Growth and Renal Control of Plasma Phosphate

Abstract

Glomerular filtration rate (GFR),maximal tubular reabsorption of phosphate (TmPO4), and fasting plasma phosphate have been measured in states of normal growth (childhood) and pathological growth (“active” acromegaly, pituitary dwarfism) and in adult controls. GFR and TmPO4 were corrected for a mean body area of 1 m2 73. GFR, TmPO4 and TmPO4/U of GFR were higher in active acromegalics than in adult controls and successfully treated acromegalics. TmPO4 and TmPO4/U of GFR were higher in normal children than in adult controls. GFR was not significantly different. GFR and TmPO4 were lower in pituitary dwarfs than in normal children, whereas TmPO4/U of filtrate was not significantly different. Fasting plasma phosphate was significantly higher in “active” acromegaly and normal children than in adult controls. A highly significant correlation was found between fasting plasma phosphate and TmPO4/U of GFR in the acromegalics, the normal children, the adult controls and also when all groups were pooled. It is concluded that the renal handling of phosphate regulates the concentration of phosphate in the plasma in normal and pathological growth as well as in normal adults. Chronic oversecretion of growth hormone alone can account for the raised tubular reabsorption capacity for phosphate seen in “active” acromegaly. From the data obtained in the pituitary dwarfs, it is apparent that the powerful tubular phosphate transport system in children is little dependent on growth hormone secretion and that additional factors must be operative.