Reply to discussion of ‘Empirical vs natural weighting in random effects meta‐analysis’

Three discussion papers raise interesting points, but at the end of the day, we continue to recommend that past meta‐analyses which have influenced public policy or clinical paradigms be reanalyzed by unweighted methods. For all future meta‐analyses that employ either (a) fixed effects where concomitant treatment and/or eligibility are diverse or (b) classical random effects weighted methods, unweighted methods should serve as the primary analysis. Other analyses would be reasonable as secondary approaches. Two commentaries suggest that weights are only random to the extent of estimation errors in the between study and within study variance components. We shall demonstrate that even if these components are known, there is still considerable random variability in the weights. In fact, methods that try to weight the estimates inversely proportional to the variance have a number of undesirable properties, including bias, incorrect standard errors, inconsistency (including coverage of confidence intervals), and counter‐intuitive properties that the expectation of the estimator changes both with the number of studies sampled and with constant multiples of sample size across all studies. These adverse properties do not exist for the unweighted approach. From the numerical example of phenylephrine 10 mg, despite the arguments of Waksman, the proper conclusion is that the collection of studies does not constitute evidence‐based support for efficacy in terms of lowering nasal airway resistance. In the final section, we present two compelling examples where questionable inferences were made, with potential major public implications. Copyright © 2010 John Wiley & Sons, Ltd.     

EFFECTS OF V2 RECEPTOR ACTIVITY ON THE PRESSOR RESPONSE TO VASOPRESSIN IN THE RAT

1. To determine the contribution of V1 and V2 receptor activity on the enhancement of reflex buffering of the pressor response to arginine-vasopressin (AVP), mean arterial pressure (MAP) and heart rate (HR) changes were examined in response to graded injections of phenylephrine, AVP, or Phe2Orn8OT, a potent, selective V1-receptor agonist in the absence and presence of Val4DArg8VP, a potent, selective V2-receptor agonist. 2. There were no significant differences in MAP responses to the V1 agonist in the absence and presence of the V2 agonist in either conscious intact or autonomic-blocked rats. 3. Autonomic blockade with methscopolamine and hexamethonium increased the pressor sensitivity to phenylephrine threefold. In contrast, the pressor sensitivities to AVP and Phe2Orn8OT were increased 14-fold and 11-fold, respectively, by autonomic blockade. 4. V2-receptor activity does not have any inherent vasocative action or synergistic vasoactive action with V1-receptor activity. 5. V2 receptors do not play a role in enhancing reflex buffering of the pressor response to AVP; V1 receptors are suggested to play the role.     

1-(2,6-二甲基苯氧基)-2-(3,4-二甲氧基苯乙氨基)丙烷盐酸盐对兔心乳头状肌的作用

DDP剂量依赖性地抑制电刺激引起的兔心乳头状肌收缩,阈浓度大于10μM。在有普萘洛尔5μM存在时,DDP 1μM使苯福林增强电刺激引起的乳头状肌收缩的量效曲线平行右移,最大反应不压低,pA_2值为6.8。DDP 30μM降低肾上腺素诱发的乳头状肌自律性,延长功能不应期,对兴奋性无明显影响。结果再次证实DDP具有阻断α_1肾上腺素受体作用,提示在较高浓度时,DDP可能有一定的抗钙作用。     

In Vivo performance of ophthalmic preparations of betamethasone and phenylephrine hydrochloride in the rabbit eye: Effect of polyvinyl alcohol

The effect of different concentrations of polyvinyl alcohol 14000 and 72000 (PVA 14 and 72) on the activity of betamethasone and phenylephrine hydrochloride in the rabbit eye was investigated. The polymer of higher molecular weight exerts a more pronounced effect at relatively lower viscosities. Effects on the intraocular pressure are more responsive to changes in viscosity than those on pupillary response.     

One year oral Toxicity of D-004, a lipid extract from Roystonea regia fruits, in Sprague Dawley rats

D-004, a lipid extract of royal palm (Roystonea regia) fruits that contains a reproducible mixture of fatty acids, has been shown to prevent testosterone and phenylephrine-induced prostate hyperplasia in rodents. This study investigated the long-term oral toxicity of D-004 in rats. Rats from both sexes were randomized into four groups (20 rats sex/group): a control and three treated with D-004 (800, 1500 or 2000 mg/kg/day, respectively). At study completion, rats were sacrificed under anaesthesia. Determinations of blood biochemical and haematological parameters and organ weight were done. Also, necropsy and histopathological studies were performed. Four of 160 rats died before study completion. No clinical signs of toxicity were observed throughout the study. Food and water consumption, bodyweight, blood biochemical and haematological parameters, organ weight ratios and histopathological findings were similar in control and treated groups. The histological lesions found in treated animals are commonly present in this specie and strain according to literature and our historical data. In conclusion, long-term (12 months) oral treatment of rats with D-004 (800–2000 mg/kg/day) did not show evidences of D-004-related toxicity under our conditions. The highest dose tested (2000 mg/kg) was a no-observed adverse effect level in this study.     

Bacopa monnieri and its constituents is hypotensive in anaesthetized rats and vasodilator in various artery types

Ethnopharmacological relevance

Bacopa monnieri (Brahmi) provides traditional cognitive treatments possibly reflecting improved cerebral hemodynamics. Little is known about the cardiovascular actions of Brahmi. We sought to assess its effects on blood pressure and on isolated arteries, thus providing insights to clinical applications.

Materials and methods

Intravenous Brahmi (20-60 mg/kg) was tested on arterial blood pressure and heart rate of anaesthetized rats. In vitro vasorelaxation was assessed in arteries, with and without blockers of nitric oxide synthase (L-NAME), cyclooxygenase (indomethacin), and mechanical de-endothelialisation. The effects of Brahmi on Ca²⁺ influx and release from stores were investigated.

Results

Intravenous Brahmi extract (20-60 mg/kg) decreased systolic and diastolic pressures without affecting heart rate. Brahmi evoked relaxation in isolated arteries in order of potency: basilar (IC50 = 102 ± 16 μg/ml) > mesenteric (171 ± 31) > aortae (213 ± 68) > renal (IC50 = 375 ± 51) > tail artery (494 ± 93) > femoral arteries (>1000 μg/ml). Two saponins, bacoside A3 and bacopaside II, had similar vasodilator actions (IC50 = 8.3 ± 1.7 and 19.5 ± 6.3 μM). In aortae, without endothelium or in L-NAME (10-4 M), Brahmi was less potent (IC50 = 213 ± 68 to 2170 ± 664 and 1192 ± 167 μg/ml, respectively); indomethacin (10-5 M) was ineffective. In tail artery, Brahmi inhibited K⁺-depolarization induced Ca²⁺ influx and Ca²⁺ release from the sarcoplasmic reticulum by phenylephrine (10-5 M) or caffeine (20 mM).

Conclusions

Brahmi reduces blood pressure partly via releasing nitric oxide from the endothelium, with additional actions on vascular smooth muscle Ca²⁺ homeostasis. Some Brahmi ingredients could be efficacious antihypertensives and the vasodilation could account for some medicinal actions.     

The anti-hypertensive effect of Danshen (Salvia miltiorrhiza) and Gegen (Pueraria lobata) formula in rats and its underlying mechanisms of vasorelaxation

Ethnopharmacological relevance

Radix Salviae miltiorrhizae (Danshen) and Radix Puerariae lobatae (Gegen) have long been used in traditional Chinese Medicine and serve as the principal herbs in treating cardiovascular disease.

Aims of the study

In the present study, an aqueous extract comprising Danshen and Gegen in the ratio of 7:3 (DG) was investigated for its anti-hypertension in vivo and vasodilative activities ex vivo.

Materials and methods

The anti-hypertensive effect of DG extract was investigated in spontaneously hypertensive rat (SHR) by measuring systolic blood pressure (SBP). Oral administration of DG extract was started at age of 6 weeks and 14 weeks for the preventive and therapeutic studies, respectively. Blood pressure was measured by tail-cuff method biweekly for 12 weeks. The ex vivo vasodilative activities of DG extract, its dependency on endothelium and the involvement of nitric oxide, prostacyclin and potassium channels were investigated using isolated rat aorta ring in organ bath.

Results

For in vivo study, systolic blood pressure was significantly reduced in DG extract-treated groups (90.2 and 300 mg/kg) as compared with the SHR control in both preventive and therapeutic studies. However, DG extract was unable to suppress or delay the onset of hypertension in the preventive study. For ex vivo study, the results showed that DG extract induced a concentration-dependent relaxation in aorta and persisted response was observed with the removal of endothelium. Besides, pretreatment with a non-selective potassium channel inhibitor tetraethylammonium (TEA) also significantly inhibited DG extract-induced vasodilation. Further investigations on specific potassium channel blockers revealed that ATP-sensitive potassium (K_ATP) channel inhibitor glibenclamide, inward rectifier potassium (Kir) inhibitor barium chloride and voltage-dependent potassium (K_v) channel inhibitor 4-aminopyridine, but not BK_Ca channel inhibitor iberiotoxin, exerted significant inhibition on DG extract-induced vasodilation.

Conclusions

The results of in vivo SHR animal model suggested that DG aqueous extract possessed blood pressure lowering effect on both pre- and post-hypertensive rats, which could be explained by its endothelium-independent vasodilation via the opening of K_ATP, Kir and K_v channels.     

Modelling of α1-adrenoceptor-mediated temporal dynamics of inotropic response in rat heart to assess ligand binding and signal transduction parameters

Background and purpose:

In order to use the transient response to an antagonist (prazosin) to evaluate properties of agonist interactions with the α₁-adrenoceptor system, an integrative mechanistic model of cardiac uptake of prazosin and its competitive interaction with phenylephrine at the receptor site was developed. Based on the operational model of agonism, the aim was to evaluate both the receptor binding and signal transduction process as determinants of the inotropic effect of phenylephrine.

Experimental approach:

In Langendorff-perfused rat hearts, prazosin outflow concentration and left ventricular developed pressure were measured, first in the presence of 12.3 µmol·L⁻¹ phenylephrine following a 1 min infusion of 1.27 nmol [³H]-prazosin, and second, when after 30 min the phenylephrine concentration in perfusate was reduced to 6.1 µmol·L⁻¹, the 1 min infusion of 1.27 nmol [³H]-prazosin was repeated.

Key results:

The kinetic model accounted for cardiac uptake and receptor binding kinetics of prazosin (dissociation constant, mean ± SD: 0.057 ± 0.012 nmol·L⁻¹), assuming that the competitive displacement of phenylephrine (dissociation constant: 101 ± 13 nmol·L⁻¹) reduced the receptor occupation by the agonist and, consequently, contractility. This competitive binding process appeared to be the rate-determining step in response generation. The relationship between receptor occupancy and inotropic response was described by an efficacy parameter (τ, ratio of receptor density and coupling efficiency) of 4.9.

Conclusions and implications:

Mechanistic pharmacodynamic modelling of the kinetics of antagonism by prazosin allows quantitative assessment of the α₁-adrenoceptor system both at the receptor and post-receptor levels.     

Diesel exhaust particles induce endothelial dysfunction in apoE-/- mice

BACKGROUND: Particulate air pollution can aggravate cardiovascular disease by mechanisms suggested to involve translocation of particles to the bloodstream and impairment of endothelial function, possibly dependent on present atherosclerosis. AIM: We investigated the effects of exposure to diesel exhaust particles (DEP) in vivo and ex vivo on vasomotor functions in aorta from apoE(-/-) mice with slight atherosclerosis and from normal apoE(+/+) mice. METHODS: DEP 0, 0.5 or 5 mg/kg bodyweight in saline was administered i.p. The mice were sacrificed 1 h later and aorta ring segments were mounted on wire myographs. Segments from unexposed mice were also incubated ex vivo with 0, 10 and 100 microg DEP/ml before measurement of vasomotor functions. RESULTS: Exposure to 0.5 mg/kg DEP in vivo caused a decrease in the endothelium-dependent acetylcholine elicited vasorelaxation in apoE(-/-) mice, whereas the response was enhanced in apoE(+/+) mice. No significant change was observed after administration of 5 mg/kg DEP. In vivo DEP exposure did not affect constriction induced by K(+) or phenylephrine. In vitro exposure to 100 microg DEP/ml enhanced acetylcholine-induced relaxation and attenuated phenylephrine-induced constriction. Vasodilation induced by sodium nitroprusside was not affected by any DEP exposure. CONCLUSION: Exposure to DEP has acute effect on vascular functions. Endothelial dysfunction possibly due to decreased NO production as suggested by decreased acetylcholine-induced vasorelaxation and unchanged sodium nitroprusside response can be induced by DEP in vivo only in vessels of mice with some atherosclerosis.