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J W Funder

Publications and source records attributed to J W Funder.

At least 307 records · Page 17Linked to original sources
PubMed1978

Glucocorticoid receptors in the guinea pig.

In cytoplasmic fractions of liver and kidney prepared from adrenalectomized guinea pigs, tritiated dexamethasone ([3H]DM) is bound with a very low affinity (Kd 4 degrees C greater than or equal to 2 X 10(-7) M). By competition studies, the specificity of this binding was shown to be comparable with that for [3H]DM binding to glucocorticoid receptors in other species. In addition, cytoplasmic preparations from guinea pig liver and kidney appear to inhibit the binding of [3H]DM to rat glucocorticoid receptors under a variety of experimentally determined circumstances. It is proposed that such inhibitory activity may reflect a system of [3H]DM sequestration, perhaps by metabolizing enzymes with a high combining power for glucocorticoids. Both low affinity glucocorticoid receptors and avid binding to sites of metabolism may represent additive cellular bases for the apparent corticoresistance of the guinea pig.

Adrenal Cortex Hormones↗
PubMed1978

19-Nor deoxycorticosterone (19-nor DOC): mineralocorticoid receptor affinity higher than aldosterone, electrolyte activity lower.

By screening urine extracts from rats with adrenal regeneration hypertension, Gomez-Sanchez et al. found a steroid, subsequently identified as 19-nor DOC, with high affinity for tritiated aldosterone (3HA) binding sites in rat kidney cytosol. We here report studies on the affinity of authentic 19-nor DOC for mineralocorticoid receptors, its binding in plasma and its activity in the rat urinary mineralocorticoid assay. When kidney slices from adrenalectomized rats were incubated in protein-free buffer with 3HA, 19-nor DOC consistently competed better (approximately 140%) for 3HA binding sites than did equivalent concentrations of non-radioactive aldosterone. Under identical conditions, save for the inclusion of 20% adrenalectomized rat plasma in the incubation medium, 19-nor DOC shows only approximately 40% the potency of aldosterone in displacing 3HA. Determination of renal binding of 3HA after injection of 3HA +/- aldosterone +/- 19-nor DOC in vivo similarly shows 19-nor DOC to be approximately one third as potent a competitor for 3HA binding sites as aldosterone. In the rat urinary bioassay, 19-nor DOC shows no antagonist activity when injected with aldosterone; in the absence of aldosterone, 19-nor DOC acts as a mineralocorticoid agonist, with an apparent potency 10-30% that of aldosterone. Conclusions of the study are therefore (i) at a molecular level, 19-nor DOC has a higher affinity than aldosterone for mineralocorticoid receptors, (ii) in vivo, its potency in terms of receptor occupancy is markedly lower than that of aldosterone, due to higher levels of plasma binding, (iii) in effector terms, 19-nor DOC is a full agonist without antagonist activity.

Aldosterone↗
PubMed1977

Arterial glucocorticoid receptors: the binding of tritiated dexamethasone in rabbit aorta.

Current concepts of the mechanism of the physiological action of both mineralocorticoids and glucocorticoids include an initial step in interaction between the steroid and specific receptors in the cytoplasm of target tissue cells. Using cells from rabbit aorta as a model system, we have studied the cytoplasmic binding of 3H-dexamethasone and 3H-aldosterone. Aorta cells appear to contain binding sites with a high affinity (Kd 4 degrees C approximately 1.3 X 10(-8) mol) for dexamethasone, and with specificity appropriate for glucocorticoid receptors. Under similar experimental conditions, mineralocorticoid receptors could not be demonstrated.

Aldosterone↗
PubMed1976

Mineralocorticoid and glucocorticoid receptors in human kidney.

Currently, studies on renal mineralocorticoid and glucocorticoid receptors have been confined to experimental animals. In experiments made upon human kidneys removed at operation, tritiated aldosterone has been shown to bind specifically to a single class of cytoplasmic sites which show steroid specificity requisite for physiological mineralocorticoid receptors. Tritiated dexamethasone, similarly, binds specifically to a single class of cytoplasmic sites with affinity characteristics appropriate for glucocorticoid receptors. The similarity between the human renal receptor profile for adrenocorticoids and that found in experimental animals may validate cautions extrapolation from animal models of adrenocorticoid effector mechanisms to man.

Aldosterone↗
PubMed1976

Increased renal sensitivity to aldosterone in the potassium-loaded rat.

1. The renal response to aldosterone (urinary sodium and potassium excretion) was determined in adrenalectomized rats previously fed either a high potassium diet or a control diet. High K+ rats showed an enhanced response to aldosterone at all doses tested. 2. This enhanced response to aldosterone required the presence of the adrenal glands during the induction period, could be suppressed by a high sodium intake, but could not be induced by a low sodium diet. 3. No difference between high K+ and control rats could be detected in renal mineralcorticoid receptors, assessed by both in vivo and in vitro binding of tritiated aldosterone. 4. The method of the induction, and the mechanism of the enhanced response, remain to be defined.

Adrenalectomy↗
PubMed1976

SC 23992: radioreceptor assays for therapeutic and side effects.

1. A new spirolactone (SC 23992) has been assayed in vitro to determine its affinity for mineralocorticoid and androgen receptors. 2. Although two to eight times as potent as anti-aldosterone agent as Aldactone in vivo, SC 23992 has only approximately 10% the potency in vitro. 3. This discrepancy between potency in vivo and in vitro appears to be explained on radioreceptor assay of the principal metabolites of Aldactone SC 23992. 4. SC 23992 may represent an antimineralocorticoid with less antiandrogen side effects.

Animals↗
PubMed1976

Glucocorticoid receptors: evidence for a second, non-glucocorticoid binding site.

Previous studies on cytoplasmic glucocorticoid receptors and enzyme induction led to the classification of steroids as inducers (optimal or sub-optimal), antagonists, or inactive steroids, with respect to their activity as glucocorticoids. The receptor was postulated to exist in allosteric equilibrium between two conformational states, one "active" and the other "inactive". Steroids behaved as inducers (optimal or sub-optimal), antagonists, or inactive steroids depending on their relative affinity for the active and inactive conformational state of the receptor. Another possible model would invoke multiple binding sites on a single receptor with interactions between the binding sites depending upon the particular steroid bound. To test this latter possibility, an experimental technique was developed to measure the rate of dissociation of tritiated dexamethasone ([3H]DM) or tritiated aldosterone ([3H]A) from the glucocorticoid receptor of rat liver or kidney cytosol. The dissociation of the [3H]DM-receptor at 25 C was not due to irreversible denaturation, and minimal recombination of the receptor with [3H]DM occurred. Progesterone and a number of other steroids consistently and significantly increased the dissociation rate of [3H]DM-receptor complexes in both liver and kidney cytosol. An identical effect was seen with hepatic glucocorticoid receptors labelled with [3H]A, like dexamethasone an optimal inducer. All steroids which enhanced glucocorticoid-receptor dissociation were either antagonists or sub-optimal inducers. Thus, it is postulated that glucocorticoid receptors have at least two classes of binding sites, and that occupation of the second site increases the dissociation rate of agonists from glucocorticoid receptors.

Aldosterone↗
PubMed1976

16Beta-hydroxydehydroepiandrosterone: the dichotomy between renal receptor binding and urinary electrolyte activity.

Excessive production of 16beta-hydroxydehydroepiandrosterone (16beta-OH-DHEA) has been suggested as a cause of low-renin essential hypertension. The mineralocorticoid effect of 16beta-OH-DHEA was reported to be one-fortieth that of aldostereone in the rat bioassay. Using kidney slices from adrenalectomized rats, the affinity of 16beta-OH-DHEA and a series of related compounds for mineralocorticoid receptors has been determined. In studies done at both 4 C and 37 C, the affinity of 16beta-OHDHEA for mineralocorticoid receptors was found to be less than 0.1% that of aldosterone (P less than 0.01). Various related steroids and/or potential metabolites similarly showed negligible affinity for the aldosterone receptor. In addition, In addition, 16beta-OHDHEA showed no significant affinity for renal dexamethasone-binding sites (Type II glucocorticoid receptors), corticosterone-binding sites (Type III glucocorticoid receptors), dihydrotestosterone binding sites, or estradiol binding sites. In in vivo competition experiments, the concurrent administration of 50 mug deoxycorticosterone reduced (3H)aldosterone binding to 20-30% of control levels; 50 mug 16beta-OH-DHEA did not compete for (3H)aldosterone binding sites. In in vivo bioassay electrolyte excretion was found-in contrast to that of aldosterone-to be variable. Within a given group, certain rats reproducibly responded to 16beta-OH-DHEA by sodium retention and kaliuresis; in others no response was observed. In vitro binding studies comparing "responders" with "non-responders" demonstrated that in neither group did 16beta-OH-DHEA have significant affinity for renal mineralocorticoid receptors. Accordingly, the mechanism whereby 16beta-OHDHEA produces changes in urinary electrolyte excretion appears independent of classical mineralocorticoid effector mechanisms. The conditions under which this effect is seen await eludication.

Aldosterone↗
PubMed1975

Steroidal 21-diazo ketones: photogenerated corticosteroid receptor labels.

The 21-diazo derivatives of 9 alpha-fluoro- and 9 alpha-bromo-21 deoxycorticosterone, 21-deoxycorticosterone, and progesterone were synthesized for use as photoaffinity labels for corticosteroid receptors. In the isolated toad bladder system, 9 alpha-bromo-21-diazo-21-deoxycorticosterone was as active as d-aldosterone and more active than 9 alpha-fluoro-cortisol in augmenting active Na+ transport. The activities of 21-diazoprogesterone and progesterone were equal; both were much less potent than d-aldosterone, however. These results indicate that the 21-diazo derivatives had significant functional activity in the toad bladder system. The rat kidney slice system was used to estimate the relative affinities of the diazo steroids for aldosterone receptor sites by competition experiments. At 100-fold excess of competitor to [3-H]aldosterone, the order of affinities was 9 alpha-fluoro-21-diazo-21-deoxycorticosterone greater than 9 alpha-bromo-21-diazo-21-deoxycorticosterone greater than 21-diazoprogesterone. Moreover, 9 alpha-bromo-21-diazo-21-deoxycorticosterone reduced binding of [3-H]aldosterone to cytoplasmic and nuclear forms of the receptor proportionately. On the basis of competition for [3-H]corticosterone binding, presumably to corticosteroid-binding globulin (CBG), the order of affinities was 21-diazo-21-deoxycorticosterone greater than 21-diazoprogesterone greater than 9 alpha-bromo-21-diazo-21-deoxycorticosterone. These findings indicate that 21-diazo steroids may be suitable as photogenerated affinity labels for mineralocorticoid receptors. The tritiated derivative, [1,2-3-H]-9 alpha-bromo-21-diazo-21-deoxycorticosterone (specific activity 25 Ci/mol) was synthesized and used in model experiments on photogenerated covalent binding to rat plasma proteins. Irradiation with uv light resulted in binding of [1,2-3-H]-9 alpha-bromo-21-diazo-21-deoxycorticosterone to plasma proteins, that was resistant to extraction with methylene dichloride and did not exchange with unlabeled corticosterone. The diazocorticosteroids, therefore, may have the requisite functional and selectivity properties for photoaffinity labeling of corticosteroid-binding proteins. Further studies are needed, however, to assure that photogenerated labeling with these steroids was site specific.

Animals↗
PubMed1975

Glucocorticoid and mineralocorticoid receptors in gut mucosa.

Both glucocorticoid and mineralocorticoid hormones are known to be involved in the physiology and pathophysiology of the gastrointestinal tract. Studies on the mechanism of action of steroid hormones indicate an initial obligatory step of binding to stereospecific receptor proteins in the cytoplasm of target tissue cells. Mucosal cells from the gastrointestinal tract of adrenalectomized, gonadectomized rats contain cytoplasmic glucocorticoid receptors which bind tritiated dexamethasone with an affinity (Kdiss4C) of approximately 10(-8)M. The concentration of glucocorticoid receptors per unit cytoplasmic protein is in order duodenum greater than jejunum greater than ileum=stomach greater than colon, and their affinity for steroid hormones is in order dexamethasone greater than corticosterone greater than deoxycorticosterone=aldosterone. No glucocorticoid receptors could be demonstrated in esophageal mucosal cells. Binding sites for tritiated aldosterone, with affinity characteristics appropriate for physiological mineralocorticoid receptors, were demonstrated in duodenum, jejunum, ileum and colon. No similar sites could be shown in the mucosa of the gastric antrum.

Aldosterone↗
PubMed1974

Renal aldosterone receptors: studies with (3H)aldosterone and the anti-mineralocorticoid (3H)spirolactone (SC-26304).

In vivo, a spirolactone (SC-26304) inhibited the effects of aldosterone on urinary K(+):Na(+) ratios and the binding of [(3)H]aldosterone to renal cytoplasmic and nuclear receptors. Cytoplasmic binding of [(3)H]aldosterone and [(3)H]spirolactone (SC-26304) was similar in magnitude and involved the same set of sites. Under three sets of conditions-(i) in the intact rat, (ii) in kidney slices, and (iii) in reconstitution studies (mixing prelabeled cytoplasm with either purified renal nuclei or chromatin), [(3)H]spirolactone (SC-26304) did not yield specific nuclear complexes in contrast to the reproducible generation of these complexes with [(3)H]aldosterone. In glycerol density gradients, cytoplasmic [(3)H]aldosterone receptor complexes sedimented at 8.5 S and 4 S in low concentrations of salt and at 4.5 S in high concentrations of salt. Cytoplasmic [(3)H]spirolactone (SC-26304) receptor complexes sedimented at 3 S in low concentrations of salt and 4 S in high concentrations of salt. These results are discussed in terms of an allosteric model of the receptor system.

Adrenalectomy↗