REGULATION OF HEPATIC VITELLOGENIN SYNTHESIS IN THE LITTLE SKATE (RAJA-ERINACEA) - USE OF A HOMOLOGOUS ENZYME-LINKED-IMMUNOSORBENT-ASSAY

An enzyme-linked immunosorbent assay (ELISA) was developed to detect v itellogenin in skates. The antibody raised against the yolk protein li povitellin was shown to recognize a sex-specific, estrogen-inducible 2 05 kD protein in plasma, previously identified in skate as vitellogeni n. The detection limit of the assay was 31.3 ng/ml, similar to that of radioimmunoassays for vitellogenin detection in other species. Using the assay, vitellogenin levels were shown to be highest (241.8 +/- 26. 5 mug/ml) in the ovarian follicular phase, decreasing approximately 1- 2 days before ovulation to a low (173.1 +/- 22.9 mug/ml) during the lu teal phase. Vitellogenin levels increased again approximately 1-2 days before oviposition to 259.8 +/- 38.8 mug/ml. The effects of estrogen and progesterone on hepatic vitellogenin production in normal and hypo physectomized male skates were also investigated. Plasma vitellogenin was not detectable in either intact or hypophysectomised male skates, but increased with estradiol treatment (intact: 48.2 +/- 4.9 mug/ml vs . hypophysectomised 252 +/- 10.6 mug/ml at day 8). Progesterone treatm ent significantly (P < .01) attenuated the effect of estrogen on plasm a vitellogenin levels in both intact (17 +/- 2.1 mug/ml) and hypophyse ctomized (44.0 +/- 9.4 mug/ml) male skates.