Changes in the position and angulation of incisura during contractions of the isolated cat stomach

Abstract Contractions change the configuration of the lesser curvature of the stomach while they indent the greater curvature. We studied these lesser curvature changes by measuring the position and angle of the gastric incisura on still frames captured from videotapes of isolated cat stomachs suspended in physiologic solution. In response to filling with 100 mL Krebs' solution stomachs generated a tonic contraction of the fundus/body segment and gave rise to a peristaltic contraction that spread from the body and through the antrum to the pylorus. In preparations where we left the duodenal cannula open we found that the incisura moves toward the gastro-oesophageal (GO) junction and the angle of the incisura widens as the contraction passes through the stomach and empties its contents. Furthermore, the angle of the incisura is most acute when the full stomach starts contracting in its fundic segment and again when the contraction involves the gastric sinus (the wedge-shaped segment adjacent to the incisura which forms the transition between the body and the antrum of the stomach). In preparations where the duodenal cannula was kept closed, the angle of the incisura becomes most acute when the contraction involves the gastric body and when the luminal pressure peaks. We conclude that changes in the position and angulation of the incisura are part of the mechanical response of the stomach to filling and emptying; unlike the peristaltic contraction along the greater curvature the net movement of the incisura goes in the orad direction. Movements of the incisura profoundly affect the configuration of the stomach and hence the distribution of luminal contents between various gastric segments. The gastric sling muscles are responsible for the formation of the gastric incisura but their role in any movements of the incisura remains to be defined.     

PROSTHESIS-ASSOCIATED PSEUDOMEMBRANE-INDUCED BONE RESORPTION

A pseudomembranous structure invariably develops at the cement-boneinterface of implanted prostheses in association with asepticloosening. The tissue has histological characteristics of aforeign body reaction presumably initiated by repetitive microtrauma-associatedrelease of methacrylate cement and polyethylene wear debris.Explant cultures of pseudo-membrane and synovial tissue derivedfrom osteoarthritic patients undergoing revision for cementedhip implant failure have been shown to produce interleukin-1,tumour necrosis factor and prostaglandin _E2, recognized mediatorsof bone resorption. Further, the conditioned media obtainedfrom pseudomembrane cultures could directly effect bone resorptionby inducing ⁴⁵Ca release from prelabelled limb bone rudiments.Results implicate the prosthesis-associated pseudomembrane inthe pathogenesis of the bone resorptive process responsiblefor prosthesis failure. KEY WORDS: Bone resorption, Interleukin-1, Polymethylmethacrylate, Prostaglandins, Prosthesis failure, Tumour necrosis factor     

The Effect of Chromium on Platelet Function In Vitro

Sodium chromate inhibits platelet function in vitro. The primary effect is inhibition of connective tissue-induced aggregation. In addition, the primarywave of epinephrine-induced aggregation is moderately inhibited andadenosine diphosphate-induced aggregation is mildly inhibited. The effect onconnective tissue-induced aggregation is due to inhibition of the platelet "release reaction"; chromate inhibited the release of adenine nucleotides, ¹⁴Clabeled serotonin and the activation of platelet factor III normally caused byconnective tissue. The amount of chromium which must be bound to plateletsto inhibit aggregation is 10-100 times the amount of radioactive chromiumbound to platelets under the usual conditions of labeling for survival studies.However, this does not imply that chromium labeled platelets functionnormally.

     

Association of β-agonists with corresponding β2- and β1-adrenergic pentapeptide sequences

Synthesized β₁- and β₂-pentapeptide sequences corresponding to published adrenoceptor transmembrane activation site subtypes were investigated in vitro for selectivity in association for drug ligands of known selectivity. Both nuclear magnetic resonance spectroscopy and molecular mechanics demonstrated that structural differences among the corresponding pentapeptide activation-site sequences can explain agonist selectivity. Results suggest the agonists bind across the activation site loop on the second transmembrane α-helix by dipole/dipole interactions between a ligand and the peptide. Since electrostatic interactions within the membrane may determine the rate of intercellular ion flux, agonist association across the activation site sequence could thereby decrease electrostatic resistance to positive ion flux into the cell. Interactions between the peptides and the ligands may provide insight into the structures and mechanisms involved in association of ligands for the identical sequences on the β-adrenoreceptors.     

Book Reviews

Book reviews in this article:
MICROBIOLOGY. Abraham I. Braude.
CLINICAL DERMATOLOGY (DIAGNOSIS AND THERAPY OF COMMON SKIN DISEASES). P. Vasarinsh.
THE MANAGEMENT AND PREVENTION OF PRESSURE SORES. Anthony Barton and Mary Barton.
PRESSURE ULCERS—PRINCIPLES AND TECHNIQUES OE MANAGEMENT. Mark B. Constantian, M.D., Editor.