THE BRANCHING OF INSULIN-LIKE GROWTH FACTOR-I AND INSULIN - AN IMMUNOHISTOCHEMICAL ANALYSIS DURING PHYLOGENY

The co-existence of insulin-like growth factor 1 (IGF-1) with the clas sical islet hormones insulin (INS), glucagon (GLUC), somatostatin (SOM ) and pancreatic polypeptide (PP) in the endocrine pancreas of represe ntative species of cyclostomes (Myxine glutinosa), cartilaginous fish (Raja clavata, Squalus acanthias) and bony fish (Cottus scorpius, Cara ssius auratus, Cyprinus carpio, Anguilla anguilla) was studied by the use of monoclonal and polyclonal antisera and the double immunofluores cence technique. In all species investigated, IGF-1-like-immunoreactiv e cells were found in the endocrine pancreas, however, in varying loca lization. In Myxine glutinosa, all INS-immunoreactive cells and some o f the SOM-immunoreactive cells contained IGF-1-like-immunoreactivity. In Raja and Squalus, only a minority of the INS-immunoreactive cells a lso displayed IGF-1-like-immunoreactivity. The majority of the IGF-1-l ike-immunoreactivity was observed in SOM- and in GLUC-immunoreactive c ells. Different results were obtained in bony fish. In Cottus, in the Brockmann bodies and the small islets IGF-1-like- and INS-immunoreacti vities co-existed to 100%. In contrast, in the other bony fish studied IGF-1-like-immunoreactivity was not observed in INS-immunoreactive ce lls: in Cyprinus, IGF-1-like-immunoreactivity was found in GLUC-, PP- and SOM-immunoreactive cells and in Carassius and Anguilla, in SOM-imm unoreactive cells only. Thus, in all bony fish species with the except ion of Cottus, IGF-1 and insulin display a distinct cellular distribut ion, similar to that of mammals. The present results, thus, may indica te that the branching of IGF-1 and insulin has occurred at the phyloge netic level of bony fish.