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Biomedical subjects

L H Heywood

Publications and source records attributed to L H Heywood.

6 recordsLinked to original sources
PubMed1988

A comparison of the effects of vasoactive intestinal polypeptide on secretion from the submaxillary gland of the sheep and pig.

The effects, on secretion of fluid and protein from the submaxillary gland of intracarotid injections of acetylcholine or vasoactive intestinal polypeptide (VIP), and intracarotid infusions of VIP during a background of muscarinic stimulation, were examined in sheep and pigs. Intracarotid injections of VIP produced secretion of saliva from the ovine gland which continued after administration of atropine, phentolamine and propranolol. The protein concentration of this saliva was over 5-fold greater than that secreted in response to acetylcholine. Intracarotid injection of VIP did not evoke secretion from the porcine submaxillary gland but increased 3-fold the protein concentration in saliva evoked by subsequent intracarotid injection of acetylcholine. Intracarotid infusions of VIP in sheep produced dose-related increases in both flow (up to 1.9-fold) and protein concentration (up to 42-fold) of submaxillary saliva secreted in response to a background infusion of bethanechol. In pigs, intracarotid infusions of VIP at 0.015, 0.15 and 1.5 nmol/min produced increases in both flow and protein concentration of bethanechol-evoked saliva. The increases in protein concentration (up to 2.8-fold) were dose-related, but the increases in flow were not, being ca. 25% with each dose of VIP. The experiments provide evidence that VIP may effect mobilization of protein into saliva even in a species (pig) in which VIP does not evoke secretion of fluid.

Acetylcholine↗
PubMed1988

Retrograde oesophageal contractions in the dog.

Retrograde oesophageal contractions were observed by simultaneous radiography and electromyography during naturally occurring post-prandial eructations in six dogs. The contractions progressed cranially at 85 +/- 16 cm s-1 (S.E.M., n = 50) displacing, to the mouth, gastric gas which had previously passed into and distended the thoracic part of the oesophagus for 304 +/- 22 ms (S.E.M., n = 30). Ninety per cent (n = 100) of retrograde oesophageal contractions were followed immediately by a slower aboral contraction (17.1 +/- 0.02 cm s-1; S.E.M., n = 15). This appears to be the first description of naturally occurring retrograde oesophageal contractions in a non-ruminant animal.

Animals↗
PubMed1986

Lack of production of thromboxane A2 by the sheep heart following coronary occlusion.

Blood pressure, heart rate and ECG were monitored continuously and coronary venous blood samples assayed for thromboxane B2. Arterio-coronary venous lactic acid differences were estimated. In anaesthetized sheep, 60 sec occlusions of the left circumflex coronary artery caused hypotension with little change in heart rate. Five minute occlusions produced similar changes accompanied by cardiac arrhythmias and a larger fall in blood pressure. In conscious sheep heart rate rose and blood pressure was maintained. ECG and lactic acid changes indicated severe myocardial ischaemia but not change in thromboxane release was detected. The apparent lack of involvement of thromboxane may reflect a relative inability of sheep platelets to produce this substance or a failure to provide an adequate stimulus for synthesis.

Anesthesia↗
PubMed1985

Thoracic oesophageal motor activity during eructation in sheep.

Concurrent radiographic and electromyographic observations were made in sheep during naturally occurring eructations. The radiographic field extended from the base of the heart to the cranial region of the rumen. Electromyographic recording was from two sites on the caudal thoracic oesophagus within 20-70 mm of the diaphragm. Passage of gas from the rumen into the oesophagus was followed by passive gaseous distension of the caudal thoracic oesophagus for period of 540 2860 ms (n = 80), at the end of which there was both electromyographic and radiographic evidence of oesophageal contraction. The pattern of radiographic change was indicative of a cranially progressing contraction of the thoracic oesophagus. Movements of the diaphragm observed radiographically during ventilation ceased (at the end of expiration), or became shallower, during the period of oesophageal distension. This resulted in a varying degree of interruption of the rhythm of ventilation. The first inspiration marking a return of ventilation to its former character was deeper than normal. The events during eructation were essentially similar whether the animals were eating, ruminating, or doing neither. When swallowing occurred during eructation it appeared to continue normally, interrupting the train of oesophageal reactions in eructation. Gas sometimes entered the caudal thoracic oesophagus after a mixing contraction of the reticulo-rumen but it was returned to the stomach by a caudally moving oesophageal contraction.

Animals↗
PubMed1980

Testosterone levels in the male laboratory rat: variation under experimental conditions.

This report describes the variation of testosterone (T) levels in male Wistar rats (250-300 g) bled under typical laboratory conditions. Plasma T in 114 rats ranged from 2-48 nmol/l (median 13.1; 95% confidence range, 10-15) and varied significantly (P < 0.01) during the day (07.30-16.30 h) with an acrophase between 09.00 h and 13.00 h. The distribution of plasma T levels was skewed (P < 0.05) and could be divided into basal values < 26 nmol/l and peaks > 26 nmol/l. Testosterone in testicular tissue and testis veins also varied during the day and was lower (P < 0.02) between 14.30 h and 16.30 h than from 11.30-13.30 h. It was shown that plasma T may differ significantly (P < 0.02) between groups (n = 6-7) of untreated rats bled under identical conditions and it is suggested that gonadotrophin stimulation be included in experimental designs to reduce the difficulty of differentiating between normal variability and treatment effects.

Animals↗