Biosynthesis and Function of VIP and Oxytocin: Mechanisms of C-terminal Amidation, Oxytocin Secretion and Transport

In this review, we provide the status of research on vasoactive intestinal peptide (VIP) and oxytocin, typical C-terminal α-amidated peptide hormones, including their precursor protein structures, processing and C-terminal α-amidation, and the recently identified mechanisms of regulation of oxytocin secretion and its transportation through the blood brain barrier. More than half of neural and endocrine peptides, such as VIP and oxytocin, have the α-amide structure at their C-terminus, which is essential for biological activities. We have studied the synthesis and function of C-terminal α-amidated peptides, including VIP and oxytocin, since the 1980s. Human VIP mRNA encoded not only VIP but also another related C-terminal α-amidated peptide, PHM-27 (peptide having amino-terminal histidine, carboxy-terminal methionine amide, and 27 amino acid residues). The human VIP/PHM-27 gene is composed of 7 exons and regulated synergistically by cyclic AMP and protein kinase C pathways. VIP has an essential role in glycemic control using transgenic mouse technology. The peptide C-terminal α-amidation proceeded through a 2-step mechanism catalyzed by 2 different enzymes encoded in a single mRNA. In the oxytocin secretion from the hypothalamus/the posterior pituitary, the CD38-cyclic ADP-ribose signal system, which was first established in the insulin secretion from pancreatic β cells of the islets of Langerhans, was found to be essential. A possible mechanism involving RAGE (receptor for advanced glycation end-products) of the oxytocin transportation from the blood stream into the brain through the blood-brain barrier has also been suggested.

Newly-identified receptors for peptide histidine-isoleucine and GHRH-like peptide in zebrafish help to elucidate the mammalian secretin superfamily

A group of ten hormones in humans are structurally related and known as the secretin superfamily. These hormones bind to G-protein-coupled receptors that activate the cAMP pathway and are clustered as the secretin or B family. We used an evolutionary approach with zebrafish as a model to understand why some of these hormones, such as peptide histidine-methionine (PHM) and pituitary adenylate cyclase-activating polypeptide (PACAP)-related peptide (PRP) in humans lack a receptor. We used molecular techniques to clone two full-length receptor cDNAs in zebrafish, which were analyzed for amino acid sequence and ligand-binding motifs, phylogenetic position, synteny, tissue expression, functional response, and signaling pathway. Evidence is provided that the two cDNAs encoded the peptide histidine-isoleucine (PHI) receptor and PRP receptor, which is known as GHRH-like peptide (GHRH-LP) receptor in non-mammals. Further, we cloned a zebrafish cDNA encoding the peptides PHI and vasoactive intestinal peptide (VIP). The PHIR had been previously labeled as one type of a VIP-PACAP (VPAC2R) shared receptor based only on sequence data. The PHIR cDNA, transfected into COS7 cells, responded to zebrafish PHI in a sensitive and dose-dependent manner (EC(50)=1.8x10(-9) M) but not to PACAP and VIP. The GHRH-LP receptor responded to both zebrafish GHRH-LP1 and GHRH with a 3.5-fold greater response to the former. For comparison, two zebrafish receptors (PAC1R and VPAC1R) and two human receptors (VPAC2R and GHRHR) were tested with human and/or zebrafish peptides. Unexpectedly, zebrafish VIP activated its PAC1R suggesting that in evolution, PAC1R is not always a specific receptor for PACAP. We conclude that zebrafish, like goldfish, have a specific receptor for PHI and GHRH-LP. Our evidence that zebrafish PHI is more potent than human PHM in activating the human VPAC2R (EC(50)=7.4x10(-9) M) supports our suggestion that the VPAC2R and PHIR shared a common ancestral receptor.

Roles of PACAP and PHI as inhibitory neurotransmitters in the circular muscle of mouse antrum

Mediators of neurogenic responses of the gastric antrum were studied in wild-type and pituitary adenylate cyclase-activating polypeptide (PACAP) -knockout (KO) mice. Electrical field stimulation (EFS) to the circular muscle strips of the wild-type mouse antrum induced a triphasic response; rapid transient relaxation and contraction, and sustained relaxation that was prolonged for an extended period after the end of EFS. The transient relaxation and contraction were completely inhibited by L-nitroarginine and atropine, respectively. The sustained relaxation was significantly inhibited by a PACAP receptor antagonist, PACAP(6-38). The antral strips prepared from PACAP-KO mice unexpectedly exhibited a tri-phasic response. However, the sustained relaxation was decreased to about one-half of that observed in wild-type mice. PACAP(6-38) inhibited EFS-induced sustained relaxation (33.5% of control) in PACAP-KO mice. Anti-peptide histidine isoleucine (PHI) serum partially (the 30% inhibition) or significantly (the 60% inhibition) inhibited the sustained relaxations in the wild-type and PACAP-KO mice, respectively. The immunoreactivities to the anti-PACAP and anti-PHI serums were found in myenteric ganglia of the mouse antrum. These results suggest that nitric oxide and acetylcholine mediate the transient relaxation and contraction, respectively, and that PACAP and PHI separately mediate the sustained relaxation in the antrum of the mouse stomach.

Disrupted circadian rhythms in VIP- and PHI-deficient mice

The related neuropeptides vasoactive intestinal peptide (VIP) and peptide histidine isoleucine (PHI) are expressed at high levels in the neurons of the suprachiasmatic nucleus (SCN), but their function in the regulation of circadian rhythms is unknown. To study the role of these peptides on the circadian system in vivo, a new mouse model was developed in which both VIP and PHI genes were disrupted by homologous recombination. In a light-dark cycle, these mice exhibited diurnal rhythms in activity which were largely indistinguishable from wild-type controls. In constant darkness, the VIP/PHI-deficient mice exhibited pronounced abnormalities in their circadian system. The activity patterns started approximately 8 h earlier than predicted by the previous light cycle. In addition, lack of VIP/PHI led to a shortened free-running period and a loss of the coherence and precision of the circadian locomotor activity rhythm. In about one-quarter of VIP/PHI mice examined, the wheel-running rhythm became arrhythmic after several weeks in constant darkness. Another striking example of these deficits is seen in the split-activity patterns expressed by the mutant mice when they were exposed to a skeleton photoperiod. In addition, the VIP/PHI-deficient mice exhibited deficits in the response of their circadian system to light. Electrophysiological analysis indicates that VIP enhances inhibitory synaptic transmission within the SCN of wild-type and VIP/PHI-deficient mice. Together, the observations suggest that VIP/PHI peptides are critically involved in both the generation of circadian oscillations as well as the normal synchronization of these rhythms to light.

Expression of vasoactive intestinal peptide/peptide histidine isoleucine in several hypothalamic areas during the turkey reproductive cycle: relationship to prolactin secretion

The present study examined the changes in vasoactive intestinal peptide (VIP) and peptide histidine isoleucine (PHI) gene expression in the hypothalamus and compared their level of expression to prolactin (PRL) secretion throughout the turkey reproductive cycle. Both VIP and PHI expression were determined using in situ hybridization histochemistry and reverse transcription-polymerase chain reaction/Southern blot analysis. Plasma PRL levels were determined by radioimmunoassay. The changes in total hypothalamic VIP and PHI mRNA steady-state levels mirrored the changes seen in plasma PRL across the reproductive stages. In situ hybridization revealed that VIP mRNA was highly expressed throughout the hypothalamus and predominated within the ventromedial nucleus (VMN), inferior hypothalamus, and infundibular nuclear complex (INF). PHI mRNA was expressed in very low abundance within the same areas expressing VIP mRNA. VIP mRNA abundance within the VMN and INF was lowest in nonphotostimulated hens (VMN, 13.8 +/- 1.7; INF, 17.0 +/- 1.8 arbitrary densitometric units (ADU)), intermediate in laying hens (VMN, 29.6 +/- 3.3; INF, 35.4 +/- 4.3 ADU), and highest in incubating hens (VMN, 76.4 +/- 10.2; INF, 119.2 +/- 3.4 ADU). Levels decreased when birds shifted from incubation to photorefractoriness (VMN, 75%; INF, 82%). This relationship was not observed within other areas of the hypothalamus. The expression of PHI mRNA was also highest in the VMN and INF of incubating hens but no correlation between PHI mRNA and the other reproductive states was observed. This study provides additional evidence that VIP is the avian PRL-releasing factor, and suggests that the central site for avian PRL regulation lies within the INF of the hypothalamus.

Sequence of a cDNA encoding chicken vasoactive intestinal peptide (VIP)

Mammalian pre-pro-vasoactive intestinal peptide (pre-proVIP) gives rise to the neuropeptides vasoactive intestinal peptide (VIP) and peptide histidine isoleucine amide (PHI). The cDNA encoding chicken VIP was cloned and sequenced. The region of chicken pre-proVIP homologous to the mammalian PHI region is not followed by an amidation signal. This unusual feature suggests that processing of the precursor may be different in the chicken.

Transgenic mice overexpressing human vasoactive intestinal peptide (VIP) gene in pancreatic beta cells. Evidence for improved glucose tolerance and enhanced insulin secretion by VIP and PHM-27 in vivo

Vasoactive intestinal peptide (VIP), a 28-amino acid peptide hormone, plays many physiological roles in the peripheral and central nervous systems. It has been proposed that endogenous VIP released from VIP-containing nerves is involved in the regulation of the secretory function of the endocrine pancreas. To test this hypothesis in vivo, we produced transgenic mice carrying the human VIP/peptide histidine methionine 27 (PHM-27) gene under the control of insulin promoter. In immunohistochemical analyses of islets, all the islet beta cells of transgenic mice were intensely stained for both VIP and PHM-27, consistent with the fact that these two peptides are encoded in a single mRNA (Itoh, N., Obata, K., Yanaihara, N., and Okamoto, H. (1983) Nature 304, 547-549). VIP was efficiently secreted from isolated transgenic islets in vitro. The blood glucose assays in free-fed mice indicated that the transgene lowered the blood glucose levels of transgenic mice (128 +/- 4 mg/dl) by about 20% below control levels (155 +/- 6 mg/dl). In the glucose tolerance test, at 60 min after glucose administration, the transgenic blood glucose levels (129 +/- 12 mg/dl) were much lower than control levels (175 +/- 13 mg/dl). The transgenic serum insulin levels at 15 min after glucose administration were 2.5-3.0-fold higher than control levels. The transgene was also effective in ameliorating glucose intolerance of 70% depancreatized mice. These results indicate that VIP and PHM-27 produced from the transgenic beta cells efficiently enhance glucose-induced insulin secretion from beta cells by an autocrine mechanism. These results also suggest that genetic manipulation of islet beta cells by the human VIP/PHM-27 gene or delivery of VIP to beta cells may ultimately provide a valuable approach to enhancing insulin secretion in clinical diabetes.

Location of PHM/VIP mRNA in human gastrointestinal tract detected by in situ hybridization

The expression of the gene for vasoactive intestinal polypeptide (VIP) and peptide histidine methionine (PHM) in the human gastrointestinal tract was studied by in situ hybridization and Northern blotting for PHM/VIP mRNA and immunocytochemistry using specific antisera against the bioactive peptides PHM and VIP. In the colon sigmoideum, antisera against all five putative processing products of the VIP precursor (prepro-VIP) were used, namely prepro-VIP 22-79, PHM, prepro-VIP 111-122, VIP and prepro-VIP 156-170. Furthermore, RNA extracted from various regions of the gastrointestinal tract was examined by Northern blots and hybridization to a VIP-cDNA probe. Throughout the gastrointestinal tract, PHM/VIP mRNA was found in neurons only. Using single- or double-staining methods, we demonstrated both PHM/VIP mRNA and the corresponding peptides PHM and VIP in the neurons. In the sigmoideum, the single-staining methods were extended to investigate whether the neurons simultaneously contained PHM/VIP mRNA and each of the five prepro-VIP-derived peptides. Only one major band of PHM/VIP mRNA (1.9 kb) was found by Northern blotting in the tissue of the gastrointestinal tract.

Gene expression and transcript size of the prepro-peptide VIP/PHM-27 in normal human tissue

The transcript size of VIP/PHM-27 mRNA (vasoactive intestinal peptide/peptide histidine methionine) and the relative distribution of VIP/PHM-27 gene expression in 10 normal human tissues was examined. After mRNA extraction from tissue, VIP/PHM-27 transcript size and relative abundance of mRNA was determined by Northern blot analysis and densitometry of the autoradiograms. VIP/PHM-27 mRNA was detectable in brain, pancreas, colon, ileum and striated muscle while no hybridization signal was observed in liver, kidney, lung, heart, prostate and placental tissue. VIP/PHM-27 transcript in human brain and gut was a single band of 1.7 kb; by contrast, a 7.0-kb transcript was detected in striated skeletal muscle. The highest relative levels of mRNA were observed in brain and pancreas.

Vasoactive intestinal peptide/peptide histidine isoleucine mRNA in the eye and suprachiasmatic nucleus of normal and monocularly enucleated rats

The localization of the messenger RNA (mRNA) encoding vasoactive intestinal peptide/peptide histidine isoleucine (VIP/PHI) in the rat eye was studied by in situ hybridization histochemistry using a synthetic 35S-labeled oligodeoxyribonucleotide. Among the layers of the retina, specific labeling was found in the soma of some cells in the innermost lamina of the inner nuclear layer. Occasionally, labeled cells were also present in the ganglion cell layer. No specific labeling was detected in any ocular structures other than the retina, including the cornea, iris, ciliary body, choroid, choriocapillaris, optic nerve and sclera. We also examined VIP/PHI mRNA expression in the suprachiasmatic nucleus (SCN) of the hypothalamus, which is the pacemaker of circadian rhythms and synchronizes them with the environmental light-dark cycle. High labeling was found in the ventrolateral part of the nucleus, which is the site of most projections from the retina. Monocular enucleation of rats at birth resulted in an increase of VIP/PHI mRNA expression in SCN ipsilateral to the removed eye after postnatal day 60. The discrete pattern of hybridization for VIP/PHI mRNA indicates that these two peptides are synthetized in rat retina and SCN and suggests that they may play a key role in the photic entrainment to the SCN regulating various circadian rhythms.

Detection of multiple hormones and their mRNAs in human neuroblastoma cell line NB-1 using in situ hybridization, immunocytochemistry and radioimmunoassay

The production and secretion of multiple peptide hormones and tyrosine hydroxylase by the human neuroblastoma cell line NB-1 and the effects of dibutyryl cAMP (Bt2cAMP) and phorbol esters such as 12-O-tetradecanoyl-phorbol-13-acetate (TPA) on them were investigated. The presence of messenger RNAs (mRNAs) of vasoactive intestinal peptide (VIP)/peptide histidine methionine (PHM), preprotachykinin, and tyrosine hydroxylase was detectable in the cytoplasm of cultured NB-1 cells by in situ hybridization. Treatment with Bt2cAMP and TPA markedly increased the number of cells immunoreactive to VIP, PHM, neuropeptide Y, Met-enkephalin, substance P and tyrosine hydroxylase and also the contents of VIP and Met-enkephalin in the culture medium. Bt2cAMP and TPA induced morphological changes characteristic of endocrine differentiation, such as an increase in neuroendocrine granules and the development of rough endoplasmic reticulum and Golgi apparatus. The results indicated that treatment with Bt2cAMP and TPA induces the expression of multiple genes of peptide hormone and tyrosine hydroxylase and increases hormone production and secretion through morphological changes into endocrine cells.

In situ hybridization reveals VIP precursor mRNA-containing neurons in monkey and rat neocortex

The cDNAs encoding monkey vasoactive intestinal polypeptide (VIP) and PHM-27 and rat VIP and PHI-27 were cloned and used to generate antisense RNA probes. Using in situ hybridization, neurons expressing the VIP/PHM or VIP/PHI precursor mRNAs were localized in monkey and rat somatic sensory and visual cortex. In both neocortical areas of both species, labeled cells were observed in all 6 layers as well as the subcortical white matter.

Lactation elevates vasoactive intestinal peptide messenger ribonucleic acid in rat suprachiasmatic nucleus

Vasoactive intestinal peptide (VIP) has been suggested to play a role in lactation; indeed several studies implied that VIP induces the release of PRL in the pituitary. Quantitative RNA studies from our laboratory show an increase in the VIP messenger RNA (mRNA) content in the hypothalamus of lactating rats. The purpose of this investigation is to determine which hypothalamic neurons are increasing the expression of VIP. A sensitive in situ hybridization assay employing synthetic oligodeoxynucleotide probes corresponding to specific exons of the VIP gene was used to study VIP gene expression at the neuronal level. We were able to detect VIP-encoding transcripts in various brain regions including the ventrolateral thalamus, neocortex, pyriform cortex, and hypothalamus with a particularly high concentration in the suprachiasmatic nucleus. When lactating animals were compared to non-lactating animals, a 2-fold increase was observed in VIP transcripts in the suprachiasmatic nucleus. Since the suprachiasmatic nucleus is not directly associated with the physiology of lactation, the response of the VIP gene to lactation may be, in part, indirect. Taken together, our results suggest that lactation and the expression of the VIP gene are interrelated.

Synthesis, cloning and expression in Escherichia coli of artificial genes coding for biologically active elongated precursors of the vasoactive intestinal polypeptide

Synthetic genes coding for elongated precursors of the vasoactive intestinal polypeptide (VIP) were synthesized and cloned in a highly efficient Escherichia coli expression vector. The synthetic genes code for VIP with its methionine (at position 17) replaced by leucine and elongated at the C-terminus by Gly (vasoactive intestinal polypeptide-Gly, i.e. VIPa) or by Gly-Lys-Arg (vasoactive intestinal polypeptide-Gly-Lys-Arg, i.e. VIPb). The synthetic genes fused to the N-terminal part of the E. coli beta-galactosidase gene were expressed to yield high amounts of fusion proteins reaching upon induction at least 60% of the total cellular protein. The fusion proteins of 314 and 316 amino acids carrying in their C-terminal portion either the 29 or 31 amino acids long VIP precursor polypeptide were shown to be immunoreactive with VIP antisera and were further purified and cleaved by CNBr. The resulting purified peptide precursors (VIPa and VIPb) were recognized by VIP receptors in rat liver plasma membranes and by antibodies to porcine VIP in a radioimmunoassay. Both precursors activated adenylate cyclase in rat liver membranes and stimulated pancreatic secretion in the cat. The affinity and potency of the cloned precursors is close to that of VIP purified from porcine intestine, suggesting that the elongated VIP precursors may act even without being converted into the C-terminal amide form of the peptide. The elongated VIP precursors expressed in E. coli may provide a cheap, large-scale source of experimental material for studies on VIP actions.

Localization of vasoactive intestinal peptide and peptide histidine isoleucine immunoreactivity and mRNA within the rat suprachiasmatic nucleus

The distribution of vasoactive intestinal peptide (VIP) and peptide histidine isoleucine (PHI) mRNA within the suprachiasmatic nucleus (SCN) of rats was evaluated by immunocytochemistry and in situ hybridization. The pattern of VIP and PHI immunoreactivity corresponded closely to the distribution of VIP/PHI mRNA within the ventrolateral SCN. Clear hybridization signal was observed within the SCN of rats killed 5 h after light onset and in rats killed 2 h after the onset of the dark phase of the light-dark cycle. Visual examination of the grain density within the autoradiographs suggested that VIP/PHI mRNA may occur in higher concentrations shortly after the onset of darkness than 5 h after the onset of the light phase.

Chromosomal assignment of human VIP/PHM-27 gene to 6q26----q27 region by spot blot hybridization and in situ hybridization

We determined the chromosomal location of the human VIP/PHM-27 gene in two different ways. First, we performed chromosome sorting with a cell sorter. Sufficient numbers of chromosomes for sorting were obtained by cultivating peripheral blood lymphocytes with interleukin-2. Spot blot hybridization of a molecularly cloned fragment of the gene to the sorted chromosomes revealed that this gene is located on chromosome 6. To define the location more precisely, in situ hybridization of the same fragment to the metaphase spreads was then performed, and human VIP/PHM-27 gene was assigned to a region near the terminus of the long arm of chromosome 6 (q26----q27).

Complete nucleotide sequence of human vasoactive intestinal peptide/PHM-27 gene and its inducible promoter

We have previously shown that the VIP precursor contains a novel PHI-27-like peptide, PHM-27, and that the synthesis of the prepro-VIP/PHM-27 mRNA is induced with cAMP and TPA in human neuroblastoma cells. In this study, we have determined the complete nucleotide sequence of the human VIP/PHM-27 gene. The gene spans 8,837 bp and consists of seven exons and six introns. Exon I of 165 bp consists of the 5' untranslated region of the gene, exon II of 117 bp encodes the signal peptide of prepro-VIP/PHM-27, exon III of 123 bp encodes the amino-terminal region, exon IV of 105 bp encodes PHM-27, exon V of 132 bp encodes VIP, exon VI of 89 bp contains the termination codon of the prepro-VIP/PHM-27 mRNA, and exon VII of 724 bp consists of the 3' untranslated region of the gene. VIP and its structurally related peptide, PHM-27, were encoded in different exons V and IV, and the sequences around the splice junctions between these exons and their adjacent introns were highly conserved, suggesting that the VIP-encoding and PHM-27-encoding exons have been duplicated from an ancestral exon over a broad area containing its adjacent introns. We also determined the 1,929-bp sequence of the 5' flanking region of the human VIP/PHM-27 gene and found that four TATA-box sequences were present at 28 bp, 145 bp, 772 bp, and 900 bp upstream of the cap site. Primer extension, exon mapping, and mung bean nuclease mapping analyses revealed that only the TATA-box sequence 28 bp upstream of the cap site was the promoter that is inducible by cAMP and TPA in the human neuroblastoma cells. An 18-bp sequence 52 bp upstream from the TATA-box sequence was suggested to be a cAMP/phorbol esters-responsive element of the human VIP/PHM-27 gene.

Localization of vasopressin-, vasoactive intestinal polypeptide-, peptide histidine isoleucine- and somatostatin-mRNA in rat suprachiasmatic nucleus

Messenger RNAs (mRNA) coding for vasoactive intestinal polypeptide (VIP), peptide histidine isoleucine (PHI), somatostatin and vasopressin were localized in the suprachiasmatic nucleus (SCN) of the rat hypothalamus using in situ hybridization histochemistry. Specific mRNA coding for each of these peptides was distributed in areas coextensive with the immunohistochemical localization of the appropriate peptide. The autoradiographic signal produced with probes to VIP and PHI created dense concentrations of silver grains over neuronal perikarya in the ventrolateral SCN, and the coextensive distribution of both VIP- and PHI-mRNAs suggests that both peptides are synthesized within the same neurons. The distribution of somatostatin-mRNA was distinct from the of VIP and PHI. Labeled neurons are observed at the interface of the two SCN subdivisions and the distribution of these neurons is identical to those shown to contain somatostatin immunoreactivity. Vasopressin-mRNA is also differentially concentrated within neurons in the dorsomedial subdivision of the SCN in an area that is coextensive with vasopressin-immunoreactive perikarya. The discrete pattern of hybridization for each of these mRNAs indicates that each of these peptides are synthesized in SCN neurons and reaffirms the differential distribution of each of these chemically defined cell populations within cytoarchitecturally distinct subdivisions of the nucleus.

Structure and expression of the gene encoding the vasoactive intestinal peptide precursor

The gene encoding the human vasoactive intestinal peptide (VIP) and the histidine-methionine amide (PHM-27) peptide hormone was isolated from lambda phage libraries. The human gene was found to be composed of seven exons spanning approximately 9 kilobase pairs. The first exon codes for an untranslated leader sequence, and the second exon codes for a putative signal peptide. DNA sequences coding for the VIP and PHM-27 hormones are located in two different exons. Southern blot analysis with genomic DNA suggested that a single copy of the VIP/PHM-27 gene is present in the human haploid genome. The expression of VIP/PHM-27 precursor mRNA in various tissues in the rat was analyzed by RNA gel blot hybridization. In the organs examined, expression was only detected in the brain and duodenum. RNA isolated from various regions of the rat brain--including the cortex, hypothalamus, and hippocampus--hybridized to both VIP- and PHM-27-specific probes. The same pattern of hybridization was found when VIP- and PHM-27-specific probes were used, suggesting that possible differences in the localization of VIP and PHM-27 peptides between different brain regions cannot be accounted for by differential RNA processing.

Hypothalamic vasoactive intestinal peptide messenger ribonucleic acid is increased in lactating rats

Vasoactive intestinal peptide (VIP) has been proposed as an inducer of PRL release. Moreover, immunocytochemical studies suggested an increase in the VIP content in the hypothalamus of lactating rats. We investigated whether this increase is regulated at the level of gene transcription. A sensitive RNA detection assay that uses in vitro transcribed RNA probes corresponding to specific exons of the VIP gene was devised to study VIP gene expression. Using this method, an approximately 2000-base long RNA containing the coding sequences for VIP was detected in rat hypothalamus. This RNA also contains the coding sequences for the VIP-related peptide PHM/I (peptide histidine methionine amide or isoleucine amide). An identical VIP-encoding RNA was previously identified in the rat cerebral cortex. A 2-fold increase was observed in hypothalamic VIP mRNA during lactation. In addition, the levels of this mRNA increased in the hypothalamus at the time of sexual maturation. Taken together, our results suggest a physiological regulation of VIP gene expression associated with its potential role as a neuroendocrine hormone.

Detection of vasoactive intestinal peptide-encoding messenger ribonucleic acid in the rat ovaries

Vasoactive intestinal peptide (VIP) has recently been detected in rat ovaries and has been shown to stimulate steroidogenesis by cultured rat granulosa cells. In this study we investigated whether the VIP-messenger RNA (mRNA) can be detected in the ovaries, thus suggesting local synthesis of the peptide. To study VIP-gene expression, a sensitive RNA detection assay which uses in vitro transcribed RNA probes corresponding to specific exons of the VIP gene was developed. Using this method, an approximately 2000-base RNA band containing the coding sequences for VIP was detected in rat ovaries. This RNA also contains the coding sequences for the VIP-related peptide (peptide-histidine-methionine). An identical VIP-encoding RNA was previously identified in the rat cerebral cortex. However, the VIP-mRNA quantity in the cortex was 12-fold-higher as compared to the ovaries. These results may reflect the differences in VIP concentration in the two organs. The finding of VIP-encoding mRNA in the rat ovaries suggests a local synthesis of VIP in the ovaries.