ß-Blockers are weak bases with acidity constants related to their secondary amine group. At environmental pH they are protonated with the tendency to shift to their neutral species at more alkaline pH. Here we studied the influence of pH from 5.5 to 8.6 on the toxicity of the four ß-blockers atenolol, metoprolol, labetalol and propranolol in zebrafish embryos, relating toxicity not only in a conventional way to external aqueous concentrations but also to measured internal concentrations.

Besides lethality, we evaluated changes in swimming activity and heartbeat, using the Locomotor Response (LMR) method and the Vertebrate Automated Screening Technology (VAST) for high throughput imaging.

Effects of metoprolol, labetalol and propranolol were detected on phenotype, heart rate and swimming activity. External effect concentrations decreased with increasing neutral fraction for all three pharmaceuticals, attributed by an enhanced uptake of the neutral species in comparison to the corresponding charged form. The LC₅₀ of metoprolol decreased by a factor of 35 from 1.91 mM with almost complete cationic state at pH 7.0 to 0.054 mM with 8% neutral fraction at pH 8.6. For propranolol the LC₅₀ of 2.42 mM at pH 5.5 was even 100 fold higher than the LC₅₀ at pH 8 with 0.023 mM where 3% were neutral fraction. No effects were detected in the zebrafish embryo exposed to atenolol.

The internal concentrations for metoprolol and propranolol were quantified at non-toxic concentrations and at the LC₁₀. Apparent bioconcentration factors (BCF) ranged from 1.96 at pH 7.0 to 32.0 at pH 8.6 for metoprolol and from 1.86 at pH 5.5 to 169 at pH 8.0 for propranolol. The BCFs served to predict the internal effect concentrations from the measured external effect concentrations.

Internal effect concentrations of metoprolol and propranolol were in a similar range for all pH-values and for all endpoints. Interestingly, the internal effect concentrations were in the internal concentration range of baseline toxicity, which suggests that the effects of the ß-blockers are rather unspecific, even for sublethal effects on heart rate. In summary, our data confirm that the pH-dependent toxicity related to external concentrations can be explained by toxicokinetic effects and that the internal effect concentrations are pH-independent.

ß-Blockers是弱碱，其酸度常数与其仲胺基团有关。在环境pH值下，它们会质子化，并在碱性更高的pH下趋向于转变为中性物质。在这里，我们研究了5.5至8.6的pH值对斑马鱼胚胎中四种ß阻滞剂阿替洛尔，美托洛尔，拉贝洛尔和普萘洛尔的毒性的影响，不仅以常规方式将毒性与外部水相浓度相关，而且还与测量的内部浓度相关。

除了致死性外，我们还使用运动响应（LMR）方法和椎体自动筛查技术（VAST）评估了游泳活动和心跳的变化，以进行高通量成像。

检测美托洛尔，拉贝洛尔和普萘洛尔对表型，心率和游泳活动的影响。三种药物的中性分数随外在浓度的增加而降低，这是由于与相应的带电形式相比，中性物质的吸收增加了。美托洛尔的LC ₅₀从1.91 mM（在pH 7.0时几乎呈阳离子状态）下降到0.054 mM（在pH 8.6时中性分数为8％），降低了35倍。对于普萘洛尔，在pH 5.5时为2.42 mM的LC ₅₀甚至比在pH 8为0.023 mM时的LC ₅₀高100倍，其中3％为中性馏分。在暴露于阿替洛尔的斑马鱼胚胎中未检测到任何作用。

美托洛尔和普萘洛尔的内部浓度在无毒浓度和LC _10下进行定量。对于美托洛尔，表观生物富集因子（BCF）的范围从pH 7.0的1.96到pH 8.6的32.0，而普萘洛尔的pH值从5.5到169在1.86到8.0。BCF用于根据测得的外部效应浓度预测内部效应浓度。

对于所有pH值和所有终点，美托洛尔和普萘洛尔的内在作用浓度都在相似的范围内。有趣的是，内部作用浓度在基线毒性的内部浓度范围内，这表明β-受体阻滞剂的作用相当不确定，即使是对心率的致死作用也是如此。总而言之，我们的数据证实，与外部浓度有关的pH依赖性毒性可以通过毒代动力学效应来解释，而内部效应浓度与pH无关。