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Biomedical subjects

D R Abernethy

Publications and source records attributed to D R Abernethy.

At least 37 records · Page 2Linked to original sources
PubMed1998

Molecular determinants of L-type Ca2+ channel inactivation. Segment exchange analysis of the carboxyl-terminal cytoplasmic motif encoded by exons 40-42 of the human alpha1C subunit gene.

Recently we have described a splice variant of the L-type Ca2+ channel (alpha1C,86) in which 80 amino acids (1572-1651) of the conventional alpha1C,77 were substituted by another 81 amino acids due to alternative splicing of exons 40-42. Ba2+ current (IBa) through alpha1C,86 exhibited faster inactivation kinetics, was strongly voltage-dependent, and had no Ca2+-dependent inactivation. An oligonucleotide-directed segment substitution and expression of the mutated channels in Xenopus oocytes were used to study the molecular determinants for gating of the channel within the 80-amino acid domain. Replacement of segments 1572-1598 or 1595-1652 of the "slow" alpha1C,77 channel with the respective segments of the "fast" alpha1C,86 gave rise to rapidly inactivating alpha1C,86-like channel isoforms. We found that replacement of either motifs 1572IKTEG1576 or 1600LLDQV1604 of alpha1C,77 with the respective sequences of alpha1C,86 caused strong but partial acceleration of IBa inactivation. Replacement of both sequences produced an alpha1C, 86-like fast channel which had no Ca2+-dependent inactivation. These results support the hypothesis that motifs 1572-1576 and 1600-1604 of alpha1C,77 contribute cooperatively to inactivation kinetics of alpha1C and are critical for Ca2+-dependent inactivation of the channel.

Amino Acid Sequence↗
PubMed1998

Thalidomide does not alter the pharmacokinetics of ethinyl estradiol and norethindrone.

OBJECTIVE: To evaluate the effect of thalidomide on the plasma pharmacokinetics of ethinyl estradiol (INN, ethinylestradiol) and norethindrone (INN, norethisterone). METHODS: Ten women who had undergone surgical sterilization were enrolled in an open-label crossover study conducted in the Georgetown University Clinical Research Center. The pharmacokinetics of single doses of 0.07 mg ethinyl estradiol and 2 mg norethindrone were measured at baseline and after 3 weeks of 200 mg thalidomide. Compliance with the thalidomide regimen was assessed with use of Medication Event Monitoring System (MEMS) caps. RESULTS: No changes were observed in the pharmacokinetics of ethinyl estradiol or norethindrone with thalidomide therapy. The mean +/- SD area under the plasma concentration-time curve (AUC0-infinity) for ethinyl estradiol was 6580 +/- 1100 ng.h/L at baseline and 5970 +/- 1560 ng.h/L after the thalidomide regimen (paired t test, P > .05). The values for norethindrone were 103 +/- 54 micrograms.h/L and 107 +/- 58 micrograms.h/L (paired t test, P > .05). No changes were observed for other pharmacokinetic parameters assessed for either ethinyl estradiol or norethindrone. No accumulation of thalidomide was seen after 21 days of therapy: day 1 AUC0-infinity 41.1 +/- 13.9 micrograms.h/mL; day 21 AUC0-infinity 59.6 +/- 27.3 micrograms.h/mL (paired t test, P > .05). No changes were observed for other pharmacokinetic parameters assessed for thalidomide between days 1 and 21. Thalidomide was well tolerated but caused variable degrees of sedation. The average thalidomide compliance rate was 97%. CONCLUSIONS: The pharmacokinetics of thalidomide do not change with 3 weeks of daily dosing. Thalidomide does not alter the pharmacokinetics of ethinyl estradiol or norethindrone. Therefore there is no drug interaction between thalidomide and these 2 drugs. The efficacy of oral contraceptives containing ethinyl estradiol and norethindrone should not be affected by concomitant thalidomide therapy.

Adult↗
PubMed1998

Nitric oxide inhibits Oct-1 DNA binding activity in cultured vascular smooth muscle cells.

Since Oct-1 is a ubiquitous DNA binding protein shown to play an important role in regulating cell proliferation and possess structural characteristics consistent with a nitric oxide (NO) target, we studied NO regulation of the DNA binding activity of Oct-1 in the A7R5 vascular smooth muscle cell (VSMC) line. Two NO donors, sodium nitroprusside (SNP) and S-nitroso-N-acetyl-penicillamine (SNAP) were directly added to the nuclear extract-oligonucleotide reaction mixture, respectively and the effect on Oct-1 DNA binding activity was evaluated by gel shift assay. Both NO donors (0.01-1 mM) inhibited the DNA binding activity of Oct-1. This inhibitory effect was not attenuated by dithiothreitol (DTT) (1 mM) while in contrast, DTT did antagonize the effect of diamide on Oct-1 DNA binding activity. The NO effect on Oct-1 has some specificity; as the NO donors had no effect on myc DNA binding activity. The inhibitory effect of NO donors was reproduced in A7R5 cells, without affecting their viability. These findings provide the first evidence that NO inhibits the DNA binding activity of Oct-1, probably through a cGMP independent mechanism and suggests that NO may inhibit mitogenesis in part through an effect on Oct-1 DNA binding activity in VSMCs.

Cells, Cultured↗
PubMed1998

Functional coupling of human L-type Ca2+ channels and angiotensin AT1A receptors coexpressed in xenopus laevis oocytes: involvement of the carboxyl-terminal Ca2+ sensors.

A human recombinant L-type Ca2+ channel (alpha1C,77) was coexpressed with the rat angiotensin AT1A receptor in Xenopus laevis oocytes. In oocytes expressing only alpha1C,77 channels, application of human angiotensin II (1-10 microM) did not affect the amplitude or kinetics of Ba2+ currents (IBa). In sharp contrast, in oocytes coexpressing alpha1C,77 channels and AT1A receptors, application of 1 nM to 1 microM angiotensin gradually and reversibly inhibited IBa, without significantly changing its kinetics. The inhibitory effect of angiotensin on IBa was abolished in oocytes that had been preincubated with losartan (an AT1A receptor antagonist) or thapsigargin or injected with 1,2-bis(o-aminophenoxy)ethane-N,N,N',N'-tetraacetate, pertussis toxin, guanosine-5'-O-(2-thio)diphosphate, or heparin, suggesting that the recombinant alpha1C channels were regulated by angiotensin through G protein-coupled AT1A receptors via activation of the inositol trisphosphate-dependent intracellular Ca2+ release pathway. Consistent with this hypothesis, no cross-signaling occurred between the AT1A receptor and a splice variant of alpha1C lacking Ca2+ sensors (alpha1C,86). The data suggest that the regulation of recombinant L-type Ca2+ channels by angiotensin is mediated by inositol trisphosphate-induced intracellular Ca2+ release and occurs at the molecular motif responsible for the Ca2+-induced inactivation of the channels.

Angiotensin II↗
PubMed1997

Pharmacologic and pharmacokinetic profile of mibefradil, a T- and L-type calcium channel antagonist.

Mibefradil is a recently introduced calcium antagonist that, as a tetralol derivative, is chemically distinct from previous calcium antagonists. This article will review pertinent results from in vitro, animal, and clinical investigations to report the pharmacologic properties that distinguish mibefradil from all of the calcium channel antagonists in use today, all of which operate on the "L-type" calcium channel. Mibefradil's pharmacokinetic profile indicates it can be used as a once-daily oral treatment for hypertension and chronic stable angina pectoris.

Animals↗
PubMed1997

Influence of oral contraceptive use and cigarette smoking, alone and together, on antipyrine pharmacokinetics.

The pharmacokinetics of antipyrine following a single 1-g intravenous dose was determined in 63 healthy women. Subjects were divided into 4 groups as follows: 1) cigarette smokers using low-dose oral contraceptives (n = 15); 2) nonsmokers using low-dose oral contraceptives (n = 12); 3) cigarette smokers not using oral contraceptives (n = 10); and 4) controls, neither cigarette smokers nor oral contraceptive users. Plasma antipyrine concentrations during 24 to 48 hours after dosage were measured by high-performance liquid chromatography. Mean kinetic variables in the nonsmoking, non-oral contraceptive using control group were: volume of distribution, 37.7 L; elimination half-life, 13.2 hours; and clearance, 34.4 mL/min. In cigarette smoking, non-oral contraceptive users versus controls, elimination half-life was reduced (8.0 vs. 13.2 hours, P < 0.05) and clearance increased (56.0 vs. 34.4 mL/min, P < 0.05). In nonsmoker oral contraceptive users, the reverse was true (elimination half-life was significantly increased: 16.6 vs. 13.2 hours, P < 0.05; and clearance was significantly decreased: 24.8 vs. 34.4 mL/min, P < 0.05). In smokers who were using oral contraceptives, values were not significantly different from controls (elimination half-life, 11.2 hours; clearance, 39.5 mL/min). Volume of distribution did not differ among the four groups. Thus the opposing effects on antipyrine clearance of the induction of metabolism by cigarette smoking and the inhibition due to low dose oral contraceptive use in effect negate each other when combined in humans.

Adolescent↗
PubMed1997

Ticlopidine inhibition of phenytoin metabolism mediated by potent inhibition of CYP2C19.

A patient who had taken a stable dose of phenytoin for 2 years had a coronary stent placed for unstable angina and ticlopidine was added to his therapeutic regimen. Twenty-five days later, he was hospitalized with acute symptomatic phenytoin toxicity and a serum concentration of 46.5 micrograms/ml. Determination of metabolic genotype revealed that the patient had a wild-type genotype for CYP2C9, CYP2C19, and CYP2D6. Using human liver microsomes, we showed that ticlopidine is a potent inhibitor of cytochrome P450 2C19, with an estimated inhibition constant (Ki) of 3.7 +/- 0.2 mumol/L. The influence of ticlopidine on CYP2C9, the other cytochrome P450 isoform that metabolizes phenytoin, is relatively weak, with a calculated Ki of 38.8 +/- 27 mumol/L. These data suggest that, in this patient, phenytoin toxicity was caused by inhibition of CYP2C19 by ticlopidine, and the data emphasize the importance of CYP2C19 in the metabolism of phenytoin.

Adult↗
PubMed1997

Pharmacological properties of combination therapies for hypertension.

Single drug therapy for the treatment of hypertension has traditionally been a standard of practice. More recently combination therapy as first-line treatment has gained acceptance both by the medical practice community and the US Food and Drug Administration. The advantages of combinations may be a synergistic or additive antihypertensive effect, metabolic improvement, or both. The combination of a thiazide-type diuretic and a potassium-sparing diuretic has been quite useful in the past to prevent the need for potassium supplementation. The combination of beta-adrenoceptor blockade and a thiazide diuretic results in an additive antihypertensive effect that permits the effective use of very low thiazide doses. The mechanism of antihypertensive effects of each member of the combination are complimentary with increased sympathetic outflow and renin-angiotensin axis activation induced by the diuretic being blunted by beta1-adrenergic blockade. Combinations not used as first-line therapy, such as angiotensin converting enzyme inhibitors or angiotensin receptor blockade and a thiazide diuretic, have complimentary antihypertensive mechanisms and have been useful in treating patient groups who do not respond well to converting enzyme inhibitor monotherapy. The combination of a calcium antagonist with diuretic therapy has an additive hypertensive effect as well; however, the complimentary mechanisms are less obvious. Finally, the combination of angiotensin converting enzyme inhibition and calcium antagonist therapy has been useful in selected patients, but again the complimentary mechanisms are less obvious. As first-line therapy, combinations for diuretics and beta1-receptor blockers have been useful for achieving increased antihypertensive effect with decreased adverse drug effect.

Antihypertensive Agents↗
PubMed1997

Dose-response characteristics of mibefradil, a novel calcium antagonist, in the treatment of essential hypertension.

The aim of this study was to determine the dose-response characteristics of the calcium antagonist, mibefradil, and to evaluate its antihypertensive efficacy and safety in varying doses in patients with mild-to-moderate hypertension. Three hundred and three eligible patients were randomized to receive once-daily 6.25-, 12.5-, 25-, 50-, 100-, 150-, or 200-mg mibefradil doses or placebo for 4 weeks. Repeated blood pressure measurements and electrocardiographic recordings were obtained for the 24 h following the last dose of the placebo run-in period and for the first and last doses of randomized treatment. A statistically significant (P < .001 versus placebo) and clinically relevant drop in sitting diastolic blood pressure (SDBP) both at trough and at peak was observed in the 50-, 100-, 150-, and 200-mg mibefradil dose groups (trough placebo-corrected reductions: -4.9, -9.1, -9.9, and -11.9 mm Hg, respectively), with a significant dose-response relationship (P < .001) and high response rates. Trough/peak ratios for the placebo-corrected change from baseline to week 4 in SDBP were >85% for the 50- and 100-mg doses and 68% and 69% for the 150- and 200-mg doses, respectively. The full antihypertensive effect of mibefradil was achieved within 1 week of treatment. Reductions in sitting systolic blood pressure (SSBP) closely paralleled those in SDBP. The antihypertensive effect of mibefradil was associated with a slight dose-dependent decrease in heart rate and increase in the pulse rate (PR) electrocardiographic interval [corrected]. The appropriate therapeutic dose range of mibefradil in the management of mild-to-moderate essential hypertension is 50 to 100 mg.

Adolescent↗
PubMed1997

Elevated blood pressure in spontaneously hypertensive rats consuming a high sucrose diet is associated with elevated angiotensin II and is reversed by vanadium.

OBJECTIVE: To determine the changes in serum angiotensin II (Ang II) and endothelin-1 levels induced by vanadium treatment of sugar-fed rats in order to investigate the relationship between changes in blood pressure and Ang II and endothelin-1 levels. METHODS: Male spontaneously hypertensive rats (SHR) were fed starch (control), sucrose, and sucrose plus vanadium compounds at various concentrations. The systolic blood pressure of the rats was estimated by tail-cuff plethysmography. Serum Ang II and endothelin-1 levels were measured by radioimmunoassay. RESULTS: There were increases in systolic blood pressure (by 8%) and in serum Ang II (by 20%) in sucrose-fed SHR compared with control. In sucrose plus vanadium-fed SHR, the lowering of the systolic blood pressure (by 11-16% of the sucrose-fed value) was accompanied by a significant decrease in Ang II levels (by 25-60% of the sucrose-fed value) and an increase in endothelin-1 level (by 61-76% of the sucrose-fed value). CONCLUSION: That Ang II levels are elevated in sucrose-induced hypertension and decreased after vanadium therapy suggests that the renin-angiotensin system plays a role in the induction of hypertension in this model. On the other hand, the elevation of endothelin-1 levels associated with a decreased systolic blood pressure might be secondary to vanadium stimulation of endothelial cells. The data suggest that endothelin-1 is not involved in sugar-induced elevations of the blood pressure.

Angiotensin II↗
PubMed1996

The effect of pharmaceutical benefits managers: is it being evaluated?

Over the last decade, the number of pharmaceutical benefits managers has increased, and their influence has expanded rapidly. These managers now provide prescription drug coverage to more than 100 million Americans. The effect of pharmaceutical benefits managers on health care delivery remains unclear. We review the development of these organizations, their current role in the delivery of pharmaceutical therapies to patients, and their relationship with pharmaceutical manufacturers. We discuss potential advantages and disadvantages of pharmaceutical benefits manager practices and suggest ways in which these organizations can be made more accountable to the employer groups that hire them.

Administrative Personnel↗
PubMed1996

Endothelin-1 induces an increase in total protein synthesis and expression of the smooth muscle alpha-actin gene in vascular smooth muscle cells.

The growth response of aortic vascular smooth muscle cells (VSMCs) to chronic hypertension includes vascular hypertrophy. We have shown previously that angiotensin II positively regulates the expression of the human vascular smooth muscle (SM) alpha-actin gene. To further expand our understanding of vasoactive peptide-induced vascular hypertrophy, we studied endothelin-1 (ET-1) regulation of total protein synthesis and cytoskeletal gene expression in VSMCs. In a concentration-dependent manner ET-1 increased [3H] leucine incorporation by VSMCs (122.4 +/- 5.5%, mean +/- SEM, n = 5). ET-1 (0.1 microM) induced expression of SM alpha-actin mRNA as detected by Northern blot analysis. Also, ET-1 in a concentration-dependent manner (0.1 nM-0.1 microM) induced expression of the chloramphenicol acetyl transferase gene driven by 896 bp of the human SM alpha-actin promoter when transiently transfected into rat aortic VSMCs by the calcium phosphate method (141.2 +/- 9.8%, mean +/- SEM, n = 10). These data suggest that part of ET-1-induced increase in protein synthesis is achieved through transcriptional regulation of the SM alpha-actin gene via activation of cis-acting element(s) in the promoter. Such findings help elucidate the role of ET-1 in regulation of vascular growth.

Actins↗
PubMed1996

An improved method of encapsulation of doxorubicin in liposomes: pharmacological, toxicological and therapeutic evaluation.

We describe here an improved method of encapsulating doxorubicin in liposomes using phosphatidylcholine, cholesterol and synthetic tetramyristoyl cardiolipin. With this new composition of lipids the entrapment of doxorubicin was found to be > 90%. Cytotoxicity studies using vincristine-resistant HL-60/VCR leukaemia cells showed that liposome-encapsulated doxorubicin reverses multidrug resistance 5-fold compared with conventional doxorubicin and at levels equivalent to that obtained using liposomes with natural cardiolipin. In normal mice, liposome-encapsulated doxorubicin was much less toxic than the conventional drug. A dose of 25 mg kg-1 i.v. of conventional doxorubicin produced 100% mortality in mice by day 14, whereas liposomal doxorubicin exhibited only 10% mortality by day 60. Liposomal doxorubicin demonstrated enhanced anti-tumour activity against murine ascitic L1210 leukaemia compared with conventional doxorubicin. At a dose of 15 mg kg-1, liposomal doxorubicin increased the median life span with 12 of 18 long-term (60 days) survivors compared with only 3 of 18 with conventional drug. Mice injected i.v. with liposomal doxorubicin had plasma levels 44-fold higher than conventional doxorubicin, producing significantly higher (P < 0.02) area under the plasma concentration curve. An altered tissue distribution was also observed with liposomal doxorubicin; cardiac tissue demonstrating at least 2-fold lower levels with liposomal doxorubicin probably accounting for its lower toxicity. This altered pharmacokinetics of liposome-encapsulated doxorubicin, providing enhanced therapeutic advantage and the ability to modulate multidrug resistance, could be useful in a clinical setting.

Animals↗
PubMed1995

Moexipril in the treatment of mild to moderate essential hypertension: comparison with sustained-release verapamil.

To compare and contrast the antihypertensive efficacy of an angiotensin-converting enzyme (ACE) inhibitor to a calcium antagonist, 88 and 90 patients with essential hypertension were randomly assigned to receive moexipril and verapamil, respectively. At the end of the first 6 weeks of active therapy, sitting diastolic blood pressure decreased by 11 mmHg in patients receiving moexipril and by 9 mmHg in patients receiving verapamil. The 24-week treatment period was completed by 72 patients who received moexipril and 71 patients who received verapamil. Mean decreases in sitting diastolic blood pressure of 10 mmHg and 11 mmHg were observed in the respective intent-to-treat moexipril and verapamil groups. At doses of 7.5 mg and 15 mg once daily, moexipril had an antihypertensive effect comparable to that of sustained-release verapamil at doses of 180 mg and 240 mg once daily.

Adult↗
PubMed1995

Local angiotensin-converting enzyme inhibition blunts endothelin-1-induced increase in forearm vascular resistance.

OBJECTIVE: The physiologic role of endothelin-1 is not well established; however, it may have a role in modulation of peripheral vascular tone complimentary to angiotensin II. In vitro and animal studies suggested an interrelationship between angiotensin II and endothelin-1 vasoconstriction. We hypothesized that local vascular or systemic renin-angiotensin II systems must be intact for endothelin-1-mediated vasoconstriction in humans. METHODS: To test this hypothesis, responses to brachial artery infusion of endothelin-1 alone and endothelin-1 plus local low-dose infusion of enaliprilat were studied in seven healthy male and seven healthy female volunteers. RESULTS: In these subjects, baseline forearm vascular resistance (mean +/- SEM; 24 +/- 3.5 mm Hg.ml/dl forearm vol/min) increased with a 38.2 ng/min endothelin-1 infusion (61.8 +/- 6.8 mm Hg.ml/dl forearm vol/min; p < 0.01). Forearm vascular resistance decreased when 38.2 ng/min endothelin-1 was infused concomitantly with a local 5 micrograms/min infusion of enaliprilat (45.5 +/- 5.9 mm Hg.ml/dl forearm vol/min; p < 0.01 compared with endothelin-1 alone). CONCLUSIONS: These data indicate that an endothelin-1-induced increase in forearm vascular resistance is inhibited by local forearm angiotensin-converting enzyme inhibition.

Adult↗
PubMed1995

Adenosine deaminase isoenzymes of the opossum Didelphis virginiana: initial chromatographic and kinetic studies.

Extracts of liver and spleen were used to isolate opossum adenosine deaminase isoenzymes (ADA1 and ADA2) and to determine their activities with adenosine and 2'-deoxyadenosine as substrates. Km values (microM) for adenosine and 2'-deoxyadenosine, respectively, as substrates for partially purified opossum liver adenosine deaminase isoenzymes were ADA1: 57 +/- 7 vs. 26 +/- 4 and ADA2: 285 +/- 25 vs. 580 +/- 92. In crude spleen extract, ADA2 activity was stable at 56 degrees C during 40 min of incubation. ADA1 activity declined in a linear fashion under the above conditions with an apparent T1/2 of 80 min. Sephadex G-150 column chromatography of crude spleen extract showed the apparent molecular weight of the ADA activity not inhibited by (+/-)-EHNA (i.e. ADA2) to be 170 kDa; ADA activity fully inhibited by (+/-)-EHNA (i.e. ADA1) eluted in the fractions corresponding to a molecular weight of 35 kDa.

Adenosine Deaminase↗