ORIGIN OF URINARY EPIDERMAL GROWTH FACTOR IN HUMANS: EXCRETION OF ENDOGENOUS EGF AND INFUSED [¹³¹I]‐HUMAN EGF AND KIDNEY HISTOCHEMISTRY

1. This study examined (i) whether blood‐infused epidermal growth factor (EGF) can pass into urine; (ii) whether infused labelled EGF behaves like endogenous plasma immunoreactive EGF; and (iii) which parts of the human nephron show morphological evidence of EGF synthesis? 2. We infused human [¹³¹I]‐EGF into a volunteer. After 6 min, only 66% of the plasma counts represented intact EGF. At the end of infusion, the T 1/2 of EGF was calculated to be 1.6 min. The tail of the curve lasted for at least another 2 h. The total excretion of the labelled EGF was 2.45% of the infused dose and was proportional to the urine volume. 3. After a water load, the excretion of endogenous EGF was, on the contrary, inversely related to urine volume. 4. Immunohistochemically, human kidneys were not stained by monoclonal anti‐EGF antibodies but showed positive in situ hybridization for EGF mRNA in the nuclei of glomerular mesangial cells, distal convoluted tubules and collecting tubules. 5. We conclude that human kidneys synthesize EGF and release it into urine. Plasma‐derived EGF constitutes under normal conditions only a small part of the urinary EGF. Contrasting volume‐dependency of the excretion of endogenous and [¹³¹I]‐EGF requires further study and cautions against extrapolating results obtained with labelled EGF to physiological conditions.