THE EFFECTS OF CHRONIC ADMINISTRATION OF EPIDERMAL GROWTH-FACTOR (EGF) TO RATS ON THE LEVELS OF ENDOGENOUS EGF IN THE SUBMANDIBULAR GLANDS AND KIDNEYS

Epidermal growth factor (EGF) is mainly produced in the submandibular glands (SMG) and in the kidneys, It has recently been reported that EG F-related ligands may induce their own biosynthesis (autoinduction) in vitro, In the present paper, we investigated whether chronic systemic treatment with EGF influenced the amount of endogenous EGF in the SMG and kidneys. Eight-week-old female Wistar rats were treated with subc utaneous injections of placebo (n = 16) or human recombinant EGF (150 mu g/kg per day, n = 8) for 4 weeks. Urine was sampled the last 24 h o f the study period, At the time of killing, the SMG and the kidneys we re removed. The SMG was larger in the EGF-treated animals, 229.8 +/- 3 5.5 (mean +/- SD) mg than in the control animals, 181.7 +/- 18.1 mg (P < 0.01), The total EGF content was smaller (0.51 +/- 0.15 vs. 1.12 +/ - 0.40 nmol EGF/SMG, P < 0.001). The kidneys were larger in the EGF-tr eated animals (1.38 +/- 0.08 vs. 1.28 +/- 0.08 g, P < 0.05), but the E GF content and urinary excretions were not changed. In conclusion, chr onic systemic treatment with EGF causes growth of the SMG with concomi tantly reduced contents of EGF, and growth of the kidneys with unchang ed content and excretion of EGF. These findings suggest that EGF may p lay a part in the regulation of the growth of the SMG and in EGF biosy nthesis.