Biomedical subjects
R Peckham
Publications and source records attributed to R Peckham.
The effect of essential fatty acid deficiency on the stimulation of intestinal calcium transport by 1,25-dihydroxyvitamin D3.
The effect of altering the lipid composition of the brush-border membrane on the ability of 1,25-dihydroxyvitamin D3 (1,25-(OH)2D3) to stimulate calcium transport across the intestinal mucosa was examined by raising chicks on a vitamin D, essential fatty acid-deficient diet (-DEFAD) and measuring calcium absorption from duodenal sacs in situ and calcium uptake into brush-border membrane vesicles in vitro. Administration of 1,25-(OH)2D3 to -DEFAD and to -D control chicks led to the same increase in calcium transport in situ, whereas calcium transport in isolated brush-border membrane vesicles was not stimulated in the EFAD group, but responded normally in the control group. When the incubation temperature was increased to 34 degrees C, brush-border membrane vesicles from 1,25-(OH)2D3-treated essential fatty acid-deficient (+DE-FAD) chicks accumulated calcium at a faster rate than did vesicles from -DEFAD chicks. There was a marked decrease in the linoleic acid content and an increase in the oleic acid content of both the total lipid extract of the brush-border membrane as well as the phosphatidylcholine and phosphatidylethanolamine fractions, which could explain the temperature sensitivity of the in vitro system. When the diet of the EFAD chicks was supplemented with linoleic acid, the rate of calcium uptake into subsequently isolated vesicles from +DE-FAD chicks correlated with the amount of linoleic acid in the brush-border membranes. These results support the concept that the action of 1,25-(OH)2D3 on membrane lipid turnover and structure plays a critically important role in the 1,25-(OH)2D3-mediated cellular transport responses.
Pituitary-adrenocortical function in chronic renal failure: blunted suppression and early escape of plasma cortisol levels after intravenous dexamethasone.
The response to iv dexamehasone was studied in patients with chronic renal failure in whom resistance to suppression of plasma cortisol levels after oral steroid had been reported previously. One milligram of dexamethasone was given iv at 2300 h, and plasma cortisol levels were measured every 20 min between 0500-1000h in patients with renal failure, normal controls, and patients with pituitary-dependent Cushing's syndrome. Normal subjects showed a decrease in mean plasma cortisol levels to less than 3 micrograms/dl; patients with Cushing's syndrome showed no suppression of cortisol secretory activity during the sampling period. In renal failure patients, morning cortisol levels fell to values lower than those achieved when the 1-mg dose was given orally or when the steroid was not given, but did not suppress to the levels seen in normals. Early resumption of cortisol secretion occurred in four of five renal failure patients during the 6-11 h after dexamethasone administration. These studies show that iv dexamethasone is more effective than the oral steroid in suppressing pituitary-adrenocortical activity in renal failure patients. However, the incomplete suppression and early resumption of cortisol secretion which are present in chronic renal failure patients even after iv dexamethasone support the suggestion that they have disordered feedback control of the hypothalamic-pituitary-adrenocortical axis.
Four new approaches to the ghetto client.
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