-dependent partial inhibition of the NANC response; 10 microM L-NOARG inhibited EFS-induced relaxation by 48.6 +/- 5.20% and 100 microM L-NOARG by 54.2 +/- 10.1%. L-Arginine (1mM), but not D-arginine (1mM) partially reversed the inhibitory effect and this was inversely proportional to the concentration of L-NOARG used. Cumulative administration of NO (acidified sodium nitrite solution; 1-100 microM) produced a concentration-dependent relaxation of the strips. L-NOARG (1 mM) did not affect either NO or isoprenaline-induced relaxations. These results provide the first preliminary evidence that NO is partially responsible for the NANC inhibitory transmission in the longitudinal muscle of the taenia coli of human colon.