A Comparative Analysis of Somatolactin-Related Immunoreactivity in the Pituitaries of Four Neopterygian Fishes and One Chondrostean Fish: An Immunohistochemical Study

An antiserum to cod somatolactin (SL) was used for immunohistochemical screening of the pars intermedia of two teleosts (Oreochromis mossambicusandGymothorax meleagris), two holostean fishes (Lepisosteus osseusandAmia calva), and a chondrostean fish (Acipenser fulvescens) for SL-immunopositive (SL-IR) cells. As expected, a subset of the epithelial cells in the pars intermedia ofO. mossambicus(tilapia) was immunopositive for SL, and the remainder of the epithelial cells was immunopositive for α-MSH-specific antiserum (α-MSH-IR). SL-IR was not detected in any of the epithelial cells in the pars intermedia of the moray eelG. meleagris.To determine whether SL-IR could be detected in nonteleost fishes, immunohistochemical analyses were done on the pituitaries of two holostean fishes and one chondrostean fish. In the pars intermedia of the gar,L. osseus,a subset of cells was immunopositive for both SL and α-MSH. The majority of the pars intermedia cells was immunopositive for α-MSH only. However, in the pars intermedia of the bowfin,A. calva,all of the epithelial cells indicated the presence of both SL and α-MSH. Finally, no SL-positive cells were detected in the pars intermedia of the sturgeon,A. fulvescens.