Pharmacokinetic and pharmacodynamic alterations of methyldopa in rats with aortic coarctation. A study using microdialysis

Reactions of d-glucose with phenolic amino acids: further insights into the competition between Maillard and Pictet–Spengler condensation pathways

The reactions of 5-S-cysteinyldopa, L-alpha-methyldopa and DL-m-tyrosine with D-glucose were investigated at 90 degrees C in phosphate buffer at pH ranging from 5.0 to 9.0. Whereas gave mainly the double Maillard condensation product N,N'-bis(1''-deoxy-D-fructos-1''-yl)-5-S-cysteinyldopa, as an inseparable mixture of beta-D-fructopyranosyl and alpha,beta-D-fructofuranosyl derivatives, 2 and 3 gave both Maillard and Pictet-Spengler products, although to different extents and with different regio- and stereochemistry. A peculiar pattern of reactivity was displayed by which gave, besides the Maillard product and the expected 6,7-dihydroxy-1,2,3,4-tetrahydroisoquinoline C-1 diastereoisomeric pairs, the unprecedented 7,8-dihydroxy-1,2,3,4-tetrahydroisoquinoline derivative via the ortho cyclization pathway. Pictet-Spengler cyclization of 2 and 3 proceeded with Felkin-Anh-type asymmetric induction, favouring the 1R isomer throughout the pH range 5.0-9.0. These results, which highlight the first example of carbohydrate-derived 7,8-dihydroxytetrahydroisoquinoline, provide new insights into the factors governing competition between Maillard and Pictet-Spengler condensation pathways.

Validation of a new intraarterial microdialysis shunt probe for the estimation of pharmacokinetic parameters

The aim of our study was to compare pharmacokinetic parameters of a highly bound protein drug, irbesartan, obtained from microdialysis data (MD) of arterial blood and conventional blood samples (BS). A new vascular shunt microdialysis probe was inserted into the carotid artery and one femoral vein was cannulated for i.v. administration of irbesartan. Microdialysis samples were collected every 15 min. Blood samples were taken every 15 min. Levels of drug were measured by HPLC. Pharmacokinetic parameters were estimated using TOPFIT program. Corrected MD were compared with BS taken at same time to determine protein binding. The irbesartan protein binding did not change during the experiment. The estimated Ke from MD and BS were similar (MD: 1.8+/-0.3 h(-1), n=5; BS: 1.7+/-0.2 h(-1), n=5). After protein binding correction for the MD, the estimated values of volume of distribution (Vd) (MD: 1.2+/-0.4 l, n=5; BS: 1.1+/-0.4 l, n=5), clearance (Cl) (MD: 32.3+/-7.3 ml min(-1), n=5; BS: 30.7+/-8.2 ml min(-1), n=5) and AUC (MD: 7.7+/-3.2 microg x ml(-1) h, n=5; BS: 8.8+/-3.4 microg x ml(-1) h, n=5) were similar between MD and BS. In conclusion, these results show that our new probe inserted in the carotid artery provides accurate MD to estimate pharmacokinetic parameters of a highly bound protein drug like irbesartan. On the other hand, MD were also useful to the in vivo study of drug protein binding and saturation in protein binding.

Intracerebral microdialysis: 30 years as a tool for the neuroscientist

1. Microdialysis is an established technique for studying physiological, pharmacological and pathological changes of a wide range of low molecular weight substances in the brain extracellular fluid. Many studies have proven its sensitivity in sampling the extracellular space in discrete brain locations, such as the striatum, and monitoring the action of exogenous substances. 2. The two main areas of application of microdialysis are the recovery of endogenous substances, primarily the neurotransmitters, and the infusion of drugs through the microdialysis cannula (retrodialysis). 3. Microdialysis in awake animals is the tool of choice for studying the relationship between changes in behaviour and neurotransmitters in certain brain areas. In addition, the concomitant recording of the electroencephalogram at the site of microdialysis has been shown to be extremely useful in determining the role of certain neurotransmitters in paroxysmal activity. 4. Clinical applications of microdialysis have included monitoring of ischaemic injury, subarachnoid haemorrhage, trauma and epilepsy. With the recent availability of standardized equipment, the use of microdialysis in the neurological clinic is likely to become more common.