Biomedical subjects
Publications and source records attributed to E U Nzekwe.
The penetration into the eye of fluorescein from a normal drop was found to increase with age and averaged twelve times more in the elderly than in the young. Examination of the literature suggests that this is a result of a greater contact time with the cornea rather than a rise in epithelial permeability.
Regulation by hormones of nervous system development is well recognized in humans, laboratory animals and cultured nerve cells. Thyroxine (T4) and triiodothyronine (T3), the major thyroid hormones, act on brain development and maturation by binding to T3 nuclear receptors. T3 responsive genes have been identified with the T3 receptor as a superfamily of genes including cortisol and estrogens, necessary for adaptation and survival. Less defined are T3 and T4 actions on the peripheral nervous system. In chromaffin cells explanted from the adrenal of immature rats, T3 induces the enzyme tyrosine hydroxylase, involved in catecholamine synthesis. This action is similar but, so far, apparently independent from Nerve Growth Factor promotion of sympathetic and chromaffin cell growth. Mechanisms based on nuclear binding depend on multiple receptors functionally diversified; their selectivity of action over a wide range of early and late developmental patterns is an attractive hypothesis to be further explored.
A simple, sensitive, selective and precise liquid-column chromatographic assay for clonazepam is described, in which 1 ml of serum containing 50 micrograms/l methylclonazepam as an internal standard is extracted by elution from a Bond-Elut column with 400 microliter of methanol. An aliquot of the eluate is injected on to a reversed-phase column and eluted with a mobile phase of acetonitrile--phosphate buffer (30:70) at a flow-rate of 2 ml/min at a column temperature of 50 degrees C. Detection is at 254 nm. Chromatography is complete in 12 min. A sensitivity of 2 ng/ml is attained when 1 ml of serum is extracted. Analytical recovery of the clonazepam added to serum ranged from 91% to 99% with a coefficient of variation of 6.0%. This assay for clonazepam has good precision, with coefficients of variation of 11% at 15 ng/ml and 2.6% at 50 ng/ml. There was no interference from any of the commonly used antiepileptics.