Quantification of propranolol enantiomers in small blood samples from rats by reversed-phase high-performance liquid chromatography after chiral derivatization

A high-performance liquid chromatographic (HPLC) technique is described for quantification of R(+)- and S(−)-propranolol from 100-μl rat blood samples. The procedure involves chiral derivatization with tert.-butoxycarbonyl- -leucine anhydride to form diastereomeric propranolol- -leucine derivatives which are separated on a reversed-phase HPLC column. The method as previously reported has been modified for assaying serial blood microsamples obtained from the rat for pharmacokinetic studies. An internal standard, cyclopentyldesisopropylpropranolol, has been incorporated into the assay and several derivatization parameters have been altered. Standard curves for both enantiomers were linear over a 60-fold concentration range in 100-μl samples of whole rat blood (12.5–750 ng/ml; r=0.9992 for each enantiomer). Inter- and intra-assay variability was less than 12% for each enantiomer at 25 ng/ml. No enantiomeric interference or racemization was observed as a result of the derivatization. No analytical interference was noted from endogenous components in rat blood samples. Preliminary data from two male Sprague-Dawley rats given a 2.0 mg/kg intravenous dose of racemic propranolol revealed differential disposition of the two enantiomers. R(+)-Propranolol achieved higher initial concentration but was eliminated more rapidly than S(−)-propranolol. Terminal half-lives of R(+)- and S(−)-propranolol were 19.23 and 51.95 min, respectively, in one rat, and 14.50 and 52.07 min, respectively, in the other.     

GENETIC RELATEDNESS OF TWO POPULATIONS OF THE SOUTHERN ELEPHANT SEAL, MIROUNGA LEONINA

Blood samples from southern elephant seals ( Mirounga leonina ) from Heard and Macquarie Islands were surveyed electrophoretically for protein variation. Thirty proteins encoded by a minimum of 35 loci were screened, four of which were found to be polymorphic. Statistically significant differences in allele frequencies were found between the two populations at three loci. Heterozygosity estimates for the Heard and Macquarie island populations were 0.034 ± 0.020 (mean ± standard error) and O.029 ± 0.017 respectively, with a Nei distance of 0.007. The findings suggest that the two populations may have diverged genetically and very limited gene flow exists between the islands, a finding consistent with limited information from mark-recapture studies.     

Down''s Syndrome Individuals Begin Life with Normal Levels of Brain Cholinergic Markers

We measured the activities of the cholinergic marker enzymes choline acetyltransferase (ChAT) and acetylcholinesterase (AChE) in autopsied brains of seven infants (age range 3 months to 1 year) with Down's syndrome (DS), a disorder in which virtually all individuals will develop by middle age the neuropathological changes of Alzheimer's disease accompanied by a marked brain cholinergic reduction. When compared with age-matched controls cholinergic enzyme activity was normal in all brain regions of the individuals with infant DS with the exception of above-normal activity in the putamen (ChAT) and the occipital cortex (AChE). Our neurochemical observations suggest that DS individuals begin life with a normal complement of brain cholinergic neurons. This opens the possibility of early therapeutic intervention to prevent the development of brain cholinergic changes in patients with DS.