| Summary: | 124 p. Thesis (Ph.D.)--University of Illinois at Urbana-Champaign, 1983. The following studies are concerned with the relationship of antifreeze peptides and glycopeptides to the processes of osmoregulation and reproduction in polar fishes. Polar fishes, like many marine teleosts, have serum osmolalities which are lower than that of sea water. As a result of being hypoosmotic to sea water, marine fishes are faced with a continuous osmotic loss of water. To replace osmotic and urinary water losses, marine fishes drink sea water and absorb salts and water from the intestine. In several species of Arctic and Antarctic fishes, the intestinal fluid osmolality is isosmotic to blood and strikingly hypoosmotic to sea water. Many of these species encounter macroscopic and microscopic ice crystals in the water column. Ingestion of ice, from feeding or drinking, is probably a common occurrence. Nucleation and subsequent freezing of intestinal fluid will occur if it should come in contact with ice. The first part of this thesis addresses the problem of how polar fishes prevent freezing of intestinal fluid as they maintain hydromineral balance. Results from this study show that low molecular weight glycopeptides (glycopeptides 7 and 8) are secreted into the intestinal lumen in sufficient quantities to prevent intestinal fluid from freezing. These glycopeptides appear to enter the intestine by biliary secretion. The second part of this thesis is concerned with the seasonal cycle of antifreeze peptides in the winter flounder. Winter flounder produce antifreeze peptides during the winter months but not during the summer. Changes in antifreeze concentration in plasma are preceded by an increase in levels of antifreeze mRNA. Such changes in mRNA levels in other systems (i.e., vitellogenin, ovalbumin, tyrosine, aminotransferase, etc.) have been shown to be induced by steroid hormones. Since winter flounder reproduce during the winter months, a possible relationship between the reproductive cycle and the induction of antifreeze ...
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