Heinz Juan

Action of peptides and other algesic agents on paravascular pain receptors of the isolated perfused rabbit ear

Summary1.The algesic effect of several substances following intraarterial injection into the rabbit ear was measured: by recording the action potentials of the auricular nerve in the isolated ear (method A) and by recording the reflex fall in systemic blood pressure elicited by intraarterial injection into the isolated perfused ear which was still connected to the body by the nerve (method B).2.The order of activity of the algesic substances was: bradykinin, substance P>ACh>ATP, histamine, serotonin, KCl. A good correlation of the actions of all substances tested was found in both preparations. Physalaemin, eledoisin, adenosine, adrenaline, angiotensin, vasopressin, oxytocin and prostaglandin E1 were found to be inactive.3.Infusion of prostaglandin E1 into the ear, however, enhanced the effect of all substances.4.The vasoconstriction in the ear observed with most of the substances was not correlated with their activity in eliciting afferent impulses.

Release of prostaglandins by bradykinin as an intrinsic mechanism of its algesic effect.

Summary1.The release of PGs from the isolated perfused rabbit ear was measured by means of a radioimmunoassay.2.Bradykinin in dose dependent amounts released mainly PGE (presumably PGE1) and in much smaller amounts also PGF.3.Bradykinin released similar amounts of PGE in innervated and chronically denervated ears.4.Indomethacin completely prevented the PGE release by bradykinin.5.ACh showed a much lower efficacy than bradykinin in releasing PGE and PGF. Synthetic substance P was devoid of any PGE releasing action.6.It is concluded that bradykinin increases its own algesic action by a concomitant rapid stimulation of the PGE synthesis, thus providing a mechanism for the facilitation of its own algesic action.

Effect of ricinoleic acid and other laxatives on net water flux and prostaglandin E release by the rat colon

Ricinoleic acid, oleic acid, dioctyl sodium sulphosuccinate, deoxycholic acid, sennoside A + B and mannitol reduced or reversed water flux from lumen to blood in rat colon in situ. Stearinic acid was without any effect. Ricinoleic acid, oleic acid, dioctyl sodium sulphosuccinate, deoxycholic acid and sennoside A + B stimulated release of PGE‐like material into the colonic lumen whereas the osmotic laxative mannitol and stearinic acid did not. Inhibition of PGE biosynthesis by pretreatment of the rats with indomethacin significantly reduced (but did not abolish) the effect of ricinoleic, oleic and deoxycholic acids on net water flux and PGE release. Indomethacin reduced the effect of dioctyl sodium sulphosuccinate and of sennoside A + B on PGE release but not their effect on the net water flux. The effect of mannitol was not influenced by indomethacin. The amount of PGE release in experiments with ricinoleic acid, oleic acid, stearinic acid and dioctyl sodium sulphosuccinate (with and without indomethacin) showed a good correlation (r = 0·99) with the change in net water flux. Deoxycholic acid, sennoside A + B and mannitol did not show this correlation. It is assumed that the action of non‐osmotic laxatives is partially mediated by PGE, although other mechanisms also seem to be involved in their mode of action.

Histamine-Induced release of arachidonic acid and of prostaglandins in the peripheral vascular bed

Summary1.Injection or infusion of histamine intraarterially into the isolated perfused rabbit ear dosedependently stimulated the release of prostaglandins (PGs) as measured by radioimmunoassay (PGE), bovine coronary artery strips (PGI2) and by the prelabeling technic with [1-14C]-arachidonic acid (PGI2, PGE2, PGF2α, PGD2).2.PG release was abolished by indometacin (1–3 μg/ml) and reduced by the phospholipase A2 inhibitor quinacrine (10 μg/ml) as well as by perfusing with calcium-free, 1 mM EGTA containing solution.3.The histamine H2-receptor antagonists burimamide (5μg/ml) and cimetidine (2 μg/ml) did not influence histamine-induced PG release. The H1-receptor antagonist mepyramine (0.1–1 μg/ml) abolished histamine-induced PG release.4.In the presence, but not in the absence, of bovine serum albumin there was a basal release of high amounts of arachidonic acid. Histamine tended to increase the released amount of radioactive arachidonic acid. In contrast to indometacin which only blocked PG release, mepyramine significantly reduced the histamine-stimulated release of arachidonic acid, too.5.The results show that in the peripheral vascular bed, histamine, via H1-receptors, activates a phospholipase A2 mainly by increasing a transfer of extracellular calcium into the cell. Activation of a phospholipase A2 results in the release of arachidonic acid possibly from a rather small endogenous pool which specifically provides substrate for the PG synthetase system.

Characterization of prostanoid receptors mediating actions of the isoprostanes, 8-iso-PGE2 and 8-iso-PGF2α, in some isolated smooth muscle preparations

We investigated the contracting actions of the isoprostanes (isoPs), 8‐iso‐prostaglandin (PG) F2α and 8‐iso‐PGE2, in comparison to the effects of the thromboxane (TX) A2‐mimetic U 46619 and the traditional prostaglandin PGE2 in the isolated rat aorta, isolated rat gastric fundus and the isolated guinea‐pig ileum. U 46619 and 8‐iso‐PGF2α caused contractions in the rat aorta and rat gastric fundus in a concentration‐dependent manner, whereas these agonists showed no effects in the guinea‐pig ileum. However, 8‐iso‐PGE2 and PGE2 caused contractions in all isolated organs used. The prostanoid TP‐receptor antagonist SQ 29,548 (10 nM) significantly antagonized vasoconstrictions induced by the agonists used in the rat aorta. SQ 29,548 at a final concentration of 3 μM, but not at lower concentrations, significantly inhibited contractions induced by U 46619, 8‐iso‐PGF2α and 8‐iso‐PGE2 in the rat fundus. Responses to PGE2 were unchanged. The prostanoid EP1‐receptor antagonist SC 51089 (3 μM) significantly inhibited contractions induced by 8‐iso‐PGE2 and PGE2 in the rat fundus and in the guinea‐pig ileum. SC 51089 had no effect on responses to any of the agonists tested. Our results show that 8‐iso‐PGE2, in contrast to 8‐iso‐PGF2α, can also cause contractions by activation of the EP1‐receptors in the rat gastric fundus and the guinea‐pig ileum. The findings of the present study do not support the existence of a unique isoP‐receptor in the tissues used.

Interaction of prostaglandins and indomethacin with algesic substances

Summary1.The isolated perfused rabbit ear connected to the body by its nerve only was used to investigate the modification of the algesic effect of bradykinin, substance P and acetylcholine (ACh) by indomethacin.2.The effect of these algesic substances was inhibited by indomethacin in proportion to the dose and duration of infusion.3.The factors by which the algesic effect was reduced by indomethacin and the factors by which it was enhanced by prostaglandin E1 were found to be correlated. The factors were greatest for bradykinin, intermediate for substance P and smallest for ACh, thus showing that the algesic effect of bradykinin is most dependent on the presence of prostaglandin E1.4.In the presence of additional amounts of prostaglandin E1, indomethacin was able to reduce the algesic effect of bradykinin and ACh to some extent. This cannot be explained by blockade of the PG synthesis.5.The vasoconstriction found after i.a. injection of bradykinin, substance P and PGF2α was partly inhibited by indomethacin. This was explained by a direct inhibitory influence of indomethacin on the vasoconstrictor effect of the prostaglandin or the algesic substances.6.Indomethacin, due to a direct and reversible antagonism, reduced the contraction of the isolated guinea-pig ileum induced by PGE2 more than the contraction induced by bradykinin.7.It is confirmed that indomethacin acts mainly by inhibition of biosynthesis of prostaglandins. An additional direct inhibition of prostaglandin-actions by indomethacin can, however, be seen under certain experimental conditions.

PGE-release, blood flow and transmucosal water movement after mechanical stimulation of the rat jejunal mucosa

Summary1.The influence of weak mechanical stimulation of the jejunal mucosa in vivo on PGE-release, on intestinal blood flow and transmucosal water movement was studied in rats.2.Mechanical stimulation of the mucosa increased PGE-release into the venous outflow and into the gut lumen. This increase is followed by an increase in intestinal blood flow and transmucosal movement of tritiated water in both directions.3.Pretreatment of the rat with idomethacin reduced the effect of mechanical stimulation on PGE-release. Indomethacin further reduced the increase in blood flow and in secretion of tritiated water. Absorption of tritiated water was not changed in these experiments.4.Pretreatment of the rat with atropine (1 mg/kg, i.p.) or perfusion of the gut with methysergide (10 μg/ml) did not influence the increase in intestinal blood flow after mechanical stimulation.5.It is suggested that enhanced intestinal blood flow and transmucosal movement of tritiated water after mechanical stimulation are mainly provoked by a preceding release of PGE.6.It is further supposed that such a mechanism may be physiologically involved in regulation of intestinal blood flow and transmucosal water movement during food intake.

Nociceptor stimulation and PGE release by capsaicin.

Summary1.Intraarterial injection of capsaicin (threshold dose 0.3 μg) into the isolated perfused rabbit ear causes a dose-dependent reflex fall in blood pressure by stimulation of chemosensitive nociceptors.2.Infusion of capsaicin (1 and 10 μg/ml) into the isolated rabbit ear dose-dependently stimulates prostaglandin biosynthesis, equally in innervated and chronically denervated preparations, therefore mainly in extraneuronal tissue. The capsaicin-induced prostaglandin E release is dependent on the presence of extracellular Ca2+.3.The nociceptive reflex fall in blood pressure induced by i.a. injection of bradykinin is progressively enhanced under infusion of 1 μg/ml capsaicin whereas that induced by acetylcholine is not. Its enhancement is explained by the capsaicin-induced increased amount of prostaglandin E at the nociceptor sites.4.Infusion of 10 μg/ml capsaicin renders the nociceptors insensitive to effects of bradykinin and acetylcholine.5.Although the stimulation of nociceptors by capsaicin in a small dose includes the release of prostaglandin E from the surrounding tissue, it cannot be said whether a prostaglandin-mediated mechanism is also involved in the long lasting functional impairment of chemosensitive fibres induced by high doses of capsaicin.

Influence of epilobium extracts on prostaglandin biosynthesis and carrageenin induced oedema of the rat paw

Epilobium species have been used as remedies in folk-medicine for the treatment of pathophysiological processes of the prostata. In this paper the influence of extracts of Herba Epilobii angustifolii L. and Herba Epilobii parviflori Schreb. on prostaglandin biosynthesis and the carrageenin rat paw oedema is described. Aqueous extracts of Herba E. angustifolii reduced the release of prostaglandins I2, E2 and D2 (in the perfused rabbit ear) approximately 5 times more effectively than did similar extracts of Herba E. parviflori. Methanolic extracts were inactive. The aqueous extract of E. angustifolium strongly reduced the carrageenin-induced rat paw oedema whereas that of E. parviflorum was inactive. The chemical nature of the active compound(s) is as yet unknown but flavonoids and sitosterol derivatives can be excluded.

PGE-mediated laxative effect of diphenolic laxatives.

Summary1.In the tied off colon of the anaesthetized rat in situ, the effect of diphenolic laxatives (bisacodyl and phenolphthalein) and of osmotic laxatives (mannitol, sodium sulfate and lactulose) on water net flux was studied. All the laxatives reduced water net flux from lumen to blood or reversed it into water net flux from blood to lumen. Pretreatment with indomethacin reduced or abolished the effect of the diphenolic laxatives on water net flux but did not change the effect of the osmotic laxatives.2.In the perfused colon of the rat in situ, the effect of the diphenolic and the osmotic laxatives on water net flux and on PGE-release into the colonic lumen was investigated. All laxatives reduced water net flux from lumen to blood in this preparation, too.PGE-release into the lumen during perfusion with osmotic laxatives was not different from the control. The diphenolic lexatives increased PGE-release dosedependently about 2-fold.3.Intraluminal perfusion of the jejunal loop of the rat in situ with bisacodyl increased intestinal blood flow by about 50%. Addition of indomethacin to the perfusion fluid abolished this increase.4.It is concluded that diphenolic laxatives exert their laxative action at least partially via stimulation of intestinal PGE-biosynthesis.