Ureogenic function and periodic urea excretion in a gobiid fish, Mugilogobius abei

Abstract

M. abei has a high ability to produce a large amount of urea, when exposed to 2mM NH₄HCO₃ or 1mM ¹⁵N-(NH₄)₂SO₄ solution, After exposure to ¹⁵N-ammonia, ¹⁵N-concentration of the amide-N in glutamine in tissues was virtually the same as that of ammonia-N, which were about 2-fold that of urea-N in the tissues as well as in the excreta. Glutamine contents and glutamine synthetase activities in the liver and muscle increased greatly following exposure to ammonia. CPSaselllmRNA expression as well as CPSaselll activity was found to be present in muscle, skin and gill, but not in liver, spleen and intestine. Furthermore, it was found that M. abei excreted urea with a periodic rhythm which might be mediated by a periodic enhancement of urea permeability at excretion sites.