[Ultrastructure of the gonadotropic cells of the pituitary gland in rat following administration of antiandrogens (author's transl)]

Effect of drugs on pituitary ultrastructure

Various drugs and hormones influence the light microscopic and especially the electron microscopic structure of the anterior pituitary and its tumors. Many structural effects are known only from animal experiments since specimens from human pituitaries are mostly not available. The structure of growth hormone (GH) cells is relatively stable. A massive GH cell hyperplasia is known only in rare cases with growth hormone releasing factor (GRF) excess from tumors. Prolactin cells can be stimulated by drugs, neurotransmitters, and hormones which decrease the dopamine inhibition. Adrenocorticotropic hormone (ACTH) cells are stimulated by stress, some hormones, loss of adrenals, and drugs which activate the alpha 1- and beta-receptors or inhibit the alpha 2-receptors. They are suppressed and changed into Crooke's cells by treatment with glucocorticoids. Thyroid-stimulating hormone (TSH) cells increase in number and size in states for overstimulation especially by thyrotropin releasing hormone (TRH). A decrease results from hyperthyroidism and possibly from somatostatin, L-dopa, and dopamine. Gonadotroph cells transform into castration cells in strongly hyperactive states (gonadectomy, antiandrogens, gonadotropin releasing hormone [Gn-RH]agonists, aminoglutethimide). Special types of pituitary adenomas can be treated with drugs which suppress hormone production and proliferation. Dopamine agonists and somatostatin reduce the tumor size of varying proportions of GH secreting adenomas in acromegaly. Ultrastructurally, a decrease of cytoplasmic and nuclear volume and an increase of lysosomes are found. Bromocriptine and other dopamine agonists are established in the treatment of prolactin secreting adenomas. They induce a shrinkage in many cases. Ultrastructurally, a reduction of cellular and nuclear size, an increase in number of secretory granules and of lysosomes, and a reduction of rough endoplasmic reticulum can be demonstrated.

Effects of drugs on pituitary fine structure in laboratory animals

Although an increasing number of chemicals are reported to affect endocrine glands, only a few studies are dealing with their toxic effect on pituitary. The drugs can induce lesions acting directly on endocrine cells or indirectly by interfering with the regulation of their endocrine activities. Some drugs stimulate pituitary cell proliferation leading to hyperplasia and tumor formation; other chemicals have an inhibitory effect on adenohypophysial cells; and only one drug, hexadimethrine bromide, has been found to induce pituitary necrosis. Although complex toxicologic studies have been carried out on many chemicals, the mechanism of action of most drugs is not completely elucidated and further studies are necessary to establish structure function correlations.