Primary Role of Plasma Hydrocortisone Concentration in the Regulation of the Normal Forenoon Pattern of Urinary Phosphate Excretion1

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Abstract
The mechanism of the forenoon phosphaturic pattern has been investigated in normal subjects and in patients with various endocrine disorders. The normal pattern consists of the excretion of a progressively increasing fraction of filtered phosphate (Cp/GFR). Patients with hyperparathyroidism exhibit a normal rhythm of increased amplitude, whereas patients with untreated hypoparathyroidism exhibit little or no change during the forenoon. Grossly abnormal rhythms were observed in patients with pituitary or adrenal dysfunction, whereas little variation from the normal basic rhythm was observed in patients with thyroid or testicular dysfunction. The degree of phosphaturia appears to depend upon the interaction of hydro-cortisone with parathyroid, thyroid and growth hormones. Whereas the last 3 of these hormones serve primarily to set the range within which the phosphaturic rhythm operates, rhythmic variations in plasma hydrocortisone concentration appear to be responsible for the rhythmic changes in phosphate excretion. Cp/GFR is negatively correlated with plasma hydrocortisone concentration, thus explaining the abnormal phosphaturic pattern observed in patients with pituitary or adrenal disease.