Growth Inhibition, Gluconeogenesis, and Morphometric Studies of the Pituitary and Interrenal Cells of Acid-Stressed Brook Trout (Salvelinus fontinalis)

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Abstract
Somatic growth was stunted in yearling brook trout (Salvelinus fontinalis) maintained for up to 73 d in pH 4.5. Plasma cortisol level increased in pulses after 1.5 h (from 10 to 82.3 ng .cntdot. mL-1) on days 4 (46 ng .cntdot. mL-1) and 15-30 (20-25 ng .cntdot. ml-1) of acid treatment. Interrenal nuclear hypertrophy and cell hyperplasia occurred respectively on days 4 and 15. Electron microscopic observations revealed that the somatotropes and thyrotropes were atrophic for about half of the experimental period whereas the corticotropes displayed sustained hypertrophy. Plasma glucose and amino acid levels rose simultaneously by 300-600 and 130%, respectively, fromday 4 of acid exposure. Hepatic L-alanine aminotransferase activity increased on day 30 just as plasma protein concentration began to decline. When adrenalin and cortisol acetate were administered to trout maintained in neutral pH to raise circulating cortisol levels form 10-20 to 1876 ng .cntdot. mL-1, blood glucose remained normal up to 6 d after treatment. These results suggested that acid stress suppressed somatotropin, thyrotropin, and indirectly thyroid hormone secretion but stimulated the pituitary-interrenal axis, leading to inhibition of protein synthesis and accumulation of amino acids in the circulation. The elevation of blood sugar level was caused by some as yet unidentified factors.

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