The binding of cortisol to adrenal mitochondria

Endothelin-1-induced incorporation of cholesterol into rat adrenals

The effect of endothelin-1 (ET-1) on cholesterol uptake by adrenal cortex was evaluated through several experimental approaches: infusion of ET-1 followed by measurement of endogenous cholesterol in excised adrenals; infusion of ET-1 followed by tritiated cholesterol incorporation into adrenal quarters in vitro; coinfusion of ET-1 with tritiated cholesterol-enriched serum and determination of adrenal-associated radioactivity; and tritiated cholesterol incorporation in incubations of adrenal cells. In all cases ET-1 increased cholesterol uptake. Subcellular fractionation showed an ET-1-mediated augmentation in mitochondrial fraction. This increase was mediated by the subpopulation B of adrenal receptors for ET-1. In addition, ET-1 also increased cytochrome P450-SCC (side-chain cleavage) activity.

Inhibition of aldosterone formation by cortisol in rat adrenal mitochondria

In this work we confirm by a metabolic method the existence of at least two enzymes with 11 beta- and 18-hydroxylase activities in rat adrenal mitochondria. The method was based on the ability of cortisol (F), a foreign alternative substrate, to inhibit competitively metabolite productions from various precursors. F inhibited a) aldosterone (ALDO) production from 11-deoxycorticosterone (DOC) without affecting the yields of corticosterone (B) and 18-hydroxy-11-deoxycorticosterone (18-OHDOC); b) 18-hydroxycorticosterone and aldosterone productions from B (Ki = 2.5 +/- 0.5 microM); and c) ALDO production from 18-OHDOC. These results suggest the existence of two categories of enzymes with both 11 beta- and 18-hydroxylase activities, one comprising those that catalyze the conversions of DOC to B and 18-OHDOC (F-insensitive reactions [FIS]) and the other one comprising the enzymes involved in the conversions of B to 18-OHB and ALDO and that of 18-OHDOC to ALDO (F-sensitive reactions [FS]). The cloned enzymes CYP11B1 and CYP11B2 would pertain respectively to the FIS and FS categories.

Cortisol: a tool to study aldosterone biosynthesis in rats

Corticosterone (B) and 18-hydroxy-11-deoxycorticosterone (18OHDOC) but not 11-deoxycorticosterone (DOC) displaced cortisol (F) specifically bound to rat adrenal mitochondria. F. competitively inhibited aldosterone formation from B, 18OHB and 18OHDOC but did not inhibit conversions of DOC to B or 18OHDOC. High concentrations of DOC increased its conversion to 18OHDOC rather than B.

Endothelin-1 stimulation of aldosterone and zona glomerulosa ouabain-sensitive sodium/potassium-ATPase

Endothelin stimulates the cells of the zona glomerulosa of the adrenal gland and releases aldosterone. While it is a less potent aldosterone secretagogue than angiotensin II endothelin also potentiates the effects of angiotensin II on aldosterone biosynthesis. Two endothelin receptors have been cloned and are expressed in the adrenal zona glomerulosa. Intravenous infusion of endothelin at a rate of 80 ng/kg/min for 30 min into rats produced increases in blood pressure, adrenal content of aldosterone and stimulated the ouabain-sensitive sodium potassium ATPase in the zona glomerulosa, but not in the zona fasciculata, of the adrenal. The simultaneous infusion of the isopeptide specific endothelin receptor A (ETA) antagonist BQ-123 blocked the pressor effects of endothelin, but did not alter the increase in aldosterone content of the zona glomerulosa or the ouabain-sensitive sodium potassium ATPase activity. Infusion of Sarafotoxin 6b, an ETB agonist, also increased the aldosterone content of the adrenal and stimulated the ouabain-sensitive sodium potassium ATPase in the zona glomerulosa, further indicating that the effect of endothelin is probably mediated by ETB or isopeptide non-specific endothelin receptor. The mechanism by which endothelin stimulates the sodium potassium ATPase is unclear as is the relation between a stimulated sodium potassium ATPase and the potentiation of angiotensin II effect on the adrenal.

Stimulation of aldosterone production by hemin in calf adrenal glomerulosa cell cultures

Aldosterone production from 11-deoxycorticosterone was stimulated by hemin in primary cultures and homogenates of calf adrenal zona glomerulosa, in a time- and dose-dependent fashion. The ferrochelatase inhibitor 3,5-diethoxycarbonyl-1,4-dihydro-2,4,6-trimethylpyridine (DDC) blocked the stimulation of aldosterone mediated by adrenocorticotropin (ACTH). Addition of hemin after treatment with DDC partially restored ACTH action. These results suggest that hemin may play a role in regulation of aldosterone production.

Effects of aging on cholinephosphotransferase activity on guinea pig lung mitochondria and microsomes

It is known that the composition of phospholipids in lung changes with age. The final step in the de novo synthesis of phosphatidylcholine, a major component of lung surfactant, by the CDP-choline pathway, requires the enzyme cholinephosphotransferase (CPT). Even though CPT has earlier been proposed to be located exclusively in the endoplasmic reticulum, we have recently demonstrated its presence also in the mitochondria. We have earlier reported a gestational variation of CPT activity in fetal mitochondria and microsomes. In the present study we examined the subcellular distribution of CPT activity in lung as a function of age. After birth, the microsomal CPT activity continued to increase until adulthood (24 wks of age), thereafter it gradually decreased. On the otherhand, the CPT activity of mitochondria continued to increase with the advancement of age and beyond 72 wks of age, it was approximately 2-fold higher than that of the microsomal fraction.

Steroid hormone specifically binds to rat kidney plasma membrane

A high-affinity and low-capacity corticosterone specific binding was detected in the purified plasma membrane preparation from rat kidney using an in vitro steroid hormone binding assay. The specific-bound hormone was efficiently distinguished from the irreversible-bound hormone with 10 microM corticosterone. Under standardized conditions of pH 7.4 at 2 degrees C and 30 min incubation time, the binding was saturable and showed Kd = 13 +/- 3 nM and Bmax = 616 +/- 34 fmol/mg of protein. Competitive binding studies with analogue steroids indicated that corticosterone binding to kidney plasma membrane is hormone-specific. Results indicated that the possible nongenomic effects of steroids could be mediated by their interaction with plasma membrane.

A corticosteroid receptor in neuronal membranes

Steroids may rapidly alter neuronal function and behavior through poorly characterized, direct actions on neuronal membranes. The membrane-bound receptors mediating these behavioral responses have not been identified. [3H]Corticosterone labels a population of specific, high-affinity recognition sites (dissociation constant = 0.51 nanomolar) in synaptic membranes from an amphibian brain. These binding sites were localized by receptor autoradiography in the neuropil, outside the regions of perikarya. The affinities of corticoids for this [3H]corticosterone binding site were linearly related to their potencies in rapidly suppressing male reproductive behavior. Thus, it appears that brain membranes contain a corticosteroid receptor that could participate in the regulation of behavior.