peritoneal fluid makes a reduction of phosphate dietary Phosphate metabolism in chronic renal failure intake impractical, the protein content of the diet being strictly linked to that of phosphate. Even though hypophosphataemia has been reportedWeekly phosphate removal in CAPD has been occasionally in chronic renal failure patients on dialysis reported to be ~70 mmol, with 4×2 l exchanges per treatment [1,2], phosphate (Pi) retention, often associday [12]. This value is quite similar to that found in ated with increased serum Pi, is the most common 35 of our CAPD patients (65.5±40.6 mmol/week), finding in this clinical setting. Pi retention is secondary and is ~20 mmol per week less than in haemodialysis to reduced or null renal excretion, and dialysis removal (HD) (84.3±19.1 mmol/week). However, in our is often, but not always, insufficient as compared with CAPD patients, urinary excretion (48.8±21.4) suba variably reduced intestinal absorption of Pi [3][4][5].stantially contributes to Pi balance, representing ~40% The main metabolic consequences of phosphate of the total Pi removed, while in most HD patients retention have been related to: (i) a possible direct [6 ] this route of Pi excretion is negligible. We found that and indirect (mediated by calcium and calcitriol reducurinary Pi excretion was linearly related to glomerular tion) [7,8] stimulation of parathyroid hormone; (ii) a filtration rate (GFR) values, evaluated as the mean direct involvement in extraosseous calcifications [9]; of creatinine and urea clearances in our CAPD and (iii) a detrimental effect on renal function [10], that can still be maintained at a significant level in patients (uPi mmol/day=−1.11+1.39×GFR; r=0.91, continuous ambulatory peritoneal dialysis (CAPD) P<0.001), stressing the importance of the preservation patients.of residual renal function in maintaining a good Before addressing the problem of Pi removal by metabolic balance in CAPD. dialysis treatment, it might be useful to recall some When we considered the factors affecting the dialytic points on Pi body distribution. Of the more than 650 g removal of phosphate in our CAPD patients by means of Pi contained in a medium-sized man, ~85% is of a multiple regression analysis ( Table 1), we found contained in bone, 14% in the cells and only 1% or that plasma Pi concentration plays the main role. less is in the plasma. It is also important to bear in Another important factor is represented by the glucose mind that the bulk of intracellular Pi is represented by concentration in the dialysate, and its influence on organic phosphate (nucleoside phosphate compounds, Pi removal was independent of ultrafiltration rate. phosphorylated enzymes, 2,3-diphosphoglycerate, pho-Finally, Pi removal by peritoneal dialysis was greatly sphocreatine, etc.) at 10-100 times the concentration affected by dialysate volume, with a calculated removal of inorganic phosphate with which it is in equilibrium. of ~95 mmol/week at a dialysate volume of 12 l per The inorganic intracellular phosphate is in turn...
The aim of the present study was to evaluate the changes in the diurnal rhythm of the hypothalamic β-endorphin (β-EP) contents in female rats as a function of circulating estrogens. With this purpose we evaluated the diurnal hypothalamic β-EP changes (1) during the estrous cycle, and (2) in ovariectomized rats with and without acute and chronic estrogen replacement. Ovariectomized rats were treated either acutely with 10 µg of estradiol benzoate (EB) or chronically with 2 µg/day of EB for 15 days. β-EP concentrations were measured in acid extracts of medial basal hypothalamus by a specific radioimmunoassay. During the estrous cycle, hypothalamic β-EP concentrations showed a significant nocturnal increase, with no difference between the 4 days of the cycle. On the day of estrus, β-EP concentrations between 12.00 and 18.00 h resulted significantly lower than in the other days of the cycle. After ovariectomy, the night-related changes in hypothalamic β-EP disappeared. The acute administration of EB induced a significant increase in hypothalamic β-EP after 21 h (18.00 h). On the other hand, the chronic replacement restored the nocturnal peak of hypothalamic β-EP (18.00, 21.00, 24.00 h). The present data emphasize the role of central β-EP in regulating the reproductive functions. Moreover, the effect of estrogen in modulating the circadian changes in hypothalamic β-EP supports the important role of estrogens in brain function.
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