A COMPARISON OF STEROIDOGENESIS IN VITRO IN TWO TELEOSTS, THE MARINE HERRING, CLUPEA, AND THE FRESHWATER ATLANTIC SALMON, SALMO

Abstract

SUMMARY Cortisol was the principal steroid biotransformed from [16-3H]pregnenolone incubated with interrenal tissues of the Atlantic herring, Clupea harengus harengus, and of the Atlantic salmon, Salmo salar. Corticosterone was the preferred product from [4-14C]progesterone in herring, and cortisol in salmon. In these two teleosts 3H:14C recrystallization ratios of cortisol produced from the equimolar amounts of precursors at various times of incubation suggested that pregnenolone was the better precursor of cortisol and that the favoured pathway to cortisol was via 17-hydroxylated rather than 17-deoxy intermediates. It was demonstrated that interrenal tissues of herring and salmon both have the capacity to 17-hydroxylate corticosterone to cortisol; aldosterone was not detected in any of the interrenal incubates. The 17-hydroxylation of 11-deoxycorticosterone to 11-deoxycortisol was shown in vitro by interrenal tissues of the Atlantic salmon, a conversion that has not been previously demonstrated in fish or in normal tissues of other vertebrates. When interrenal tissue of Atlantic salmon was incubated with equimolar amounts of [1,2-3H] 11-deoxycorticosterone plus [4-14C]corticosterone, there was more conversion of 11-deoxycorticosterone to 11-deoxycortisol (0·39%) than of corticosterone to cortisol (0·12%) and only a small amount (1·0%) of the 3H-labelled precursor was associated with corticosterone after 4 h incubation. Biotransformed cortisol was isolated from both herring and salmon interrenals incubated with each of the following pairs of equimolar substrates: [3H]21-deoxycortisol plus [4-14C]11-deoxycortisol, [3H]21-deoxycortisol plus [4-14C]corticosterone, and [7-3H]11-deoxycortisol plus [4-14C]corticosterone. Isotope ratios of product cortisol suggested that, under the in-vitro conditions employed, substrate efficiency to cortisol synthesis was in the order: 11-deoxycortisol ⪢ 21-deoxycortisol > corticosterone. The results indicated that steroid hydroxylations at C-11, C-17 and C-21 could occur in any order in vitro in interrenals of herring and of salmon.