Frog oocyte in vitro maturation test as a method to investigate Ni²⁺ toxicity

The ability of gonadotropic hormone (GTH) of sturgeon fish Acipenser göldenstödti Br. to initiate a specific stimulatory effect on grass frog Rana temporaria L. oocytes, producing its in vitro maturation, was employed as a method to investigate the effect of nickel ion concentration on test oocytes in a highly sensitive test system, "Oocyte-GTH". Oocytes of four frogs with different hormone sensitivity were used in the investigation. It was shown that Ni²⁺ at a concentration of 0.1 mg/L produced a considerable stimulatory effect only in test frog oocytes with low hormonal sensitivity and maturation activity, while a Ni²⁺ concentration over 0.25 mg/L caused a significant decrease and produced even total blocking of the hormonal sensitivity and maturation ability of all oocytes, regardless of their initial hormonal sensitivity. The frog oocyte maturation test was shown to be a useful method to assess toxic effect of Ni²⁺ on water frog reproduction.