ON THE PITUITARY GLAND OF THE SAFFRON COD, ELEGINUS GRACILIS, AND THEIR COLD ADAPTATION (14th Symposium on Polar Biology)

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The seasonal variation of the pituitary gland of the saffron cod, Eleginus gracilis, was investigated by light microscopy and immunohistochemistry. Growth hormone(GH)-secreting cells were found in the proximal pars distalis. Prolactin(PRL)-secreting cells were located in most part of the rostral pars distalis. In the fish collected during the winter, the immunoreactions with both GH and PRL were very weak. On the contrary, in the fish collected during the summer, the positive immunoreactions with both GH and PRL were remarkable. However, there were no seasonal differences in the sizes of nuclei of GH- and PRL-secreting cells between the winter and the summer fish. GH action for annual antifreeze glycoprotein cycle and PRL role for the kidney function are discussed. The results may suggest the possibility of PRL clearing of antifreeze glycoprotein of the serum by increasing glomerular filtration during the summer.
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