Effect of Salivary Epidermal Growth Factor on Hamster Oral Carcinogenesis

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Epidermal Growth Factor (EGF) is a polypeptide hormone that is secreted by submandibular gland and stimulates cellular proliferation in many tissues. It has been shown that EGF may enhance the carcinogenic potential of methylcholanthrene in the skin and stimulate mouse mammary tumorigenesis. However, the role of EGF in the oral carcinogeneisis has not been studied in detail. In the present study, the effect of sialoadenectomy on the 9, 10-Dimethy-1, 2Benzanthrwacene (DMBA) -induced tumor formation in hamster cheek pouch was investigated.Six-week-old male syrian hamsters were treated by painting both cheek pouches biweekly with a 0.5% solution of DMBA dissolved in mineral oil for 6 weeks. On the 7th week after the beginning of the experiment, hamsters in group 2 to 4 received sialoadenectomy. Thereafter, in group 1 and 2 the animals were given subcutaneous injections of 0.9% NaCl solution thrice weekly for 8 weeks. In group 3 and 4, urogastrone/EGF was injected subcutaneously thrice weekly at the doses of 0.025 mg/Kg and 0.25 mg/Kg, respectively. The experiment was terminated after 16 weeks.There was no significant difference in body weights and the weights of liver and kidney among the comparable groups of animals. The mean numbers of tumor per cheek pouch in group 1 to 4 were 3.4, 2.1, 2.5. and 3.2, respectively. The difference between group 2 and group 1 or group 4 was significat (P<0.05, Student's t test). In regard to tumor volume per cheek pouch, the values of group 1 and group 4 were higher than that in group 2, though the difference was not significant. When the number of stomach tumors was counted, the values of group 1 and group 4 were significantly higher than that in group 2. These findings indicate that EGF synthesized in hamster submandibular gland may play an important role in the formation of cheek pouch and stomach tumors induced by DMBA.