Study of the integument that covering back and stinger of the freshwater stingray Potamotrygon rex (Chondricthyes, Potamotrygonidae).

The objective of this study was to describe the histology and histochemistry of the integument covering the back and stinger of the freshwater stingray Potamotrygon rex, endemic to the Middle Upper Tocantins River. The species has a dark back and yellowish circular spots that extend to the tail, which has one to two stings located in the median portion of the tail. Through histological study it was observed that the epithelia of the back and stinger are composed of non-keratinized stratified pavement epithelial tissue, and are organized in three layers: basal, intermediate and superficial. The differences between the tissues are related to the cell types that compose them. The back is organized with epithelial cells, mucus cells, granulocyte cells and chromatophores. The mucus cells are distributed in different layers along the animal's back, influencing the thickness of the tissue. The tissue that covers the stinger is composed of epithelial cells, chromatophores and specialized cells in protein synthesis. In the histochemistry, the stinger epithelial cells were stained with Bromophenol Blue, especially those of the intermediate layer, which were called specialized cells. In the back the epithelial cells were stained with Bromophenol Blue, Alcian Blue and PAS, and the mucous cells with PAS. In both tissues the presence of protein reserves was detected, areas so called because they are stained strongly with Bromophenol Blue. The results show that the stinger presents activity directed to the production of proteins, and that the back is organized to produce different components, which constitute the cuticle that covers the animal's body.

Dissociated effects of somatostatin analogs on arginine-induced insulin, glucagon and growth hormone release in acromegalic patients.

Two analogs of somatostatin (Ala2,D-Trp8,D-Cys14-Somatostatin and L-5F-Trp8-Somatostatin) infused into acromegalics at the rate of 4.5 micrograms/min suppressed arginine-stimulated growth hormone release more strongly than 6 micrograms/min somatostatin (110 +/- 11% and 129 +/- 14%, respectively). Under the same conditions the two somatostatin analogs induced a much smaller inhibition of insulin (33 +/- 13% and 44 +/- 18%) and glucagon (28 +/- 10% and 45 +/- 17%, respectively) release than somatostatin did. Somatostatin analogs with dissociated actions could be promising for the treatment of diseases such as acromegaly, diabetes mellitus and some ectopic hormone syndromes.