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Biomedical subjects

R C Clark

Publications and source records attributed to R C Clark.

35 records · Page 2Linked to original sources
PubMed1985

The primary structure of avian phosvitins. Contributions through the Edman degradation of methylmercaptovitins prepared from the constituent phosphoproteins.

Methylmercaptovitins were prepared from the constituent phosvitin phosphoproteins as well as from the CNBr cleavage peptides derived from the methionine-containing phosphoproteins. Edman degradation of these methylmercaptovitins has afforded partial sequence information and identifies the serine phosphorylation sites in the phosphoprotein. Primary structure, determined for approximately seventy-seven residues from the amino terminus of the hen methionine-containing phosphoprotein, agrees fully with that deduced from recently published nucleotide sequence data, and provides corrections to results of earlier work on enzymatically dephosphorylated samples. Partial sequence data, together with corrections to earlier results, are also provided for phosphoproteins from duck and turkey phosvitins, as well as for the methionine-free phosphoprotein from hen phosvitin. All phosphoproteins have N-terminal leader sequences of low serine content. Sequences of the methionine-containing group are homologous, as are the sequences of the methionine-free group, but the groups differ significantly from one another. Unphosphorylated sites appear to have a fractional distribution over all available serine residues.

Amino Acid Sequence↗
PubMed1980

Does the nonprofit form fit the hospital industry?

Nonprofit hospitals currently enjoy favored legal status. In this Article, Professor Clark critically examines the basis for such preferential treatment. He begins by identifying endemic problems in the health care industry and then explores the relationship between nonprofit hospitals and these problems. He finds that the evidence does not persuasively establish that nonprofit hospitals serve as fiduciaries rather than exploiters, and that nonprofits engage in much involuntary cross-subsidization of medical services. He concludes that the legal favoritism for the nonprofit form is based not on sound reasoning and hard data but on intuition. Professor Clari proposes that the legal rules affecting nonprofit hospitals reflect this reality by treating both nonprofits and for-profits neutrally, by controlling cross-subsidization, and by strengthening consumers' information about and control over health care decisionmaking.

Community Participation↗
PubMed1976

The effect of vasopressin upon the excretion of calcium by the sheep.

Vasopressin (140 muU/min) was infused intravenously into 12 conscious merino ewes for 2 hr. Urine flow rate and free water clearance were consistently reduced. There was no effect upon renal plasma flow, glomerular filtration rate or the rate of excretion of sodium, potassium, magnesium, chloride or phosphate. Although all animals received 75 mmol calcium chloride into the rumen on the previous day, five commenced the experiment with calcium excretion rates of less than 1 mumol/min. In these, vasopressin further decreased calcium excretion. In seven animals with calcium excretion rates between 2 and 20 mumol/min vasopressin had no effect upon either total calcium or free ionized calcium excretion rate.

Animals↗
PubMed1975

The acute effects of intravenous infusion of parathyroid hormone on urine, plasma and saliva in the sheep.

Following an intravenous loading injection of 75 U.S.P. Units of Para-Thor-Mone (Eli Lilly and Co), seven conscious, non-pregnant, non-lactating Merino ewes were infused with a maintenance dose of the hormone at a rate of 4-75 U.S.P. units/min for 2 hr. The classical hypercalcaemia and hypophosphataemia of the non-ruminant was observed, but the hypercalcaemi- was only small. Plasma potassium concentration decreases, while there were no changes in plasma sodium, chloride or mangesium. The classical phosphaturic effect of the hormone was not observed, only trace amounts of phosphate being exreted throughout the experiment. Urinary excretion of calcium and magnesium decreased, urine flow and urinary excretion of sodium, potassium, chloride, bicarbonate and urine pH increased. Glomerular filtration rate was unaffected, but renal plasma flow increased. The concentration and secretion rate of salivary phosphate increased markedly. Changes in the other important salivary electrolytes (sodium, potassium, chloride, bicarbonate and hydrogen ion) also occurred, but it was difficult to separate primary from secondary effects of the hormone. Saliva flow rate increased transiently following hormone injection, but the effect was not sustained by the maintenance infusion.

Animals↗
PubMed1975

The effect of potassium chloride infusion of parotid salivary flow and composition in conscious sheep.

The composition and flow of parotid saliva in conscious sheep was measured before, during and after the intravenous infusion of 0-43 M-KCl or 0-43 M-NaCl at 2 ml./min for 2 hr. The salivary flow rate was depressed during the infusion of potassium chloride into both intact sheep and adrenalectomized sheep. As the salivary flow was unchanged by sodium chloride infusion it was concluded that the potassium ion was responsible for the decrease in flow and that this effect was not mediated through any of the adrenal hormones. The highly significant negative correlation between plasma potassium concentration and salivary flow throughout all potassium infusions indicated that the extent to which the salivary flow was depressed varied with the degree of hyperkalaemia. Except for situations where mineralocorticoid levels were likely to be elevated the concentrations of sodium and potassium in the saliva were positively correlated with the plasma concentrations of these ions. The salivary bicarbonate concentration of the saliva was negatively related to flow. The chloride concentration of the saliva was negatively correlated with salivary flow during all potassium chloride infusions.

Adrenalectomy↗
PubMed1975

Changes in renal haemodynamics and electrolyte excretion during acute hyperkalemia in conscious adrenalectomized sheep.

The p-aminohippurate (PAH) clearance, inulin clearance and the excretion of electrolytes by 10 adrenalectomized sheep were measured before, during and after the infusion of 0-43 M-KCl at 2 ml./min for 2 hr. The PAH clearance increased as the plasma potassium concentration increased up to approximately 6-0 m-mole/l. Further increases in plasma potassium were associated with a progressive return of the PAH clearance to or below the pre-infusion levels. At its maximum the PAH clearance was 1-228 +/- 0-032 (S.E. of mean) times the pre-infusion levels. The inulin clearance increased to reach a mazimum coincident with or subsequent to the maximum PAH clearance. The maximum level of inulin clearance during the hyperkalaemia was 1-158 +/- 0-020 times the pre-infusion clearance. The increments in the clearance of potassium and of bicarbonate rose rapidly to exceed the increment in inulin clearance during the hyperkalaemia in all experiments. The increments in the clearance of sodium and of chloride exceeded the increment in inulin clearance in more than half the experiments. It was concluded that although hyperkalaemia was associated with increased glomerular filtration much of the increased excretion of sodium, chloride and bicarbonate was derived from depressed tubular reabsorption of the ions. When the infusion experiments were repeated on the same animals the sheep demonstrated an improved ability to control the rise in plasma potassium concentration which was similar to potassium adaptation described in other species. There were no apparent differences between sheep maintained on 1-5 mg and 5 mg deoxycorticosterone acetate daily in their adaptation to potassium loading and the effect was tentatively attributed to the level of steroid maintenance being chronically high. The toxicity of hyperkalaemia was not lessened by this adaptation to potassium loading.

Adrenalectomy↗
PubMed1975

The composition and flow of parotid saliva during acute hyperkalaemia in sodium-deficient sheep.

Sheep were infused intravenously with 0-43 M-KCl at 2 ml/min for 2 hr while they were either sodium-replete or sodium-deficient after the unilateral loss of parotid saliva for 18 hr or 3 days. Salivary flow was depressed during potassium infusion and the flow rates observed at maximum hyperkalaemia were similar in all three states of sodium balance despite the large differences in flow rate before potassium infusion. The fall in salivary Na/K ratio during potassium administration was diphasic, the initial decline being slow and followed by a more rapid fall in the ratio. The duration of the initial period of slow decline in this ratio ranged from 75-105 min, 45-60 min, and about 15 min in the sodium-replete, mildly sodium-deficient and severely sodium-deficient states respectively. The decline in salivary flow during sodium depletion was associated with decreasing salivary bicarbonate concentration and increasing salivary phosphate and hydrogen ion concentrations with the concentration of chloride showing no consistent trend. During acute hyperkalaemia the chloride and phosphate concentrations were negatively correlated with salivary flow, the bicarbonate concentration was positively correlated with flow and the hydrogen ion concentration was unaltered. The sodium concentration of the saliva showed a statistically significant correlation with flow only when the sheep were severely sodium-deficient.

Animals↗
PubMed1970

The isolation and compsotion of two phosphoproteins from hen's egg.

1. Phosvitin extracted from domestic hen's-egg yolk was resolved on Sephadex G-100 into two phosphoprotein components. 2. The major component has a molecular weight of about 3.4x10(4) and alanine as an N-terminal residue. Glucosamine is present, but tyrosine is virtually absent. 3. The minor component has a molecular weight of about 2.8x10(4) and lysine as an N-terminal residue. Missing residues are glucosamine, methionine and leucine. Lysine, histidine, threonine, glycine, phenylalanine and tyrosine contents differ significantly from those of the major component. 4. Sephadex G-100 also removes small amounts of an impurity with a much higher molecular weight.

Alanine↗