Metabolic Alterations of Catechoiamines and Other Compounds In Elasmobranch Tissues

Abstract

It has been suggested that many of the biodegradation reactions which inactivate drugs and foreign compounds are essentially absent in fishes(1), since the fish and its surrounding medium represented in essence an infinitely large dialysing system. More recent evidence, however, indicates that a number of the detoxication reactions observed in mammals also are operative in fishes(2). In this communication we report studies on the metabolic alteration of catechoiamines. For purposes of comparison, the presence of a number of microsomal detoxication enzymes was determined in some of the tissues studied.

Materials and methods. The tissues were excised from sharks anaethesized with tricane methane sulfonate (Sandoz MS 222) and excised from sharks anaesthetized with tricane or were frozen (in dry ice) for later use. Unless otherwise noted, preparation of the enzymes was as follows: the tissue was homogenized first in a blender with 3 volumes of 1.15% KCl and then re-homogenized in a tight fitting glass-Teflon Potter-Elvehjem homogenizer. In the case of the liver, the homogenates were centrifuged for 10 minutes at 2,000 rpm and the large fatty layer was removed. Subsequently, the homogenates were centrifuged at 9,000 rpm for 10 minutes to obtain the so-called microsomal and soluble supernatant fractions (9,000 × g fraction). Microsomes were sedimented from this fraction by centrifugation at 30,000 rpm for 60 minutes, resuspended in 1.15% KCl and sedimented again. Catechol-O-methyl trans-ferase was estimated by the method of Axel-rod et al(3) using S-adenosylmethionine-C¹⁴ (New England Nuclear, 52.6 mc/mM) as the methyl donor. The reaction mixture was adjusted to pH 7.9-8.0 with either phosphate or Tris buffer and incubated in a final volume of 0.5 ml for 60 minutes at 25°C. The reaction was stopped by the addition of Na₂B₄O₇ (pH 10.0) and the methylated products were extracted with toluene : isoamyl alcohol (3:2;v/v).