Anterior pituitary studies

The neurotransmitter histamine (HA) exerts several functions in the hypothalamus [1-2] including an involvement in the neuroendocrine regulation of pituitary hormone secretion [3]. HA has no effect directly at the level of the pituitary gland, but influences the secretion of anterior pituitary hormones either by an exerted e.g. in the paraventricular nucleus (PVN) on other central transmitters or hypothalamic regulating factors, which subsequently regulate the release of anterior pituitary hormones. In addition, HA acts on the supraoptic nucleus (SON) in the hypothalamus where the posterior pituitary hormones are synthesized and thereby exerts a direct effect on the release of the posterior pituitary hormones. Immunohistochemical studies have revealed that the histaminergic neurons, which originate in the tuberomammillary nuclei of the posterior hypothalamus, densely innervate most of the hypothalamic areas involved in the neuroendocrine control of pituitary hormone secretion [4-5]. Within the last two decades the effect of HA on pituitary hormone secretion have been explored in several studies and it has been... 

Administration of 2,3,7,8-TCDD to rodents was also shown to reduce blood corticosterone levels (Balk and Piper 1984 DiBartolomeis et al. 1987 Mebus and Piper 1986). This effect has been attributed to decreased corticosterone synthesis by decreasing cholesterol side-chain cleavage in the adrenal gland. More recent studies suggested that 2,3,7,8-TCDD may interfere with secretion or synthesis of appropriate, bioactive ACTH from the anterior pituitary gland, which could compromise adrenal steroidogenenesis (Bestervelt et al. 1993). 

Although earlier studies failed to find consistent effects of DA on cAMP levels or adenylate cyclase activity in anterior pituitary cells [13], intact pituitary gland [14,15] or homogenates [13,16], a functional connection between the two is now supported by many experimental approaches. DA and DA agonists inhibit cAMP levels in cultured rat pituitary cells at concentrations in the nanomolar range, comparable to those which inhibit PRL release [17-21], DA also inhibits cAMP accumulation stimulated by VIP or TRH [20]. Inhibition is also seen in human prolactinoma cells [22]. 

PURPOSE AND RATIONALE Anterior pituitaries may be incubated directly, kept in culture or used for cell lines (Mittler and Meites 1964, 1966 Mittler et al. 1970 Sandow et al. 1972) in order to study the synthesis and release of gonadotropins in response to LH-RH. 

Barros etal. (1986) studied the effect of TRH on cultured GH3 rat anterior pituitary cells using the wholecell voltage clamp technique. 

Schally AV, Redding TW (1967) In vitro studies with thyrotropin releasing factor. Proc Soc Exp Biol Med 126 320-325 Vale W, Grant G, Amoss M, Blackwell R, Guillemin R (1972) Culture of enzymatically dispersed anterior pituitary cells Functional validation of a method. Endocrinology 91 562-572... 

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