An enzyme linked immunosorbent assay (ELISA) for plasma medroxyprogesterone acetate (MPA)

Hormone therapy modulates ET(A) mRNA expression in the aorta of ovariectomised New Zealand White rabbits

OBJECTIVE

To study the effect of 17beta-estradiol (E(2)) or conjugated equine estrogens (CEE) alone and in combination with norethisterone acetate (NETA) or medroxyprogesterone acetate (MPA) on the endothelin-1 (ET-1) system.

METHODS

New Zealand White rabbits were treated with E(2), CEE, E(2) + NETA, CEE + MPA or placebo. The thoracic aorta and the epicardial coronary artery were used for mRNA expression and myograph analyses, respectively.

RESULTS

E(2) and CEE alone significantly reduced ET-1 receptor subtype A (ET(A)) mRNA expression compared with placebo treatment. The E(2)-induced reduction in ET(A) mRNA expression persisted with the co-administration of NETA, but the CEE induced reduction in ET(A) mRNA expression was not maintained with the co-administration of MPA. Treatment with CEE alone significantly increased endotelin-1 converting enzyme (ECE) mRNA expression and CEE combined with MPA reduced prepro-endothelin-1 (ppET-1) mRNA expression when compared with placebo. ET-1 receptor subtype B mRNA expression and ET-1 induced vasocontraction was unaffected by treatment.

CONCLUSIONS

E(2) and CEE treatment exert potentially beneficial vascular effects through regulation of the ET(A) receptor. The effect was maintained with the co-administration of NETA, but not MPA. The differential effects of specific hormone components may explain the variable effects of hormone therapy on the arterial wall.

Progestins oppose the effects of estradiol on the endothelin-1 receptor type B in coronary arteries from ovariectomized hyperlipidemic rabbits

OBJECTIVE

Progestins may be associated with the adverse cardiovascular outcomes observed with estrogen plus progestogen therapy, but the mechanism is not resolved. In this study we examined the effect of 17beta-estradiol (E2) alone and in combination with two progestins on the endothelin-1 (ET-1) system in coronary arteries.

DESIGN

Watanabe heritable hyperlipidemic rabbits were treated orally with either E2 (4 mg/d), medroxyprogesterone acetate (MPA) (10 mg/d), norethisterone acetate (NETA) (2 mg/d), E2 + MPA, E2 + NETA, or placebo for 16 weeks (n=10 in each group). Coronary arteries were used for mRNA and myograph analyses.

RESULTS

E2 alone but not in combination with MPA or NETA increased ETB mRNA expression in coronary arteries. Accordingly, E2 alone but not in combination with MPA or NETA reduced the maximal contraction to ET-1, and the reduction was sustained after ETA but not after ETB blockade. E2 reduced preproendothelin-1 mRNA expression; however, this effect was not blunted by MPA or NETA. ETA and ET-converting enzyme-1 mRNA expression was unaffected by treatment.

CONCLUSIONS

The data suggest that long-term E2 treatment selectively attenuates ET-1-induced vasoconstriction, possibly by increasing ETB gene expression in rabbit coronary arteries and that this effect is abolished by the two progestins investigated. This observation may help to explain how progestins oppose the supposed beneficial effects of estrogen on the arterial wall.

Rapid Determination of Time-Resolved Fluoroimmunoassay for Medroxyprogesterone Acetate Residues in Pork Tissues and Comparison with Liquid Chromatography and Tandem Mass Spectrometry

A competitive time-resolved fluoroimmunoassay (TR-FIA) was developed for the determination of medroxyprogesterone acetate (MPA) residues in pork tissues. The limits of detection (LOD) was determined to be 0.06 ng g-1 and the limits of quantification (LOQ) was less than 0.8 ng g-1. The intra-assay variations were below 10% and the interassay variations ranged between 9.7 and 12.7%. The mean recoveries established at six concentration levels varied from 87.3 to 108.3%. The results obtained by the TR-FIA and ELISA showed a good correlation. The established TR-FIA was validated for the determination of incurred pork tissues and confirmed by high-performance liquid chromatography and tandem mass spectrometry (LC-MS-MS). This proposed technique could be applied to routine residue analysis.

Medroxyprogesterone acetate attenuates long-term effects of 17beta-estradiol in coronary arteries from hyperlipidemic rabbits

OBJECTIVE

The progestin component in hormone replacement treatment may oppose the effects of estrogen on vascular function. This study examined the effect of long-term treatment with 17beta-estradiol (E(2)) alone and in combination with two progestins on K(+) and Ca(2+)-mediated mechanisms in coronary arteries.

METHODS

Watanabe heritable hyperlipidemic rabbits were treated orally with either E(2) (4 mg/day), medroxyprogesterone acetate (MPA) (10 mg/day), norethindrone acetate (NETA) (2 mg/day), E(2)+MPA, E(2)+NETA, or placebo for 16 weeks (n=10 in each group). Coronary arteries were used for mRNA and myograph studies.

RESULTS

E(2) increased vasodilatation induced by sodium nitroprusside and decreased vasocontraction induced by potassium. The first but not the latter response was opposed by MPA. The combination of MPA and E(2), but neither compound alone enhanced nimodipine-induced vasodilatation and increased the expression of L-type voltage-gated Ca(2+) channel mRNA. NETA had no opposing effects. Hormone treatment did not affect large-conductance Ca(2+) activated or ATP-sensitive K(+) channels or cGMP-dependent protein kinase mRNA expression. Hyperlipidemia had no effect on vascular reactivity.

CONCLUSION

When E(2) is administered with MPA, effects of E(2) on nitric oxide and Ca(2+)-mediated vascular reactivity in rabbit coronary arteries are modulated. The results suggest that the progestin component in hormone replacement treatment may interfere with the supposed beneficial vascular effects of estrogen.

Ouabain is not detectable in human plasma

An enzyme-linked immunosorbent assay is described for the measurement of ouabain in human plasma. This assay is specific for ouabain, strophanthidin, and ouabagenin, with other steroids, including digoxin and vasopressor hormones, exhibiting negligible cross-reactivity. Assay sensitivity was 0.06 nmol/L if 1 mL plasma was extracted and less than 0.005 nmol/L when 20 mL plasma was analyzed. Extracted plasma samples showed ouabainlike immunoreactivity that diluted in parallel with the ouabain standard curve. Repeated extraction and assay of single plasma samples, however, did not produce consistent results in the assay. Increased specificity was obtained by high-performance liquid chromatography of sample extracts before assay. When high-performance liquid chromatographic profiles of plasma spiked with ouabain standard or following bolus intravenous injections of ouabain into normal human volunteers were compared with profiles of unspiked plasma, there was no support for the immunoreactive material in the latter samples being ouabain. We propose that if ouabain is present in the human circulation, its concentration is less than 0.005 nmol/L.

Enzyme immunoassay for nomegestrol acetate in human plasma

Currently available chromatographic assays of the progestative drug nomegestrol acetate in human plasma are not suitable for monitoring drug kinetics more than 24 h after clinical dosage. A specific and sensitive enzyme immunoassay was therefore developed. A 3(O-carboxymethyl)oxime derivative of nomegestrol acetate was synthesized and coupled to bovine serum albumin in order to raise polyclonal antibodies in rabbits. The enzymatic tracer was obtained by coupling the 3(O-carboxymethyl)oxime derivative to acetylcholinesterase (E.C.3.1.1.7.). HPLC fractionation of human plasma samples followed by enzyme immunoassay revealed the presence of cross-reacting metabolites. An automated procedure of metabolite separation was developed using silica bonded with diol groups (Diol Bakerbond column). This procedure ensured assay specificity. The quantification limit in human plasma was 0.1 ng/ml. Mean repeatability (intra-assay variation) and reproducibility (inter-assay variation) were 9 and 15%, respectively. The enzyme immunoassay allowed monitoring of the kinetics of nomegestrol acetate 144 h after oral administration of a single 5 mg dose. Values for human samples were in excellent agreement with those assayable by HPLC followed by u.v. detection.