The role of pituitary in regulating antifreeze protein synthesis in the winter flounder

The antifreeze proteins are a unique class of serum proteins found in some polar and cold water fish. These proteins prevent the fish from freezing and are essential for their survival [ 1,2] . At present, there are two different types of antifreeze proteins known; the glycoproteins isolated from some Antarctic [3] and Arctic fishes [4] and the polypeptide antifreeze from the winter flounder [5,6]. The glycoproteins consist of repeating tripeptide units of alanyl-alanylthreonine with a disaccharide linked to the threonyl residue. Flounder antifreeze protein, on the other hand, contains 8 amino acids and no carbohydrate moiety. The only similarity between these two types of antifreezes are the abundance of alanine in their amino acid composition. The occurrence of the antifreeze protein (AFP) in the winter flounder inhabiting Newfoundland seawater is seasonal [7]. It appears in the plasma during November and disappears during May of each year. Both temperature and photoperiod are involved in regulating this annual cycle [S] . We have recently shown that the pituitary is necessary for the seasonal disappearance of the antifreeze from the plasma [9]. However the detailed mechanisms whereby the pituitary regulates plasma antifreeze has yet to be investigated. Here we describe our findings on the effect of hypophysectomy on AFP synthesis using both in vivo and in vitro procedures. Our results show that while control animals lose the ability to synthesis AFP during the summer months, the hypophysectomized animals continue to synthesize the protein.