Evolutionary aspects of gonadotropin-releasing hormone and its receptor

Summary 1. Gonadotropin-releasing hormone (GnRH) was originally isolated as a hypothalamic peptide hormone that regulates the reproductive system by stimulating the release of gonadotropins from the anterior pituitary. However, during evolution the peptide was subject to gene duplication and structural changes, and multiple molecular forms have evolved.2. Eight variants of GnRH are known, and at least two different forms are expressed in species from all vertebrate classes: chicken GnRH II and a second, unique, GnRH isoform.3. The peptide has been recruited during evolution for diverse regulatory functions: as a neurotransmitter in the central and sympathetic nervous systems, as a paracrine regulator in the gonads and placenta, and as an autocrine regulator in tumor cells.4. Evidence suggests that in most species the early-evolved and highly conserved chicken GnRH II has a neurotransmitter function, while the second form, which varies across classes, has a physiologic role in regulating gonadotropin release.5. We review here evolutionary aspects of the family of GnRH peptides and their receptors.     

Brain motilin-like peptides are localized within the cell nucleus

The subcellular localization of motilin-like immunoreactive (MLIP) peptides in comparison to vasoactive intestinal polypeptide (VIP) and peptide histidine isoleucine amide-27-like peptide (PLP) was investigated in rat brain applying different subcellular fractionation techniques. Unlike VIP or PLP [17], motilin-like peptides were not located in synaptosomes, but in the cell nucleus. This is the first report of a non-vesicular localization of this neuropeptide and is suggestive of a possible non-neurotransmitter role of MLIP. Previous developmental studies point to a possible role for motilin-like peptides as trophic or developmental factors. These results open the possibility that brain motilin-like peptides may operate by binding to chromatin and regulating gene expression.     

Evolutionary relationships of the gut hormones.

Peptides identical or related to mammalian gut hormones occur widely, not just in gut endocrine cells but also in central or peripheral nerves, amphibian skin glands, and a variety of invertebrate tissues. The dual distribution in brain and gut was probably already established early in the vertebrate line; representatives of the oldest vertebrate group, the cyclostomes, have cholecystokinin-like factors in gut endocrine cells and in brain. The related sequences of certain gut peptides, notably gastrin and cholecystokinin (CCK), and secretin, glucagon, vasoactive intestinal polypeptide (VIP), and gastric inhibitory peptide (GIP), indicate evolution from common ancestral molecules by gene duplication and divergence. Functionally important residues are conserved. Thus the COOH-terminal pentapeptide common to gastrin and CCK also contains their minimal active fragment. There are also evolutionary changes at the level of the target organ receptor mechanisms: these are also evolutionary changes at the level of the target organ receptor mechanisms; these are illustrated by evidence suggesting that secretin regulates the flow of pancreatic juice in mammals whereas the structurally related peptide VIP has a similar role in birds.     

垂体腺苷酸环化酶激活肽的研究概况

垂体腺苷酸环化酶激活肽（PACAP）及其受体存在于许多动物的下丘脑和垂体中,而且在肾上腺、睾丸、卵巢、肝脏、肾脏、胰腺、松果腺、心脏、脊椎、神经节、呼吸系统和消化系统等组织或系统中也存在,其中肾上腺含量最高.在这些组织或系统中,通过Ca²⁺、Na⁺、腺苷酸环化酶或磷酸肌醇等作用通路,PACAP发挥神经递质/调质、或神经营养因子等生物学功能.     

Comparative Endocrinology of Piscine Hypothalamic Hypophysiotropic Peptides: Distribution and Activity

Fishes display a variety of anatomical relationships betweenbrain and pituitary to a degree unique among vertebrates. Thisgroup is pivotal for understanding evolution of functions ofhypophysiotropic peptides. We review information concerningoccurrences, distributions and physiological activities of threeidentified peptides in fish brain, and biological propertiesof fish brain extracts. Thyrotropin releasing hormone may bepresent universally in piscine central nervous tissue; however,this peptide has not been clearly demonstrated to have hypophysiotropicactivity in fishes. Somatostatin also has been shown to occurin fish brains; studies of actions of this substance are virtuallyabsent. Gonadotropin releasing hormone is apparently of broadoccurrence in fishes; its hypophysiotropic activity is wellestablished for several teleostean species. Anatomical relationshipsbetween brain and pituitary are particularly varied among elasmobranchs.Investigations involving additional elasmobranch representatives,as well as other fishes, are needed before generalizations canbe made. Widespread extrahypothalamic distribution of hypophysiotropicpeptides in lower vertebrates and neurotransmitter (or related)functions of neurones containing these peptides provide a basisfor proposals concerning evolution of hypothalamic control ofthe pituitary gland.     

Autocrine expression and ontogenetic functions of the PACAP ligand/receptor system during sympathetic development

The superior cervical ganglion (SCG) is a well-characterized model of neural development, in which several regulatory signals have been identified. Vasoactive intestinal peptide (VIP) has been found to regulate diverse ontogenetic processes in sympathetics, though functional requirements for high peptide concentrations suggest that other ligands are involved. We now describe expression and functions of pituitary adenylate cyclase-activating polypeptide (PACAP) during SCG ontogeny, suggesting that the peptide plays critical roles in neurogenesis. PACAP and PACAP receptor (PAC(1)) mRNA's were detected at embryonic days 14.5 (E14.5) through E17.5 in vivo and virtually all precursors exhibited ligand and receptor, indicating that the system is expressed as neuroblasts proliferate. Exposure of cultured precursors to PACAP peptides, containing 27 or 38 residues, increased mitogenic activity 4-fold. Significantly, PACAP was 1000-fold more potent than VIP and a highly potent and selective antagonist entirely blocked effects of micromolar VIP, consistent with both peptides acting via PAC(1) receptors. Moreover, PACAP potently enhanced precursor survival more than 2-fold, suggesting that previously defined VIP effects were mediated via PAC(1) receptors and that PACAP is the more significant developmental signal. In addition to neurogenesis, PACAP promoted neuronal differentiation, increasing neurite outgrowth 4-fold and enhancing expression of neurotrophin receptors trkC and trkA. Since PACAP potently activated cAMP and PI pathways and increased intracellular Ca(2+), the peptide may interact with other developmental signals. PACAP stimulation of precursor mitosis, survival, and trk receptor expression suggests that the signaling system plays a critical autocrine role during sympathetic neurogenesis.     

On the immunocytochemical localization of the vasoactive intestinal polypeptide.

The distribution of vasoactive intestinal polypeptide (VIP) immunoreactive nerves and endocrine cells in the gastrointestinal tract and pancreas of a number of mammalian and submammalian species has been examined in order to throw light on the exact localization of this peptide. Seven out of 8 VIP antisera demonstrated numerous nerve fibers in the gut, whereas one antiserum (TR2) revealed only scattered, few nerve fibers. The distribution of endocrine cells demonstrated by the different VIP antisera varied considerably. Thus, some antisera demonstrated only endocrine cells in the feline antrum, others only colonic endocrine cells and still others only endocrine cells of the upper gut and pancreas. The variability in staining pattern of endocrine cells as well as recent radioimmunological data makes it opportune to suggest that true VIP is a neuronal peptide and that endocrine cells store peptides resembling, but not being identical with, VIP (VIPoids).     

Brain evolution by brain pathway duplication

Understanding the mechanisms of evolution of brain pathways for complex behaviours is still in its infancy. Making further advances requires a deeper understanding of brain homologies, novelties and analogies. It also requires an understanding of how adaptive genetic modifications lead to restructuring of the brain. Recent advances in genomic and molecular biology techniques applied to brain research have provided exciting insights into how complex behaviours are shaped by selection of novel brain pathways and functions of the nervous system. Here, we review and further develop some insights to a new hypothesis on one mechanism that may contribute to nervous system evolution, in particular by brain pathway duplication. Like gene duplication, we propose that whole brain pathways can duplicate and the duplicated pathway diverge to take on new functions. We suggest that one mechanism of brain pathway duplication could be through gene duplication, although other mechanisms are possible. We focus on brain pathways for vocal learning and spoken language in song-learning birds and humans as example systems. This view presents a new framework for future research in our understanding of brain evolution and novel behavioural traits.     

Peptide YY-2 (PYY2) and pancreatic polypeptide-2 (PPY2): species-specific evolution of novel members of the neuropeptide Y gene family

Several gene duplication events have led to the creation of at least five distinct members of the neuropeptide Y gene family. We now reveal that the most recent of these events, involving the PYY-PPY gene cluster on chromosome 17q21.1, has led to the creation of novel PYY- and PP-like genes on chromosome 17q11 in the human genome. Sequence analysis of the novel human PYY2 and PPY2 genes shows an extensive homology to the peptide YY-pancreatic polypeptide genes, at the level of gene structure, nucleotide sequence, and primary amino acid sequence. The extremely high degree of homology between the PYY-PPY and the PYY2-PPY2 gene clusters, in both coding regions and especially noncoding regions, suggests that the PYY2 and PPY2 genes have arisen by a very recent gene duplication. Similar gene duplication events of the PYY-PPY gene cluster have also occurred in other species, including cow and baboon, but have not been confirmed in the rat and mouse genomes. Interestingly, despite the greater than 92% nucleotide sequence identity between these new genes, a few specific mutations have resulted in significantly altered peptide sequences. These altered sequences are accompanied by acquisition of new functions apparently unrelated to the neurotransmitter/endocrine role of PYY and PPY, as demonstrated by the major involvement of bovine PYY2, also known as seminal plasmin, in the fertilization process.     

Detection of mRNAs containing regulatory peptide coding sequences using synthetic oligodeoxynucleotides

To understand the regulation of the production of peptide hormones, it is vital to elucidate their biosynthetic pathways. We chose to study a major regulatory peptide, vasoactive intestinal peptide (VIP), a peptide possessing both neurotransmitter and neurohormone actions. To identify the specific peptide mRNA we are using, as hybridization probes, radiolabeled synthetic oligodcoxynucleotides with sequence complementary to the predicted peptide mRNA sequence. Employing this approach, we identified and partially purified a ～ 1600-base long mRNA containing VIP related sequences which can be translated in vitro into VIP-immunoreactive polypeptides. Such mRNA was detected in normal VIP producing tissue (rat brain), as well as in a tumor producing VIP (human buccal tumor). This mRNA differs in size from a known VIP-mRNA identified in human neuro-blastoma cells, suggesting the possibility of different VIP-mRNAs in different cell types.     

On the possible existence of multiple endocrine, paracrine and neurocrine messengers in secretory cell systems

A multiplicity of regulatory molecules, messengers, are secreted by a large variety of neuronal, endocrine and paracrine cell populations. To some extent the anatomical locus of messenger production or the cytophysiological characteristics of cells producing a messenger determines its role as a hormone, transmitter, modulator or paracrine regulator. Thus, the same messenger may function as a hormone in one location and as a neurotransmitter in another. This versatility in functions makes it difficult to assign a definite physiological role to a given messenger. Our evidence for the occurrence of cell systems producing more than one type of messenger is presented. The practical and conceptual difficulties in determining definite functions of messengers leads to our present inability to examine critically well-known dogmas like the "one hormone-one cell" concept and "Dale's principle". Recognition of the fact that some cell systems do indeed produce multiple messengers provides us with valuable tools for investigating endocrine and neurocrine secretion and has far-reaching implications for studies of cell differentiation and cell pathology.     

Evolutionary significance of the phylogenetic distribution of the mammalian hypothalamic releasing hormones

The hypophysiotrophic hormones isolated from the mammalian hypothalamus are distributed throughout the nervous system of vertebrate species. Although their role in regulating pituitary hormone secretion in mammals is clear, a similar function in lower species has not been established. Thyrotropin-releasing hormone is unable to stimulate thyroid function in amphibia and fish, despite being present in the hypothalamus and brain of these species of high concentration. The tripeptide is also found in high concentration in frog skin, a tissue derived from (or programed by) primitive neuroectoderm that is also a rich source of other peptides structurally related to neural peptides located in mammalian brain and gut. Luteinizing hormone-releasing hormone (LHRH) is able to activate gonadotropin secretion in submammalian species but there is evidence that the LHRH material present in avian, reptilian, and piscine brain is not identical to the mammalian decapeptide. An LHRH-like material present in frog sympathetic ganglia appears to function as a neurotransmitter in this location. Somatostatin is present in high concentrations in the hypothalamus, brain, pancreas, and gastrointestinal tract of all vertebrates and chromatographically is identical to the mammalian material, suggesting that this peptide is an "ancient" molecule with an important role in neuronal pancreatic and digestive function. The hypothalamic releasing hormones are part of a family of neural peptides that have a widespread anatomic and phylogenetic distribution and form a diffuse neuroendocrine system. It an material, suggesting that this peptide is an "ancient" molecule with an important role in neuronal pancreatic and digestive function. The hypothalamic releasing hormones are part of a family of neural peptides that have a widespread anatomic and phylogenetic distribution and form a diffuse neuroendocrine system. It an material, suggesting that this peptide is an "ancient" molecule with an important role in neuronal pancreatic and digestive function. The hypothalamic releasing hormones are part of a family of neural peptides that have a widespread anatomic and phylogenetic distribution and form a diffuse neuroendocrine system. It appears likely that the releasing hormones initially arose with a neurocrine or paracrine function, and that only later in evolution did they acquire the role of regulating adenohypophysial secretion.     

PHI--a new brain-gut peptide

The detection of the C-terminal amide structure in porcine intestinal extracts has led to the discovery of a 27 amino acid residue peptide designated PHI (PHI-27, peptide HI). The peptide was found to have structural homologies to vasoactive intestinal peptide (VIP) and growth hormone-releasing factor (GRF). Subsequent studies have revealed that PHI exhibits a variety of biological activities which resemble those of VIP. Moreover, it was found that the peptide is able to inhibit the binding of VIP to its receptors, and to stimulate cyclic AMP production. PHI is present in both brain and gut in high concentrations and probably acts as a neurotransmitter or neuromodulator rather than a hormone. A comparison of the amino acid sequences of porcine, human and bovine PHI indicated that human PHI differs from the porcine peptide in two positions (12 and 27), and bovine PHI differs in one position (10). The amino acid sequence (deduced from the cDNA sequence) of the VIP precursor recently obtained from human neuroblastoma cells also contains an identical sequence to the newly-isolated human PHI from human colonic extracts. PHI has thus been shown to be co-synthesized with VIP in the same precursor molecule.     

Minireview. The ascent of cholecystokinin (CCK) - from gut to brain

Cholecystokinin (CCK), a classical gastrointestinal polypeptide hormone, appears to have an equally important role as a brain neurotransmitter. CCK is widely distributed throughout both the central and peripheral nervous system. Of the known brain peptides, only CCK and VIP are predominately cerebral cortical peptides. In the pituitary, CCK is found in the posterior pituitary, while gastrin-like peptides are present in the anterior and intermediate lobes. Phylogenetically, gastrin-CCK-like peptides arose extremely early in evolution being present in the primitive nerve cells of the coelenterate, Hydra. Specific high affinity CCK-receptors have been demonstrated in rat and guinea-pig brains with highest concentrations in the cerebral cortex, caudate nucleus and olfactory bulb. Alterations in CCK binding have been reported during fasting and in genetically obese rats and mice. The low levels of CCK receptors in patients with Huntington's Chorea, the coexistance of CCK with dopamine in the same mesolimbic neurons and the rotational syndrome produced after central administration in rats suggests a potential physiological role for CCK in the regulation of extra-pyramidal function. CCK and/or gastrin have been demonstrated to have a number of effects on anterior pituitary hormones and the high concentrations in the posterior pituitary suggest a possible neuromodulatory role in the regulation of vasopressin and/or oxytocin release. CCK is a putative satiety hormone which appears to produce satiety both by peripheral and central effects. The presence of CCK in the periaqueductal gray and the fact that it produces naloxone reversible analgesia suggest a potential role for CCK in the regulation of pain perception. Central administration of CCK produces hyperglycemia which appears to be partly mediated via an adrenal mechanism. CCK also produces mild hypothermia and appears to be a central nervous system depressant. Present evidence indicating that CCK is a central neurotransmitter or neuromodulator includes its regional distribution with localization within neuronal cell bodies and axons; the demonstration that it can be synthesized in neuronal tissue; the fact that it is released by depolarizing stimuli $\text{in vitro}$; the presence of specific, high affinity receptors for CCK in the brain; and the finding that it can activate isolated neurons. The high concentrations of CCK in the cerebral cortex suggest that future studies will produce further surprises concerning the physiological role of this gall-bladder contracting hormone which came of age with the discovery of its wide distribution in the central nervous system.     

Endocrine Aspects of Homeostasis

SYNOPSIS. Recent findings in endocrine research have greatlyincreased our understanding of the relationship between hormonesand homeostasis. The present paper reviews selected major advancesin such areas as neuropeptides, peptide biosynthesis in endocrineand neuronal cells, peptide receptors and intracellular pathwaysin target cells, "new" peptide hormones, and evolutionary considerationsof peptide hormones. Further understanding of hormone interactionsand of relationships between nervous, endocrine, and immunesystems has added to the growing complexity of the mechanismsof fine tuning and regulating our internal environment. Moreover,discovery of the same or similar peptides throughout the courseof evolution, i.e., from unicellular organisms through vertebrates,has led to a new unifying theory of intercellular communication.Endocrine aspects of homeostasis is an expanding and excitingfield of biology.     

Bioactive analogues and drug delivery systems of vasoactive intestinal peptide (VIP) for the treatment of asthma/COPD

Vasoactive intestinal peptide (VIP) is one of the major peptide transmitters in the central and peripheral nervous systems, being involved in a wide range of biological functions. In an airway system where VIP-immunoreactive nerve fibers are present, VIP acts as neurotransmitter or neuromodulator of the inhibitory non-adrenergic and non-cholinergic airway nervous system and influences many aspects of pulmonary biology. A clinical application of VIP has been believed to offer potential benefits in the treatment of chronic inflammatory lung diseases such as asthma and chronic obstructive pulmonary disease (COPD), however, its clinical application has been limited in the past for a number of reasons, including its extremely short plasma half-life after intravenous administration and difficulty in administration routes. The development of long-acting VIP analogues, in combination with appropriate drug delivery systems, may provide clinically useful agents for the treatment of asthma/COPD. In this review, development of efficacious VIP derivatives, drug delivery systems designed for VIPs and the potential application for asthma/COPD are discussed. We also include original data from our chemical modification experiments and formulation studies, which led to successful development of [R(15, 20, 21), L(17)]-VIP-GRR (IK312532), a potent VIP analogue, and a VIPs-based dry powder inhaler system.