Humic acid reduces gonadotropin activity and hormonal sensitivity of frog oocytes

The specific stimulatory effect of sturgeon Acipenser güldenstädti Br. gonadotropic hormone (GTH) on frog Rana temporaria L. oocyte maturation in vitro was investigated in relation to humic acid (HA) concentrations from 12.5 to 50 mg/l. HA was observed to bind to both the follicular membrane of the oocytes and the GTH molecule, reducing the oocytes' hormone sensitivity and maturation ability. It was also shown that HA inactivated GTH, lowering its specific ability to stimulate oocyte maturation.