The effects of hypophysectomy on seasonal changes in plasma freezing-point depression, protein 'antifreeze,' and Na+ and Cl− concentrations of winter flounder (Pseudopleuronectes americanus)

Abstract

The annual changes in plasma Na⁺ and Cl⁻ concentrations took place in the absence of the pituitary, although the magnitude of the change was significantly reduced. The annual increase in plasma freezing-point depression also occurred in the absence of the pituitary. However the decrease normally observed in the spring and early summer did not occur.Sham-operated winter flounder transferred from ambient seawater (−1 °C) and day length to warm water (6–12 °C) and 18-h day length showed a reduction in plasma Cl⁻ concentration and freezing-point depression and a loss of the protein 'antifreeze.' Hypophysectomized flounder treated in the same way showed a reduction in plasma Cl⁻, but no decline in freezing-point depression and protein 'antifreeze.'These results suggest that an intact pituitary is necessary for the disappearance of the protein 'antifreeze' from the plasma of the winter flounder.