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Biomedical subjects

P C Gregory

Publications and source records attributed to P C Gregory.

34 records · Page 2Linked to original sources
PubMed1985

Control of stomach motility in the llama (Lama guanacoe f. glama).

Manometric and electromyographic recordings of stomach motility were made in five conscious llamas to investigate the influence of distension of the stomach compartments, of temporary cervical vagal blockade and the influence of atropine, acetylcholine and adrenaline. The frequency of A-contractions was slowed by distension of the canal joining compartment 2 (C2) and compartment 3 (C3), or of the proximal region of C3, and either increased and/or reduced by distension of the distal region of C3 or the hind stomach. The number of B-contractions in a cycle was increased according to the degree of distension of the cranial sac of compartment 1 (C1). B-contractions were also induced by distension of the canal or proximal region of C3 and were inhibited by distension of the distal region of C3 or the hind stomach. Contractions of C3 were not influenced by distension of C1 or C2 but were inhibited by distension of the canal, while distension within C3 caused a local excitation and an inhibition both proximal and distal to the point of stimulation. The hind stomach was only affected by local stimuli. Temporary vagal blockade abolished all contractions of C1, C2, and the canal and C3, but had little effect on the motility of the hind stomach. Infusion of atropine (0.01 mg/kg), acetylcholine (7-33 micrograms/kg . min) and adrenaline (0.3 micrograms/kg . min) inhibited motility in all stomach compartments except the hind stomach where acetylcholine was stimulatory. It is concluded that while the hind stomach may have intrinsic motility, the contractions of C1, C2, the canal and C3 of the llama stomach are dependent upon a vagal motor nerve supply and that the pattern of contractions observed is regulated at least partially according to the individual degree of distension of each of the stomach compartments.

Acetylcholine↗
PubMed1984

Control of intrinsic reticulo-ruminal motility in the vagotomized sheep.

The intrinsic motility of the reticulo-rumen was studied by electromyography in nineteen sheep subjected to bilateral thoracic vagotomy and maintained by intragastric infusion of a complete liquid diet. The influences of distension, temperature and tactile and chemical stimuli on the intrinsic reticulo-ruminal motility were investigated. The level of electrical discharge in the reticulum and rumen in the first 3 days after vagotomy was increased progressively with distension without giving rise to the large group discharges characteristic of the long-term vagotomized sheep, and was reduced by atropine (0.1-1 mg kg-1) but not by hexamethonium (2 mg kg-1). In the long-term vagotomized animals, the frequency of the large group discharges over the reticulo-rumen varied with the degree of reticulo-ruminal distension. The discharges were absent below a threshold rumen volume; above the threshold they increased progressively with volume until a maximal rate of six to seven regular discharges per minute was established at large ruminal volumes. The discharges were abolished by atropine (0.1-1 mg kg-1) or hexamethonium (2 mg kg-1). With the rumen volume below the threshold, in all areas of the reticulo-rumen localized distension stimulated local discharge only and did not induce large group discharge. Replacement of rumen contents with an equal volume of 0.2 M-acetic, -propionic or -butyric acid buffered to pH 4.0 rapidly abolished the large group discharges over the entire reticulo-rumen. Replacement of rumen contents by an equal volume of 0.9% NaCl at 30 degrees C immediately abolished the large group discharges; at temperatures between 35 and 43 degrees C this had no effect. Gentle tactile stimulation increased local discharge in the reticulum and cranial dorsal sac but not in other areas of the rumen and did not affect large group discharge in any region. It is concluded that the intrinsic reticulo-ruminal motility of chronically vagotomized sheep is principally regulated by the degree of reticulo-ruminal distension. Like the C.N.S.-controlled motility of the vagus-intact sheep it is inhibited by high concentrations of volatile fatty acids. Local control mechanisms therefore may interact with central control in the over-all regulation of motility in vagus-intact sheep.

Animals↗
PubMed1984

Initiation of migrating myoelectric complex in sheep by duodenal acidification and hyperosmolarity: role of vagus nerves.

Gastrointestinal motility was studied in conscious sheep by X-radiography and by electromyography from chronically implanted electrodes before and after total thoracic vagotomy. Duodenal infusion of 0.5-3 mmol HCl (0.035-0.1 M-HCl) induced premature duodenal regular spiking activity (r.s.a.) within 1-7 min in fifteen of seventeen sheep studied when infused at 20 min after a natural r.s.a. There was no correlation between abomasal pH and any phase of the migrating myoelectric complex (m.m.c.). Duodenal alkalinization by infusion of 0.3 M-Tris buffer (pH 10.2) or 0.1 M-NaHCO3 had no influence on the occurrence of the m.m.c. Duodenal infusion of 20-50 ml 0.5 M-NaCl induced a premature duodenal r.s.a. within 1-5 min in seven of eight sheep. Vagotomy did not prevent the initiation or migration of the m.m.c., but reduced the rate of propagation of the r.s.a. from 40.5 +/- 7.2 (mean +/- S.E. of mean) to 16.7 +/- 0.1 cm/min in the duodenum, from 27.3 +/- 4.1 to 16.6 +/- 0.8 cm/min in the jejunum, and from 21.4 +/- 1.1 to 13.7 +/- 0.7 cm/min in the proximal ileum. Initially the frequency of r.s.a. increased, especially in the duodenum where they recurred at an interval of 98.4 +/- 6.8 min before vagotomy; and at 23.4 +/- 1.8 min in the first 24 h after vagotomy; the interval had lengthened to 86.7 +/- 5.2 min 2-3 weeks after vagotomy. Premature duodenal r.s.a. was not induced by duodenal infusion of HCl in five, or by duodenal infusion of hyperosmolar NaCl in three chronically vagotomized sheep. It is concluded that the vagus nerves contribute to the regulation of the frequency and propagation of the m.m.c. in sheep; duodenal acidification is not essential nor is it the normal stimulus for initiation of r.s.a., but duodenal infusion of HCl or hyperosmolar NaCl can initiate a premature duodenal r.s.a. via the vagus nerves.

Abomasum↗
PubMed1982

Forestomach motility in the chronically vagotomized sheep.

1. The motility of the reticulo-rumen and omasum in conscious sheep was studied by electromyography from chronically implanted nichrome wire electrodes. The sheep were subjected to vagotomy and were maintained totally by intragastric infusion of liquid nutrients before and after vagotomy. Before vagotomy the motility of the forestomach was essentially similar to that seen in roughage-fed sheep.2. Bilateral thoracic vagotomy transiently abolished all electrical activity of the reticulo-rumen and omasum, but within 1 day some activity returned. Frequent periods of rhythmic local small group discharges were seen over the reticulo-rumen, while the omasum showed prolonged (1-5 min) bursts of mainly slow wave activity.3. Within 1-2 weeks of vagotomy strong contractions of the reticulo-rumen were visible by radiography. Electromyographically, they comprised a rhythmic series of some two to five large group discharges recurring approximately once a minute. Each series of activity was separated from the next by a short period of quiescence. The discharges occurred almost simultaneously over the whole reticulo-rumen and so contrasted with the progressive forward or backward spread of activity seen in the intact animal. The bursts of activity in the omasum, lasting 0.5-2 min, were not co-ordinated with the activity of the reticulo-rumen as they are in the intact animal.4. The activity in the reticulo-rumen and omasum was not affected by bilateral section of the splanchnic nerves and removal of the coeliaco-mesenteric ganglia. Reticulo-rumen but not omasal activity was abolished by atropine (0.1 mg/kg) or hexamethonium (2 mg/kg), while both were stimulated by pentagastrin (3 mug/kg).5. Following vagotomy reticulo-rumen motility was no longer influenced by feeding, or by tactile stimulation of the buccal cavity or oesophagus. Severe distension of the abomasum caused a slight acceleration of the motility rhythm compared to the inhibition seen before vagotomy.6. It is concluded that the reticulo-rumen motility observed after vagotomy is an intrinsic cholinergic motility which is dependent upon the activity of the myenteric plexus. The motility of the omasum after vagotomy is similar to that seen in the intact animal and differs from that of the rumen in that it appears not to depend wholly upon cholinergic control.

Animals↗
PubMed1980

Adenosine response on pial arteries, influence of CO2 and blood pressure.

The television image-splitting technique was used to study the influence of arterial pCO2 and blood pressure on the dilatatory response of pial arterioles to topically applied adenosine in chloralose anaesthetised cats. At normocapnia (pCO2 congruent to 35 mm Hg) 10(-5) adenosine caused pial arteriole dilatation of 29.2 +/- 2.7% (S.E.M.). This was significantly reduced to 14.5 +/- 1.6% (P < 0.001) at pCO2 25 mm Hg and to 8.5 +/- 1.6% (P Ø 0.001) at pCO2 48 mm Hg. Lowering the blood pressure to 65--85 mm Hg had no significant effect on the adenosine response, but raising the blood pressure to 140--160 mm Hg significantly reduced the adenosine response to 22.1 +/- 1.8% (P < 0.005). The response was independent of vessel size except at hypertension where vessels < 150 micrometer were significantly more reactive than the larger vessels (P < 0.01). These results indicate that adenosine induced vasodilatation of pial arterioles shows little change in the face of alterations in vessel tone induced by altering blood pressure, but is markedly decreased by the combination of changing perivascular pH and vascular resistance through moderate changes in arterial pCO2. The importance of these results in assessing the role of adenosine as a cerebral vasodilator is discussed.

Adenosine↗
PubMed1980

The response of feline spinal pial arterioles to norepinephrine.

The effect of norepinephrine on the diameter of feline spinal pial arteries and arterioles was studied by microapplication of the drug to the perivascular environment. Vascular diameter was determined by the television image-splitting method. Application of norepinephrine over the range of 5 x 10(-8) M to 5 x 10(-3) M to spinal pial arterioles resulted in constriction of the vessels. The dose-response curve showed a tendency to plateau at concentrations above 5 x 10(-5) M, with a maximal constriction of 28.8 +/- 5.1% at 5 x 10(-3) M. The reduction in vessel diameter to microapplication of norepinephrine was prevented with the inclusion of an equimolar concentration of the alpha-adrenergic blocker, phentolamine, in the injectate. The data indicate the presence of alpha-adrenergic receptors on the smooth muscle of spinal pial arterioles, and it is suggested that the arguments pertaining to the sympathetic control of blood flow in the brain apply also to the spinal cord.

Animals↗
PubMedDate not supplied

A system for adaptive transportation.

In our society, we take for granted the ability to travel with few restrictions. For most travelers, the major factor that limits travel is cost. However, for a significant number of Americans, the phrase "freedom to travel" is meaningless. These are the physically handicapped, a group with special needs that has long been denied what every American assumes to be a natural right.

Automobiles↗
PubMedDate not supplied

A new, improved flotation device for deep-water exercise.

The purpose of this study was to determine the position and size of flotation devices that permit deep-water exercise with the exerciser's thoracolumbar spine in a vertical position and without restriction of movement of the arms and legs. The buoyant force of the flotation device had to be at least 94.0 N to allow the exerciser to be suspended in water with the head above water. The position of the flotation devices had considerable influence on the thoracolumbar angle. When the large pad with a buoyant force of 55.0 N covered the lower abdominal wall and the small pad with a buoyant force at 39.0 N was located over the lower back, the exerciser's thoracolumbar spine assumed an almost vertical position. Anterior placement of the flotation devices resulted in marked extension of the thoracolumbar spine. Conversely, posterior placement of the buoyant devices resulted in flexion of the thoracolumbar spine. On the basis of these results, an ideal flotation device for deep-water exercise can now be developed.

Anthropometry↗
PubMedDate not supplied

Effects of hemorrhagic hypotension on the cerebral circulation. II. Electrocortical function.

The effects of graded hemorrhagic hypotension on electrocortical function was investigated in 12 cats anesthetized with alpha-chloralose. Cerebral function was assessed both in terms of spontaneous activity (EEG) and the somatosensory evoked response. No significant changes in the EEG trace or in the amplitude of the positive/negative waves of the primary evoked response were observed at mean arterial pressures of between 120 mm Hg and 40 mm Hg. At levels of systemic arterial pressure of less than 40 mm Hg cortical rhythms became slower as pressure was decreased and an isoelectric EEG was recorded in the pressure range 10--30 mm Hg. The earliest sign of any change in the amplitude of the primary evoked responses was observed at arterial pressures of approximately 35--40 mm Hg. Below this value the amplitude decreased with decreasing systemic pressure and became zero in the pressure range 15--25 mm Hg.

Animals↗