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Biomedical subjects

R M Clark

Publications and source records attributed to R M Clark.

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

Evidence for both luminal and systemic factors in the control of rat intestinal epithelial replacement.

1. Isolation of a self-emptying sac of rat small intestine in vivo halved the cell production rate in the crypts of Lieberkühn as measured by colchicine blockade. 2. Starvation for 48 h of rats with isolated intestinal sacs caused a further halving of cell production rate in the sac. 3. Infusion of distilled water into isolated intestinal sacs for 72 h caused a similar degree of stimulation of cell production in sacs in fed and starved rats, suggesting that the fall in cell production rate on starving a rat bearing an isolated sac is not due to t-e non-availability of the substances required for cell synthesis. 4. The possible contribution of innervation of the gut, and of systemic hormonal influences, on intestinal epithelial replacement is discussed.

Animals↗
PubMed1976

The release of endogenous amino acids from the rat visual cortex.

The release of endogenous taurine, GABA, glycine, aspartate, glutamate, glutamine and alanine from the rat visual cortex was measured using a cortical cup technique. The electrocorticogram (ECoG) was monitored throughout most experiments. 2. Spreading depression, evoked by the dropwise placement of 10% KCl solution on to the brain outside the cup was associated with a significant increase in the release of GABA and glutamine but a marked fall in that of glutamate. The evoked release of GABA and glutamate but not of glutamine was Ca2+ dependent. 3. A solution containing 50 mM-K+ placed within the cup elicited a significant increase in the release of taurine and GABA, whereas 100 mM-K+ additionally released aspartate and glutamate. The K+-evoked release of these amino acids with the exceptions of taurine and glutamine was Ca2+-dependent. 4. Three series of experiments were carried out in which the preparations were stimulated electrically. Bipolar stimulation (100 Hz, 1 msec pulse width, 2-5 mA for 5 min) with the electrode within the cup was followed by significant increases in taurine, GABA and glutamate release; using a 5 mA current, there was an additional release of aspartate and alanine. Only the evoked release of GABA and glutamate was Ca2+ dependent. 5. In the second and third series of experiments, the electrode was sited adjacent to the cup or on the contralateral cortex respectively. Following stimulation (100 Hz, 1 msec pulse width, 2-5 mA for 5 min) there was a significant increase in taurine and GABA release and a significant fall in the release of aspartate and glutamate. With the exception of taurine, these changes in release were Ca2+ dependent. Reducing the stimulus current to 1-5 mA or the period of stimulation to 2-5 min initiated similar but statistically insignificant changes in release. A range (10-100 Hz) of stimulation frequencies was examined: the evoked release of GABA was linearly related to frequency whereas that of taurine was frequency-independent. The fall in aspartate and glutamate release was maximal at a frequency of about 50 Hz. 6. The results are discussed in relation to (a) the possible sites of release of the amino acids and (b) the proposed neurotransmitter roles of the physiologically active amino acids.

Alanine↗
PubMed1976

Optimum amino acid complement for protein synthesis by rat mammary cells in tissue culture.

The amino acid requirement of rat mammary cells for milk protein synthesis was investigated in dispersed cell culture. A three-dimensional central composite design utilizing three variables (X1 = lysine; X2= methionine, valine, and arginine; X3 = isoleucine, tryptophan, threonine, phenylalanine, and histidine) at five concentrations each, was duplicated twice with mammary cells from lactating Sprague-Dawley rats. The optimum combination of amino acids for maximum milk protein synthesis from multiple regression models was X1 15.0-, X2 4.5-, and X3 1.5-fold their quantities in Eagle's minimal essential medium with leucine, tyrosine, cystine, and glutamine at the base 1-fold in the medium.

Amino Acids↗
PubMed1975

Method for measuring brain tissue pressure. Response to alteration in pCO-2 systemic blood pressure, and middle cerebral artery occlusion.

The authors report a method for measuring total local brain tissue pressure (BTP) using a miniature catheter transducer stereotaxically introduced into the white matter of the cat's cerebrum. Quantitative rapid phasic pressure changes were satisfactorily demonstrated. Due to some drift of baseline of the transducers and inability to perform in vivo calibration, reliable long-term quantitative pressure measurements sometimes could not be studied. The BTP from each cerebral hemisphere and the cisternal pressure (CP) were monitored during alterations of pCO-2 and systemic blood pressure, and distilled H20 injection prior to and after right middle cerebral artery (MCA) ligation. The catheter transducers functioned well on chronic implantation for up to 6 weeks. Compared to the chronically implanted catheters, acutely implanted catheters responded identically except for drift. The response of intracranial pressure and CP to MCA occlusion, alterations in pCO2, and systemic blood pressure were similar. No BTP gradients appeared in response to MCA ligation, hypercapnia, hypertension, or progressive swelling of the resulting infarction.

Animals↗
PubMed1973

An approach to the detection and management of early breast cancer.

The mortality rate for breast cancer has not changed for 40 years. The ultimate results using the various surgical techniques differ very little. Local tumour excision produces survival rates comparable with those for more radical operations. Ideal treatment should give optimal quality and quantity of survival with minimal trauma. Survival is mainly determined by the ability to live in symbiosis with the disease and in most cases clinically obvious tumours are already incurable. Clinical examination alone will not detect disease at a stage early enough for more effective treatment. Mammography and thermography can detect occult breast cancer and, in particular, thermography can be used for serial examinations in high-risk patients because the procedure is simple and without hazard.

Adenocarcinoma↗
PubMed1970

Microdiverticula and submucosal epithelial elements in ulcerative and granulomatous diseases of the ileum and colon.

A case of granulomatous ileocolitis which also showed features of ulcerative colitis, and in which lesions were believed to be due to inflammation of previously undescribed structures, microdiverticula, was reported previously. Subsequently, sections of the segments of bowel received from 17 cases of regional enteritis and 16 cases of ulcerative colitis were re-examined for the presence of similar microdiverticula and submucosal epithelial elements. The same structures were present in five cases of regional enteritis and in 14 of ulcerative colitis. A granulomatous type of inflammatory response was found in the bowel and lymph nodes in 14 of the 17 cases of regional enteritis, and in none of the cases labelled ulcerative colitis. In spite of this, difficulty was experienced in placing some cases in one or other diagnostic category. This re-emphasizes the possibility that the two conditions may not be etiologically discrete, and that both may be, in fact, related to the presence of microdiverticula. In addition, it may be that colitis cystica profunda is a result of microdiverticulosis in which the submucosal glandular structures attain unusually large proportions.

Adult↗
PubMed1968

Elastofibroma.

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Adult↗