Gossypol isomers bind specifically to blood plasma proteins and spermatozoa of rainbow trout fed diets containing cottonseed meal

zWe investigated the role of gossypol isomers binding to blood plasma, semi nal plasma and spermatozoa to elucidate gossypol anti-fertility action in t he teleost fish, rainbow trout (Oncorhynchus mykiss). Growth and hematologi cal indicators of males were depressed when fish meal protein in diets was completely replaced with cottonseed meal. The cottonseed meal contained equ al proportions of (-) (47.8 +/- 1.6%) and (+) gossypol isomers. Concentrati ons of spermatozoa were decreased with increasing proportions of gossypol i n diets (from 0.22% to 0.95%); however, sperm motility and fertilizing abil ity were not affected. In contrast to mammals, steroid hormone concentratio ns were not suppressed in fish given diets with gradual increase of gossypo l level. Gossypol concentrations were 100-fold higher in blood plasma than in seminal plasma, confirming a barrier in gossypol transfer between the ge neral circulation and the testis. Spermatozoa accumulated predominantly (+) enantiomer (65-75%) with decreasing proportions as dietary gossypol concen trations increased. Spermatozoa bound most of the gossypol contained in the semen; however, this did not result in impairment of the sperm motility ap paratus. Teleost fish sperm rely on ATP stores that accumulate during matur ation as a source of energy during activation. In addition, the duration of sperm movement is short in these fish. As such, we hypothesize that the ma jor action of gossypol on mammalian sperm, which is uncoupling of oxidative phosphorylation, does not impair the energy supply required for flagellar beating in fish spermatozoa. (C) 2001 Elsevier Science B.V. All rights rese rved.