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Modification by phosphate of PTH-dependent renal cyclic AMP response
1Service de Biochimie, Faculté de Médecine Pitié-Salpêtrière, Paris, France.
Hormone and Metabolic Research = Hormon- Und Stoffwechselforschung = Hormones Et Metabolisme
|April 1, 1993
Summary
Oral calcium supplements affect parathyroid hormone (PTH) and renal cyclic adenosine monophosphate (cAMP) levels differently. Tricalcium phosphate, unlike calcium gluconolactate, may decouple PTH suppression from renal cAMP response, impacting phosphate reabsorption.
Area of Science:
- Endocrinology
- Renal Physiology
- Calcium Metabolism
Background:
- Parathyroid hormone (PTH) regulates calcium and phosphate homeostasis.
- Renal cyclic adenosine monophosphate (cAMP) acts as a second messenger in PTH's action on the kidneys.
- The impact of different oral calcium salts on PTH and renal cAMP responses requires further elucidation.
Purpose of the Study:
- To compare the effects of tricalcium phosphate and calcium gluconolactate on parathyroid hormone (PTH) and renal cyclic adenosine monophosphate (cAMP) responses in healthy males.
- To investigate the relationship between serum ionized calcium, PTH suppression, and renal cAMP secretion after oral calcium administration.
- To determine the influence of co-administered phosphate on the PTH-renal cAMP axis.
Main Methods:
- A randomized controlled study involving 12 young adult males.
- Oral administration of tricalcium phosphate (1.2 g calcium + 0.6 g phosphorus) or calcium gluconolactate (0.5 g calcium).
- Measurement of serum ionized calcium, serum phosphate, PTH levels, urinary cAMP, and tubular maximal reabsorption of phosphate before and after calcium ingestion.
Main Results:
- Both calcium salts significantly increased serum ionized calcium, suppressing PTH levels similarly.
- Tricalcium phosphate caused a modest increase in serum phosphate, while calcium gluconolactate did not.
- Calcium gluconolactate significantly decreased renal cAMP and increased tubular maximal reabsorption of phosphate; tricalcium phosphate did not significantly alter renal cAMP or phosphate reabsorption.
- A decoupling effect between PTH suppression and renal cAMP response was observed with tricalcium phosphate.
Conclusions:
- Suppression of PTH secretion is primarily dependent on the rise in serum ionized calcium.
- Co-administration of phosphate with calcium (as in tricalcium phosphate) may interfere with the normal PTH-mediated renal cAMP response.
- This decoupling effect suggests that phosphate load influences the downstream signaling of PTH in the kidney, impacting phosphate handling.