Hypertensive drugs and plasma kinins in rats

The influence of phenylephrine (PHE), methoxamine (MET) and ephedrine (EPH) on kininogen and prekallikrein level in plasma was investigated in male Wistar rats. Simultaneously the effect of these drugs on blood pressure was monitored. No changes in kininogenesis were observed during the hypertension period (2 h after ip injection). The significant decrease in kininogen level (by 20-30%) was found 4 h after PHE (5 mg/kg) or EPH (40 mg/kg) and 4-12 h after MET (40 mg/kg) injection. The reduction of kallikrein utilization, indicating an increase in prekallikrein level in plasma, was noted only after PHE (by 34%) or MET (by 44%) administration. Phentolamine (REG) in a dose of 20 mg/kg, which counteracted the hypertensive effect of investigated drugs, abolished the influence of these drugs on kininogen level. The results indicate that the hypertension induced by alpha-adrenoceptor agonists evokes the delayed activation of kininogenesis parallel to the secondary decrease in blood pressure. Such a reaction of kinin system seems to be related to primary alpha-adrenoceptor stimulation, not to the direct influence of hypertensive drugs on kinin system in rat plasma.