The reproductive biology of the rainbow runner, Elagatis bipinnulata (Quoy & Gaimard, 1825) caught in the São Pedro and São Paulo Archipelago.

The rainbow runner, Elagatis bipinnulata, which belongs to the Carangidae family, has a circumtropical distribution. It is found throughout the Atlantic Ocean, from Massachusetts (USA) to Bahia (Brazil). The reproductive biology of the rainbow runner was studied, using specimens captured off the São Pedro and São Paulo Archipelago. From July 1999 to November 2003, a total of 352 fishes were analysed (201 females and 151 males). Fork length (FL) was measured and specimens were gutted for gonads collection. In the laboratory, gonads length, width and weight were measured, and sexes identified macroscopically. Through histological analysis, five different maturation stages were identified for females: immature, maturing, mature, spent and resting. A predominance of maturing and mature females was observed from January to May. The highest gonad index (GI) values were also observed during this period, ranging from 7.7 to 55. Mean sexual maturity size (L50) for females was estimated at 64.6 cm (FL). In the studied area the species exhibited total spawning, with two synchronous groups. Testicles were histologically very similar making them impossible to differentiate sexual maturation stages. Considerable variation was observed in the male gonads weight, hampering the assessment of size at maturity. However, GI values for males were also higher from January to May. These results suggest that the spawning period of the rainbow runner in the São Pedro and São Paulo Archipelago occurs during the first semester of the year.

An immunohistochemical study on the pancreatic endocrine cells of the three-toed sloth, Bradypus variegatus.

The cellular composition and relative frequency of the occurrence of pancreatic endocrine cells were studied immunohistochemically in a primitive eutherian and arboreal folivore, the three-toed sloth, since previous histochemical and ultrastructural studies on the endocrine pancreas of the sloth have detected only a single islet cell type, the A cell. In the sloth pancreas, four types of endocrine cells immunoreactive for glucagon, insulin, somatostatin and serotonin (5-hydroxytryptamine) were found as reported in the pancreas of human and common experimental mammals, but pancreatic polypeptide-immunoreactive cells were not detected by either avian- or bovine-pancreatic polypeptide antiserum. The endocrine cells were distributed mainly in the islets and partly also in the exocrine tissue including the pancreatic ducts. Larger or smaller clusters consisting of glucagon- and insulin-immunoreactive cells were also found frequently in the interlobular connective tissue. In the islets, glucagon- and insulin-immunoreactive cells were the most prominent cell type, while somatostatin- and serotonin-immunoreactive cells were sparse. The most striking feature in the sloth pancreas is the high frequency of glucagon-immunoreactive cells, because these cells are by far less in number than insulin-immunoreactive cells in the islets of human and common experimental mammals. This appears to be an intriguing characteristic of the sloth pancreas in a possible relation to the animal's unique metabolic system and the phylogenetical position.

Demonstration of insulin in the pancreas of the Didelphis albiventris (opossum) by immunocytochemical techniques.

The exocrine secretion of insulin by the suckling opossum was demonstrated by indirect immunofluorescence and immunoperoxidase techniques. In weanling and adult marsupial insulin is present in the pancreatic islets and in scattered cells located in the exocrine secretory units. Positive reaction was also observed in the brush border and in some isolated cells of the proximal segment of the suckling opossum small intestine.

The fine structure of the placental labyrinth in the sloth, Bradypus tridactylus.

The placental labyrinth of the three-toed sloth (Bradypus tridactylus) was examined by electron microscopy. The material available was from two fetuses of 55 mm and 150 mm crown-rump length (CRL). The placenta of the younger specimen was a transition form between the syndesmochorial type and the endotheliochorial type. The interhemal membrane of the 55 mm CRL specimen consisted of the following components: 1) hypertrophied maternal endothelial cells surrounding the maternal vessels; 2) a small amount of extracellular material and spindle-shaped cells, both presumed to be of maternal origin; 3) a layer of syncytial trophoblast that had an unusual, reticulated or sponge-like appearance; and 4) the fetal capillary endothelium. In addition, the fetal connective tissue contained hypertrophied mesenchymal cells that were characterized by abundant granular endoplasmic reticulum. The placenta of the 150 mm CRL fetus was poorly preserved, but it was possible to determine that the placenta was of the endotheliochorial type. There was a close apposition of maternal endothelium and trophoblast. The results confirmed virtually all of lhe light microscopic observations of Wislocki (1927; 1928b). The ultrastructure of the sloth interhemal membrane is compared to that of other endotheliochorial placentas, particularly that of the shrew, with which it shows many cytological similarities.

Ultrastructure of the pancreas of Bradypus tridactylus.

The fine structure of the pancreas of the South American three toed sloth, Bradypus tridactylus, is described. In exocrine cells two types of granules are found. The first variety of granules is circular, of about 0.9 micrometer mean diameter, and probably represents zymogen granules. The second type of granule is larger (up to 1.4 micrometer in diameter) and contains a granular electron-dense material which is separated from the limiting membrane by a wide space. Only one type of islet cell was found. It contains spherical membrane-bound granules of uniform size.

Some histological and histochemical studies of the pancreas of the Brasilian sloth, Bradypus tridactylus.

The histological and histochemical study of the pancreas of the three-toed sloth, Bradypus tridactylus, demonstrated that with the methods employed the pancreatic islets are apparently formed by A cells exclusively. Two different types of argyrophilic cells were noticed in the exocrine secretory units when Grimelius' method was used. The methods for the demonstration of D cells showed negative results. Aldehyde fuchsin-positive granules were only noticed at the apex of the exocrine pancreatic cells. These results are discussed in relation to current hypotheses concerning the evolution of insulin secretion mechanisms.