Epidermal Growth Factor (EGF) is a polypeptide which stimulates both proliferation and differentiation of epithelial tissues. Since it has been found that for many cellular lines these processes are under the control of the cyclic nucleotides systems, the levels of cAMP, adenylate cyclase and phosphodiesterase have been assaied in the epidermis of both EGF-treated and normal newborn mice. Phosphodiesterase activity of the two groups of animals does not show significantly differences, while cAMP level and adenylate cyclase specific activity decrease of about 30% 96 hours after EGF injection. cAMP and cGMP levels were estimated in homogenates of both epidermis and corneal epithelium incubated in vitro with EGF (10-6 M). The factor increases in one min the cAMP content of bovine corneal epithelium, with a contemporary moderate depression of cGMP levels and a rebound effect in the following minutes. Similar but delayed is the effect of EGF on the levels of cyclic nucleotides in mice's epidermis incubated in vitro. These data are suggestive for a mechanism of action of EGF that involves directly the cAMP system few minutes after hormone-receptor interaction. Later on cAMP system is affected in vivo probably as secondary effect of the stimulated by EGF protein synthesis.
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