From the School of Pharamacy, Mashhad University of Medical Sciences, Mashhad, Islamic Republic of
Abstract: (5400 Views)
Generally, plasma proteins owe their binding capacity to the presence of
aminoacid units which enter into intra- and intermolecular hydrophobic bonding
with a diverse range of endo- and exogenous chemical substances. The intermolecular
interactions between the hydrophobic areas of drug molecules and those of plasma
proteins play an important role in drug-macromolecular complex formation and
stabilization. This largely accounts for the carrier capacity of proteins for lipid
soluble drugs. Albumin may be particularly responsible for the binding of local
anaesthetics in plasma, but another binding factor may be lipoproteins present in
blood cell membranes. Thus, and due to the special importance of the drug-protein
binding phenomenon and its influence on the biological response, this investigation
has been commenced on the purpose of establishing whether the degree of drug-protein
interaction could be correlated with the duration of action of certain new
potential local anaesthetics. These are derivatives of 2-phenoxyethyldialkylamine
hydrochloride. Equilibrium dialysis, being generally the most reliable of the various
methods available, was chosen as a means of determining the extent of drug-protein
binding, and bovine serum albumin CBSA) of molecular weight around 70,000 was
employed. An ultraviolet assay method was used to measure the concentration of
free, unbound local anaesthetic molecules in the protein-free compartment, once
equilibrium had been attained. It was found that the affinity of the test compounds
for BSA does not parallel their duration of action produced in the guinea pig
intradermal wheal test. Moreover, the ability of BSA to bind these local anaesthetics
appeared not to depend on the number of binding sites on the protein molecule, but
rather on the proportion of :::union:::ised lipophilic species. This suggests that ionic
forces probably play no essential part in the binding process.