Hydrolysis kinetics of diacetyl nadolol

Diacetyl nadolol, a prodrug of nadolol and a beta-blocker, has corneal permeability approximately 20 times higher than that of its parent compound due to its higher lipophilicity. Hydrolysis studies were conducted for diacetyl nadolol at various elevated temperatures and pH values to provide stability information for its ophthalmic preparations. The apparent rate constants for diacetyl nadolol hydrolysis to acetyl nadolols and nadolol were determined. Within the neutral pH range (6.8 to 8.2), the hydrolysis of diacetyl nadolol may be proposed as specific base catalysis. Various constants for diacetyl nadolol hydrolysis to acetyl nadolols and acetyl nadolols to nadolol were respectively listed as following: activation energy, 9.78 and 11.39 kcal/mol; entropy at 25 degrees C, -9.78 and -5.86 cal/mol.deg; second-order rate constant at 75 degrees C, 3.47 X 10(4) and 2.22 X 10(4) M-1h-1. According to these kinetic constants, a diacetyl nadolol aqueous solution with pH 6.5 may be prepared as an antiglaucoma agent. The shelf-life was estimated to be only 43 d at room temperature (25 degrees C). However, when the storage temperature is lowered to 5 degrees C, the shelf-life can be extended to greater than 2 years.

Control of gene expression in bacteriophage P22 by a small antisense RNA. I. Characterization in vitro of the Psar promoter and the sar RNA transcript

The characterization in vitro of a newly discovered promoter (Psar) in the bacteriophage P22 immI region is described. Psar is located within the ant gene and is directed toward the major immI promoter, Pant. The entire intercistronic region between the P22 arc and ant genes (69 bp) is transcribed. The initiation and termination of sar (small antisense regulatory) RNA transcription are unusual. Frequent abortive initiation occurs in the presence of all four NTPs; RNA products 3-13 nucleotides in length are produced in about 15- to 25-fold larger numbers than full-length transcripts. Termination of sar RNA synthesis occurs after transcription of the first and second Ts of a TTTA sequence following a region of hyphenated dyad symmetry. The effects of convergent transcription between Pant and Psar were investigated on linear and supercoiled templates. Active transcription from Pant interferes with full-length transcription from Psar; several factors that interfere with Pant initiation (e.g., Pant down-mutation, Mnt repressor protein, Arc repressor protein) result in indirect activation of sar RNA synthesis. The sar RNA pairs rapidly with ant mRNA to form a stable stoichiometric complex. The location and properties of Psar suggest an important regulatory function for sar RNA as a negative effector of ant expression. The results of Wu et al. (this issue) support this suggestion.

Quantitative study of the ganglion neurons of the mouse trachea

The ganglionated plexus of the trachea of mice was studied quantitatively with a histochemical method that stains electively the ganglion nerve cells in whole-mount preparations. The plexus lies exclusively over the muscular part of the trachea, dorsal to the muscle itself, and it varies considerably in pattern and extent between individual animals. In young adult mice the plexus contains on average 235 neurons, occurring singly or gathered in packed ganglia. The ganglion neurons are relatively small, the profile area of three quarters of them measuring between 150 and 275 microns 2 with an average of 251 microns 2. In ageing mice the average number of ganglion neurons is the same as in young animals; however, cell sizes are markedly increased, the average being 341 microns 2. Among the ultrastructural features of the ganglia, is a capsule (perineurium) of very regular structure, the presence of collagen, capillaries and myelinated axons inside the ganglia, and the presence of only few and short dendrites, some of which are abutted by synapsing nerve endings.

Central cardiorespiratory effects of glutamate in dogs

Metabolism of certain amino acid neurotransmitters such as glutamate and gamma-aminobutyric acid (GABA) are closely linked in the brain to CO2 fixation and H+ metabolism. Additionally they may also affect central modulation of cardiorespiratory function. Therefore central cardiorespiratory effects of L-glutamate were determined in lightly anesthetized dogs using ventriculocisternal perfusion with artificial cerebrospinal fluid (CSF) (pH 7.25-7.28) containing 30 or 60 mM glutamate at a flow rate of 1.0 ml/min for 20 min followed by perfusion with artificial CSF alone. Tidal volume and minute ventilation increased with 60 mM glutamate, as did respiratory drive. These changes returned to normal with mock CSF perfusion. Glutamate (30 mM) had no significant effect on ventilation. At both concentrations, glutamate significantly increased mean femoral arterial pressure and mean pulmonary arterial pressure, which was accompanied by bradycardia. All these increases rapidly returned to normal with mock CSF perfusion. Cardiac output and pulmonary capillary wedge pressure did not change with glutamate perfusion. The results suggest that glutamate may have a significant central excitatory role in modulation of ventilatory drive as well as of hemodynamic functions.

Ocular pharmacokinetic models of clonidine-3H hydrochloride

A single topical instillation of clonidine-3H HCl solution (0.2%) was administered to the rabbit eye (30 microliter) in order to study the drug's ocular pharmacokinetics. Seven different tissues and plasma were excised and assayed for drug over 180 min. By 45-60 min pseudoequilibrium is reached for the cornea, iris/ciliary body, and aqueous humor. Thereafter, drug levels in these tissues decline in parallel. The data are fit separately to a physiological model and a classical diffusion model for which seven ocular tissue compartments and a plasma reservoir are constructed for each model. Clearance terms and distribution equilibrium coefficients are determined from the tissue level data and used as parameters in fitting the mass balance differential equations representing the physiological model. The model parameters can also be fit to a 0.4% single dose. In a separate experiment, a topical infusion technique was designed to provide a constant rate input to the cornea until an apparent steady state was reached in aqueous humor at 55 min. Aqueous humor levels were assayed for clonidine over the infusion and postinfusion periods. The physiological model parameters are fit to the topical infusion data and show good agreement between the predicted and experimental data. The classical model is too complex to fit the data to integrated exponential equations primarily because the method of residuals is inadequate in determining a sufficient set of initial estimates. This is overcome by dividing the eight-compartment model into seven fragmental models, each representing one to five compartments. A stepwise procedure is developed in which initial estimates are obtained for each separate fragmental model and refined. The refined parameter values can then be used as initial estimates for the complex model. Differential equations for the complex model are fit simultaneously to tissue levels representing each compartment. By observation, the classical model fit the data more closely than the physiological model. Statistical moment theory is also applied to the topical infusion data to determine ocular pharmacokinetic parameters for clonidine. The calculated values are: corneal absorption rate constant ka, 0.00139 min-1, aqueous humor elimination rate constant k10, 0.0658 min-1; mean residence time MRTd, 35.6 min; apparent steady-state volume of distribution Vss, 0.530 ml; and ocular clearance Qe, 14.9 microliter/min. The fraction absorbed from the single instillation is estimated as 0.0163.

Arsenic concentration in the urine of patients with Blackfoot disease and Bowen's disease

Extensive epidemiological study implicates that high arsenic content in artesian well water is the causal factor responsible for Blackfoot disease. We determine the arsenic concentration in urine samples of patients with Blackfoot and Bowen's diseases and examine whether there exists any discrepancy of urinary arsenic concentrations among patients and the normal population. The analyses were made by hydride atomic absorption spectrophotometry (AAS) and the analytical reliability of the method was checked with a standard urine sample (ORTHO Bi-Level Urine Metal Control). The results show that the mean urinary arsenic concentration in 100 healthy adults is 63.4±29.7 μg/L, and those means for 23 and 11 patients with Blackfoot disease and Bowen's disease are 75.7±39.1 μg/L (P vs controls >0.05) and 201±58 μg/L (P vs controls <0.001), respectively. From the analytical results obtained, we cannot conclude that urinary arsenic is associated with Blackfoot disease, as was disclosed from the epidemiological studies. However, urinary arsenic concentrations are possibly very closely associated with Bowen's disease.