On the immunocytochemical localization of the vasoactive intestinal polypeptide

A new hypothalamic substance, and not luteinizing hormone-releasing hormone, is detected immunocytochemically by antibody to luteinizing hormone-releasing hormone

Adjacent paraffin sections of rat hypothalami fixed in Bouin's fluid were treated either with buffer or with luteinizing hormone-releasing hormone (LHRH) before immunocytochemical staining with anti-LHRH. Upon buffer pretreatment, pituitary gonadotrophs were unstained and hypothalamic fibers were stained. Upon LHRH pretreatment, pituitary gonadotrophs were stained (receptor reaction) and hypothalamic fibers were unstained. Extension of washes and use of series of neutralizing antisera between LHRH application and immunocytochemical staining, as well as the absence of inhibiting concentrations of LHRH in the later washes and neutralizing antisera removed from the sections, excluded the possibility that the disappearance of visualization of hypothalamic fibers was due to blockage of anti-LHRH in immunocytochemical staining. The results suggested that LHRH removed from the sections an immunocytochemically stainable but as yet unknown analog of LHRH and replaced it with LHRH, which in turn became lost during subsequent immunocytochemical processing. This idea was confirmed by the isolation by high-pressure liquid chromatography of a peak, distinct from LHRH, upon treatment of hypothalami with LHRH. It is suggested that the new substance may be carrier-held and that this substance, rather than LHRH, is normally detected by immunocytochemistry with anti-LHRH. Added LHRH binds not only to high-affinity pituitary receptors but also to low-affinity hypothalamic carriers.

Histological and immunohistochemical studies of the endocrine cells of the gastrointestinal mucosa of the toad (Bufo regularis)

Using histological and immunhistochemical techniques, nine endocrine cell types were observed in the mucosa of the gastrointestinal tract of the toad, Bufo regularis, viz. enterochromaffin, somatostatin, glucagon, pancreatic polypeptide (PP), secretin, gastric inhibitory peptide (GIP), gastrin-C-terminal pentapeptide (GTPP), neurotensin and bombesin cells. The enterochromaffin cells were distributed throughout the gastrointestinal tract except the rectum. Somatostatin, glucagon, PP, secretin, GIP and GTPP cells were observed both in the stomach and in the small intestine. Neurotensin cells were seen only in the ileum and bombesin cells only in the pyloric and antral parts of the stomach. Immunostaining of consecutive sections did not reveal more than one polypeptide hormone in any of these cell types. It is concluded from the present results that the toad gastrointestinal mucosa contains endocrine cell types that are more or less homologous to those in the mammal alimentary tract, though some of them exhibit a different topographic distribution.

VIP immunoreactivity in enteric nerves and endocrine cells of the vertebrate gut

The gastrointestinal tracts of various species chosen as representatives of the seven vertebrate classes were investigated for the occurrence of VIP immunoreactivity. The study was carried out with identically fixed and embedded tissue using the peroxidase-antiperoxidase (PAP) technique after primary incubation with a C-terminally directed antiserum (R 501). In the mammalian and avian species the antiserum failed to demonstrate VIP immunoreactive endocrine cells, while in the gut of all representatives of the lower vertebrate classes such cells were seen. The VIP immunoreactive cells were scattered among the epithelial cells of the entire intestine with a slightly higher density in the duodenum of bony fish, amphibians and reptiles. In contrast, VIP immunoreactivity in enteric nerve fibers and perikarya was found in all species studied except for the cyclostomes where the presence of VIP immunoreactive enteric fibers is questionable. The results may support, at least for mammals and birds, the hypothesis that true VIP is of nervous origin, while the endocrine cells contain VIP-related peptides.

Neuropeptides in the gut: quantification and characterization of cholecystokinin octapeptide-, bombesin- and vasoactive intestinal polypeptide-like immunoreactivities in the myenteric plexus of the guinea-pig small institute

The localization of CCK8-, bombesin- and VIP-like immunoreactivities in the myenteric plexus of the guinea pig small intestine has been studied by radioimmunoassay of extracts of longitudinal muscle strips obtained with and without adherent myenteric plexus; concentrations were compared with those in other regions of the gut. In innervated strips of longitudinal muscle of ileum there was approximately 14 pmol/g CCK8-, 32 pmol/g bombesin- and 135 pmol/g VIP-like immunoreactivity; concentrations were reduced by over 70% in denervated strips. Gel filtration and ion exchange chromatography indicated that over 80% of CCK immunoreactivity was due to CCK8; no evidence was found of significant amounts of smaller COOH-terminal fragments. Bombesin immunoreactivity occurred in two forms, the major one resembling the amphibian tetradecapeptide in its elution from gel filtration columns. Immunoreactive VIP differed markedly from porcine VIP in immunochemical and chromatographic properties; the data suggest that guinea pig VIP is less basic than porcine VIP and that the two peptides differ in structure in their NH2-terminal regions. Some functional implications of these findings are discussed.

Vasoactive intestinal polypeptide-like immunoreactivity in nerves of the pancreatic islet of the teleost fish, Gillichthys mirabilis

In the teleost fish, Gillichthys mirabilis, vasoactive intestinal polypeptide (VIP)-like immunoreactivity is present in some nerve fibres of the principal pancreatic islet and surrounding tissues, the vagus and splanchnic nerves, the coeliac ganglion and the wall of the intestine. The nerves of the pancreatic islet that contain VIP-like immunoreactivity probably correspond to one of the two types of non-cholinergic, non-adrenergic (peptidergic) nerve previously described in this fish. Similarities in the localisation of hormonal peptides in fish and mammals suggest that the regulation of gastroenteropancreatic physiology in fish may resemble that of mammals.

The distribution and cellular origin of vasoactive intestinal polypeptide in the avian gastrointestinal tract and pancreas

The distribution and origins of vasoactive intestinal peptide (VIP) in the gut and pancreas of the turkey were studied by radioimmunoassay of tissue extracts and by immunocytochemistry. Several antisera were used that vary in their specificity for different regions of porcine or chicken VIP. Radioimmunoassays using NH2-terminal specific antisera that react almost equally with porcine and chicken VIP's revealed signficant amounts of immunoreactive VIP in extracts of pancreas, brain and all regions of the gastrointestinal tract from crop to colon. Highest concentrations (300 pmol/g) were found in the colon muscle, and concentrations were generally low (< 20 pmol/g) in the mucosal layers of the small intestine. After ion exchange chromatography of extracts on CM-Sephadex three immunoreactive forms of VIP were separated corresponding to the three molecular forms previously found in mammalian gut extracts. In immunocytochemical studies nerve fibres were found throughout the gut, and in the pancreas. Immunoreactive nerve cell bodies were also identified in the submucous plexus throughout the gut, but were particularly prominent in the oesophagus and pancreas. It has previously been shown that VIP is a strong stimulant of the flow of pancreatic juice in birds whereas the structurally related hormone secretion, which is known to control the flow of pancreatic juice in mammals, is a weak stimulant. It is proposed that in birds VIP might regulate the pancreas, and other aspects of gut function, as a neurotransmitter or neurohormone.

Immunoreactivities of gastrin (G-) cells. II. Non-specific binding of immunoglobulins to G-cells by ionic interactions

Various gastro-entero-pancreatic (GEP) endocrine cells have been shown to contain concomitantly immunoreactivities against several peptide hormones. In the present study the "immunoreactivities" of gastrin (G-) cells of the rat stomach against 21 specific antisera and 10 control sera were investigated by means of the unlabelled antibody enzyme (PAP) technique using modifications of single steps in the immunocytochemical staining sequence. The results indicate that immunoglobulins can bind to gastrin cell granules obviously by non-specific ionic interactions. This non-specific binding of immunoglobulins occurs even in dilution ranges of the sera commonly used in immunohistochemical investigations of the GEP endocrine system. Since "adsorption controls" (preadsorption of the antisera with their respective antigens) will not discriminate between specific and non-specific binding of immunoglobulins to GEP endocrine cells additional specificity controls are necessary. In contrast to the immunostaining of various GEP endocrine cells by "established" antisera and of G-cells by gastrin antiserum immunoglobulins of sera from non-immunized animals as well as antibodies against corticotropin-lipotropin related peptides could be displaced from their binding sites in G-cells by alterations of the NaCl content of the buffers used as diluents or as rinsing solutions. To exclude immunostaining of GEP endocrine cells by nonspecific binding of immunoglobulins the following working procedures are recommended for immunocytochemical investigations of these cells: 1. Use of high titer antisera at low concentrations (diluted 1:1,500 or more). 2. Elevation of the salt (NaCl) content up to 0.5 M of the buffer used as diluent or as rinsing solution. 3. Adsorption controls will show reliable results only if point 1. and 2. have been taken into account.

The location of VIP in the pancreas of man and rat

VIP has powerful stimulatory effects on both endocrine and exocrine pancreas but its localisation within the gland has not been established. In this study, human pancreas was obtained fresh at surgery (eleven) or within four hours of death (seven). The pancreas was also removed from rats (twenty-two). Immunocytochemical staining showed VIP to be present in fine nerve fibres in all areas of the pancreas. Many fibres were seen in the exocrine pancreas, running between the acini, and around ducts and blood vessels. In addition, dense networks of fibres were observed forming meshes around islets and occasional ganglia were found containing immunoreactive cell bodies. In general, there were fewer VIP fibres in the rat pancreas than in the human, but overall distribution was identical. The mean VIP content of whole human pancreatic tissue was 42 +/- 10 pmol/g wet weight (38 +/- 9 pmol/g in head, 49 +/- 6 pmol/g in body and 42 +/- 11 pmol/g in tail). Whole rat pancreatic tissue contained 28 +/- 7 pmol/g wet weight while preparations of isolated islets were found to contain 374 +/- 30 pmol/g. It is possible that the heavy VIP innervation of the islets described here indicates a role in the regulation of islet hormone release.