Anterior pituitary adenomas

Mastronardi, L., Guiducci, A., Spera, C., Puzzilli, F., Liberati., and Maira, G. 1999. Ki-67 labelling index and invasiveness among anterior pituitary adenomas Analysis of 103 cases using the MIB-1 monoclonal antibody./. Clin. Pathol. 52 107-111. 

Anterior pituitary Pituitary prolactin-secreting adenoma Hypothyroidism Med ications—antipsychotics, verapamiI T Prolactin suppresses HPO axis TRH causing T prolactin, other abnormalities T Prolactin suppresses HPO axis... 

In pituitary adenoma cells, dopamine was found to activate K+ currents through D2 type receptor, leading to cell hyperpolarization (Israel et al., 1985). Similar effects have been described in lactotroph and melanotroph cells in the anterior pituitary as well as in the mesencephalic neurons in the CNS (Israel et al., 1985 Lacey et al., 1988 Greif et al., 1995). The K+ current-induced hyperpolarization appears to underlie the inhibition of DA release mediated by D2 autoreceptors in dopamine neurons and of prolactin release in lactotroph cells. In particular, the blockade of K+ channel by 4-aminopyridine or tetramethylammonium abolished the inhibitory effect of D2 agonists on DA release (Bowyer and Weiner, 1989 Cass and Zahniser, 1991 Tang et al., 1994a). 

The most common secretory neoplasm of the anterior pituitary gland is a prolactin-secreting adenoma (prolactinoma). An early symptom of prolactin excess is a milky discharge from the breasts. Because hyperprolactinemia may suppress the secretion of gonadotropic hormones (e.g., LH, FSH), menstrual irregularity, amenorrhea, and infertility may occur in women. In men, gonadotropic hormone dysfunction may lead to reduced libido, sexual impotence, and infertility. 

A direct regulatory role for endocannahinoids in normal human anterior pituitary gland and pituitary adenomas has also been postulated (Fagotto et al. 2001). Pituitary adenomas had higher 2VEA and 2-AG concentrations, pointing to a role for endocannahinoids in the development of pituitary adenomas too. 

Lloyd RV, Chandler WF, Kovacs K, et al. Ectopic pituitary adenomas with normal anterior pituitary glands. Am J Surg Pathol. 1986 10(8) 546-552. 

MEN type I is characterized by hyperparathyroidism, together with pituitary and pancreatic tumours. Hyper-calcaemia caused by excess PTH. secretion is the dominant feature in this syn-drt)me. The most common pituitary tumour is a non-functioning chromophobe adenoma which, although it dws not secrete a hormone itself, may have effects on the secretion of other anterior pituitary hormones. The most common pancreatic tumour in MEN type 1 is an islet cell tumour secreting gastrin. The secretion of gastrin may lead to gastric ulceration. 

The hypothalamic factors which control anterior pituitary hormone secretion are shown in Figure I. Tumours secreting each of the anterior pituitary hormones have been identified. T.SH and gonadotrophin secreting tumours are rare. Gil and ACTH secreting tumours arc more common. Prolactin secreting adenomas (prolactinomas) arc the most common. 

Adenomas secreting each of the anterior pituitary hormones have been identified. 

Fig. 2. A scheme of the hypothalamic-anterior pituitary-target organ axis systems and pituitary adenoma pathogenesis (Mehned [8]). (+) Stimulatory regulation (-) inhibitory regulation. Reproduced from Zhan and Desiderio [14], with permission from Wiley-VCH, copyright 2005, and modified from Mehned [8], with permission from Copyright Clearance Center Inc. (Re Journal of Clinical Investigation), copyright 2003.

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