Clinical investigations of catecholaminergic systems using liquid chromatography with electrochemical detection

Microcylinder electrodes as sensitive detectors for high-efficiency, high-speed liquid chromatography

A carbon fiber microcylinder electrode (r = 3.5 microns) is used as a detector for high-efficiency and high-speed liquid chromatography. The microcylinder has a detection volume of a few picoliters, and can be placed directly at the outlet frit of the column. With proper positioning equipment, the electrode can be placed at the region of the outlet frit where the separation efficiency is highest. Such selective sampling results in greatly increased measured efficiency over a conventional electrochemical detector when short (4 cm) columns of conventional diameter (3.2 mm) are used. The microcylinder detector is sensitive and subpicomole detection limits are obtained in less than 30 s for norepinephrine. The need for expensive positioning equipment is eliminated by mounting the electrode into a fitting which can be mated directly with the column.

Cardiovascular and endocrine effects of naloxone compared in normotensive and hypertensive patients

Naloxone, a competitive antagonist of opioid receptors, and placebo (dextrose 5% in water (D5W) were administered on separate days to healthy normotensive (NT) male volunteers and to male patients with essential hypertension (HT). A single-blind, placebo-controlled, cross-over design was employed. Increasing doses of naloxone (0.4, 1.2, 3.6, 10.8, 32.4, 97.2 mg) were given every 30 min as slow i.v. boluses. On a separate day, i.v. boluses of D5W were given according to a similar protocol. Naloxone failed to significantly modify systolic and diastolic blood pressure (BP), heart rate (HR), respiratory rate, oral temperature or plasma catecholamines. No adverse reactions or behavioral effects were seen with naloxone. Naloxone produced a dose-dependent increase in plasma cortisol, whereas plasma cortisol showed a gradual decline on the placebo day (circadian variation). HT and NT showed similar maximal increases in plasma cortisol. Hypertensives responded to lower doses of naloxone with greater increases in plasma cortisol. The results were significantly different only if corrected by using the baseline values obtained on the placebo day. The study suggests that in awake, resting men, endogenous opioids play no role in regulating BP, HR, respiration, temperature or the activity of the sympathetic nervous system. It also suggests that the sustained elevation of BP in HT is not due to endogenous opioid substances. However, endogenous opioid substances produce a tonic inhibitory effect on the release of cortisol. This tonic inhibition seems to be greater in hypertensives than in normotensives.