Calcium metabolism in relation to ovarian functions during early and late pregnancy in the viviparous blenny Zoarces viviparus

Calcium metabolism was studied in relation to ovarian functions and embryonic development during early and late pregnancy in the viviparous blenny Zoarces viviparus . The level of total calcium in the maternal serum decreased during pregnancy from 21·7 (± 2·6) to 8·7 (± 1·1) mg 100 ml −1 . Calcium in the ovarian fluid surrounding the embryos appeared at a level which was always lower than in the maternal blood. The calcium content of the embryos increased during their development in the ovarian cavity. During early pregnancy, oestradiol‐treatment increased the level of total calcium and alkkali‐labile protein P (vitellogenin) in serum of the maternal organism, but did not have any effect on the level of ultrafiltrable calcium. However, in the untreated females, the post‐ovulatory follicles, believed to act as calyces nutriciae in the pregnant ovary, were able to concentrate the ultrafiltrable calcium above the level in the serum. The activity of injected 45 Ca per unit plasma and follicular fluid volume was always higher in oestradiol‐pretreated fish when compared with controls over a time course range. Embryos from females, which were not treated with oestradiol, accumulated high levels of labelled calcium and the accumulation was time‐course dependent. Embryos from oestradiol‐treated females showed low levels of tracer accumulation at all samplings and their appearance indicated an overall negative effect of oestradiol. During late pregnancy, labelled calcium showed a rapid turnover within 24 h post‐injection in the maternal blood and ovarian fluid and a large accumulation in the embryos. Calcium influx in embryos, which were incubated with labelled calcium during 72 h in in vitro systems was largest during the initial 4·5–24h time interval.