Effects of steroids and sex reversal on intestinal absorption of L-[14C]leucine in vivo, in rainbow trout, Salmo gairdneri.

The effects of steroids (17 alpha-methyltestosterone (MT), 17 beta-oestradiol (E2)), and of sex reversal (XX male) on intestinal absorption and accumulation of L-[14C]leucine (5 mM), were investigated in unanaesthetized rainbow trout (Salmo gairdneri), using an in vivo gut perfusion technique. Each steroid was luminally perfused through the gut at a concentration of 50 micrograms/ml perfusate, during five separate perfusions carried out on the same fish at 30-min intervals (perfusion periods 1 to 5), for a total of 120 min at 14 degrees. Experiments were also conducted on masculinized, genetically female trout (XX male) with steroid-free perfusate. MT treatment significantly increased the intestinal absorption of radioleucine during periods 1 and 2, whilst E2 was without effect. Neither MT nor E2 influenced intestinal accumulation (mid- and hindgut) of radioleucine, and accumulation of 14C-solutes in skeletal muscle. Sex reversal, however, whilst having no effect on leucine absorption, nevertheless significantly increased intestinal accumulation of radioleucine, and accumulation of 14C-solutes in skeletal muscle. The effects observed in the present study are in agreement with previous work in trout using everted gut sac preparations. It is suggested that the growth-promoting effects of anabolic-androgenic steroids in fish may be partly explained by their action on gastrointestinal function.