Methionine-enkephalin and thyrotropin-stimulating hormone are intimately related in the human anterior pituitary

Pituitary neuropeptides and B lymphocyte function

This review discusses the accumulated evidence that pro-opiomelanocortin (POMC) gene products as well as other pituitary neuropeptides derived from related genes (Proenkephalin, PENK; Prodynorphin, PDYN, and Pronociceptin, PNOC) can exert direct effects on B lymphocytes to modulate their functions. We also review the available data on receptor systems that might be involved in the transmission of such hormonal signals to B cells.

The effects of opioids and opioid analogs on animal and human endocrine systems

Opioid abuse has increased in the last decade, primarily as a result of increased access to prescription opioids. Physicians are also increasingly administering opioid analgesics for noncancer chronic pain. Thus, knowledge of the long-term consequences of opioid use/abuse has important implications for fully evaluating the clinical usefulness of opioid medications. Many studies have examined the effect of opioids on the endocrine system; however, a systematic review of the endocrine actions of opioids in both humans and animals has, to our knowledge, not been published since 1984. Thus, we reviewed the literature on the effect of opioids on the endocrine system. We included both acute and chronic effects of opioids, with the majority of the studies done on the acute effects although chronic effects are more physiologically relevant. In humans and laboratory animals, opioids generally increase GH and prolactin and decrease LH, testosterone, estradiol, and oxytocin. In humans, opioids increase TSH, whereas in rodents, TSH is decreased. In both rodents and humans, the reports of effects of opioids on arginine vasopressin and ACTH are conflicting. Opioids act preferentially at different receptor sites leading to stimulatory or inhibitory effects on hormone release. Increasing opioid abuse primarily leads to hypogonadism but may also affect the secretion of other pituitary hormones. The potential consequences of hypogonadism include decreased libido and erectile dysfunction in men, oligomenorrhea or amenorrhea in women, and bone loss or infertility in both sexes. Opioids may increase or decrease food intake, depending on the type of opioid and the duration of action. Additionally, opioids may act through the sympathetic nervous system to cause hyperglycemia and impaired insulin secretion. In this review, recent information regarding endocrine disorders among opioid abusers is presented.

The autocrine/paracrine regulation of thyrotropin secretion

Peptides originally described in other tissues have been located in the anterior pituitary gland. Detection of their encoding mRNAs and specific receptors, together with demonstration of peptide local action led to the postulation of the existence of a paracrine/autocrine regulation of pituitary function. Direct evidence for the role of endogenous peptides has come from studies aiming to block their action through immunoneutralization or pharmacologic blockade. Here we review evidence of pituitary produced peptides as potential candidates as local regulators of thyrotropin secretion. Few studies have approached the subject and most data are not conclusive. Until now, the most consistent data relate to neuromedin B, a bombesin-like peptide. The combined observation of high peptide concentration in rat thyrotrophs, the ability of the exogenous peptide to inhibit thyrotropin (TSH) release in physiologic doses plus the effect of the specific neuromedin B antiserum to increase basal TSH release from isolated pituitaries suggest that neuromedin B acts as a constitutive autocrine TSH-release inhibitor. Neuromedin B is upregulated by thyroid hormones and downregulated by thyrotropin-releasing hormone (TRH) that is consistent with proposed role of local factors, namely to partially mediate or modulate the effects of hormones on pituitary function. However, future studies will certainly confirm other candidates as local regulators of TSH secretion, as well as their relevance at physiologic and pathologic conditions.

Peptide quantification by tandem mass spectrometry

This manuscript reviews the literature on the mass spectrometry (MS) and tandem mass spectrometry (MS/MS) quantification of biologically important peptides that have been extracted from tissues. The most important aspect of this quantification process is the use of MS/MS to link the protonated molecule ion, (M + H)(+) , of the peptide with one or more of its amino acid sequence-determining fragment ions. The actual name of a peptide cannot be used in any study until the amino acid sequence of that peptide has been firmly established. This article reviews the analytical data obtained from the measurement of opioid peptides in human pituitary tissues. For example, the proopiomelanocortin (POMC)-derived beta-endorphin (BE) and the proenkephalin-derived methionine enkephalin (ME) opioid peptides have been quantified. The biogenesis of opioid neuropeptides is briefly reviewed; critical aspects of pituitary neuropeptides are discussed, including their localization and regulation, and their role in tumor formation; other analytical methods used to detect and measure neuropeptides are mentioned, including radioimmunoassay (RIA), radioreceptorassay (RRA), in situ hybridization, mRNA, and cDNA methods; and the MS and MS/MS methods are described. The use of stable isotope-incorporated synthetic peptide internal standards is described. Data are presented on the measurement of BE and ME in control pituitaries and in pituitary tumors (PRL-secreting and nonsecreting tumors). A significant alteration in the POMC peptide BE was found between the control and tumor tissues. That difference suggests that the POMC neuropeptidergic system had been down-regulated in those tumors. © 1997 John Wiley & Sons, Inc.

Bioactive peptides in anterior pituitary cells

The anterior pituitary (AP) has been shown to contain a wide variety of bioactive peptides: brain-gut peptides, growth factors, hypothalamic releasing factors, posterior lobe peptides, opioids, and various other peptides. The localization of most of these peptides was first established by immunocytochemical methods and some of the peptides were localized in identified cell types. Although intracellular localization of a peptide may be the consequence of internalization from the plasma compartment, there is evidence for local synthesis of most of these peptides in the AP based on the identification of their messenger-RNA (mRNA). In several cases the release of the peptide from the AP cell has been shown and regulation of synthesis, storage and release have also been described. Because the amount of most of the AP peptides is very low (except for POMC peptides and galanin), endocrine functions are not expected. There is more evidence for paracrine, autocrine, or intracrine roles in growth, differentiation, and regeneration, or in the control of hormone release. To demonstrate such functions, in vitro AP experiments have been designed to avoid the interference of hypothalamic or peripheral hormones. The strategy is first to show a direct effect of the peptide after adding it to the in vitro system and, secondly, to explore if the endogenous AP peptide has a similar action by using blockers of peptide receptors or antisera immunoneutralizing the peptide.

Regulatory peptides produced in the anterior pituitary

Several peptide families have been detected in the anterior pituitary of several species, including man, and for many of them evidence for local synthesis has been found. Although a paracrine action seems evident for a few, the precise function of most of these peptides remains unknown.

Mapping enteroendocrine cell populations in transgenic mice reveals an unexpected degree of complexity in cellular differentiation within the gastrointestinal tract

The gastrointestinal tract is lined with a monolayer of cells that undergo perpetual and rapid renewal. Four principal, terminally differentiated cell types populate the monolayer, enterocytes, goblet cells, Paneth cells, and enteroendocrine cells. This epithelium exhibits complex patterns of regional differentiation, both from crypt-to-villus and from duodenum-to-colon. The "liver" fatty acid binding protein (L-FABP) gene represents a useful model for analyzing the molecular basis for intestinal epithelial differentiation since it exhibits cell-specific, region-specific, as well as developmental stage specific expression. We have previously linked portions of the 5' nontranscribed domain of the rat L-FABP gene to the human growth hormone (hGH) gene and analyzed expression of the fusion gene in adult transgenic mice. High levels of hGH expression were noted in enterocytes as well as cells that histologically resembled enteroendocrine cells. In the present study, we have used immunocytochemical techniques to map the distribution of enteroendocrine cells in the normal adult mouse gut and to characterize those that synthesize L-FABP. In addition, L-FABP/hGH fusion genes were used to identify subsets of enteroendocrine cells based on their ability to support hGH synthesis in several different pedigrees of transgenic mice. The results reveal remarkable differences in transgene expression between, and within, enteroendocrine cell populations previously classified only on the basis of their neuroendocrine products. In some cases, these differences are related to the position occupied by cells along the duodenal-to-colonic and crypt-to-villus axes of the gut. Thus, transgenes appear to be sensitive tools for examining the cellular and regional differentiation of this class of intestinal epithelial cells.

Effects of chronic experimental streptozotocin-induced diabetes on the noradrenergic and peptidergic innervation of the rat alimentary tract

Immunohistologic localization of tyrosine hydroxylase (TOH), dopamine-beta-hydroxylase (DBH) and selected neuropeptides (vasoactive intestinal polypeptide, gastrin-releasing peptide (GRP)/bombesin, substance P, Leu-enkephalin, Met-enkephalin, dynorphin B, neuropeptide Y (NPY), somatostatin) was used to investigate the innervation of the small bowel in a rat model of diabetic autonomic neuropathy. Paravascular mesenteric nerves (extrinsic) and intramural nerves of chronically (12-18 month) diabetic rats were characterized by the presence of numerous, markedly swollen dystrophic axons which stained intensely for TOH and DBH. The peptidergic complement of axons, however, showed no evidence of comparable dystrophic axonopathy.