The endocrine pancreas of Alligator mississippiensis. An immunocytochemical investigation

Comparison of metabolic substrates in alligators and several birds of prey

On average, avian blood glucose concentrations are 1.5-2 times those of mammals of similar mass and high concentrations of insulin are required to lower blood glucose. Whereas considerable data exist for granivorous species, few data are available for plasma metabolic substrate and glucoregulatory hormone concentrations for carnivorous birds and alligators. Birds and mammals with carnivorous diets have higher metabolic rates than animals consuming diets with less protein whereas alligators have low metabolic rates. Therefore, the present study was designed to compare substrate and glucoregulatory hormone concentrations in several birds of prey and a phylogenetically close relative of birds, the alligator. The hypothesis was that the combination of carnivorous diets and high metabolic rates favored the evolution of greater protein and fatty acid utilization leading to insulin resistance and high plasma glucose concentrations in carnivorous birds. In contrast, it was hypothesized that alligators would have low substrate utilization attributable to a low metabolic rate. Fasting plasma substrate and glucoregulatory hormone concentrations were compared for bald eagles (Haliaeetus leucocephalus), great horned owls (Bubo virginianus), red-tailed hawks (Buteo jamaicensis), and American alligators (Alligator mississippiensis). Avian species had high circulating β-hydroxybutyrate (10-21 mg/dl) compared to alligators (2.81 ± 0.16 mg/dl). In mammals high concentrations of this byproduct of fatty acid utilization are correlated with insulin resistance. Fasting glucose and insulin concentrations were positively correlated in eagles whereas no relationship was found between these variables for owls, hawks or alligators. Additionally, β-hydroxybutyrate concentrations were low in alligators. Similar to carnivorous mammals, ingestion of a high protein diet may have favored the utilization of fatty acids and protein for energy thereby promoting the development of insulin resistance and gluconeogenesis-induced high plasma glucose concentrations during periods of fasting in birds of prey.

Identification of the pancreatic endocrine cells of Pseudemys scripta elegans by immunogold labeling

The endocrine pancreatic cells of Pseudemys scripta elegans were investigated immunocytochemically by light and electron microscopy. Insulin-, somatostatin (SST)-1, SST-28 (1-12)-, salmon (s)SST-25-, glucagon-, pancreatic polypeptide (PP)-, peptide tyrosine tyrosine (PYY)-, and neuropeptide tyrosine (NPY)-like immunoreactivities were observed. Insulin cells were immunogold labeled with bonito insulin antiserum and secretory granules were characterized by a wide halo and a dense core of varying shape. Consecutive PAP-immunostained sections showed that SST-28 (1-12), SST-14, and sSST-25 immunoreactivities occurred in the same cells. However, preabsorption tests demonstrated that anti-sSST-25 serum detected the invariant SST-14 molecule. The SST-28 (1-12)/SST-14-immunogold-labeled cells mainly had round or ovoid medium electron-dense granules. Glucagon-IR cells were characterized by round secretory granules with an electron-dense core, with or without a narrow clear halo. There were PP, PYY, and NPY (NPY-like) immunoreactivities in a population of glucagon-IR cells in the pancreatic duodenal region (glucagon/NPY cells). Most of the secretory granules of these glucagon/NPY-like cells had an electron-dense content and were round, although there were also pyriform or ovoid secretory granules which were smaller than those of glucagon-IR cells. Preabsorption tests proved that the NPY-like peptides detected in the endocrine pancreas of P. scripta elegans were more similar to NPY or PYY than to PP.

Purification and characterization of islet hormones (insulin, glucagon, pancreatic, polypeptide and somatostatin) from the Burmese python, Python molurus

Insulin was purified from an extract of the pancreas of the Burmese python, Python molurus (Squamata:Serpentes) and its primary structure established as: A Chain: Gly-Ile-Val-Glu-Gln-Cys-Cys-Glu-Asn-Thr10-Cys-Ser-Leu-Tyr-Glu-Leu- Glu-Asn-Tyr-Cys20-Asn. B-Chain: Ala-Pro-Asn-Gln-His-Leu-Cys-Gly-Ser-His10-Leu-Val-Glu-Ala-Leu-Tyr- Leu-Val-Cys-Gly20-Asp-Arg-Gly-Phe-Tyr-Tyr-Ser-Pro-Arg-Ser30. With the exception of the conservative substitution Phe --> Tyr at position B25, those residues in human insulin that comprise the receptor-binding and those residues involved in dimer and hexamer formation are fully conserved in python insulin. Python insulin was slightly more potent (1.8-fold) than human insulin in inhibiting the binding of [125I-Tyr-A14] insulin to the soluble full-length recombinant human insulin receptor but was slightly less potent (1.5-fold) than human insulin for inhibiting binding to the secreted extracellular domain of the receptor. The primary structure of python glucagon contains only one amino acid substitution (Ser28 --> Asn) compared with turtle/duck glucagon and python somatostatin is identical to that of mammalian somatostatin-14. In contrast, python pancreatic polypeptide (Arg-Ile-Ala-Pro-Val-Phe-Pro-Gly-Lys-Asp10-Glu-Leu-Ala-Lys-Phe- Tyr20-Thr-Glu-Leu-Gln-Gln-Tyr-Leu-Asn-Ser-Ile30-Asn-Arg-Pro-Arg -Phe.NH2) contains only 35 instead of the customary 36 residues and the amino acid sequence of this peptide has been poorly conserved between reptiles and birds (18 substitutions compared with alligator and 20 substitutions compared with chicken).

Endocrine cells with gastrin/cholecystokinin-like immunoreactivity in the pancreas of the spiny dogfish, Squalus acanthias

Endocrine cells containing gastrin/cholecystokinin (CCK)-like immunoreactivity were localized to the islet tissue in the pancreas of the spiny dogfish. Most of these cells were located in the 'intestinal' lobe of the pancreas; only occasional cells were observed in the 'splenic' lobe. The gastrin/CCK-like immunoreactive cells were often co-localized with the 'classical' pancreas hormones (insulin, glucagon and somatostatin). Radioimmunoassay of water extracts with a C-terminally directed antiserum revealed high levels of immunoreactive material in the intestinal part (48.6 +/- 19.9 pmol/g) and lower levels (4.5 +/- 0.6 pmol/g) in the splenic part. Acetic acid extracts of the intestinal lobe contained low levels (6.8 +/- 3.3 pmol/g) of gastrin/CCK-like immunoreactivity, whereas corresponding extracts of the splenic part showed no immunoreactivity. When the extracts were subjected to DEAE ion-exchange chromatography the gastrin/CCK-like peptides eluted as a major peak. After Sephadex gel filtration, pooled immunoreactive material from the main DEAE chromatographic peak eluted at a position close to that of CCK4. Further characterization by ion-exchange and reversed-phase HPLC showed that, in general, the immunoreactive material behaved like the shorter forms of the gastrin/CCK family (CCK4/G5 and CCK8/Cae 3-10).

Isolation and structural characterization of insulin, glucagon and somatostatin from the turtle, Pseudemys scripta

The chelonians occupy an important position in phylogeny representing a very early branching from the ancestral reptile stock. Hormonal polypeptides in an extract of the pancreas of the red-eared turtle were purified to homogeneity by reversed phase HPLC and their primary structures were determined. Turtle insulin is identical to chicken insulin. Turtle glucagon differs from chicken glucagon by the substitution of a serine by a threonine residue at position 16 and from mammalian glucagon by an additional substitution of an asparagine by a serine residue at position 28. Turtle pancreatic somatostatin is identical to mammalian somatostatin-14. The crocodilians are phylogenetically much closer to the birds than are the chelonians. Alligator insulin, however, contains three amino acid substitutions relative to chicken insulin. Thus, caution is required when inferring phylogenetic relationships based upon a comparison of amino acid sequences of homologous peptides.

Immunocytochemical study of the endocrine pancreas in the grey kangaroo (Macropus fuliginosus)

The endocrine pancreas of the grey kangaroo, Macropus fuliginosus, was investigated by means of immunocytochemistry using the PAP method on the same section at the light- and electron-microscopic levels. Semithin plastic sections were stained individually with primary antibodies for insulin, glucagon, somatostatin and pancreatic polypeptide (PP), and then photographed. Sections were osmicated, re-embedded in BEEM capsules, and ultrathin sections made and examined. The same labelled cells as in the semithin sections were localised in the thin sections, photographs taken and the morphology of secretory granules studied. The insulin cells were pleomorphic; their secretory granules displayed an electron-dense core surrounded by an empty halo. The glucagon cells possessed granules with an electron-dense core usually surrounded by a halo of less dense granular material. Somatostatin cells had larger, less dense secretory granules. The PP cells showed small, dense secretory granules. In order for an ultrastructural study to be considered reliable for the definite identification of endocrine cell types, it is essential that it be corroborated by correlated immunocytochemical data at the light- and electron-microscopic levels.

Comparative immunohistochemical study of the gastroenteropancreatic endocrine system of three reptiles

The gastroenteropancreatic (GEP) endocrine system of three reptiles, Testudo graeca, Mauremys caspica, and Lacerta lepida, was investigated by means of immunocytochemistry. Single and double immunostaining methods have demonstrated immunoreactivity for insulin, glucagon, pancreatic polypeptide (PP), somatostatin, serotonin, and peptide tyrosine tyrosine (PYY) in endocrine cells of the pancreas of the reptiles studied. Islet-like structures with insulin-immunoreactive (IR) cells surrounded by glucagon-IR cells were observed only in the splenic portion of the pancreas of M. caspica. Occasionally, somatostatin- and PP-IR cells were associated with glucagon-containing cells. Endocrine cells were also observed in the excretory ducts of the exocrine glands. Serotonin, bombesin, neurotensin, gastrin, glucagon, somatostatin, PYY, and insulin were demonstrated immunocytochemically in open-type GEP cells of the digestive tract of the animals studied. Serotonin, somatostatin, and glucagon-immunoreactive cells were the most abundant endocrine cell types. In L. lepida, PP- and peptide tyrosine tyrosine-immunoreactive cells were also frequently observed. Cells containing cholecystokinin, gastric inhibitory peptide, met- and leu-enkephalin, motilin, secretin, and vasoactive intestinal peptide could not be detected. The present work demonstrates that the reptilian GEP endocrine system is a complex structure containing most of the regulatory peptides similar in structure to those found in higher vertebrates.

Comparative study on the endocrine cells in the pancreas of Mauremys caspica (chelonia) in summer and winter

Four endocrine cell types were identified using peroxidase-antiperoxidase (PAP) technique and ultrastructurally characterized in the pancreas of Mauremys caspica in both winter and summer. In winter, insulin-immunoreactive cells were more abundant and the cell groups larger in the splenic than in the duodenal region, whereas in summer, medium or small cell groups were evenly distributed. Glucagon- and somatostatin-immunoreactive cells were found throughout the gland; they were more numerous in the splenic than in the duodenal region. Polypeptide pancreatic (PP)-immunoreactive cells were found only in the duodenal region. Somatostatin-immunoreactive cells were mainly isolated in winter and grouped in summer. Glucagon- and PP-immunoreactive cells had a similar arrangement in both seasons. Somatostatin- and PP-containing cells showed cytoplasmic processes and could be found next to the pancreatic ducts; the latter were also observed near insulin-immunoreactive cells. Some large secretory granules and numerous, isolated and long rough endoplasmic reticulum (RER) cisternae were seen in winter B cells; in summer B cells numerous lysosomes and few, dilated RER cisternae were found. Summer A cells showed well-developed, dilated RER cisternae and numerous vacuoles; secretory granules were more numerous in winter A cells. In winter B cells and summer A cells some nuclear filamentous inclusions were observed. Few RER cisternae were observed in winter D cells and many in summer D cells; secretory granules were found, the shape and electron density of which differed with the season. PP cells were characterized by their small secretory granules, which were less numerous in winter than in summer, being clustered at the cell pole or dispersed in the cytoplasm, respectively; in winter, the well-developed RER cisternae were dilated and irregularly distributed.

Histological and immunocytochemical study of the endocrine pancreas of the lizard Podarcis hispanica Steindachner, 1870 (Lacertidae)

The endocrine pancreas of the lizard Podarcis hispanica is described using light and electron microscopy. The endocrine pancreas of this reptile is located throughout the spleen side of the organ and consists of islet-like structures, small groups of two to five cells, and single scattered endocrine cells. The endocrine cells, including the islet-like structures, are not discrete units; on the contrary, they are intermingled with the endocrine component, both forming the glandular units. The endocrine islet-like structure shows a peculiar pseudoacinar pattern. The tridimensional reconstruction allows us to recognize the true structure of the glandular units. They are made up of two or three tubules closely arranged around a blood vessel, the endocrine component being disposed in the facing aspects of the tubules, around the vessel. Silver methods, Giemsa, and peroxidase-antiperoxidase techniques for light microscopy, immunogold, and routine methods for electron microscopy were used to demonstrate the regulatory peptide-producing cells present in the endocrine pancreas. Four major pancreatic endocrine cells, immunolocalized with the light and electron microscope, have been described: glucagon-containing cells (granules of 440 nm in diameter), insulin cells (400 nm), somatostatin cells (610 nm), and pancreatic polypeptide-containing cells (460 nm).

Immunocytochemical localization of peptides in the endocrine pancreas of the snakes Vipera aspis and Natrix maura

The endocrine pancreas of Vipera aspis and Natrix maura has been investigated by immunocytochemistry for the presence of six peptides reported to occur in Mammals or in Reptiles. Gastrin/CCK and PP were absent in the endocrine cells, VIP was located within nerve terminals only. Insulin, Glucagon, and Somatostatin were localized both in Vipera and Natrix, generally with a ring of D (Somatostatin) cells surrounding a core of Glucagon (A) and Insulin (B) producing cells; however frequent clusters of D cells are intermingled with the other endocrine cells. Statistical evaluations on the percentages of these 3 cell types showed preponderance of A cells in Natrix whereas in Vipera no significant difference was found between the number of A and B cells. The D cells showed a uniform distribution in the pancreas of the 2 studied species, in any case with a percentage slightly inferior to those of B cells.

Endocrine pancreas of Testudo graeca L. (Chelonia) in summer and winter: an immunocytochemical and ultrastructural study

Insulin-, glucagon-, somatostatin-, and PP-immunoreactive cells were identified immunocytochemically using antisera raised against mammalian hormones in the pancreas of Testudo graeca in both winter and summer. The endocrine cells were present throughout the gland, forming scarce islets except in the splenic region. The insulin cell islets were larger and more numerous in the splenic region than in the duodenal one. Winter glucagon-immunoreactive cells were found mainly in isolation while the summer ones occurred in groups which showed no immunoreactive central area; in both seasons these cells were more numerous in the splenic region than in the duodenal one. Somatostatin-immunoreactive cells were found isolated or grouped together more frequently in the splenic region in the summer specimens. No PP-immunoreactive cells were found in the splenic region, although they were numerous and isolated in the duodenal zone. Four cell types (B, A, D, and PP cells) were ultrastructurally characterized by the shape, size, and electron density of their respective secretory granules. Certain ultrastructural differences were detected in the summer and winter endocrine pancreatic cells. In summer specimens a fifth cellular type was observed. The presence of B, D, and PP cells among the epithelial pancreatic duct cells may confirm the comparatively primitive organization of the T. graeca endocrine pancreas.

Quantitative immunocytochemical analysis of the endocrine pancreas of the Nile crocodile

Four major pancreatic hormones were immunolocalized at the light and electron microscopic levels in the pancreas of the Nile crocodile, Crocodilus niloticus. Immunogold was used for electron microscopy, and peroxidase-antiperoxidase was used for light microscopy. Somatostatin-positive D-cells and pancreatic polypeptide-containing F-cells accounted for about 60% of the immunoreactive cells in the ventral pancreas. Glucagon-positive A-cells were the least frequent cell type in the ventral pancreas, about 15%, but were the predominant cell type, about 40%, in the pancreas that was dorsal in character. An expanded population of D-cells (relative to mammals and other higher vertebrates) in association with two very different numbers of A-cells can be expected to have important consequences for the homotropic control of secretory activity of the endocrine pancreas as well as for the function of the acinar pancreas. F-cells were absent from the dorsal part of the pancreas, whereas insulin-containing B-cells were slightly more abundant in this portion of the pancreas. The regional character of the endocrine pancreas was related to the complex looping of the proximal small intestine. Without immunolabeling, only B-granules were morphognomonic in electron micrographs. The insulin-reactive B-granules were the smallest (370 nm) of the secretory granules and were followed in size by somatostatin-positive D-granules (380 nm). The pancreatic polypeptide-containing secretory granules were the largest (580 nm). Glucagon-reactive A-granules (430 nm) sometimes exhibited a protuberance or extension of secretory granule matrix and limiting membrane. Such a morphological feature has previously been associated with secretion of glucagon and the initiation of insulin secretion. Taken together these studies indicate that protuberances have a significant, but as yet undefined, role in pancreatic endocrine cells.

Immunostaining of a cell type in the islets of Langerhans of the monkey Macaca irus by antibodies against S-100 protein

S-100 protein-immunoreactive cells were demonstrated by immunocytochemical procedures in the pancreatic islets of Langerhans in the monkey Macaca irus. By use of antibodies against human S-100 protein or bovine S-100 protein, these cells were observed in all islets in the head and tail portions of the pancreas. Immunostained cells were usually located in the center of the islets or sometimes found in a more widely distributed form, but they were never arranged in a regular concentric fashion. The number of immunoreactive cells varied from one islet to another but it was relatively limited making up only 0.75%-6.3% of all insular cells. With the use of the double-immunoenzymatic procedure for demonstration of the four main endocrine cell types (insulin-, glucagon-, somatostatin- and pancreatic polypeptide producing elements), it was possible to establish that S-100 protein-immunoreactive cells represent a distinct cell type. Antibodies against S-100 protein-stained neuroinsular complexes. The present findings speak in favor of a new cell type to be added to the large variety of S-100 protein-immunoreactive cells outside the central nervous system.

An immunocytochemical and ultrastructural study of the endocrine pancreas of Pseudemys scripta elegans (Chelonia)

Immunocytochemical and ultrastructural methods have shown four cell types in the endocrine pancreas of the turtle Pseudemys scripta elegans: insulin-, glucagon-, somatostatin-, and pancreatic polypeptide-immunoreactive cells. Each endocrine cell type was distributed differently in the duodenal or splenic regions of the turtle pancreas. Round or fusiform insulin- and glucagon-containing cells could be seen as single scattered cells which were more numerous in the duodenal regions, and the cell groups becoming progressively smaller from splenic to duodenal region. Round or fusiform somatostatin cells with thick processes and spindly pancreatic polypeptide cells with long protrusions were less numerous the nearer they were to the splenic regions; they were isolated in the duodenal zone. Insulin cells were surrounded by somatostatin cells and an outer layer of glucagon cells around the cell groups could be seen. Insulin cells were characterized by their round secretory granules which contained a polygonal, irregular or rod-shaped dense core. They also contained numerous clustered mitochondria, large multivesicular bodies, and cilium. Glucagon cells, joined by desmosomes to adjacent ones, had numerous filamentous mitochondria with longitudinal cristae and round electron-dense secretory granules with closely applied membrane. Somatostatin cells contained two kinds of secretory granules, some of which showed an electron-dense core, while others had moderately electron-dense floccular material. PP cells were characterized by round secretory granules, smaller than those of other cell types, and a large euchromatinic nucleus. Lysosomes, microtubules, bundles of microfilaments, a well-developed Golgi apparatus, and scarce rough endoplasmic reticulum were present in the cytoplasm of all these endocrine cell types.

Light microscopic histochemistry on plastic sections

As compared with conventional paraffin, celloidin, and frozen sections, semithin plastic sections offer a superior quality of the light microscopic image in terms of better resolution, absence of distortion and shrinkage artifacts, and suitability for calcified tissues. Application of histochemical methods to such sections often encounters, however, serious difficulties resulting from a considerably reduced reactivity of plastic-embedded biological material. Factors involved include a poor penetration of reagents into plastic embedding media due to a steric or hydrophobic hindrance, as well as a blockade of the reactive chemical groups in the sample due to interactions with fixatives and plastics. Embedding in polar (hydrophilic) plastics, such as glycol methacrylate, permits carrying out a large number of histochemical reactions, including the demonstration of enzymatic activities, directly on sections, but is less suitable for combined light/electron microscopic studies because of an imperfect ultrastructural preservation of tissues. Embedding in nonpolar epoxy resins, particularly if combined with a double aldehyde-osmium fixation, results in a high quality ultrastructure but almost fully inhibits the histochemical reactivity of the embedded material. In order to restore this reactivity, i.e. to unmask chemical groups bound by the polymerized resin, semithin epoxy sections require the removal of the embedding matrix by alkoxides prior to the histochemical procedure. Additional steps are also often necessary: treatment of osmium-fixed sections with oxidative agents, e.g., hydrogen peroxide or periodate which reoxidize the bound osmium and remove it from tissue, and a controlled proteolytic digestion, especially useful in immunocytochemical studies, which probably cleaves the bonds between the primary aldehyde fixative, and the reactive sites. This article reviews histochemical methods which have been successfully applied to plastic-embedded material. Using polar methacrylates and/or nonpolar epoxy resins as embedding media, it has been possible to demonstrate proteins and aminoacid residues, carbohydrates, lipids, nucleic acids, biogenic amines, inorganic ions, and some enzymes, although the spectrum of methods found as suitable for plastic-embedded material is far narrower than that available for paraffin or frozen sections.(ABSTRACT TRUNCATED AT 400 WORDS)

The gastro-entero-pancreatic system of the turtle, Chrysemys picta

Pancreatic endocrine cells were stained immunocytochemically for insulin, glucagon, somatostatin and pancreatic polypeptide by the PAP technique or sequentially for two hormones by the PAP followed by an indirect immunogold procedure. Pancreatic endocrine cells of Chrysemys are found scattered as single cells or small aggregates throughout the exocrine parenchyma; only the splenic region shows islets consisting of a B cell core surrounded by a loose mantle of A cells and occasional D cells. PP cells were not found in this splenic portion but were found scattered throughout the remainder of the pancreas. In contrast to the typical vertebrate islet, Chrysemys pancreatic endocrine cells are characterized by a lack of preferential association of one cell type with another and suggests that paracrine regulatory mechanisms may not be operable in this species. Insulin secretion from pieces of Chrysemys pancreas has been measured in incubation and perifusion systems employing a heterologous radioimmunoassay. Insulin release by Chrysemys B cells is enhanced by elevated levels of glucose (300 mg/dl), however, response appears to be somewhat slower compared to other vertebrate B cells. Gastrin, secretin, neurotensin, motilin, serotonin, PYY, glucagon, gastric inhibitory polypeptide, somatostatin and insulin were demonstrated immunocytochemically in open-type GEP cells of the mucosal epithelium of the Chrysemys intestine. Of these cells, gastrin, neurotensin and insulin cells appear to be the most numerous while the other types appear less frequently. Cells containing PP, bombesin, cholecystokinin and substance P could not be demonstrated. The localization of insulin to GEP cells of the turtle intestine is an unusual finding but has been confirmed by radioimmunoassay of extracts of the intestinal mucosa.

Isolation and characterization of reptilian insulin, glucagon, and pancreatic polypeptide: complete amino acid sequence of alligator (Alligator mississippiensis) insulin and pancreatic polypeptide

The insulin, glucagon, pancreatic polypeptide, and somatostatin contents of acid-alcohol extracts of alligator pancreas have been estimated by heterologous radioimmunoassay, and the insulin, glucagon, and pancreatic polypeptide have been isolated. The amino acid sequences of the insulin and pancreatic polypeptide were determined. The sequence of the insulin A chain is identical to that of chicken insulin A chain, while the B chain exhibits three conservative substitutions when compared to that of the chicken. Pancreatic polypeptide from the alligator is similar in sequence to that of chicken PP, but contains seven substitutions, most of which are conservative and preserve characteristics essential for conformation. The amino acid composition of alligator glucagon is identical to that of duck glucagon.

An immunocytochemical study of endocrine pancreas of snakes

The pancreas from eleven species of snakes representing both advanced and primitive families has been investigated for the presence of eleven regulatory peptides reported to occur in the mammalian endocrine pancreas. Of the eleven peptides studied, insulin, pancreatic glucagon and somatostatin were present in endocrine cells within the islets of all the species investigated. The neuropeptide, vasoactive intestinal polypeptide, was located within nerve terminals innervating the islets in the Boidinae, Colubrinae, Elaphidae and Crotalidae but absent from the Natricinae investigated. No immunoreactivity was demonstrable with the antisera to substance P, met-enkephalin, C-terminal gastrin, bombesin, glicentin and gastric inhibitory polypeptide. Pancreatic polypeptide-like immunoreactivity was demonstrable only in the boid snakes and exclusively stained by a C-terminal specific antiserum.

Regulatory peptides in the gastrointestinal tract of Alligator mississipiensis. An immunocytochemical study

The gastrointestinal tract of the alligator Alligator mississipiensis has been investigated for the presence of immunoreactivity to fourteen regulatory peptides all known to occur in the mammalian gut system. Mucosal endocrine cells reacting specifically with the antisera to neurotensin, C-terminal gastrin, somatostatin, bombesin, secretin, pancreatic glucagon and enteroglucagon were detectable, the distribution of these cells being, in general, similar to the mammalian pattern. Peripheral nerve cell bodies and nerve fibres were detected with the antisera to vasoactive intestinal polypeptide, substance P, bombesin and somatostatin again with a distribution similar to that seen in mammals. No immunoreactivity was observed with the available antisera to glicentin, motilin, gastric inhibitory polypeptide, gastrin 34, cholecystokinin 9-20 and met-enkephalin.

The endocrine pancreas of a squamate reptile, the desert lizard (Chalcides ocellatus). A histological and immunocytochemical investigation

The endocrine pancreas of the desert lizard (Chalcides ocellatus) was investigated histologically and immunocytochemically. The endocrine tissue was concentrated in the dorsal lobe, where it constituted about 7% of the total volume. In the ventral lobe the endocrine tissue formed approximately 1% of the total volume. Four endocrine cell types were observed in the pancreas of this species, namely insulin-, glucagon-, somatostatin- and pancreatic polypeptide (PP)-immunoreactive cells. The volume occupied by these cells was 1, 1, 0.6 and 0.3% of the total volume of the pancreas, respectively. Insulin-immunoreactive cells were located in the islet centre and comprised 3% of dorsal and 0.2% of the ventral lobe volume. Glucagon cells occurred at the islet periphery and amounted to 3 and 0.2% of the volume of the dorsal and ventral lobes, respectively. Somatostatin-immunoreactive cells were located at the islet periphery as well as in between the exocrine parenchyma. They constituted 1 and 0.2% of the volume of the dorsal and ventral lobes, respectively. PP-immunoreactive cells occurred mainly among the exocrine parenchyma as solitary cells. They formed only 0.03% of the volume of the dorsal lobe. The corresponding figure in the ventral lobe was 0.6%.