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

The effects of estradiol-17 beta (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 mu 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 mu 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 mu 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 mu g/g of E-2 doses in comparison to the control value. Simultaneous injection of ICI-182780 (1.0 mu g/g), a very pure and specific antiestrogenic compound, with E-2 (1.0 mu 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 mu g/g), a protein synthesis blocker, caused a significant inhibition of the E-2 (1.0 mu 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. (C) 1998 Elsevier Science Ltd. All rights reserved.