A. Bennett

Effects of prostaglandins E1 and E2 on human, guinea-pig and rat isolated small intestine

1 . Prostaglandins E1 and E2 contracted the longitudinal muscle of human, guinea‐pig and rat isolated ileum. 2 . The site of action varied with the species. In the rat and in some strips of human tissue prostaglandin appeared to have only a direct action on or in the muscle cells. In the other strips of human tissue and in guinea‐pig ileum the prostaglandins seemed to stimulate both the intrinsic cholinergic nerves and the muscle cells. 3 . In contrast to the longitudinal muscle, the circular muscle of human, guinea‐pig and rat isolated ileum was usually inhibited by prostaglandin, apparently by an action directly on the muscle cells. 4 . Prostaglandins may play a part in the control of intestinal motility.

BREAST CANCER, PROSTAGLANDINS, AND BONE METASTASES

Human malignant breast tumours from 23 patients contained and synthesised more prostaglandin-like material than normal breast tissue from the same patients or benign neoplasms (5 patients). Bone metastases were associated with tumours having high levels of P.G.-like material, which usually resembled P.G.F compounds, and this may be important since some P.G.S are potent bone-resorbing substances.

THE EFFECTS OF PROSTAGLANDINS ON GUINEA-PIG ISOLATED INTESTINE AND THEIR POSSIBLE CONTRIBUTION TO MUSCLE ACTIVITY AND TONE

1 Prostaglandins F1α and F2α caused contraction of the longitudinal muscle of both guinea‐pig isolated ileum and colon, apparently by acting directly on the muscle and on cholinergic nerves. They had little effect on ileal circular muscle. 2 Prostaglandins E1 and E2 caused contraction of the longitudinal muscle of guinea‐pig isolated colon, apparently by acting directly on the muscle and on excitatory nerves which are non‐cholinergic. Prostaglandin E1 seems more effective than E2 in stimulating these nerves. 3 It seems likely that prostaglandin release in vitro maintains the tone of the longitudinal muscle of guinea‐pig colon, whereas release of a prostaglandin E compound inhibits circular muscle tone.

Metabolites of arachidonic acid formed by human gastrointestinal tissues and their actions on the muscle layers.

1 Gas chromatography‐mass spectrometry demonstrated the presence of arachidonic acid (AA), 6‐keto‐prostaglandin F1α and thromboxane B2 (TxB2) in all extracts of homogenized muscle or mucosa from human stomach, terminal ileum or sigmoid colon. Prostaglandin D2 (PGD2), PGE2 or PGF2α were usually found more often in the mucosal extracts. The 12‐hydroxy‐derivative of AA (12‐HETE) was detected in all extracts of the colon but in only some of the other tissues 2 Most prostanoids tested contracted the longitudinal muscle, the order of potency being U‐46619 (an epoxymethano analogue of PGH2)>PGE2>PGF2α>PGD2; PGI2 usually caused relaxation, whereas its breakdown products or TxB2 had weak and variable effects 3 U‐46619 or, less potently, PGF2α contracted the circular muscle, whereas PGI2 and usually PGE2 caused relaxation. PGD2, 6‐keto‐PGF1α, 6, 15‐diketo‐PGF1α or TxB2 usually had little or no effect 4 PGI2 antagonized contractions to some excitatory prostanoids, without greatly affecting contractions to acetylcholine 5 For both muscle layers there was a gradient in sensitivity to prostanoids along the gastrointestinal tract. The sensitivities were stomach>distal ileum>sigmoid colon 6 The results are discussed in relation to gastrointestinal physiology and pathophysiology.

Cancer growth, response to treatment and survival time in mice: beneficial effect of the prostaglandin synthesis inhibitor flurbiprofen.

Adult mice were injected subcutaneously with cells from a syngeneic metastasizing mammary cancer. Daily treatment with flurbiprofen starting before injection of the cancer cells reduced tumour growth and lengthened the survival of mice whose tumours were excised at 3 weeks. When low doses of radiotherapy and chemotherapy were given, additional treatment with flurbiprofen starting 25 days after injecting the cancer cells substantially inhibited tumour growth.

Estimation and characterization of prostaglandins in the human gastrointestinal tract.

1 Prostaglandin‐like material was extracted from muscle and mucosa of surgically removed human stomach, ileum and colon and assayed against prostaglandin E2 on strips of rat gastric fundus. Superfused human isolated gastric mucosa released prostaglandin‐like material and release was increased by stretching or clamping the tissue. 2 The relative amounts of extracted biological activity were broadly as follows: gastric antral mucosa > colon muscle > gastric body mucosa ≅ ileal mucosa > colon mucosa ≅ gastric muscle ≅ ileal muscle. 3 Prostaglandin E and F were tentatively identified by chromatography and sensitivity to inactivation by alkali. 4 Prostaglandin E apparently contributed most to the biological activity, possibly because the assay tissue is more sensitive to prostaglandin E than to F. Chromatography of gastric body mucosal extracts located material running with prostaglandin E2 and a little with E1. Colonic muscle and mucosal extracts contained material with RF values of prostaglandins E1, E2, E3 and F1α, whereas F2α and F3α‐like substances were found only in the mucosa. The proportions of prostaglandin F varied between specimens. 5 The amount of extracted prostaglandin‐like activity was increased by adding cofactors and arachidonic acid, and lessened by homogenization with acid‐ethanol. 6 The type and amount of activity generated from arachidonic acid by partly purified colonic mucosal prostaglandin synthetase depended on the substrate concentration. 7 The possible relationships of prostaglandins to mucus secretion and other physiological and pathological gut functions are discussed.

Effect of prostaglandins E1 and E2 on intestinal motility in the guinea-pig and rat

1 . Prostaglandins E1 and E2 affected intestinal activity both in vitro and in vivo. 2 . Serosal application of prostaglandin to guinea‐pig isolated ileum stimulated the longitudinal muscle but reduced peristaltic contractions of the circular muscle and the propulsion of fluid through the gut. Intraluminal application had little effect. 3 . Injection of prostaglandin into the bloodstream of anaesthetized rats stimulated the longitudinal muscle of the ileum and increased the intraluminal pressure. A similar response sometimes occurred in the guinea‐pig, but in general the effect was variable. 4 . Release of prostaglandin in the gut wall, but probably not into the blood or into the lumen of the gut, may play a part in controlling intestinal motility.

Modulation by prostaglandins of contractions in guinea-pig ileum

A high concentration of indomethacin (40mu-g/ml) substantially reduced contractions of guinea-pig isolated ileum in Krebs solution to nerve stimulation with electrical pulses or nicotine. Responses to acetylcholine and histamine were also inhibited, but to a smaller extent. Low concentrations of prostaglandin E-2 (2 or 4ng/ml) mainly restored all the excitatory responses. Using a modified bathing solution (lacking in phosphate and with some other changes) indomethacin 0.36mu-g/ml selectively inhibited nerve-mediated contractions. The results explain differences in various reports, and support the possibility that prostaglandins modulate the response to cholinergic nerve activity.

Cytosolic phospholipase A2, cyclo-oxygenases and arachidonate in human stomach tumours.

Human stomach tumours usually form more prostaglandins (PGs) than their associated normal mucosa/submucosa, but the mechanisms are not fully understood. The key enzymes are cytosolic phospholipase A2 (cPLA2, Mr 85,000) and the cyclo-oxygenases (COXs) which exist in constitutive (COX-1) and inducible forms (COX-2). In human stomach tumours and associated macroscopically normal tissues, we determined the fatty acid composition by gas chromatography, amounts of cPLA2, COX-1 and COX-2 by immunoblotting with specific antibodies and cPLA2 enzyme activity using a tritiated substrate. Although compared to normal mucosa there was less arachidonate in tumours (P < 0.05), the arachidonate/total fatty acid ratio was higher. Mean amounts of cPLA2 and COX-1 and cPLA2 activity were similar in tumours and normal mucosa. However, substantial amounts of COX-2 were found in the tumours but not in the mucosa, which may explain why many gastric tumours form increased amounts of PGs.

INHIBITION OF PERISTALSIS IN GUINEA‐PIG ISOLATED ILEUM AND COLON BY DRUGS THAT BLOCK PROSTAGLANDIN SYNTHESIS

1 Methods of analysing peristaltic activity have been evaluated by the use of recordings of longitudinal and circular muscle activity and of propulsion in whole segments of guinea‐pig ileum and colon. 2 Some prostaglandin synthesis inhibitors, and antagonists of prostaglandin action were tested for their suitability for studying the role of prostaglandins in peristalsis. Aspirin was suitable; at 10–200 μg/ml it had little effect on responses of longitudinal muscle strips of the guinea‐pig ileum to acetylcholine (ACh), histamine, nicotine or prostaglandin E2. Indomethacin (1–4 μg/ml) reduced responses to nicotine and prostaglandin E2. The prostaglandin antagonists polyphloretin phosphate and SC‐19220 reduced contractions of ileal longitudinal muscle caused by nerve excitation with either nicotine or transmural stimulation. 3 Aspirin (20–100 μg/ml) or indomethacin (1–4 μg/ml) applied serosally greatly inhibited all aspects of peristalsis in guinea‐pig ileum and colon. Inhibition of peristalsis of the ileum by aspirin was antagonized by prostaglandin E2 and that by indomethacin was removed by prostaglandin F2α or ACh. Inhibition of colonic peristalsis by aspirin was antagonized by prostaglandin E2 but rarely by ACh, and that by indomethacin by prostaglandin E1 or E2. Mucosal application of aspirin had little effect on either ileum or colon but indomethacin caused some inhibition. 4 These results support the supposition that prostaglandins contribute to peristaltic activity.