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The intestinal transport of L-leucine and fluid was studied in response to in vitro administration of 17 alpha-methyltestosterone (MT; 50 micrograms/ml) and 11-ketotestosterone (KT; 10 micrograms/ml), using strips of rainbow trout intestine incubated for 60 min in vitro. Both MT and KT increased the intestinal absorption of the amino acid without significantly affecting fluid transport. Addition of ouabain, 2,4-dinitrophenol (DNP) and sodium fluoride (NaF) reduced the intestinal transport of leucine. It would appear that ouabain and DNP significantly impair the action of MT, although their effect on KT is uncertain. It is suggested that the steroid-induced leucine transport during the latter 40 min of incubation might be, in part, the result of an increased activity of Na+,K+-ATPase.

Cellular growth responses of rainbow trout (Salmo gairdneri) fed different levels of dietary protein (35, 45, and 55%), with and without the anabolic steroid ethylestrenol, have been studied over a 60-day period. With an increase in dietary protein, total liver proteins increased in fish fed the steroid-free (control) diets, whereas no change occurred in the other tissues. Muscle and spleen RNA was unchanged, but RNA increased in liver, kidney, and brain. The DNA content increased in muscle, decreased in brain, but remained constant in liver, kidney, and spleen. Feeding the ethylestrenol-supplemented (experimental) diets resulted in an increase in total proteins, RNA, and DNA of kidney over the respective control value at each level of dietary protein. In the other tissues, total proteins and DNA were essentially unchanged, but total RNA content decreased in liver and increased in muscle in the experimental groups. It is concluded that in trout, the dietary protein level exerts marked differential effects on cellular growth parameters (RNA/DNA, RNA/protein, protein/DNA), which are further modified by steroid treatment. Evidence that cellular growth responses in muscle keep pace with total body growth was also indicated.

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.

The in vivo dynamics of bolus-injected, unlabelled bovine insulin in eels (Anguilla anguilla L.), analysed by compartmental and noncompartmental methods, were found to be significantly influenced by acclimation temperature and insulin dose level. At 12 degrees, plasma clearance of insulin was essentially monoexponential, whereas at 22 degrees, the disappearance curves could be resolved into two exponential components. Metabolic clearance rate (MCR) and apparent distribution volume (Vdist) of insulin were significantly higher at 22 degrees than 12 degrees, and irrespective of temperature, MCR was more rapid at a lower (130 mU/kg) than a higher (260 mU/kg) dose, while Vdist was more variable in this respect. These results indicate that the dynamics of insulin in eels are temperature-sensitive, and that over the dose range employed, routes of insulin elimination are saturable. Of particular significance were the inordinately high values for derived Vdist indicating that following bolus injection, substantial loss of the hormone occurred.

The effects of D-glucose on the differential secretion of glucagon-like (GLI) and somatostatin-like (SLI) immunoreactivity have been studied using the perfused eel pancreas. During control perfusions with 2.7 mM glucose, basal secretion of GLI and SLI remained essentially stable for a period of 46 min, with an overall mean rate of 381 +/- 20 and 268 +/- 23 pg/min/100 mg dry wt of pancrease, respectively. An acute increase in perfusate glucose to 8.3, 16.7, and 33.3 mM resulted in a monophasic, dose-dependent decline in GLI secretion over 30 min. However, acute return of control glucose concentrations (2.7 mM) from 16.7 or 33.3 mM did not result in return of GLI to control levels, whereas from 8.3 mM glucose this was achieved slowly. By contrast, 8.3 mM glucose was without effect on SLI secretion, but at 16.7 and 33.3 mM a dose-dependent, biphasic pattern of release was evident, with a rapid return to control SLI levels during the terminal perfusion period with 2.7 mM glucose. The results suggest that the A and D cells of teleosts are sensitive to changes in glucose concentration, and, in terms of secretory profiles, release of GLI, and SLI, are qualitatively similar to those of mammals.