Action of estradiol-17beta on the synthetic activity of the silk gland in Bombyx mori L.

The effects of estradiol-17beta (E(2)) were studied on several metabolic parameters in the silk gland of Bombyx mori L. race Nistari. Topical application of different doses (0.05-4.0&mgr;g/g body weight) of E(2) on the first and second day of the fifth instar larvae showed a dose dependent effect when studied on the fifth day. A significant increase in silk gland weight and fibroin content was observed between the doses 0.05 and 0.1, and 0.1 and 1.0&mgr;g/g of E(2). A similar pattern of dose-dependent rise in DNA and RNA content of posterior silk gland (PSG) was observed with the doses of E(2) when the contents were expressed per pair of PSG. Higher doses of E(2) (2.0 or 4.0&mgr;g/g) demonstrated relatively less increase, unchanged level or a decrease in the above parameters in comparison to the control values. The glutamate-pyruvate transaminase of PSG showed a significant increase from 0.1 to 2.0&mgr;g/g of E(2) doses in comparison to the control value. Simultaneous injection of ICI-182780 (1.0&mgr;g/g), a very pure and specific antiestrogenic compound, with E(2) (1.0&mgr;g/g) caused a significant counteraction of E(2)-induced increase in silk gland activity, which was reflected in DNA and RNA content of PSG, wet weight and fibroin content of silk gland, and on glutamate-pyruvate transaminase activity. Cycloheximide (0.5&mgr;g/g), a protein synthesis blocker, caused a significant inhibition of the E(2) (1.0&mgr;g/g)-induced silk gland activity when treated along with estradiol. From this study it appears that estradiol has a specific effect on silk gland function and that it may act in a nuclear mediated way.