Parathyroid hormone does not increase nephrogenous cyclic AMP excretion by the dog

Area of Science:

• Endocrinology
• Renal Physiology
• Calcium Metabolism

Background:

• Nephrogenous cyclic AMP (NcAMP) excretion is a recognized indicator of parathyroid hormone (PTH) action in humans.
• Previous observations in dogs suggested urinary cyclic AMP (UcAMP) does not reflect endogenous PTH levels.

Purpose of the Study:

• To investigate the effect of physiological and pharmacological parathyroid hormone (PTH) levels on nephrogenous cyclic AMP (NcAMP) and total urinary cyclic AMP (UcAMP) excretion in dogs.
• To determine if NcAMP can serve as a reliable biomarker for PTH activity in canine models.

Main Methods:

• Dogs underwent hypocalcemia to stimulate endogenous PTH secretion.
• Dogs received infusions of parathyroid extract to achieve pharmacologic PTH levels.
• Measurements included plasma calcium, plasma and urinary cyclic AMP (cAMP), and urinary fractional phosphate excretion (FEP).

Main Results:

• Physiological hyperparathyroidism (8-fold PTH increase) did not alter NcAMP or UcAMP excretion, despite increased fractional phosphate excretion.
• Pharmacological PTH administration (15 U/min) increased plasma cAMP and UcAMP excretion threefold, but did not affect NcAMP excretion.
• Fractional phosphate excretion increased by 50% under both physiological and pharmacological PTH stimulation.

Conclusions:

• Nephrogenous cyclic AMP (NcAMP) excretion is not stimulated by parathyroid hormone (PTH) in dogs.
• NcAMP is not a suitable index for assessing PTH action in vivo in canine studies.
• Increased UcAMP excretion under high-dose PTH is likely due to filtration of elevated plasma cAMP, potentially originating from bone metabolism.