Evidence Against D2 Dopaminergic Influence on Phosphoinosotde Metabolism in Pituitary and Neural Cells
Prolactin secretion from the adenohypophysis is known to be under the tonic inhibitory control of the hypothalamus. Dopamine (DA) is believed to be the major inhibitory influence, being released from tuberoinfundibular dopaminergic neurons and transported to the pituitary gland via the hypophysial portal vessels. High affinity saturable and stereoselective DA receptors have been identified in adenohypophysial homogenates (see refs. 1–3); these have been characterized as the D2 type (4). Immunostaining has shown these receptors to be located on the lactotrophs (5). While there is considerable evidence from our group and others to show that dopamine can reduce intracellular cyclic AMP (cAMP) levels in adenohypophysial cells (see refs. 6,7), this cannot fully account for the observed inhibition of prolactin secretion, nor its mechanism.
KeywordsDopamine Adenoma Prolactin Theophylline Neuroblastoma
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