Vitellogenesis in the lizard Lacerta vivipara jacquin. II. Vitellogenin synthesis during the reproductive cycle and its control by ovarian steroids.

An analysis of the development of the vitellogenic process following artificial hibernation in the lizard Lacerta vivipara was undertaken. For that purpose, organ weights (ovaries, oviducts, liver, fat bodies) and plasma concentrations of total proteins, calcium, and estrogens were monitored. The induction of the vitellogenic growth of 2-5 oocytes per ovary was characterized by a rapid increase in calcemia (from 2.4-2.6 mM to 4-10 mM), and in oviduct and liver weights. During the active and continuous phase of vitellus incorporation (congruent to 3 weeks, follicle diameter 1.6-2.0 mm to greater than 5 mm) the developments of ovaries and oviducts were positively correlated, liver weight and calcemia remained elevated (respectively, 1.2-2.2 times and 2.5-3.5 times the previtellogenic values). Ovulation was preceded by a significant rise in calcemia and followed by a decrease in liver weight, but no modification of oviduct mass. Plasma concentration in total proteins (50-60 mg/ml) was not modified during the entire process. Plasma estrogens were difficult to measure in this small species. Levels of estradiol-17 beta were very often below the assay sensitivity (less than 0.3-0.6 ng/ml), never above 2 ng/ml, and very variable among individuals. No correlation with vitellogenin production could be established. Therefore, the abilities of different ovarian steroids to induce vitellogenin synthesis were tested in vivo. To reduce the rise of plasma estradiol titer (observed during a 4-week experiment), the steroids were implanted in ovariectomized lizards for a short time (5 days). The vitellogenic response was assessed by measuring the distribution of the 32P radioactivity between the acidoprecipitable plasma fraction and the plasma vitellogenin recognized by the lizard antivitellogenin serum. Plasma titers of estradiol-17 beta were monitored. The estrone potencies could not be determined as this treatment involved an important rise in estradiol level. Progesterone, delta 4, testosterone, and 5 alpha-androstanediol were unable to stimulate vitellogenin synthesis. Estradiol-17 beta was the only effective steroid. It was further demonstrated that the estradiol-induced hypercalcemia, hyperproteinemia, and liver growth in ovariectomized lizards were dependent upon the total amount of estrogen injected.