Does ammonia trigger hyperventilation in the spiny dogfish ?

Published online on 20. November 2014

Does ammonia trigger hyperventilation in the elasmobranch,
Squalus acanthias suckleyi ?

Gudrun De Boeck, Chris M. Wood

ABSTRACT:

We examined the ventilatory response of the spiny dogfish, to elevated internal or environmental ammonia. Sharks were injected via arterial catheters with ammonia solutions or their Na salt equivalents sufficient to increase plasma total ammonia concentration [T_Amm]_a by 3–5 fold from 145 ± 21 μM to 447 ± 150 μM using NH₄HCO₃ and a maximum of 766 ± 100 μM using (NH₄)₂SO₄. (NH₄)₂SO₄ caused a small increase in ventilation frequency (+14%) and a large increase in amplitude (+69%), while Na₂SO₄ did not. However, CO₂ partial pressure (P_aCO2) also increased and arterial pH_a and plasma bicarbonate concentration ([HCO₃⁻]_a) decreased. NH₄HCO₃ caused a smaller increase in plasma ammonia resulting in a smaller but significant, short lived increases in ventilation frequency (+6%) and amplitude (36%), together with a rise in P_aCO2 and [HCO₃⁻]_a. Injection with NaHCO₃ which increased pH_a and [HCO₃⁻]_a did not change ventilation. Plasma ammonia concentration correlated significantly with ventilation amplitude, while ventilation frequency showed a (negative) correlation with pH_a. Exposure to high environmental ammonia (1500 μM NH₄HCO₃) did not induce changes in ventilation until plasma [T_Amm]_a increased and ventilation amplitude (but not frequency) increased in parallel. We conclude that internal ammonia stimulates ventilation in spiny dogfish, especially amplitude or stroke volume, while environmental ammonia only stimulates ventilation after ammonia diffuses into the bloodstream.

Respiratory Physiology & Neurobiology,
Volume 206, 15 January 2015, Pages 25–35

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