Ultrastructure of intermediate lobe of the pituitary and melanocyte-stimulating hormone secretion in oestrogen-induced kidney tumours in male hamsters.

One group of male Syrian hamsters was killed after various periods of diethylstilboestrol (DES) treatment, ranging from 6 to 36 weeks. All developed renal tumours by 24 weeks. DES also induced hyperplastic and neoplastic changes in the pars intermedia of the pituitary with proliferation of MSH-secreting cells and elevated serum MSH concentration. Another group of male Syrian hamsters was given DES for 36 weeks followed by cessation of hormone treatment. The animals were killed at various intervals from 12 to 36 weeks after DES withdrawal. In these animals the DES-induced renal tumours underwent regression whilst the pituitary changes persisted until the termination of the experiment. The findings suggested that the hormone MSH may be implicated in renal carcinogenesis but plays no role in the maintenance of the established tumours.