Cardiovascular Effects of Nifedipine and Bay K 8644 in Hypertensive Rats

BACKGROUND: Calcium plays a key role in vascular contraction and regulates receptor sensitivity to certain neurotransmitters. Calcium channel blockers are useful in the treatment of both clinical and experimental hypertension. The present study was designed to examine whether there is an alteration of the activity of calcium channels in association with the development of hypertension. METHODS: Deoxycorticosterone acetate(DOCA)-salt hypertension was made by subcutaneous implantation of DOCA(200mg/kg)strip plus saline drinking(1%) and 2-kidney, 1 clip(2KIC)hypertension by clipping the left renal artery with a silver clip(internal gap of 0.2mm). They were used 4 weeks later. Age-matched normal rats served as a control. Mean arterial pressure(MAP) and heart rate(HR) were continuously recorded from the right femoral artery. The drugs were administered intravenously. RESULTS: Vehicle alone was without effect on MAP or HR. In normotensive rats, nifedipine infusion(5 and 10ug/kg/min)caused a dose-dependent decrease in MAP without significant changes in HR, while Bay k 8644(Bay K, 5 and 10 ug/kg/min) increased MAP transiently. Both the depressor response to nifedipine and the pressor response to Bay k were more marked in DOCA-salt hypetensive rats than in normotensive rats. The maximal changes in MAP indced by nifedipine(5 and 50 ug/kg) or Bay K(5 and 50 ug/kg) were also enhanced in 2KIC hypertensive rats as compared with control rats. CONCLUSION: These results indicate that calcium channel inhibitors and activators can affect on the regulation of blood pressure in an opposite fashion. It is also suggested that the activity of calcium channels might be altered in the developement of experimental hypertension.

Two Cases of Stimulus Sensitive Spinal Myoclonus

Myoclouns is a complicated and poorly-understood phenomenon caused by many pathological conditions. Myoclonus which is triggered by sensory stimuli has been termed reflx myoclonus and divided into cortical, reticular and spinal types depending on the generator sites. Segmental myoclonus of spinal origin consists of synchronous rhythmical jerks confined to a group of muscles supplied by either one segment or several contiguous segments of the spinal cords. We present two cases of spinal reflex myoclonus. One was 50 years old female who showed complex myoclonic jerks involving the abdominal wall and paraspinal muscibs resembling 'belly dance'. The other was 26 years old male who showed intermittent synchronous upper cervical axial muscle contractions. In both cases, jerks were increased with certain stimuli, but disappeared during sleep. They showed normal EEGs and absence of enhancement of SSEPS.