The endocrine pancreas of the toad consists of rounded islets of various sizes embedded in the exocrine tissue. Isolated cells are also present. At least 4 types of endocrine cell are distinguishable by shape, size and electrondensity of the secretory granules as well as by their immunoreactivity with different antisera : insulin, somatostatin, pancreatic polypeptide, and glucagon cells. Insulin cells can be divided into 2 types according to their cytoplasmic electrondensity. Colocalisation of different hormones in the same cell is rarely observed. The close contact between endocrine and exocrine cells and the scarcity of nerve supply is indicative of a paracrine control of hormone secretion.Key words : Amphibia ; toad ; insulin ; somatostatin ; glucagon ; pancreatic polypeptide.
The endocrine pancreas of amphibians consists of islets located within the exocrine tissue. The islets are composed of at least 4 types of cell. Not many studies have dealt with the morphology of endopancreatic cells in adult amphibians. The anatomy of the pancreas in several species of amphibians and reptiles was described by Epple (1966), Penhos & Ramey (1973), Hellman & Hellerstro$ m (1962, Lange (1973), Lange et al. (1975), and Khanna & Kumar (1973). A histological description and demonstration of immunoreactivity by different cell types was made by Kaung & Elde (1980) in Rana pipiens, by Buchan (1985) in several species of anurans and urodeles, Kowan et al. (1991) in Xenopus laevis, El-Salhy et al. (1982) in several anurans, and Putti et al. in Triturus (1990) and in Rana arvalis (1995). An ultrastructural description of the islet cells in amphibians is still lacking, except for those by Tomita & Pollock (1981) in Rana catesbeiana and Trandaburu et al. (1995) describing the somatostatin-immunoreactive-cells in Rana esculenta.The aim of this work is the immunocytochemical identification of endocrine cells of the toad Bufo bufo by means of the immunogold labelling reaction which allows a precise identification of the different cells together with their fine structural description.Correspondence to Dr Fiorenza Accordi, Dipartimento di Biologia Animale e dell'Uomo, Universita ' ' La Sapienza ', Viale dell'Universita, 32-00185 Rome, Italy. Tel. : 0039 6 49914754 ; fax : 0039 6 4958259 ; e-mail : Accordi!axrma.uniroma1.it
Five adult specimens of the toad Bufo bufo L. of each sex were collected from ponds in the surroundings of Rome, killed by fast decapitation and dissected to remove the pancreas. This was fixed in a mixture of 1 % glutaraldehyde and 2 % paraformaldehyde in 0n1 cacodylate buffer (pH 7n3), after being divided into 5 regions : central body, gastric lobe, hepatic lobe, splenic lobe and duodenal lobe. Following 2 h fixation, the specimens were rinsed in cacodylate buffer and postfixed in 1 % OsO % in 0n1 cacodylate buffer (pH 7n4), for 1 h, then dehydrated in an ascending series of ethanol and embedded in Araldite resin.Ultrathin sections for conventional electron mic...
