Relations between blood pressure and plasma norepinephrine concentrations after administration of diltiazem to rats: HPLC-peroxyoxalate chemiluminescence determination on an individual basis.

A calcium antagonist, diltiazem, was infused continuously into Sprague-Dawley rats through the left femoral vein at four different flow rates. The mean arterial blood pressure and concentrations of plasma norepinephrine (NE) were measured in each single rat (n = 5) and the correlations between them were studied. Blood (150 microL) was collected 13 times during the infusion. Plasma NE was determined by HPLC-ethylenediamine condensation reaction-peroxyoxalate chemiluminescence detection system (HPLC-ED-PO-CL). In four cases from 5 rats, the blood pressure reduction caused by diltiazem was inversely correlated to logarithm of plasma NE concentration. The relation was expressed as Y = -alogX+m. The coefficients of correlation were -0.9506, -0.9293, -0.9341 and -0.8675, respectively. The correlation for the last rat was worse (r = -0.0799). The good correlation would imply that the sympathetic nervous system released NE to maintain blood pressure up to the normal level, responding to the sympathetic nervous system released NE to maintain blood pressure up to the normal level, responding to the blood pressure reduction caused by diltiazem. The present experiment proved the feasibility of the determination method of NE utilizing HPLC-ED-PO-CL detection in applying to the individual rats.