In vivo uptake and metabolism of [3H]ecdysone in the vitellogenic follicles ofSarcophaga bullata(Diptera) and its localisation by autoradiography

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Abstract
Within 4 h after injection of [3H]ecdysone, almost all tritiated material has disappeared from the haemolymph, indicating that the uptake by the tissues is very fast. After only 15 min, 19% of the label was found in the ecdysterone fraction and 4% in the highly polar products (HPP) fraction. The uptake of [3H]ecdysone by the ovary (mid-vitellogenic) is almost complete within 1 h after injection. The pattern of [3H]ecdysteroids in the ovaries follows a well ordered sequence: firstly, [3H]ecdysone is the major component of the [3 H]ecdysteroids but it disappears within 2 h, next a peak value of [3H]ecdysterone was found at 1 h, whereafter this also disappeared, and from 2 h on, there was a considerable increase in HPP. The HPP consisted of 3 fractions (A, B and C). Glusulase treatment revealed that apparently only fraction B consisted of glucuronide and/or sulphate-conjugates of ecdysteroids. Autoradiographic experiments confirmed that the uptake of [3H]ecdysone was a very rapid process. In ovaries fixed 1 h after injection, the silver grains were abundant in the ooplasm but were also found in the follicle cell cytoplasm and in trophocytes. In follicles examined 16 h after injection, only a few silver grains were observed in the trophocytes and follicle cells. However, the cytoplasm of the oocyte was labelled. The border cells also accumulated label. The major results indicate that all cell types of the follicle seem to be able to absorb ecdysone from the haemolymph and that there seems to be a rather selective uptake of ecdysone. In the ooplasm, ecdysone is converted to highly polar conjugates.