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Biomedical subjects

J L Robinson

Publications and source records attributed to J L Robinson.

At least 127 records · Page 7Linked to original sources
PubMed1976

Evidence of a novel role for monovalent cations in pyruvate kinase catalysis.

In the pyruvate kinase (EC 2.7.1.40) reaction, the complete enzyme-products complex consists of enzyme, pyruvate, ATP, a divalent cation, and a monovalent cation, usually K+. The dissociation of this complex can be slow permitting reversible enolization of pyruvate in this complex during the course of the forward reaction. High concentrations of each component in the enzyme-products complex inhibits the forward reaction, but only elevated concentrations of the monovalent cation decrease the net rate of product dissociation relative to that of pyruvate enolization. This result indicates that the monovalent cation can be the first component released from the enzyme-products complex and that the presence of an inhibiting monovalent cation concentration leads to re-formation of the complete complex, which is necessary for pyruvate enolization. The evidence suggests that the monovalent cation can bind and release with each turnover of the enzyme. While the data do not permit the conclusion that first release of monovalent cation is the exclusive pathway for dissociation of the enzyme-products complex, no other component once released can reassociate rapidly enough to form a complete complex during the forward reaction. Inhibition by these components must be attributed to the formation of abortive complexes.

Adenosine Triphosphate↗
PubMed1975

Carotid baroceptor re-setting in the hypertensive dog.

1. The behaviour of forty-four single carotid baroreceptor fibres from nine dogs with normal blood pressure was contrasted with that of forty-seven single fibres from nine dogs with renal (nephrectomy--clip) hypertension. 2. It was found that in response to a square-wave pressure step, the mean steady-state threshold pressure was 99.23 mmHg for the normotensive dogs and 129.13 mmHg for the hypertensive dogs. 3. The degree of re-setting appeared to correlate with the duration of the hypertension but was not seen until an animal had been hypertensive for more than 4 days. 4. In one animal, hypertensive for 7 weeks but whose blood pressure returned towards normal after removal of the clip, the receptor characteristics was normal. 5. No change in the gain of the receptor sensitivity was seen. 6. Light-microscopy and electron miscroscopy of the opposite (non-perfused) carotid sinus revealed no differences in the fibre morphology or density between the hypertensive and normotensive animals (a random sampling, four normal and six hypertensive).

Animals↗
PubMed1975

Enhanced carotid sinus baroreflex responses in dogs with chronic A-V block.

Effects of carotid sinus pressure on arterial pressure, atrial rate, and ventricular rate were examined in anesthetized normal dogs and in dogs with chronic complete A-V block. Change in arterial pressure per mmHg change in sinus pressure was 0.8 plus or minus 0.2 mmHg for controls but increased (P is less than 0.001) to 1.6 plus or minus 0.1 mmHg in A-V blocked dogs. Arterial pressure was 140-145 mmHg at low sinus pressure in both groups, but at high sinus pressure arterial pressure was significantly lower in A-V blocked dogs (44 plus or minus 4 mmHg) than in controls (92 plus or minus 8 mmHg). These differences were virtually abolished after vagotomy. Heart rate increased in normal dogs as sinus pressure was increased before vagotomy, but decreased after vagotomy. In blocked dogs atrial and ventricular rates decreased at high sinus pressure either before or after vagotomy. The results show that reflex circulatory responses to changes in carotid sinus pressure are enhanced in dogs with A-V block. This enhancement may involve attenuation of buffering influences exerted from other baroreceptors whose afferents are in the vagus nerves.

Animals↗
PubMed1975

The action of clonidine on the baroreflex control of heart rate in conscious animals and man, and on single aortic baroreceptor discharge in the rabbit.

Changes in mean arterial pressure (M.A.P.) have been produced in conscious rabbits by inflation of balloon cuffs previously implanted round the inferior vena cave and aorta; Sigmoid stimulus/response curves (M.A.P./Heart Period, H.P.) were constructed. Clonidine caused a striking dose dependent increase in gain of the reflex arc in both normal rabbits and rabbits with renal hypertension. The largest effect was upon vagal motorneurones but a similar but smaller effect was present in vagotomised animals. Similar changes in the baro-reflex arc were produced by injection of very much smaller doses of clonidine into the lateral cerebral ventricle. Recordings made from single aortic baroreceptor fibres in anaesthetised rabbits showed again a dose dependeent sensitisation. These results suggest that the bradycardia caused by clonidine is largely mediated via an action in the brain on the baroreflex arc, with an additional action on the baroreceptors themselves. Preliminary results in normal man show a similar increase in the gain of this reflex after intravenous clonidine (150 mug).

Animals↗
PubMed1974

Anion effects on pyruvate kinase.

Rabbit muscle pyruvate kinase is shown not to be activated by several anions (acetate, chloride, lactate, nitrate and sulphate) when tested as their tetramethylammonium salts. This contradicts the conclusions of Focant & Watts (1973).

Acetates↗
PubMed1974

Bipolar diathermy.

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Electrocoagulation↗
PubMed1972

Operative treatment of aneurysms and Coanda effect: a working hypothesis.

The Coanda effect has been known to mechanical engineers for many decades. Consideration of this effect both by a neurosurgeon and a mechanical engineer revealed that it might be of importance during the operative treatment of intracranial aneurysms. If a jet effect were produced in the stream of blood after clipping an aneurysm, most of the flow of blood might be directed down only one limb of a bifurcation occurring in a vessel near to a clipped aneurysm. Blood might also be entrained from the other limb of the bifurcation. This boundary wall effect, which can occur without the rate of flow through the vessel being altered appreciably, could explain some of the unfortunate sequelae of aneurysm surgery which occur in the absence of any obvious cause such as postoperative thrombosis, etc. A possible mechanism for some of the complications after gradual occlusion of the common carotid artery in the neck is also proposed on this basis. Other details of how this data might be of clinical significance, together with suggestions for how to avoid fluidic effects during aneurysm surgery, are presented.

Basilar Artery↗