Pituitary serotonin: responsiveness of levels to hormonal change and ultrastructural alterations associated with amine depletion.

The level of serotonin in the pituitary gland of young dogs was significantly increased following treatment with thyroxine and after the injection of reserpine. Electron miscroscopic examination of the pituitary gland of thyroxine treated animals failed to reveal any ultrastructural alterations. Treatment with reserpine induced the appearance of annulate lamellae in the cytoplasm of cells containing very small granules and having the morphology of thyrotrophs. These observations suggest that biogenic amines within the gland may be involved in regulating the cellular activity of the pituitary.