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Impaired clearance of beta-lipotropin in uremia
Insights
Plasma levels of adrenocorticotropic hormone (ACTH) and beta-lipotropin (beta-LPH) are elevated in hemodialysis patients. Reduced clearance, not increased secretion, likely causes higher beta-LPH levels in uremic individuals.
Area of Science:
- Endocrinology
- Nephrology
- Pharmacokinetics
Background:
- Patients with chronic renal failure undergoing hemodialysis exhibit elevated plasma concentrations of immunoreactive adrenocorticotropic hormone (ACTH) and beta-lipotropin (beta-LPH).
- The precise etiology behind these elevated peptide levels in uremic patients remains incompletely understood.
Purpose of the Study:
- To investigate the metabolic clearance rate (MCR), volume of distribution, and fractional disappearance rate of synthetic human ACTH and beta-LPH in patients with chronic renal failure on hemodialysis.
- To elucidate the contribution of altered peptide metabolism versus increased secretion to elevated beta-LPH levels in uremia.
Main Methods:
- Simultaneous bolus injection of synthetic human ACTH and purified human beta-LPH into two clinically stable chronic renal failure patients undergoing hemodialysis.
- Analysis of plasma peptide concentrations over time to determine pharmacokinetic parameters, including MCR and disappearance rates.
- Comparison of pharmacokinetic data with established normal subject values.
Main Results:
- Beta-lipotropin (beta-LPH) exhibited biphasic disappearance curves, while ACTH showed triphasic disappearance curves.
- The metabolic clearance rate (MCR) of ACTH in patients was within the normal range observed in healthy subjects.
- The MCR of beta-LPH was significantly reduced, less than half the rate observed in normal individuals.
Conclusions:
- The findings suggest that a decreased metabolic clearance rate (MCR) of beta-lipotropin (beta-LPH), rather than an increased pituitary secretory rate, is the primary factor contributing to the elevated plasma levels of beta-LPH observed in patients with uremia.
- These results highlight the importance of altered peptide catabolism in the pathophysiology of hormonal imbalances in chronic renal failure.
Abstract:
Immunoreactive ACTH and beta-lipotropin (beta-LPH) plasma concentrations are elevated in clinically stable chronic renal failure patients on hemodialysis (LPH: patients, 271.8 +/- 35.7 fmol ml-1; normal subjects; 6.6 +/- 0.5; ACTH: patients, 56.4 +/- 15.3; normal subjects, 19.4 +/- 1.7). To begin to study the etiology of such elevated levels, the MCR, apparent volume of distribution, and fractional rate of disappearance of synthetic human ACTH and highly purified human beta-LPH were determined in two clinically stable chronic renal failure patients on hemodialysis, after bolus simultaneous injection of both peptides. Biphasic disappearance curves were obtained for beta-LPH; triphasic for ACTH. The MCR of ACTH was within the range seen in normal subjects, whereas the MCR of beta-LPH was less than one half the normal rate. The data indicate that a decrease in MCR (rather than an increase in pituitary secretory rate) may account for the higher plasma levels of beta-LPH in uremic patients.