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Biomedical subjects

D C Kem

Publications and source records attributed to D C Kem.

At least 19 recordsLinked to original sources
PubMed2000

Ischemic inactivation of G protein-coupled receptor kinase and altered desensitization of canine cardiac beta-adrenergic receptors.

BACKGROUND: G protein-coupled receptor kinases (GRKs) modulate myocardial beta-adrenergic receptor (betaAR) signaling. We examined whether GRK activity was altered 6, 24, and 96 hours after left anterior descending coronary artery ligation (LAD CAL) in the dog. METHODS AND RESULTS: GRK activity was measured in arrhythmogenic subepicardial border zone (EBZ) tissue overlying the infarct and from nonischemic remote-site (RS) subepicardial tissue from the same animal. GRK activity in the ischemic EBZ was 15% of RS (P:=0.03, n=6) 24 hours after CAL and appeared to start as early as 6 hours through 96 hours. GRK activity and immunoblot data demonstrated a marked decrease of GRK2 but not GRK5 at 24 hours. EBZ tissue exhibited high-affinity binding for (-)-isoproterenol (K:(i) of 0. 076+/-0.026 nmol/L [SEM]) at 24 hours, which was not significantly different from control tissue from nonoperated animals (1.2+/-0.8 nmol/L, P:>0.05, n=6). A significantly lower K:(i) of 13.8+/-2.8 nmol/L (P:<0.001, n=6) was observed for RS taken from the ischemic animals. This was reflected by a 4-fold increase in the EC(50) of isoproterenol-stimulated adenylyl cyclase activity from 18 nmol/L in EBZ tissue to 73 nmol/L in RS (P:<0.05, n=4). CONCLUSIONS: There is a selective decrease in GRK2 activity and a loss of the ability of the arrhythmia-prone EBZ tissue to desensitize to beta-adrenergic stimulation 24 hours after CAL. This correlates temporally with a second (late) peak in sudden cardiac death previously observed between 6 and 24 hours in dog and rat models of myocardial infarction.

Adenylyl Cyclases↗
PubMed1997

Thromboxane A2 receptor mediation of calcium and calcium transients in rat cardiomyocytes.

We have examined the effect of the selective thromboxane A2 (TxA2) receptor agonist U46,619 on intracellular ionized Ca ([Ca2+]i) and the calcium transient rate (CATR) in cultured neonatal rat cardiomyocytes using the Ca-sensitive probe fura 2 and ratiometric microfluoroscopy. U46,619, 10(-6)-10(-8)M, increased basal diastolic Ca fluorescence and 10(-6) and 10(-7) M increased CATR. These effects were completely blocked by the highly selective TxA2 receptor antagonist SQ-29,548 (p > 0.5, n = 4 compared to baseline), confirming this response is a specific receptor-mediated event in the cardiomyocytes. TxA2 blockade did not diminish the Angiotensin (Ang II)-mediated [Ca2+]i and calcium transient rate response from that observed in non-blocked cells (p = 0.18 and 0.21 respectively, n = 4). The TxA2-mediated changes in Ca2+ fluorescence did not exhibit homologous desensitization as does Ang II, they did not exhibit heterologous desensitization, and maximally stimulating concentrations were additive in their effect on peak [Ca2+]i. These data support the hypothesis that TxA2 secretion or release following ischemia or other pathophysiologic events could alter cardiac calcium homeostasis. Although Ang II is reported to stimulate the release of TxA2 in a variety of tissues, including the heart, the Ca2+ and CATR response to Ang II are not diminished when TxA2 receptors are blocked. This study cannot rule out the possibility that Ang II-mediated increases in TxA2 may have an additive effect on Ca homeostasis.

15-Hydroxy-11 alpha,9 alpha-(epoxymethano)prosta-5↗
PubMed1996

Protein kinase C modulation of cardiomyocyte angiotensin II and vasopressin receptor desensitization.

Angiotensin II (Ang II) and arginine vasopressin (AVP) increased intracellular free Ca2+ concentration [Ca2+]i and/or the [Ca2+]i transient rate (CaTR) in cultured neonatal rat cardiomyocytes. These agents increased membrane-bound protein kinase C (PKC) with peak activity at 5 and 10 minutes, respectively. Two-minute exposure to Ang II produced homologous desensitization to a repeated stimulation with Ang II and heterologous desensitization to AVP. Two-minute exposure to AVP also produced homologous desensitization to AVP but not heterologous desensitization to Ang II. When the AVP exposure time was increased from 2 to 10 minutes coincident with maximal AVP-mediated PKC activation, heterologous desensitization to Ang II was also observed. Acute activation (15 minutes) of PKC by phorbol 12-myristate 13-acetate (PMA) blocked responsiveness to both Ang II and AVP. When PKC activation was inhibited by 20 hours of prior exposure to PMA, as confirmed by PKC assay, homologous desensitization of Ang II still occurred, confirming an alternative mechanism(s) for homologous desensitization in the cardiomyocytes. In contrast, 20-hour PMA suppression of PKC markedly diminished the ability of the cardiomyocytes to exhibit AVP-mediated heterologous desensitization for Ang II. These data indicate that PKC activation plays a primary role in mediating vasopressin V1 receptor-induced heterologous desensitization of the Ang II receptor and participates in a hierarchy of two or more kinase systems mediating homologous desensitization of the Ang II receptor in cardiomyocytes.

Analysis of Variance↗
PubMed1994

[Ca2+]i and protein kinase C in vasopressin-induced prostacyclin and ANP release in rat cardiomyocytes.

Exposure of cultured, spontaneously beating rat cardiomyocytes to arginine vasopressin (AVP) led to marked increases in the release of prostacyclin (PGI2) and atrial natriuretic peptide (ANP). These responses were accompanied by a rapid, transient rise of cytosolic free Ca2+ concentration ([Ca2+]i) and of membranous protein kinase C (PKC) activity. Ca2+ influx and PKC activity appeared to play important but distinct roles in AVP-induced cellular responses, insofar as only AVP-induced ANP secretion was abolished by the Ca2+ channel antagonist nifedipine, whereas both AVP-induced PGI2 production and ANP release were abolished by the PKC inhibitors staurosporine and CGP-41251. The AVP-induced increase in [Ca2+]i could also be mimicked with the vasopressin (V1-subtype) agonist Octapressin, but not with the V2-agonist 1-desamino-8-D-arginine vasopressin, and was fully abolished by the V1-antagonist [d(CH2)5Tyr(Me)]AVP, but not by d(CH2)5-D-Leu-VAVP (V1-/V2-antagonist). These results indicate that V1-vasopressinergic receptors mediate AVP-induced PGI2 production and ANP secretion in rat cardiomyocytes and that, whereas both Ca2+ influx and PKC activation are required for AVP-induced ANP secretion, AVP-induced PGI2 formation is mainly regulated by PKC.

Alkaloids↗
PubMed1991

Effect of angiotensin II on cytosolic free calcium in neonatal rat cardiomyocytes.

The effect of angiotensin II (ANG II) on cytosolic free Ca2+ concentration ([Ca2+]i) was studied in cultured neonatal rat ventricular myocytes. [Ca2+]i was estimated in groups of one to three cells by dual-wavelength microfluorometry or in cell populations using conventional fluorometry. ANG II (10(-8) M) produced an acute short-lived increase over the control basal diastolic [Ca2+]i and increased the frequency of the [Ca2+]i transients. The amplitude of the [Ca2+]i transients was decreased to 64.4% of basal values. The effect of ANG II on [Ca2+]i was blocked by the selective AT1 receptor subtype antagonist Du Pont 753 but not by the AT2 antagonist PD 123319. Removal of extracellular Ca2+ or blockade of voltage-gated Ca2+ channels in cells cultured for 5-7 days abolished the [Ca2+]i transients, but only partially diminished the effect of ANG II on [Ca2+]i. Thapsigargin, an inhibitor of sarcoplasmic reticulum Ca(2+)-Mg(2+)-ATPase, reduced or abolished the [Ca2+]i response to ANG II. Phorbol 12-myristate 13-acetate (PMA), 10(-6) and 10(-7) M, also decreased the amplitude of the Ca2+ transients similar to ANG II. Pretreatment with 10(-6) M PMA or 10(-6) M 1-oleoyl-2-acetyl-glycerol (OAG) inhibited the initial rise in [Ca2+]i and the Ca2+ transients. Thus ANG II produces an acute rise in [Ca2+]i which is derived predominantly from sarcoplasmic reticulum intracellular stores. This acute effect is followed by a significant reduction in the amplitude for the Ca2+ transient and may be mediated by activation of protein kinase C.

Angiotensin II↗
PubMed1990

The mechanism of polyethylene glycol-induced natriuresis in rats: role of atrial natriuretic hormone.

A putative role of atrial natriuretic hormone (ANH) in a polyethylene glycol (PEG) 200-induced natriuresis was examined in conscious Wistar rats. Low molecular weight PEG 200 (0.5 or 1.0 ml/100g body weight) was orally administered to rats by gavage. Urine was collected during a 3 hr test period and blood was obtained at the end of each experiment for measurement of ANH, PRA, clearance studies and for indirect indices of plasma volume. Urinary excretion of sodium and volume increased while plasma ANH concentrations were markedly decreased in a dose-related manner following PEG 200 administration. The osmotic clearance was also elevated following PEG 200 administration. No significant change was observed in any of the parameters following high molecular weight PEG 8000. The observed decrease in ANH was associated with an apparent contraction of plasma volume despite the increased serum osmolality. These data indicate that the ANH inhibitory influence of the decreased plasma volume takes precedence over the stimulatory effect of the hyperosmolality and the latter is primarily responsible for the increased osmotic clearance and natriuresis observed in this model.

Administration, Oral↗
PubMed1989

Calcium infusion increases plasma atrial natriuretic factor in spontaneously hypertensive rats.

The effect of calcium on plasma atrial natriuretic factor (ANF) concentration was determined in spontaneously hypertensive rats (SHR) and their control, Wistar-Kyoto (WKY) rats. CaCl2 10.5 mg (0.095 mmol) in 0.54 ml 5% glucose or an equal volume of vehicle alone was infused intravenously for 30 minutes into conscious precannulated SHR (vehicle, n = 16; CaCl2, n = 16) and WKY rats (vehicle, n = 25; CaCl2, n = 15). Direct systolic blood pressure was measured throughout the infusion period. Blood samples for serum total calcium and plasma ANF were obtained at the end of each experiment. The systolic blood pressure did not change significantly during infusion of the vehicle or CaCl2 in either strain. No significant difference was observed in serum total calcium concentration between SHR and WKY rats after vehicle (9.8 +/- 0.1 [mean +/- SEM] mg/dl vs. 10.0 +/- 0.1) or after CaCl2 infusion (12.2 +/- 0.3 vs. 12.2 +/- 0.2). Plasma ANF concentrations after both vehicle and CaCl2 infusion were significantly higher in SHR than in WKY rats (vehicle, 211 +/- 24 pg/ml vs. 129 +/- 11, p less than 0.05; CaCl2, 395 +/- 21 vs. 278 +/- 33, p less than 0.05). There were high degrees of correlation between serum total calcium and plasma ANF both in SHR (r = 0.77, p less than 0.001) and in WKY rats (r = 0.76, p less than 0.001). No significant difference was observed in the slopes of the regression lines of ANF as a function of the serum total calcium concentration between SHR and WKY rats.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1989

Infusion of atrial natriuretic hormone in DOCA/salt and spontaneously hypertensive rats.

The effects of a 6-day infusion of atrial natriuretic hormone (ANH) on blood pressure and urinary sodium excretion were determined in conscious DOCA/salt and spontaneously hypertensive rats. The DOCA/salt rats were randomly divided into two groups after 4 weeks and either infused by osmotic minipump with 32.5 pmol/h of ANH in 0.1% gelatin vehicle or sham operated with emplacement of a blind cannula. Thirteen-week-old spontaneously hypertensive rats were studied in a similar fashion. The baseline systolic blood pressure prior to the infusion was 176 +/- 7 mmHg (x +/- SEM) in the ANH group and 169 +/- 5 mmHg in the sham group of DOCA/salt animals. The ANH infusion in the DOCA/salt animals dropped their blood pressure to 160 +/- 10 mmHg (p less than 0.01) compared to that in the sham controls which continued to rise to 200 +/- 7 mmHg. The blood pressure response to ANH infusion in the spontaneously hypertensive rats was slightly greater, with a blood pressure of 192 +/- 5 mmHg in the sham group and 132 +/- 3 mmHg in the ANH-infused animals. ANH infusion produces a qualitatively similar blood pressure response in the DOCA/salt rat as well as the other hypertensive models. This response is relatively less on a quantitative basis than that observed in the spontaneously hypertensive rats and is not related to changes in sodium balance or volume contraction.

Animals↗
PubMed1988

Effect of atrial natriuretic peptide on ACTH, dibutyryl cAMP, angiotensin II and potassium-stimulated aldosterone secretion by rat adrenal glomerulosa cells.

We examined the effect of rat atrial natriuretic peptide (ANP) on ACTH, dibutyryl cAMP, angiotensin II and potassium-stimulated aldosterone secretion by dispersed rat adrenal glomerulosa cells. ANP inhibited ACTH, angiotensin II and potassium-stimulated aldosterone secretion with IC50's between 0.15-0.20 nM. Inhibition by 10 nM ANP could not be overcome with higher concentrations of these stimuli. ANP shifted the dibutyryl cAMP dose-response curve slightly to the right but did not blunt the maximal aldosterone secretory response. The sites of ANP inhibition in the aldosterone biosynthetic pathway for these stimuli were also examined. ANP inhibited activation of the cholesterol desmolase (CD) enzyme complex by ACTH, angiotensin II and potassium. Activation of the corticosterone methyl oxidase (CMO) enzyme complex by potassium was inhibited by ANP, however, activation by ACTH was not blocked. We concluded that: 1) ANP is a potent inhibitor of ACTH, angiotensin II and potassium-stimulated aldosterone secretion; 2) inhibition of ACTH stimulation is primarily due to lower cAMP levels and; 3) inhibition of angiotensin II and potassium stimulation reflects a block in the activating mechanism of the CMO and/or CD enzyme complexes, whereas CD but not CMO activation by ACTH is inhibited by ANP.

Adrenal Glands↗
PubMed1988

Atrial natriuretic peptides: the role of phenylalanine on biological activity.

Previous studies have shown that atrial natriuretic peptides (ANPs) inhibit the secretion of aldosterone by isolated rat adrenal glomerulosa cells stimulated by angiotensin II, ACTH, and potassium. Structure-function studies have concentrated on the significance of the C- and N-terminal chains for the biological activity of the peptide. We investigated the role of phenylalanine at positions 8 and 26 by using [Ala8]human (h) ANP or [Ala26]hANP analogs to inhibit potassium-stimulated aldosterone secretion in granulosa cells. hANP-(1-28) inhibited potassium-stimulated aldosterone secretion with an IC50 of 0.48 nM. Synthetic [Ala26]hANP inhibited the aldosterone response to potassium with an inhibitory curve relative to hANP-(1-28) (rIC50) of 6.0 nM, which was significantly greater than that for hANP (P less than 0.001). Synthetic [Ala8]hANP was markedly less effective as an inhibitor, with an estimated rIC50 of 3.0 microM (P less than 0.0001). To determine whether the analogs act as competitive antagonists to hANP-(1-28), experiments were performed in which a fixed concentration (0.1 microM) of the analog was incubated in the presence of increasing concentrations of hANP-(1-28). When hANP-(1-28) was incubated with [Ala8]hANP, the rIC50 (0.2 nM) was significantly less than that for hANP-(1-28) alone (P less than 0.02). When hANP-(1-28) was incubated with [Ala26]hANP, the rIC50 was 0.1 nM. In summary, [Ala8]hANP and [Ala26]hANP were significantly less potent than hANP-(1-28) as inhibitors of aldosterone production from granulosa cells. Both analogs shifted the hANP-(1-28) dose-response curve to the left. Neither analog functioned as a competitive antagonist to hANP-(1-28). Our results indicate that the hydrophobic phenyl groups at these two positions are required for full biological potency of ANP as an inhibitor of aldosterone production.

Adrenal Glands↗
PubMed1988

The adrenal capsule alters the response of zona glomerulosa cells to atrial natriuretic peptide.

Atrial natriuretic peptide (ANP) is a potent inhibitor of potassium-stimulated aldosterone secretion. In the present study, we observed rat alpha ANP to inhibit aldosterone secretion stimulated by 10 mM potassium with an IC50 of 0.15 +/- 0.02 nM (mean +/- SE) in dispersed rat adrenal glomerulosa cells. However, when rat adrenal capsules, which contain the zona glomerulosa, were superfused in vitro, ANP had no effect on aldosterone secretion. Superfusion with 10 mM potassium increased aldosterone secretion 3- to 4-fold above baseline. Addition of 10 nM ANP to the superfusate did not lower potassium-stimulated aldosterone secretion. When this same ANP-containing superfusate was incubated with dispersed adrenal glomerulosa cells, potassium-stimulated aldosterone secretion was inhibited by 90%, proving sustained biological potency of the superfused ANP. Incubation of [125I]iodo-ANP with adrenal capsules for 60 min resulted in 83% degradation of [125I]iodo-ANP, whereas no detectable degradation was observed with dispersed adrenal glomerulosa cells. Removal of blood from the adrenal capsules or culturing the capsules for 48 h did not render them responsive to superfused ANP. In contrast, superfusion of 0.1 mM cycloheximide inhibited potassium-stimulated aldosterone secretion by 90%. These results suggest that the adrenal capsule contains an ANP-degrading enzyme(s). This enzyme may be produced by adrenal glomerulosa cells. The local existence of a degrading enzyme for ANP may allow the zone glomerulosa to regulate its response to ANP.

Adrenal Cortex↗
PubMed1985

The prediction of anatomical morphology of primary aldosteronism using serum 18-hydroxycorticosterone levels.

Serum 18-hydroxycorticosterone, aldosterone, and potassium were measured under basal conditions in 34 patients with documented primary aldosteronism, 10 patients with essential hypertension, and 9 normal subjects. The results revealed that 22 of 23 patients with aldosterone-producing adenomas had 18-hydroxycorticosterone levels greater than 100 ng/dl, and all 9 patients with idiopathic adrenal hyperplasia had plasma levels less than 100 ng/dl. Two patients with unusual macromicronodular hyperplasia of the adrenal glands had levels greater than 100 ng/dl. We found a significant relationship between serum potassium and the ratio of 18-hydroxycorticosterone to aldosterone in patients with idiopathic adrenal hyperplasia, but not in those with an aldosterone-producing adenoma. We conclude that measurement of serum 18-hydroxycorticosterone is a useful predictor of the etiology of primary aldosteronism.

18-Hydroxycorticosterone↗
PubMed1985

Effect of human beta-endorphin on plasma aldosterone concentrations in normal human subjects.

beta-Endorphin recently was proposed as a possible physiological stimulus of aldosterone secretion based on studies in animals. Since human beta-endorphin (beta h-endorphin) does not contain the ACTH-(4-10) homology common to other ACTH-related neuropeptides that stimulate aldosterone, its mechanism of stimulation might differ from that of the other peptides. In the present study, we infused beta h-endorphin into six normal subjects under carefully controlled conditions at dosage levels several orders of magnitude higher than endogenous levels. No increase in plasma aldosterone was found in these subjects ingesting a normal sodium intake despite the fact that other biological actions of beta h-endorphin were manifest. By contrast, an equimolar infusion of ACTH-(1-24) caused a significant increase in plasma aldosterone. These studies do not support a significant role for beta h-endorphin in control of aldosterone secretion in man and are consistent with the concept that the ACTH-(4-10) amino acid sequence, common to ACTH, beta-lipotropin, gamma-lipotropin, beta MSH, and alpha MSH, is a major determinant of their aldosterone-stimulating capacity.

Adult↗
PubMed1985

Antihypertensive effect of riboflavin analogues in spontaneously hypertensive rats.

Our study was designed to use the antimineralocorticoid property of the riboflavin analogue 7,8-dimethyl-10-(3-chlorobenzyl)isoalloxazine (CBI) to investigate the involvement of mineralocorticoids in the hypertension of the Kyoto strain of the spontaneously hypertensive rat (SHR) and Dahl salt-sensitive (S) rat. Wistar Kyoto (WKY) mildly hypertensive rats were used as controls. The administration of the riboflavin antagonist CBI at 5.0 mg/kg body weight twice weekly for 7 weeks lowered the systolic blood pressure (SBP) of the unanesthetized SHR from 188 +/- 7 mm Hg to 148 +/- 2 mm Hg (P less than 0.05). This was concurrent with a 36% and 11% decrease in iliopsoas muscle Na+ concentration and water content, respectively. The simultaneous administration of CBI and hydrochlorothiazide (HCTZ) reduced the SBP to 126 +/- 4 mm Hg (P less than 0.05). There was a profound suppressive effect of CBI on the secondary hyperaldosteronism generated by HCTZ (17.6 +/- 4.3 vs. 50.4 +/- 7.2 ng/dl, P less than 0.05), which was also reflected in the iliopsoas muscle K+ concentration. The effects of CBI on the SBP and iliopsoas muscle Na+ and K+ concentrations of age-matched WKY mildly hypertensive control rats were qualitatively similar to the effects on the SHR. In contrast to the SHR and the WKY rats, the administration of CBI for 8 weeks at 5.0 mg/kg body weight twice weekly to the Dahl S rats did not reduce their mean SBP (205 +/- 5 vs. 200 +/- 4 mm Hg, not significant). CBI treatment did not significantly decrease iliopsoas muscle Na+ concentration or water content.(ABSTRACT TRUNCATED AT 250 WORDS)

Aldosterone↗
PubMed1985

Plasma norepinephrine, blood pressure and heart rate response to graded change in body position.

In this study, 44 human subjects underwent either an orthostatic postural change (supine to stand, n = 17) or a graded change in body position (head-up) on a tilt-table (n = 27). No significant changes in systolic blood pressure or mean blood pressure were observed during either maneuver; significant increases, under both conditions, were observed in diastolic blood pressure and heart rate. Plasma norepinephrine concentrations after orthostatic position change increased significantly (supine 181 +/- 14 (S.E.M.) pg X ml-1; stand, 472 +/- 35 pg X ml-1, p less than 0.01). Plasma norepinephrine concentrations during graded postural change increased proportionately with increasing degrees of tilt (r = 0.76, p less than 0.01). A significant correlation between plasma norepinephrine and heart rate was observed during both positional change maneuvers (graded tilt-table, r = 0.80, p less than 0.01; orthostatic, r = 0.50, p less than 0.01). These results suggest that the degree of sympathetic nervous system activity for blood pressure regulation during graded postural change is appropriately reflected by plasma norepinephrine concentrations.

Adult↗
PubMed1984

Concurrent Cushing's and Zollinger-Ellison syndromes in a patient with islet cell carcinoma. Case report and review of the literature.

This report documents the simultaneous occurrence of Cushing's and Zollinger-Ellison syndromes in a patient with islet cell carcinoma. The clinical concurrence of these two syndromes has been recorded in only three previous case studies, while three other case reports record evidence suggesting the presence of both gastrin and ACTH within the tumor but without clinical sequelae. In the present report, evidence based on multiple clinical and biochemical data supports the concept that both syndromes are a result of "ectopic" hormone production by the tumor.

ACTH Syndrome, Ectopic↗
PubMed1984

Evaluation of a test using saralasin to differentiate primary aldosteronism due to an aldosterone-producing adenoma from idiopathic hyperaldosteronism.

We evaluated a new method utilizing saralasin to differentiate primary aldosteronism due to an aldosterone-producing adenoma from idiopathic hyperaldosteronism. The test is based on the marked difference in sensitivity to angiotensin II of aldosterone-producing adenomas and hyperplastic adrenal glands and the partial angiotensin II agonist property of saralasin in low-renin states. Saralasin was infused into 14 patients with primary aldosteronism and the plasma aldosterone responses determined. Plasma aldosterone concentration increased in all eight patients with idiopathic hyperaldosteronism, whereas there was no increase in plasma aldosterone in six patients who had a solitary adenoma. We concluded that saralasin may be a clinically useful, noninvasive tool to distinguish patients with an aldosterone-producing adenoma from those who have idiopathic hyperaldosteronism.

Adenoma↗