Characterization and repartition of epidermal growth factor-urogastrone receptors in gastric glands isolated from young and adult guinea pigs

Physiological studies indicate that epidermal growth factor-urogastrone (EGF) acts on stomach epithelium as mitogen and modulator of acid secretion. Here, we studied the binding of 125I-EGF to gastric glands isolated from the guinea-pig fundus (acid-secreting part) and antrum. At 20 degrees C, the association of 125I-EGF to gastric glands was time-dependent (plateau at 90 min) and reversible (75-85% dissociation in 1 h). No degradation of the peptide was detected, but a time-dependent loss of binding capacity was observed. At apparent equilibrium (90 min, 20 degrees C) unlabelled EGF (80 pM to 80 nM) competed with 125I-EGF-binding in the same manner in antrum and fundus (50% inhibition, with 0.6 nM EGF). Whereas kinetics properties were similar in antrum and fundus, the binding capacity was 40-55% lower in fundus than in antrum in young animals (6-8 weeks). By contrast, in adult animals (20-30 weeks), binding was the same in both parts of stomach. Scatchard analysis showed that two orders of binding sites were present in all cases (Ki 0.34-0.47 nM, Ki 2.2-3.4 nM), and that the differences observed were only accounted for by number of binding sites. These results show that EGF possess high affinity binding sites on gastric epithelium. These sites, dependent upon the age of the animals, may be related to the modulations by EGF of gastric trophism and secretions.