[Regulation of prolactin secretion at the cellular level]

The present review compiles and discusses about two decades of research concerning the mechanisms involved in the regulation of the secretory activity of mammalian prolactin (PRL) containing cells. The topics include methodological aspects (such as dispersion, culture and isolation of anterior pituitary cells), the action of catecholamines, second messengers (calcium, cyclic AMP and phosphatidylinositol metabolites), neuroendocrine modulators and peptides, as well as a chapter about the morphology and biochemistry of the PRL secretory granule. Most of the accumulated data--often dispersed or disconnected--do not allow definitive conclusions and it becomes clear that we are still far away from understanding the mechanisms regulating PRL secretion. One exception is the knowledge about the dopaminergic inhibition of PRL release. Many evidences indicate that dopamine acts as a physiological inhibitor on mammalian PRL secreting cells. Some significant advances also were made studying the mechanism of action of the second messengers and, to a lesser extent, of the thyrotropin-releasing hormone. On the other hand appears an open field, which can be called the "new neuroendocrinology", with its enormous and still growing world of peptides interacting with other neuronal and humoral effectors, and which has overrun and changed the whole traditional neuroendocrinology. In this area much more information is needed and we are hopeful that the study of subpopulations and functionally related cell groups with modern cytochemical techniques (multiple immunostaining, in situ hybridization, etc.) and the development of new specific agonists, antagonists and inhibitors for the characterization of receptors and defined cellular events will lead us to a better understanding of the biochemistry and physiology of PRL secreting cells.