The influence of gender in the evaluation of platelet and plasma catecholamines

Switching from generic to brand clopidogrel in male patients after ST-elevated myocardial infarction

OBJECTIVE

To detect residual platelet aggregation following the switch from generic (GC) to brand clopidogrel (BC) in male patients after ST-elevated myocardial infarction (STEMI).

METHODS

The study was designed as an open-label, prospective cohort trial. Thirty-three male STEMI patients were enrolled. All patients received dual antiplatelet therapy with aspirin (100 mg/daily) and one of six GC at a daily dose of 75 mg. After 2 weeks, all patients were switched to BC. Adrenaline- and adenosine diphosphate (ADP)-induced platelet aggregation was assessed twice: on day 14 (before the switch) and on day 21 (after 1 week of BC therapy).

RESULTS

Adrenaline-induced platelet aggregation did not differ among clopidogrel formulations. In contrast, residual 5 µM ADP-induced platelet aggregation after BC differs from GC by 14% (28.0 ± 2.5 vs. 23.9 ± 2.1%; p = 0.03). When 20 µM ADP was used as agonist, the difference was smaller (36.2 ± 2.9 vs. 34.6 ± 2.8%) but still significant (p = 0.04) favoring BC.

CONCLUSIONS

After 2 weeks of therapy, switching from GC to BC was associated with a mild but significant reduction in ADP-induced platelet aggregation in male post-STEMI patients. The observed differences between GC and BC should be confirmed in a larger randomized study, but may represent a risk in underdeveloped countries, where GC therapy is mandatory for post-MI inpatients.

Increased dopamine is associated with the cGMP and homocysteine pathway in female migraineurs

BACKGROUND

The group of catecholamines, which include dopamine, adrenaline, and noradrenaline, are neurotransmitters which have been considered to play a role in the pathogenesis of migraine. However, the impact of catecholamines, especially dopamine on migraine as well as the exact mechanisms is not clear to date as previous studies have yielded in part conflicting results.

OBJECTIVE

This study aimed to produce a comprehensive examination of dopamine in migraineurs.

METHODS

Catecholamines and various parameters of the homocysteine, folate, and iron metabolism as well as cyclic guanosine monophosphate (cGMP) and inflammatory markers were determined in 135 subjects.

RESULTS

We found increased dopamine levels in the headache free period in female migraineurs but not in male patients. Increased dopamine is associated with a 3.30-fold higher risk for migraine in women. We found no significant effects of aura symptoms or menstrual cycle phases on dopamine levels. Dopamine is strongly correlated with cGMP and the homocysteine-folate pathway.

CONCLUSION

We show here that female migraineurs exhibit increased dopamine levels in the headache free period which are associated with a higher risk for migraine.

Platelet Dopamine: D2 Receptor Binding in Patients with Migraine

Clinical, genetic and pharmacological evidences suggest an abnormality of the dopaminergic system in the pathogenesis of migraine. Direct evidence of an abnormal metabolism of dopamine in migraine, however, is lacking. Platelets are a useful model to understand brain dopaminergic mechanisms. The present study has been undertaken to study the status of platelet dopamine receptor binding by carrying out radioligand receptor binding assay. Binding of3H-spiperone to platelet membranes, known to label dopamine (DA)—D2 receptors, was conducted in 20 patients with migraine and an equal number of healthy controls. The equilibrium dissociation constant (Kd) in patients with migraine (1.71 ± 0.19 nM) was found to be significantly lower ( P < 0.001) as compared with controls (3.14 ± 0.33 nM). However, no significant change was observed in the maximal number of binding sites (Bmax) in patients with migraine. No relationship of Kd with type of migraine, presence of vomiting, family history, frequency of attack, duration of illness and menstrual migraine was observed. The findings of the present study provide support for the involvement of the dopaminergic system in migraine.

Sympathetic nonnoradrenergic cutaneous vasoconstriction in women is associated with reproductive hormone status

We tested whether a nonnoradrenergic component of reflex vasoconstriction of skin blood flow (SkBF) is sensitive to female reproductive hormones. Six women taking oral contraceptives underwent whole-body cooling during high-hormone (HH) and low-hormone (LH) phases of oral contraceptive use. SkBF was monitored by laser Doppler flowmetry (LDF) at sites treated by intradermal injection of yohimbine-propranolol (5 mM and 1 mM; YOPR) to block the effects of norepinephrine (NE) or at saline (Sal) control sites. Mean arterial pressure (MAP) was measured with the use of the Penaz method. Cutaneous vascular conductance (CVC = LDF/mean arterial pressure) was expressed as a percentage of baseline. Whole body skin temperature was decreased from 34 to 31 degrees C in HH and LH. In both HH and LH, CVC at Sal-treated sites was reduced during cooling (CVC = 53.1 +/- 8.6% and 54.4 +/- 4.2%, both P < 0.05). In HH, CVC at YOPR sites was reduced during cooling (78.8 +/- 3.6%, P < 0.05). In contrast, CVC at YOPR sites was not reduced significantly during cooling in LH (CVC = 95.9 +/- 2.8%, P > 0.05). Across phases, CVC at YOPR sites during cooling was significantly different (P < 0.05). After cooling, the effects of NE at YOPR sites were completely blocked. These data indicate that a nonnoradrenergic mechanism of reflex cutaneous vasoconstriction is present in women and is associated with reproductive hormone status.

Plasma noradrenaline response to a cognitive stressor in subtypes of depressive illness

Noradrenergic function has been shown to be disrupted in depressive illness. The plasma noradrenaline response to a cognitive stressor (the Stroop test) was used to investigate noradenergic activity in subtypes of depressive illness. A Stroop test was carried out, under standardised conditions, on patients with melancholic or psychotic depression, non-melancholic depression, general anxiety disorder and normal controls. Blood samples were taken during testing for measurement of plasma noradrenaline. Although there was a trend for the plasma noradrenergic response to be reduced in the melancholic/psychotic depressed patients compared to all other groups, this did not reach statistical significance. No other inter-group comparisons were statistically significant. The plasma noradrenaline response to a cognitive stressor does not discriminate subtypes of depressive illness from normal controls. Copyright 2000 John Wiley & Sons, Ltd.

Plasma epinephrine levels in hypertension and across gender and ethnicity

Epinephrine (E) infusions raise blood pressure and there is an excess incidence of hypertension among males and blacks. However, reports of E levels by ethnicity, gender, and blood pressure status are inconsistent. Insensitive assays, variability in plasma E levels within individuals, and the small size of most studies have contributed to these conflicting reports. We measured plasma E levels in a large diverse sample of subjects, using a highly sensitive assay. A total of 361 individuals participated in the study: 61% were men and 39% women, 74% were normotensive and 26% hypertensive, 59% were white and 41% were black. Except for difference in blood pressure and body mass index between the normotensives and hypertensives, subjects had similar baseline characteristics and took no antihypertensive medications for at least five days prior to sampling. All blood samples were collected after resting for a least 30 minutes following the insertion of an indwelling i.v. catheter. Catecholamine levels were determined using a radioenzymatic assay (assay sensitivities for E and norepinephrine were 6 pg/ml and 10 pg/ml, respectively). An ethnicity by gender interaction was found (F(1,315) = 5.126, p = .024). Subsequent analysis revealed that white women had significantly lower basal plasma E levels than white men (p <0.001) and black women (p = 0.036). There were no significant differences in E levels between black men and women or between white men and black men. Uncorrected E levels were lower in normotensive than hypertensive subjects (p = .009) but this difference was not significant when corrected for body mass index (BMI). Uncorrected norepinephrine levels were higher in women than men (p = .03) but the difference was no longer significant when corrected for BMI. Plasma E levels were significantly lower among white women than men or black women. In contrast to prior studies, E levels were lower in hypertensives, but this may reflect obesity among hypertensives.

Plasma norepinephrine response to a cold pressor test in subtypes of depressive illness

Noradrenergic systems have been shown to be disordered in depressive illness. The plasma norepinephrine response to a cold pressor test was used to investigate norepinephrine activity in subtypes of depressive illness. Patients with melancholic or psychotic depression, non-melancholic depression, general anxiety disorder and normal control subjects had a cold pressor test carried out under standard conditions. Blood samples were taken to measure plasma norepinephrine during the test. The plasma norepinephrine response to a cold pressor test was reduced in the melancholic/psychotic depressed patients compared to control subjects. No other intergroup comparisons were statistically significant. These results suggest noradrenergic systems are disturbed and subresponsive to stress in melancholic/psychotic depressed patients. This does not appear related to other clinical or biochemical factors.

Differences and variability in plasma noradrenaline between depressive and anxiety disorders

Plasma noradrenaline (NA) levels were compared between two groups of patients with major depressive disorder (melancholic/psychotic and non-melancholic), patients with general anxiety disorders and healthy controls. The melancholic/psychotic depressed group had the highest plasma NA levels. This only reached statistical significance with respect to the control group. Within the depressed group, there was no association between plasma NA levels and age, weight loss, ratings of depression, anxiety or plasma cortisol levels. Variance of plasma NA was greatest in the melancholic/psychotic depressed group. A review of previous studies shows an association between raised plasma NA, depressive illness and alterations in NA variance. This association may be limited to melancholic/psychotic depressed patients. The above findings support a dysregulated noradrenergic system in depressive illness.

Simultaneous determination of L-dopa and 3-O-methyldopa in human platelets and plasma using high-performance liquid chromatography with electrochemical detection

Various high-performance liquid chromatographic (HPLC) methods for the determination of plasma levels of L-dopa and of its metabolite, 3-O-methyldopa (3-OMD), have been previously described. In this study, we report a modification of these methods, that enables the assay of these two compounds in platelets and plasma obtained from the same sample of whole blood. Reversed-phase (RP) HPLC with electrochemical (coulometric) detection was used. The within-run and between-run coefficients of variations, for the two compounds, were less than 10%, in both platelets and plasma; the detection limits for platelet levels of L-dopa and 3-OMD were 2 and 6 ng/10(9) platelets, respectively. In plasma, the detection limits for L-dopa and 3-OMD were 1 and 3 ng/ml, respectively. The method is rapid and simple. When applied to a population of patients with Parkinson's disease under treatment with L-dopa, this method revealed detectable levels of L-dopa and 3-OMD in the platelets of all patients. The application of this technique may provide new insights into the pharmacokinetics of L-dopa in patients with Parkinson's disease.

Combined response of plasma and platelet catecholamines to different types of short-term stress

Platelet catecholamines (CAs) do not seem to reflect the acute increases in plasma CAs observed during stress, at least over short periods of time. However, it is well known that stress, via the release of plasma CAs, is capable of affecting platelet function. To better address this issue, we studied platelet and plasma levels of free noradrenaline (NA), adrenaline (A), and dopamine (DA) in 10 healthy subjects undergoing three different stress tests: insulin tolerance test (ITT), cold pressor test (CPT) and handgrip test (HT). We also evaluated platelet count and platelet mean volume (MPV). ITT caused a considerable increase in plasma NA and a massive release of plasma A, while CPT and HT induced discrete increases only in plasma NA. ITT induced a significant decrease in platelet DA and a trend toward a decrease in platelet NA, along with a significant increase in MPV. All these changes occurred in coincidence with the peak levels of plasma CAs. No changes in platelet variables were observed in response to both CPT and HT. The modifications observed during ITT are likely to represent signs of an initial platelet activation in response to the acute plasma CA elevations this test was able to elicit. Our data show that platelet CA content does not represent a mere reflection of the circulating concentrations of plasma CAs, but it is the result of a dynamic balance between these two compartments.

Clinical recovery from panic disorder is associated with evidence of changes in cardiovascular regulation

Cardiovascular measures (spectral derivatives of heart rate variability, the blood pressure response to standing and plasma noradrenaline levels) have been shown to change as clinical recovery follows the treatment of panic disorder patients with either imipramine or cognitive therapy. These findings can be interpreted as evidence of changes in baroreflex modulation, an important feature of the cardiovascular expression of arousal. This offers further evidence of a dysregulation of arousal in this disorder.