Search PubMed⌕ Search

Biomedical subjects

A Bennett

Publications and source records attributed to A Bennett.

At least 253 records · Page 14Linked to original sources
PubMed1977

The effects of prostaglandins E1, E2, F1alpha and F2alpha on guinea-pig ileal and colonic peristalis.

Prostaglandins (PGE1, E2, F1alpha and F2alpha) have been tested on the peristaltic reflex in isolated segments of guinea-pig ileum and colon using simultaneous recordings of fluid propulsion and longitudinal and circular muscle activity. Propulsion and circular muscle peristaltic activity were increased by serosally applied PGF compounds in the ileum and PGE or PGF compounds in the colon following initial contraction of the longitudinal muscle. This is consistent with a role for prostaglandins in peristalsis. Mucosally applied PGF compounds has no significant effect.

Animals↗
PubMed1977

Relaxations mediated by adrenergic and non-adrenergic nerves in human isolated taenia coli.

In human taenia coli electrical field stimulation after cholinergic blockade excited mainly non-adrenergic inhibitory nerves. Adrenergic relaxations during stimulation were demonstrated only with short electrical pulses at high frequencies or with ganglion stimulants. Reduction by tetrodotoxin of relaxations to indirectly acting sympathomimetics supports the histochemical finding that colonic adrenergic nerves are mainly preganglionic, and possibly synapse with non-adrenergic inhibitory nerves. When the latter undergo direct maximal stimulation, responses to adrenergic nerve excitation are masked.

Adenosine Triphosphate↗
PubMed1976

Peridinin-Chlorophyll a Proteins of the Dinoflagellate Amphidinium carterae (Plymouth 450).

The marine dinoflagellate Amphidinium carterae (Plymouth 450) releases several water-soluble peridinin-chlorophyll a proteins after freezethawing. These chromoproteins have a molecular weight of 39.2 x 10(3) and are comprised of noncovalently bound peridinin and chlorophyll a and a nonoligomeric protein. They have distinct isoelectric points and may be resolved into six components by either isoelectric focusing on polyacrylamide gel or ion exchange chromatography. The predominant chromoprotein, which has a pI of 7.5, constitutes about 90% of the extractable peridinin-chlorophyll a protein. It consists of an alanine-rich apoprotein of molecular weight 31.8 x 10(3) stoichiometrically associated with 9 peridinin and 2 chlorophyll a molecules. Additionally, the peridinin-chlorophyll a proteins with pI values of 7.6 and 6.4 were purified and found to have amino acid and chromophore composition essentially identical with the pI 7.5 protein. Peridinin-chlorophyll a protein, pI 7.5, after treatment at alkaline pH was transformed into several more acid pI forms of the protein, strongly suggesting that the naturally occurring proteins are deamidation products of a single protein. Fluorescence excitation and emission spectra demonstrate that light energy absorbed by peridinin induces chlorophyll a fluorescence presumably by intramolecular energy transfer. The peridinin-chlorophyll a proteins presumably function in vivo as photosynthetic light-harvesting pigments.

Journal Article↗
PubMed1976

Intestinal pH and propulsion: an explanation of diarrhoea in lactase deficiency and laxation by lactulose.

Subjects deficient in lactase may experience bloating, cramps and diarrhoea after ingesting milk, due to the unhydrolysed and poorly-absorbed lactose. The diarrhoea may result from an osmotic effect of the lactose itself or its poorly-absorbed acidic products of fermentation (Weijers, van de Kamer & others, 1961; Christopher & Bayless, 1971), possibly together with an alteration of sodium and water absorption due to the lowered colonic pH (Rousseau & Sladen, 1971). Laxation by lactulose (1-4-beta-galactosidofructose) may operate through an analogous mechanism. The drug is a synthetic dissaccharide which, in oral doses of 10-20 g, relieves chronic constipation (Wesselius-de Casparis, Braadbaart & others, 1968). It is neither hydrolysed by intestinal dissaccharidase (Dahlqvist & Gryboski, 1965) nor absorbed in the gut, but it is converted in the colon mainly to lactic and acetic acids by various bacteria including Lactobacillus acidophilus. Apart from the increased osmotic effect, the pH in the proximal colon falls markedly (Bown, Gibson & others, 1974), and larger doses may reduce stool pH. Weijers & others (1961) inferred that the acidic products formed from lactose in the colon stimulate propulsion, and K.S. Liem (Philips-Duphar) suggested to us that lactulose may relieve constipation partly by stimulation of propulsion due to the lowered pH. The experiments described below support this view.

Animals↗
PubMed1976

Prostaglandin release in canine acute haemorrhagic pancreatitis.

Acute haemorrhagic pancreatitis was induced in greyhound dogs by a bile salt/trypsin injection into the main pancreatic duct. Prostaglandin-like activity in the pancreatic venous blood, right atrial blood, and arterial blood was measured by bioassay. Activity rose significantly in the pancreatic venous blood of test dogs but not in controls. Chromatographic analysis of the peritoneal exudate from the dogs with pancreatitis showed high levels of prostaglandin E-like material (mean 43 ng/ml prostaglandin E2 equivalents). It seems likely that prostaglandins contribute to the induced pancreatitis.

Acute Disease↗
PubMed1976

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 mug/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 mug/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 mug/ml) or indomethacin (1-4 mug/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 F2alpha 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.

Animals↗
PubMed1975

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.

Adult↗
PubMed1975

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.

Acetylcholine↗
PubMed1975

The effects of prostaglandins on guinea-pig isolated intestine and their possible contribution to muscle activity and tone.

1 Prostaglandins F(1alpha) and F(2alpha) 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 E(1) and E(2) 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 E(1) seems more effective than E(2) 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.

Animals↗