Steroidogenesis in vitro by homogenates of adrenocortical tissue of the European eel (Anguilla anguilla L.)

Aldosterone and the conquest of land

The sequence of the phylogenetic events that preceded the appearance of aldosterone in vertebrates is described, starting from the ancestral conversion of cytochrome P450s from oxygen detoxification to xenobiotic detoxification and synthesis of oxygenated endobiotics with useful functions in intercellular signalling, such as steroid hormones. At the end of the Silurian period [438-408 million yr ago, (Mya)], a complete set of cytochrome P450s for corticoid synthesis was presumably already available, except for mitochondrial cytochrome P450c18 or aldosterone synthase encoded by CYP11B2. This gene arose by duplication of the CYP11B gene in the sarcopterygian or lobe-finned fish/tetrapod line after its divergence from the actinopterygian or ray-finned fish line 420 Mya, but before the beginning of the colonization of land by tetrapods in the late Devonian period, around 370 Mya. The fact that aldosterone is already present in Dipnoi, which occupy an evolutionary transition between water- and air-breathing but are fully aquatic, suggests that the role of this steroid was to potentiate the corticoid response to hypoxia, rather than to prevent dehydration out of the water. In terrestrial amphibians, there is no differentiation between the secretion rates and gluco- and mineralocorticoid effects of aldosterone and corticosterone. In sauropsids, plasma aldosterone concentrations are much lower than in amphibians, but regulation of salt/water balance is dependent upon both aldosterone and corticosterone, though sometimes with opposed actions. In terrestrial mammals, aldosterone acquires a specific mineralocorticoid function, because its interaction with the mineralocorticoid receptor is protected by the coexpression of the enzyme 11beta-hydroxysteroid dehydrogenase type 2, which inactivates both cortisol and corticosterone. There is evidence that aldosterone can be also synthesized extra-adrenally in brain neurons and cardiac myocytes, which lack this protection and where the effects of aldosterone oppose those of glucocorticoids. In conclusion, the phylogenetic history of aldosterone documents the erratic progression of evolutionary changes in the course of the strenuous struggle for environmental resources and survival.

A mineralocorticoid-like receptor in the rainbow trout, Oncorhynchus mykiss: cloning and characterization of its steroid binding domain

Using reverse transcriptase polymerase chain reaction (PCR) (RT-PCR) with degenerate primers followed by 3' rapid amplification of cDNA ends PCR (3'Race-PCR) we have isolated a new fish steroid receptor cDNA sequence of 1806 bp from rainbow trout (Oncorhynchus mykiss) testis. This sequence has clear homology with various mineralocorticoid receptor cDNA sequences (rat, human, African toad: 68-70% amino acid identity), and encompasses the second part of DNA binding domain (C domain), the whole hinge region (D domain) and the steroid binding domain (E domain) plus 726 bp of 3'untranslated sequence. COS-1 cells transfected with a pCMV5 expression vector containing the whole E domain (pCMV5-rtMR) showed high affinity binding for cortisol (K(a) = 0.53+/-0.03 nM, K(d) = 1.9 nM) in the cytosol, which could not be detected in untransfected cells. Aldosterone displaced (3)H-cortisol binding, though was less effective by than unlabeled cortisol (P<0.05). Competition experiments with other steroids gave the following hierarchy for the displacement of the (3) dexamethasone, whereas 17, 20beta-dihydroxy-4-pregnen-3-one and 17,20beta,21beta-trihydroxy-4 pregnen-3-one (two fish specific progestins) did not show any specific binding. These results strongly suggest that this cDNA sequence encodes a rainbow trout mineralocorticoid-like receptor, and represent the first description of such a receptor in teleost fish where aldosterone, the classic mineralocorticoid, is believed to be absent.

Corticosteroid biosynthesis in the interrenal cells of the teleost fish, Oreochromis mossambicus

Applying high-performance liquid chromatography and thin-layer chromatography to separate corticosteroids, we studied the biosynthesis of steroids by the interrenal cells of the head kidneys (the adrenocortical homolog) of Oreochromis mossambicus. Intact head kidneys converted exogenous 17 alpha-hydroxyprogesterone into mainly cortisol, but 11-deoxycortisol, cortisone, and androstenedione were also recovered from the medium. Incubation of intact tissue with pregnenolone in addition resulted in the formation of large amounts of an unidentified product, which was absent in incubations of tissue homogenates with pregnenolone.

Aldosterone response to renin, angiotensin, ACTH, hemorrhage and sodium depletion in a freshwater teleost, Catostomus macrocheilus

1. Plasma aldosterone activity (PAA) was measured in individual large-scale suckers (Catostomus macrocheilus) by radioimmunoassay. 2. PAA in control groups was 12.0 +/- 6.0 (mean +/- SEM) pg/ml; one control group showed a sixfold elevation of PAA, possibly reflecting a seasonal effect. 3. Injections of sucker renin preparation, synthetic angiotensin II and synthetic adrenocorticotrophin had no effect upon PAA. PAA was also unaffected by sodium depletion, sodium loading and moderate hemorrhage. 4. Prolonged restraint stress coupled with severe hemorrhage significantly increased PAA to 47.1 +/- 5.1 pg/ml. 5. This study indicates that aldosterone secretion in teleost fish has either rudimentary or yet to be discovered controls and functions.

Studies on oocyte maturation of the medaka, Oryzias latipes. V. On the structure of steroids that induce maturation in vitro

The response of oocytes within isolated follicles (800-950 micron in diameter) to various steroids was examined with the teleost fish, Oryzias latipes. Continuous exposure of oocytes, which were removed from ovarian investments 17 hours before predicted germinal vesicle breakdown (GVBD), to C19- or C21-steroids brought about maturation in vitro but never triggered ovulation. The steroids effective in inducing maturation have in common a C=0 (or alpha-OH) group at 3C and a beta-OH group at 17C in the C19-steroids, and a C=O (or beta-OH) group at 3C and a C=O (or alpha-OH) group at 20C in the C21-steroids, in addition to an delta4- or delta5-unsaturated for 5alpha-saturated configuration. The orientation of the hydrogen at 5C seems to be critical in determining the ability of a particular steroid to stimulate oocyte maturation. Maturation of oocytes in the ovaries of hypophysectomized females was induced by administering progesterone, but the mature oocytes did not subsequently undergo ovulation. Thus the steroid hormone is capable of inducing oocyte maturation but apparently does not participate directly in the ovulation of Oryzias latipes oocytes.