SUMMARY1. Electromyographic (e.m.g.) recordings of reactions of the oesophagus, vertebral and costal fibres of the diaphragm and from the reticulum -one of the cranial divisions of the stomach were made during the regurgitation of rumination in sheep.2. E.m.g.s indicated that a contraction of the caudal thoracic oesophagus developed over a period of about 2 sec before, and ceased at the time of, the more forceful inspiratory effort associated with regurgitation.3. This contraction was confined to the caudal region of the thoracic oesophagus in which it was characteristically more prolonged and intense in its most caudal part within 15-25 mm of the hiatus oesophageus. It is interpreted to contribute to development or intensification of a caudal thoracic oesophageal sphincter.4. The more forceful inspiratory effort at the time of regurgitation was due to costal fibres of the diaphragm. Although active normally during inspiration the vertebral fibres of the hiatus oesophageus do not contribute to this more forceful inspiration. This may facilitate regurgitation of digest. Similarly, inactivity of vertebral but not postal fibres detected during primary oesophageal contractions (of swallowing) may make for easier passage of digesta into the stomach.
Parotid salivary secretion, reticular (gastric) contractions and blood osmolality were examined in conscious sheep prepared with re-entrant parotid duct cannulae and given 1000 g of lucerne chaff daily. Osmolality of blood (portal, carotid and jugular) rose by 2-4 mosmoles.kg' within 5 min of fresh food being given, continued to rise (up to 12-30 mosmoles.kg-1) over the next 3 h and remained above levels detected before fresh food was given for up to 10 h. The greatest changes were in portal blood which was characteristically hyperosmolal to jugular and carotid blood; a difference which disappeared on fasting for 36 h. Parotid saliva which was 5-20 mosmoles.kg' I hyposmolal to jugular blood, increased to up to 6 ml. min-1 within 30 sec of the sheep starting to eat and although they continued to do so for some hours remained at these high levels for only about 30 min.Attempts were made to see whether parotid salivary secretion was affected by changing the osmolality of the blood. Reductions in the rate of parotid salivary secretions and sometimes in the rate of reticular contractions were produced in conscious, anaesthetized and decerebrate preparations by making intravenous infusions of hyperosmolal solutions. The effects were stronger, and the latency shorter, when the infusions were made into the portal vein than when made into the posterior vena cava or a jugular vein. They were reduced by vagotomy and splanchnotomy although not abolished by both.Increases in parotid salivary secretion and frequently, but not invariably, in the rate of reticular contractions followed intravenous infusions of isosmolal and hyposmolal solutions. In 6 experiments (of a total of 12) increases in parotid salivary secretion followed the intravenous injection of arginine vasopressin (0-06 mU.kg-1), in none was saliva reduced by antidiuretic hormone.The possible involvement of peripheral osmoreceptors in the inhibitory effects, and of receptors sensitive to changes in blood volume in the excitatory effects, is raised in relation to post-prandial changes which occur in blood composition.Salivary secretions increase markedly when sheep first eat freshly provided food but although eating continues salivation declines and may fall to levels below those observed immediately before food was made available. Explanations advanced for the reductions in salivary secretion and apparent failure for buccal, oesophageal and gastric stimulation to remain effective as eating continues have included inhibitory effects of gastric distention as digesta and
The galactan preparations were made as described in detail for galactan F by Hudson et al. (1967) except that the Sephadex G200 column formerly used (80 x 270 mm) was replaced with one 50 x 1000 mm, and that a pneumatically-driven Padberg supercentrifuge was used instead of a steam-driven Sharples supercentrifuge. Three batches of galactan F were made; these were identified as LS30, LS31, LS32. In the case of LS31 the supernate of the culture was heated before and not, as with LS30 and LS32, after acidification with glacial acetic acid; in other respects the procedures for preparation of the three batches were identical.Control solutions. Uninoculated culture medium (BVFOS) of the same type as that used in the preparation of galactan F was subjected to the same extraction procedures as those used for preparation of the galactan. This provided one of the control solutions injected intravenously into calves. The other control solution used was the 0.85% (w/v) NaCl in which freeze-dried galactan preparations were dissolved for intravenous inject ion.Testing for pyrogenic activity. This was done in conscious rabbits (2-6-3.3 kg) by the method described in the British Pharmacopoeia (1968) except that two rabbits were used for each preparation and rectal temperatures were monitored continuously with a thermistor probe (Yellow Springs Instrument Co., Yellow Springs, Ohio).Chemical analyses. Quantitative amino-acid analyses of the galactan preparations were made after hydroiodic acid hydrolysis (Inglis, Nicholls and Roxburgh, 1971). The method has been found suitable for preparations of high carbohydrate content (Nicholls and Inglis, personal communication). Total percentage of protein was calculated as the sum of the individual amino-acid contents of the preparation.Animal experiments. Most of the experiments were done on 41 calves that were 10-12 weeks old, and weighed 30-90 kg. They were of the Jersey, Hereford and Friesian breeds and crosses of the Jersey and Friesian breeds; the majority were females. All had been taken from their mothers 4 weeks before the experiments and were being maintained on reconstituted skim-milk powder and calf-concentrate pellets. All had begun ruminating. Experiments were undertaken both in conscious and anaesthetised calves.The experiments on conscious calves were done with the animals standing in a stall, or restrained in lateral recumbency on a table to minimise movement artefacts in electrocardiograms. A venous cannula (Bard, International Ltd, Sunderland) was introduced into one or both jugular veins, and in some experiments a polythene tube was introduced into the pulmonary artery, being passed from the right jugular vein via the right atrium and ventricle. The pressure profiles recorded from these saline-filled tubes on pressure transducers were used to identify the final sites of the tips of the cannulae and verification was obtained at necropsy. Standard limb leads were used, and recordings made of either lead I, I1 or I11 of the electrocardiogram (ECG). Respiratory movements ...
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