Effect of maturation on gastrointestinal absorption of epidermal growth factor in rats.

Epidermal growth factor (EGF) was iodinated and administered orally to 13- to 15-day-old suckling rats and 29- to 31-day-old weanling rats. After 30 min, stomach, small intestine, plasma, liver, lung, and skin were removed. The tissues were homogenized and 125I radioactivity was extracted. Compared with suckling rats, the delivery of total radioactivity into peripheral tissues was enhanced in skin of weanling rats and tended to be higher in plasma and liver. In contrast, there was a 3.3-fold reduction in radioactivity remaining in the intestinal wall. Sephadex G-25 chromatography of most samples, especially liver and intestinal wall, revealed a decrease in the proportion of intact 125I-EGF eluting in the void volume. As a result, because the amount of total radioactivity also differed, the overall recovery of radioactivity of void volume 125I-EGF was similar in both age groups except for an increase in skin and a decrease in the intestinal wall of weanling rats. Extracts of all tissues of weanling rats examined contained immunoreactive 125I-EGF. Samples obtained from tissues and content of the gastrointestinal tract of both age groups bound specifically to A431 cell surface receptors. These results thus indicate that EGF is absorbed and delivered to various tissues of weanling rats. Nevertheless, quantitative and qualitative changes in these processes occur during the postnatal period.