Assimilation and metabolism of exogenous glucose by yolk-sac embryos after intraovarian preincubation and in vitro in Zoarces viviparus

Abstract

The ability of yolk-sac embryos of the blenny Zoarces viviparus (L.) to assimilate and metabolize exogenous glucose was investigated by in vivo and in vitro experiments. The investigations in vivo (experiment I) were performed by simultaneously injecting 14C-labelled glucose (30 μL (5 μCi)/100 g body weight) and unlabelled carrier glucose (100 mg/100 g body weight) into the ovary (loaded group). Controls received only 14C-labelled glucose (nonloaded group). The shape of the disappearance curve for the tracer glucose in the glucose-loaded group was similar to that for carrier glucose, with a gradual decrease during the first 9 h postinjection. Half-lives were calculated to be 5.17 h for tracer glucose and 5.41 h for carrier glucose in the loaded group. Both tracer and carrier glucose levels returned to control levels after 24 h in the loaded group. Accumulation of tracer glucose was significantly higher in yolk-sac embryos from the nonloaded control group compared with embryos from the loaded group. Tracer accumulation in maternal liver and kidney was low and showed an opposite pattern to accumulation in the embryos, with more tracer accumulated in the maternal liver and kidney from the loaded group compared with controls. After intraovarian preincubation with [14C]glucose, release of 14CO2 and DO14C (dissolved organic carbon) from assimilated tracers in the embryos in vitro was low. In another experiment (experiment II) the embryos were dissected out of the ovary of untreated females and incubated in vitro with [14C]glucose. The embryos assimilated the labelled glucose, and uptake rates were correlated with the ambient concentration of carrier glucose. Release from embryos into the medium of 14CO2 and DO14C from assimilated tracer glucose was at the same low level as after intraovarian preincubation with [14C]glucose in experiment I. In combination, the results show that as early as their yolk-sac period, embryos from Zoarces viviparus have the capacity for assimilating and metabolizing glucose from naturally occurring concentrations in the ovarian fluid in vivo or from media in vitro.