Corticoidogenesis in Bufo arenarum H. I. In vitro biosynthesis of [3H]pregnenolone and [3H]corticosterone metabolites and of endogenous 3-oxo-4-ene intermediates at 28 degrees C and 37 degrees C.

Sliced interrenal tissue from Bufo arenarum H. was incubated without exogenous substrate (to determine endogenous corticosterone (B) and progesterone), as well as in the presence of [3H]pregnenolone ([3H]Pre) and [3H]corticosterone, at 28 and at 37 degrees C. When yields of radiometabolites were analyzed as such, [3H]Pre at 28 degrees C was found to be a good precursor for 18-hydroxycorticosterone (18-HO-B), aldosterone (aldo), and an unknown N very similar but not equal to 19-hydroxycorticosterone. However, [3H]Pre at 28 degrees C was not a good precursor for corticosterone. When the same tritiated substrate was incubated at 37 degrees C, the yields of 18-HO-B and N diminished significantly, aldo remained as it was at 28 degrees C, and B increased. [3H]B was a poor precursor to aldo, 18-HO-B, and N, irrespective of incubation temperatures, but a good precursor to material with the mobility of 11-dehydro-B and an aldo-like compound X. Measurement of endogenous B and progesterone pools followed by calculations of specific activities lead to the conclusion that these differences should not be ascribed to artifactual competitions between precursor pools for enzyme systems. This species is thus characteristic in its capacity to bypass, at least at 28 degrees C and under the in vitro conditions employed, corticosterone during aldo biosynthesis. Furthermore, the vast ambient temperature ranges to which this and many other amphibian species are exposed and the temperature dependence observed in corticoidogenesis of B. arenarum suggest that corticoidogenic studies in these species should be carried out at more than one temperature.