Possible mechanism for the first response to short captivity stress in the water frog, Rana esculenta.

To clarify the endocrine mechanism involved in the short captivity stress in the water frog, Rana esculenta, the activity of 9-ketoreductase, the enzyme which converts prostaglandin E2 (PGE2) into prostaglandin F2 alpha (PGF2 alpha), and aromatase, which converts testosterone into oestradiol-17 beta, were studied. Adult male and female frogs were sacrificed 0, 1.5, 3, 6, 12, 24, 48, 72, 168 and 336 h after capture in the field. PGE2, PGF2 alpha, progesterone, testosterone, oestradiol-17 beta and corticosterone plasma levels were detected by RIA at each time point. 9-Ketoreductase (conversion of [3H]PGE2 into [3H]PGF2 alpha) and aromatase (conversion of [3H]testosterone into [3H]oestradiol-17 beta) activities in the brain, testis, ovary and interrenal were also determined at each time point. After capture, levels of plasma PGF2 alpha increased (male: 228%; female: 288%) and PGE2 decreased (male: 68%; female: 81%) at 1.5 h, oestradiol-17 beta increased (male: 399%; female: 425%) and testosterone decreased (male: 87%; female: 83%) at 6 h, and corticosterone increased (male: 421%; female: 426%) at 72 h. 9-Ketoreductase activity in the brain was enhanced at 1.5 h after capture (male: 249%; female: 262%); aromatase activity increased at 6 h in the testis (261%), ovary (273%) and interrenal (male: 227%; female: 267%). These results indicate that short captivity stress could induce an increase in plasma PGF2 alpha through activation of brain 9-ketoreductase. In turn, PGF2 alpha might enhance the levels of circulating oestradiol-17 beta through activation of gonadal and interrenal aromatase.