A study of steroid 11beta-hydroxylation by adrenal mitochondria of marsupials--Part I. A comparision of 11beta-hydroxylase activity and specificity for different steroid substrates by possum (Trichosurus vulpecula), kangaroo (Macropus major) and beef

Identification of 5 beta-pregnane and 5 beta-androstane derivatives in adrenal venous and peripheral blood plasma of the female possum (Trichosurus vulpecula)

In the possum a marked sex difference has been found in the steroids in adrenal venous plasma. Four 5 beta-pregnane and four 5 alpha (beta) androstane derivatives together with ten 4-ene-3-keto steroids were isolated from the adrenal venous plasma of the female and definitively identified by gas chromatography-mass spectrometry. The major reduced steroids were: 5 beta-pregnane-3 alpha,17 alpha-diol-20-one and 5 beta-pregnane-3 alpha,17 alpha,20 alpha-triol, at concentrations of 52 +/- 12 micrograms/100 ml and 44 +/- 8 micrograms/100 ml mean +/- SEM respectively. The concentration of cortisol was 198 +/- 47 micrograms/100 ml. The concentration of the 2 reduced steroids in peripheral plasma were approx. 100 times less. In contrast the adrenal venous plasma of a male contained 14 steroids of which only three, found in trace amounts, were reduced. The results confirm previous in vitro observations that reduced steroids are produced by the adrenocortical special zone, which is only present in the female. The physiological significance of the presence of reduced steroids of adrenocortical origin in the circulation of the female possum is discussed.

Differences in steroidogenesis by the subcellular fractions of adrenocortical special zone and cortex proper of the female possum (Trichosurus vulpecula)

Steroidogenesis by subcellular fractions of adrenal cortex proper (C.P.) and special zone (S.Z.) of female possum (Trichosurus vulpecula) was studied. Mitochondrial, microsomal and cytosol cell fractions were incubated with appropriate substrates in the presence of an NADPH-generating system. The major products formed from [3H]progesterone and [3H]17 alpha-hydroxyprogesterone by the microsomal fraction of the C.P. were 11-deoxycortisol and 11-deoxycorticosterone and 3 alpha (beta)-hydroxy-5 alpha-androstan-17-one by the S.Z. The mitochondrial fraction converted [3H]11-deoxycortisol to cortisol in yields twenty times higher by the C.P. than by the S.Z. and to 17 alpha, 20 beta,21-trihydroxy-4-pregn-3-one thirty times higher by the S.Z. The conversion of [3H]androstenedione to 11 beta-hydroxyandrostenedione by the C.P. was approximately double that of the S.Z., while 18-hydroxyandrostenedione (tentatively identified) formed the highest yield in both zones. Incubation of the same substrates with cytosol formed two 5 beta-pregnane and two 5 beta-androstane derivatives in total yields less than 5% by C.P. and greater than 60% by S.Z. Aromatase activity, estimated by the release of [3H2O] from [1 beta 3H]testosterone, in the adrenals of 8 possums, was in each experiment negligibly low. Determination of total enzyme activities in the two zones revealed that 11 beta, 18 and 21-hydroxylases were higher in the C.P., while 17 alpha-hydroxylase was higher in the S.Z. Similar results were obtained when the rates of formation of hydroxylated products were estimated in the presence of saturating amounts of substrates. Active 5 alpha- and 5 beta-reductases, C17-20-lyase and 3 alpha (beta) and 20 beta-hydroxysteroid dehydrogenases were found almost exclusively in the S.Z. We conclude that the S.Z. at lower levels of activity than the C.P. could contribute to the basal secretion of corticosteroids. In addition, the S.Z. has a high capacity to form C19 steroids and 5 alpha- and 5 beta-reduced steroids. The possible role of the S.Z. in possum is discussed.

The effects of ACTH on adrenal steroidogenesis and blood corticosteroid levels in the echidna (Tachyglossus aculeatus)

1. The effects of short-term (S.T., 30 min) and long-term (L.T., 4 days) administration of ACTH on peripheral blood corticosteroid levels and on in vitro steroidogenesis were investigated. 2. Control levels of cortisol, corticosterone and aldosterone were 58 +/- 12, 130 +/- 26 and 10 +/- 6 (SEM) ng/100 ml respectively. 3. Corticosterone was 70% higher after S.T. and 150% higher after L.T., when cortisol was 800% higher. 4. Adrenal homogenates from control echidnas converted [14C]progesterone predominantly to 11-deoxycorticosterone (45%) and 11-deoxycortisol (12%). 5. After L.T. the principal product was corticosterone (25%), but S.T. had no effect. 6. In control echidnas the Km and V for 11 beta-hydroxylation of 11-deoxycorticosterone were 20 microM and 2.8 rho mol/min/mg respectively. After L.T. V increased to 10 rho mol/min/mg.