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J C Melby

Publications and source records attributed to J C Melby.

At least 37 records · Page 2Linked to original sources
PubMed1991

19-Nordeoxycorticosterone synthesis by rat kidney inner medullary collecting duct cells.

19-Nordeoxycorticosterone (19-nor-Doc), a potent mineralocorticoid, was found to be synthesized by the isolated rat kidney perfused by an adrenal precursor (19-oxo-Doc). To determine if this bioconversion is a function of renal tubular cells, various adrenal precursors of 19-nor-Doc were added separately to rat kidney inner medullary collecting duct cells culture media at a concentration of 10 nM. While 4.6% +/- 1.0% of 19-oxo-Doc (n = 3) and 14.4% +/- 1.4% of 19-oic-Doc (n = 3) were converted to 19-nor-Doc after 24 hours of incubation, Doc, and 19-OH-Doc were not converted. This represents further evidence that Doc has to be metabolized to 19-oxo-Doc or 19-oic-Doc (19-carboxy-Doc) before it can be converted by the kidney inner medullary collecting duct cells to 19-nor-Doc.

Analysis of Variance↗
PubMed1991

Could intranasal insulin be useful in the treatment of non-insulin-dependent diabetes mellitus?

To evaluate whether intranasal insulin might be useful as a meal-adjunct in the treatment of NIDDM we compared plasma glucose and insulin responses to a mixed breakfast (9 kcal/kg, 50% carbohydrate) following either intranasal insulin (INI) or placebo in eleven patients with NIDDM. Five patients treated with subcutaneous insulin and in good to moderate glycemic control and six patients who were 'failing' on oral agents and in poor glycemic control were studied. In the patients usually on sc insulin, INI inhibited postprandial hyperglycemia. Lower doses (1 U/kg vs 1.5 U/kg b.w.) were needed to accomplish this in 2 patients with low fasting glucose (less than or equal to 7.8 mmol/l) than in three patients with higher fasting glucose (10.5 +/- 0.5 mmol/l). In the patients on oral agents who had marked fasting hyperglycemia (14.8 +/- 0.8 mmol/l) an only transient reduction (for 90 to 120 min) of postprandial hyperglycemia was achieved when INI (1 U/kg) was given in addition to po glyburide (10 mg) prior to the meal. Following placebo in the group previously treated with sc insulin, plasma free insulin levels increased maximally by 23 mU/l, 75 min after the meal. The group on oral agents had a comparable but later peak increment (at 180 min) indicative of an even greater impairment of endogenous insulin secretion in response to hyperglycemia. Following INI, the peak increment in plasma insulin occurred earlier (30 min after the meal) and was greater in all patients (55 +/- 18, 139 +/- 68, 86 +/- 24 mU/l respectively for the prior sc insulin therapy group at doses of 1.0 and 1.5 U/kg and for the oral agent group at 1.0 U/kg).(ABSTRACT TRUNCATED AT 250 WORDS)

Administration, Intranasal↗
PubMed1991

19-nor-DOC biosynthesis in the isolated perfused rat kidney.

19-nor-deoxycorticosterone (19-nor-DOC) is a potent salt retaining and hypertensinogenic mineralocorticoid that is excreted in the urine. While the precursor of 19-nor-DOC, 19-oxo-DOC, is produced by the adrenal cortex, conversion to 19-nor-DOC does not occur in the adrenal gland. We have examined the hypothesis that 19-nor-DOC is synthesized from precursors in the kidney. 19-oxo-DOC was added to the perfusate of isolated rat kidney preparations (n = 5) at a concentration of 10 microM. During 1 h of perfusion following addition of 19-oxo-DOC, 71 +/- 6% of the precursor was converted to 19-oic-DOC, an immediate precursor of 19-nor-DOC, and 8.3 +/- 1.8% was converted to 19-nor-DOC. This represents the first definitive evidence that 19-nor-DOC is produced in the kidney from adrenal precursors.

Animals↗
PubMed1991

Characterization of the adrenal 11 beta-hydroxylase in inbred salt-sensitive and resistant rats.

Rats have been bred for susceptibility and resistance to the hypertensive effect of dietary salt (S/JR & R/JR). S/JR have an abnormal adrenal steroid 11 beta,18-hydroxylase activity resulting in increased production of 18-OH-DOC. S/JR also produce increased quantities of 19-nor-DOC, which may be related, since the 11 beta,18-hydroxylase also catalyzes the 19-hydroxylation of DOC, a pivotal step in 19-nor-DOC biosynthesis. The purpose of the present studies was to further characterize the mutant S/JR adrenal steroid 11 beta,18-hydroxylase. Preliminary studies are also presented on assessing the renal 19-desmolase, the last step in 19-nor-DOC biosynthesis. Adrenal glands were harvested from R/JR and S/JR and prepared for incubation studies, protein immunoblotting, and RNA analysis. Kidneys from Sprague-Dawley rats were also used for isolated renal perfusion studies. Both S/JR and R/JR strains had a single immunostaining band for 11 beta,18-hydroxylase at 51,000 molecular weight which were equal in intensity. Both strains had a single RNA transcript at 4.3 kilobases which hybridized with equal intensity to the bovine cDNA (pB11-9). The Km for 11 beta- and 18-hydroxylation was identical within strains but was different between strains. The Km for 19-hydroxylation was different between S/JR and R/JR, and was much greater than 11 beta- and 18-hydroxylation in both strains. This suggests that the catalytic site for 19-hydroxylation is different than that for 11 beta- and 18-hydroxylation and that the S/JR enzyme binds the substrate with higher affinity than the R/JR enzyme. In the isolated perfusion studies the rat kidneys converted 80% of 19-oxo-DOC to either 19-oic-DOC or 19-nor-DOC. These data demonstrate that the difference in S/JR enzyme activity is probably due to a point mutation in the enzyme or to a change in a regulatory protein.

Adrenal Glands↗
PubMed1991

Antihypertensive effects of an aromatase inhibitor in inbred salt-sensitive rats.

Rats susceptible to the hypertensive effect of dietary salt (SS/Jr) have excess urinary 19-nordeoxycorticosterone compared with salt-resistant control rats (SR/Jr). 19-Nordeoxycorticosterone is a hypertensinogenic mineralocorticoid, but whether it contributes to the salt sensitivity of SS/Jr is unknown. This study sought to evaluate the contribution of 19-nordeoxycorticosterone to the salt sensitivity of SS/Jr by lowering its production with an aromatase inhibitor, 10-propargyl-androst-4-ene,3,17-dione (19-acetylenic-androstenedione, 19-AA). This aromatase inhibitor also preferentially inhibits nonaromatizing adrenal 19-hydroxylation, an essential step in the formation of 19-nordeoxycorticosterone. To test this hypothesis, inhibitor (120 mg) or vehicle pellets were implanted into male and female weanling SS/Jr at 42 days of age. A high salt diet (8% NaCl) was started and two additional pellets were implanted at 52 and 62 days of age. Systolic blood pressure was measured in all animals and urinary corticosteroids in males. Compared with vehicle, the inhibitor lowered blood pressure at 50 days of age (when it could first be measured) until 64 days of age in females and 71 days of age in males. Corticosterone and aldosterone levels were not different between 19-AA- and vehicle-treated SS/Jr. 19-Nordeoxycorticosterone levels, however, were mildly reduced with the inhibitor (0.05 less than p less than 0.10). After 28 days of high salt diet all 23 of the 19-AA-treated SS/Jr were alive, whereas almost one half of the control animals had died. These data demonstrate that 19-AA attenuates the hypertension in SS/Jr; this effect may be through reduction in 19-nordeoxycorticosterone production.(ABSTRACT TRUNCATED AT 250 WORDS)

Aldosterone↗
PubMed1991

Elevated 18-hydroxy-corticosterone in inbred salt-sensitive rats.

Rats susceptible to the hypertensive effect of dietary salt (SS/Jr) have excess 18-hydroxydeoxycorticosterone (18-OH-DOC) and 19-nor-DOC compared to control rats (SR/Jr). This may be caused by an abnormal adrenal 11 beta-hydroxylase, which catalyzes the 11 beta, 18, and 19-hydroxylations of DOC. A comparison of the urinary products of this enzyme including 18-OH-DOC, 19-nor-DOC, corticosterone (B), and 18-OH-B have not been described in the SS/Jr. Therefore, these steroid products were measured at 7 and 12 weeks of age in 36 weanling male and female, SS/Jr and SR/Jr (n = 9 in each group), on a low-salt diet. In both the male and female SS/Jr urinary free levels of 18-OH-DOC, 19-nor-DOC, and 18-OH-B were elevated, while B was not different at 6 and 10 weeks of age. The largest increases were in 18-OH-B levels, and these levels correlated with 18-OH-DOC and B but not 19-nor-DOC. The high degree of correlation between these steroids probably reflects their closely related dependence on adrenal 11 beta-hydroxylase biosynthesis.

18-Hydroxycorticosterone↗
PubMed1991

Diagnosis of hyperaldosteronism.

Hyperaldosteronism is associated with hypertension, potassium depletion, and suppressed plasma renin activity. It may involve one or both adrenal glands. This article reviews the different types of hyperaldosteronism and the diagnosis and management of each.

Adenoma↗
PubMed1990

Inhibition of hamster adrenal 11 beta/19-hydroxylase activity.

Increased mineralocorticoid activity has been associated with elevated urinary levels of 19-nordeoxycorticosterone in several forms of experimental and human hypertension. Biosynthesis of 19-norsteroids involves hydroxylation of the C-19 methyl group. We synthesized the 4-hydroxy analogs of deoxycorticosterone, deoxycorticosterone acetate, progesterone, and androstenedione and evaluated them as inhibitors of deoxycorticosterone 11 beta/19-hydroxylase using hamster adrenal mitochondrial preparations. These 4-hydroxy analogs were inhibitors of this P 450 hydroxylase, with approximately 10 times weaker affinity than their respective natural substrates. 4-Hydroxydeoxycorticosterone was the most potent inhibitor evaluated in this study. The half-maximal inhibitory concentration of deoxycorticosterone hydroxylation was 5 microM, 15 microM, more than 50 microM, and 14 microM, respectively, for the above compounds.

Adrenal Glands↗
PubMed1990

Alterations in aldosterone secretion and metabolism in low renin hypertension.

Low renin essential hypertensives (LRH) have normal plasma aldosterone levels which are inappropriately high in relation to their PRA. Posture is the major determinant for plasma aldosterone and PRA levels, but it is not known whether postural increments (delta) of plasma aldosterone and (delta) PRA are also abnormal in LRH. To evaluate this, LRH (n = 8), normal renin hypertensives (NRH; n = 9), normotensive controls (n = 18), and subjects with idiopathic hyperaldosteronism (IHA; n = 5) were studied in a metabolic unit on a controlled diet over 7 days. Overnight supine and 4-h upright PRA, plasma aldosterone, and 24-h urinary tetrahydroaldosterone (THA) and aldosterone secretion rates (ASR) were measured. The delta in plasma aldosterone after 4 h of upright posture was not different in the four groups. The ratio of delta plasma aldosterone/delta PRA, however, was elevated in both IHA and LRH compared to that in NRH and normals. THA excretion was also elevated in IHA and LRH, but LRH had a normal ASR. This resulted in a higher fractional THA excretion (THA/ASR) in LRH compared to the other three groups. These data further support enhanced adrenal angiotensin-II sensitivity in LRH. Aldosterone was preferentially metabolized to THA in LRH. Since THA has reduced biological activity, this may be a compensatory mechanism to reduce mineralocorticoid activity in LRH.

Adult↗
PubMed1990

The effects of CGS 16949A, an aromatase inhibitor on adrenal mineralocorticoid biosynthesis.

The family of cytochrome P450 enzymes that mediates steroid hydroxylations are distinct but structurally related proteins. Inhibitors of these steroidogenic steps generally exhibit only relative and dose-related specificity. We evaluated an imidazole, cytochrome P450-related inhibitor, CGS 16949A, in postmenopausal patients with metastatic breast cancer. While a relatively specific aromatase inhibitor at daily dosages of 1-2 mg, CGS 16949A significantly blunted cortisol responses to ACTH at a dose of 16 mg daily. To further evaluate other inhibitory effects of this drug, we determined blood levels of aldosterone (ALDO) and 18-hydroxycorticosterone and their respective urinary metabolites, tetrahydroaldosterone and tetrahydro-18-hydroxy-11-dehydrocorticosterone in 16 postmenopausal women receiving CGS 16949A. At a dose of 16 mg/day, CGS 16949A produced significant (P less than 0.001) suppression of both basal and ACTH-stimulated ALDO production. This was accompanied by a significant rise in the blood 18-hydroxycorticosterone/ALDO ratio (11.4 +/- 0.19; normal, less than 2; P less than 0.001), consistent with a corticosterone methyloxidase type II inhibition. A similar significant elevation (7.5 +/- 1.2; normal, less than 5; P less than 0.001) in the urinary tetrahydro-18-hydroxy-11-dehydrocorticosterone/tetrahydroaldosterone ratio was also observed. These results suggest that CGS 16949A is a potent inhibitor of the corticosterone methyloxidase type II enzyme at a dose of 16 mg daily. At doses of 1-2 mg daily, CGS 16949A blocks aromatase without altering basal aldosterone production and, thus, exhibits dose-related specificity.

18-Hydroxycorticosterone↗
PubMed1989

Renal 21-hydroxylation of 19-hydroxy-progesterone to 19-hydroxy-deoxycorticosterone.

19-Nor-deoxycorticosterone (19-nor-DOC) is a mineralocorticoid present in both rat and human urine, and it is elevated in some forms of experimental and human hypertension. Although the exact steps in the biosynthesis of 19-nor-DOC are uncertain, it is probably produced from a 19-oxygenated derivative of DOC, which undergoes 19-desmolation in the kidney. Since DOC biosynthesis is partly due to renal 21-hydroxylation of progesterone (Prog), we sought to determine whether a parallel pathway could exist for the biosynthesis of 19-hydroxy-DOC, a precursor to 19-nor-DOC. In order to test this hypothesis, authentic 19-hydroxy-progesterone was incubated with homogenized renal tissues from either rat or human sources. Formation of 19-hydroxy-DOC was found to be the major metabolite in both rat and human incubations, as demonstrated by an HPLC retention time identical to authentic 19-hydroxy-DOC. 19-Hydroxy-DOC formation was further verified by GC/MS analysis with highly sensitive selected ion recording. Since it has been demonstrated that the placenta can convert progesterone to 19-hydroxy-progesterone, the renal 21-hydroxylation of 19-hydroxy-progesterone to 19-hydroxy-DOC could be an alternate pathway of 19-nor-DOC production especially during pregnancy.

Animals↗
PubMed1989

Reversal of diuretic-induced secondary hyperaldosteronism and hypokalemia by trilostane, an inhibitor of adrenal steroidogenesis.

Correction of diuretic-induced hypokalemia is usually accomplished by potassium supplementation or antagonism of aldosterone's renal action. This study sought to determine if inhibition of aldosterone biosynthesis could reverse diuretic-induced hypokalemia and whether trilostane would be clinically useful in this regard. Essential hypertensives (n = 22) were treated with hydrochlorothiazide (HCTZ) 50 mg/d, and patients who became hypokalemic were randomly assigned to receive in addition to HCTZ either a placebo (n = 7), trilostane 240 mg/d (Trilo 240) (n = 7), or trilostane 60 mg/d (Trilo 60) (n = 3). Following 12 weeks of therapy the placebo patients remained hypokalemic with hyperaldosteronism, while the patients who received Trilo 240 had a correction of hypokalemia and hyperaldosteronism (P less than .05) along with a reduction in diastolic blood pressure (P less than .05). The Trilo 60 patients, however, remained hypokalemic with no significant reduction in aldosterone excretion or blood pressure compared with HCTZ. Body weight and urinary free cortisol levels along with routine biochemical tests were unchanged during this study. Three Trilo 240 patients developed diarrhea but did not discontinue the study. These results demonstrate that trilostane can correct diuretic-induced hypokalemia by lowering aldosterone secretion. Furthermore, this reduction in aldosterone may enhance the antihypertensive effects of diuretic therapy.

Aldosterone↗
PubMed1989

19-Hydroxylase inhibition of adrenal mitochondrial P450 11 beta/18/19-hydroxylase by a suicide inhibitor.

19-Nor-deoxycorticosterone (19-nor-DOC) is a mineralocorticoid that is increased in some forms of experimental and human hypertension. The pivotal step in 19-nor-DOC biosynthesis is adrenal P450 19-hydroxylase, but this enzyme has not been clearly distinguished from P450 11 beta/18-hydroxylase. This study attempted to specifically inhibit adrenal 19-hydroxylation of deoxycorticosterone (DOC) using a suicide aromatase inhibitor, 19-acetylenic androstenedione (19-AA). Purified bovine P450 11 beta/18/19-hydroxylase was incubated with excess substrate DOC, adrenodoxin, and adrenodoxin reductase in the presence of increasing doses of the inhibitor, 19AA. 11 beta-, 18-, and 19-hydroxylation were measured by quantification of corticosterone, 18-OH-DOC, and 19-OH-DOC respectively. Measurements of these products demonstrated that 11 beta- and 18-hydroxylation was not inhibited whereas 19-hydroxylation was inhibited as manifested by decreased 19-OH-DOC formation (p less than .05). The IC50 of 19-AA was approximately 10(-12) M. The specific inhibition of 19-hydroxylation suggests that the 19-hydroxylase may be an enzyme distinct from the P450 11 beta/18-hydroxylase. This further suggests that 19-nor-DOC biosynthesis may be under independent regulation and may be amendable to specific in vivo inhibition.

Adrenal Glands↗
PubMed1989

Renin inhibition with A-64662: effect on blood pressure and hormonal response in man.

We studied the effects of intravenous injections of the renin inhibitor A-64662 on blood pressure, plasma renin activity (PRA), angiotensin II (Ang II) and aldosterone levels in patients with essential hypertension. While PRA was completely suppressed with doses as small as 0.001 microgram/kg, blood pressure was affected only in a few instances in doses of 0.4-1.0 mg/kg. In the six patients in whom Ang II and aldosterone results were available these hormones were concomitantly reduced with PRA, although the PRA inhibition lasted much longer (up to 24 h). There was little relationship between the blood pressure changes and plasma levels of renin activity, Ang II and aldosterone, suggesting that the plasma pool of these variables may not be the crucial factor determining blood pressure responses in patients with essential hypertension.

Aldosterone↗
PubMed1989

An adrenal cyst associated with 19-nor-deoxycorticosterone excess and low renin hypertension.

Adrenal cysts are rare, but they have been disproportionately associated with hypertension. This report describes a hypertensive patient with increased levels of 19-nor-deoxycorticosterone (19-nor-DOC), a potent mineralocorticoid. The patient was a thirty year old man with hypokalemia, moderately severe hypertension, suppressed PRA, and low aldosterone secretion. Following surgical removal of a 10 cm adrenal cyst, the hypertension improved, the hypokalemia resolved, and the PRA and the aldosterone secretion normalized. Urinary 19-nor-DOC pre-op was elevated 4.6 microgram per day (normal less than 1.0 microgram/day and subsequently became normal at 0.7 microgram per day following surgery. The adrenal cyst was a fibrous walled structure containing mucinous straw-colored fluid. Pericystic adrenocortical tissue demonstrated increased 19-OH-DOC production (a 19-nor-DOC precursor) which may have been responsible for the 19-nor-DOC excess. We hypothesize that compressive adrenal damage from the cyst may produce a form of adrenal regeneration hypertension which is known to be associated with 19-nor-DOC excess.

Adrenal Gland Diseases↗
PubMed1988

Identification of 19-hydroxy-progesterone in human placenta.

We have tentatively demonstrated the presence of a 19-hydroxylated C21 steroid, 19-hydroxy-progesterone, in normal human placenta. A 19-hydroxylated steroid such as 19-hydroxy-progesterone, if produced by the placenta, could serve as a precursor for such hypertensinogenic 19-nor-steroids as 19-nor-deoxycorticosterone and 19-nor-progesterone. Freshly delivered, homogenized placental tissue was extracted and subjected to thin layer chromatography. A steroid corresponding to standard 19-hydroxy-progesterone was subsequently purified in HPLC, where authentic 19-hydroxy-progesterone and the sample had the same retention time. The identity of the sample was further confirmed by repeat HPLC after acetylation and mass spectrometry. Our experiment indicates that 19-hydroxy-progesterone is present in term placental tissue, where it appears to be synthesized.

Acetylation↗