ABSTRACT
Molecular endocrinology is the domain of biomedical science focused on the study of mechanisms underlying (1) hormone synthesis and secretion, (2) hormone action, (3) the ontogenesis of the endocrine system, and (4) the pathogenesis of various endocrine disorders at the cellular, molecular, and genetic levels. Hormones are defined as molecules synthesized and secreted by specialized cells within the endocrine organs, diffuse cellular groups with endocrine function (e.g., the neuropeptide-producing cells within the gastrointestinal tract and the bronchial tree), or-in selected cases-other nonendocrine organs [e.g., erythropoietin (EPO) secretion from the renal cortex and atrial natriuretic peptide from cardiacmyocytes] (1). Hormones exert their action (1) at a distance from their site of origin after their release into the circulation and eventual access to target cells (endocrine action), (2) upon adjacent cells ( paraacrine action; e.g., the effects of cortisol on catecholamine production by the adrenal medulla), or (3) upon cells that themselves have produced the relevant hormone (autocrine action; e.g., the inhibitory effect of h-endorphin upon secretion of proopiomelanocortin
cleavage products by the anterior pituitary corticotrophs) (1,2). The traditional concept of hormones as intercellular signaling molecules has been expanded to include substances produced in the nervous and immune systems. Indeed, neurons secrete molecules acting as local hormones, while several hormones act as neurotransmitters or neuromodulators. In a similar fashion the immune system shares molecules with the endocrine system, whereas an ever-increasing number of immune peptides is shown to influence endocrine function (3).
