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Polyamines as mediators of the effect of prolactin and growth hormone on the growth of N-nitroso-N-methylurea-induced rat mammary tumor cultured in vitro in soft agar.

This study evaluated the role of polyamines in mediating the effect of ovine prolactin (oPRL) and ovine growth hormone (oGH) on the growth of the N-nitroso-N-methylurea [(NMU) CAS:684-93-5]-induced rat (Sprague-Dawley) mammary cancer cultured in soft agar. oPRL and oGH had a dose-related growth-promoting effect when added to NMU-induced mammary tumors cultured in soft agar in the absence of serum. The effect of oPRL and oGH was blocked by alpha-difluoromethylornithine (DFMO), a suicide inhibitor of ornithine decarboxylase, the rate-limiting enzyme of polyamine biosynthesis. Exogenous administration of polyamines reversed the inhibitory effect of DFMO and completely restored the action of oPRL and oGH. Our results indicated that polyamines are essential in mediating the growth of the NMU-induced mammary tumor under these experimental conditions.