Cholecystokinin-octapeptide fragments: binding to brain cholecystokinin receptors.

Structural determinants of cholecystokinin octapeptide (CCK-8) binding to central nervous system receptors have been studied to assess the relative importance of the amino and the carboxyl end of the active peptide sequence, CCK-(26-33). The relative ability to inhibit equilibrium binding of [125I]CCK-33 to guinea pig cortical membranes was determined for a series of amino and carboxyl terminal fragments of CCK-8. While N-acetyl CCK-(26-29), N-acetyl CCK-(26-30) amide and N-acetyl CCK-(26-31) amide were inactive, the N-acetyl CCK-(26-32) amide fragment displayed binding to central receptors. Of the carboxyl terminal peptide fragments, both CCK-(29-33) and CCK-(30-33) bound less potently than CCK-8; CCK-(31-33) interacted more weakly than the tetra- and pentapeptide, but with a higher affinity to brain receptors than to peripheral receptors. The heptapeptide, CCK-(26-32) amide, and the tripeptide, CCK-(31-33), are known to antagonize CCK action at peripheral receptors. The heptapeptide bound to central receptors 25 times more potently than a known peripheral antagonist, dibutyryl cyclic GMP. Thus these peptides may act centrally to oppose CCK-8 mediated functions

Affinities and intrinsic activities of dopamine receptor agonists for the hD21 and hD4.4 receptors

The affinity and intrinsic activity of dopamine receptor agonists were determined at the human dopamine hD(21) and hD(4.4) receptors. (-)-3-Hydroxy-N-n-propylpiperidine ((-)3-PPP) had an intrinsic activity of 46% and 83%, whereas (+)-N-propylnorapomorphine ((+)-NPA) had intrinsic activities of 61% and 58% at the dopamine hD(21) and hD(4.4) receptors, respectively. Affinities also varied. A single, or multiple, dopamine D-2-type receptor(s) may be involved in schizophrenia and agonists are being tested as therapy. Understanding their properties at the individual dopamine D-2-family receptors is important

Route of tracer administration does not affect ileal endogenous nitrogen recovery measured with the 15N-Isotope dilution technique in pigs fed rapidly digestible diets

The 15N-isotope dilution technique (15N-IDT), with either pulse-dose oral administration or continuous i.v. administration of [15N]-L-leucine (carotid artery), both at 5 mg/(kg body weight · d), was used to measure ileal (postvalve T-cecum cannula) endogenous nitrogen recovery (ENR) in pigs (9 ± 0.6 kg). Diets were cornstarch, enzyme-hydrolyzed casein with no (control) or high (4%) content of quebracho extract (Schinopsis spp.) rich in condensed tannins. Blood was sampled from a catheter in the external jugular vein. Mean plasma 15N-enrichment at d 8-10 was higher (P = 0.0009) after i.v. than after oral administration [0.0356 vs. 0.0379 atom% excess (APE)]. Plasma 15N-enrichment for i.v. infused pigs was 0.01117 APE higher (P <0.0001) and for orally dosed pigs 0.0081 APE lower (P <0.0001) at 11 h postprandial compared with 1 h postprandial. Apparent ileal N digestibility was higher (P <0.0001) for the control (85.5%) than for the quebracho diet (69.5%). ENR was calculated from the ratio of 15N-enrichment of plasma and digesta. The ENR for the quebracho diet was 300% higher than for the control diet (6.03 vs. 1.94 g/kg dry matter intake, P <0.001). The real N digestibility (92.2 ± 0.4%) was equal for both diets (P = 0.1030) and both tracer methods (P = 0.9730). We concluded that oral administration of [15N]leucine provides reasonable estimates of ENR in pigs fed semipurified diets with high or low content of tannins; however, one must be careful in extrapolating this conclusion to studies with other protein sources or feeding frequencie

An optimized methodology for combined phenotyping and genotyping on CYP2D6 and CYP2C19

A method for simultaneous phenotyping and genotyping for CYP2D6 and CYP2C19 was tested. Six healthy volunteers were selected (three extensive and three poor metabolisers for CYP2D6). CYP2D6 was probed with dextromethorphan and metoprolol and CYP2C19 was probed with omeprazole. Blood samples were collected and analysed for dextromethorphan, dextrorphan, metoprolol, alpha -hydroxymetoprol, omeprazole and 5-hydroxyomeprazole by HPLC. Genotyping was performed for both CYP2D6 and CYP2C19. Generally, plasma levels could be measured up to 8 h post-dose except for alpha -hydroxymetoprolol in poor metabolizers (PMs) and dextromethorphan in extensive metabolizers (EMs) (35% below quantification limit). The correlation between the metabolic ratio based on timed individual measurements and the metabolic ratio based on the AUC(0-12) values was significant at 3 h postdose for all probes. In conclusion, the following procedure is suggested: administer metoprolol (100 mg) and omeprazole (40 mg); after 3 h, take a blood sample to assess the genotype and the metabolic ratio for CYP2D6 (metoprolol over alpha -hydroxymetoprolol) and CYP2C19 (omeprazole over 5-hydroxyomeprazole) in plasma. With this procedure, all necessary information on the individual CYP2D6 and CYP2C19 metabolising capacity can be obtained in a practical, single-sample approach.</p