Pharmacokinetics and biodistribution of technetium 99m labelled standard heparin and a low molecular weight heparin (enoxaparin) after intravenous injection in normal volunteers

For a better understanding of low molecular weight heparin pharmacokinetics, 99m technetium labelled heparin and enoxaparin were injected intravenously to four normal volunteers, after approval by the Ethics Committee and preliminary animals studies. In vitro and in vivo, the labelled products proved to be stable and identical to the non-labelled drugs. Radioactivity curves in blood, organs and urines were similar for both products. Anti Xa plasma half-life was 3 times longer for enoxaparin than for heparin. Anti IIa plasma half-lives were similar. However, radioactivity persisted much longer than biological activities for both products. After chromatography, most of the radioactivity was bound to AT III, where an anti Xa activity peak was also detected. The anti Xa activity peak seen after adding AT III to plasma was much higher with heparin than with enoxaparin. In urine, biological activities, measured with AT III supplementation, were higher with enoxaparin than with heparin. These results suggest that phenomena other than biodistribution are responsible for the differences in pharmacokinetics observed between these two products. The two most likely explanations are differences in metabolism and/or a release of an endogenous factor.

Labelling of peripheral-type benzodiazepine binding sites in human brain with [3H]PK 11195: anatomical and subcellular distribution

The peripheral-type benzodiazepine binding site, erstwhile characterized in the rodent and feline brain, has now been characterized in post-mortem human brain using [3H]PK 11195. The kinetics and pharmacological properties of the binding of this ligand are similar to peripheral-type benzodiazepine binding sites elsewhere. The potency of RO5-4864 for this site in human brain is close to that seen in ruminant and carnivore tissues but considerably lower than in rodent tissues. The regional distribution of these binding sites would suggest a neuronal rather than a glial localization. [3H]PK 11195 bound in a similar fashion to slide-mounted sections of human brain, thus allowing quantitative studies of the regional distribution of peripheral-type benzodiazepine binding sites to be made. The binding sites were distributed heterogeneously, but were restricted to the grey matter. Highest densities of binding sites were found in forebrain structures. The localization was not limited to any functional system, nor did it resemble any previously described transmitter system. The similarities between peripheral-type benzodiazepine binding sites in human and in feline brain in terms of their pharmacological characteristics and their regional and subcellular distribution suggest that the cat, rather than the rat, may be the better model for studying a possible role for this site in human cerebral function.

Characterization of peripheral type benzodiazepine binding sites in human and rat platelets by using [3H]PK 11195. Studies in hypertensive patients

Peripheral type benzodiazepine binding sites have been studied in human and rat platelets and platelet membranes by using PK 11195 (1-(2-chlorophenyl)-N-methyl-N-(1-methyl propyl)-3-isoquinolinecarboxamide) as a ligand. [3H]PK 11195 binding to the intact cells and membranes is saturable, with a high affinity and presents the pharmacological specificity corresponding to the peripheral binding sites (PK 11195 greater than RO5-4864 greater than diazepam greater than clonazepam). [3H]PK 11195 affinity is not affected by cell lysis, but there is a loss of binding capacity, contrarily to RO5-4864 whose affinity is greatly diminished. For this reason [3H]RO5-4864 binding can only be demonstrated in intact cells. Furthermore opposite to RO5-4864, PK 11195 affinity is not decreased by increasing temperatures. No difference was found between binding parameters (KD and Bmax) for [3H]PK 11195 between normotensive and hypertensive subjects. The very high binding capacity of human and rat platelets (Bmax greater than pmole/10(8) cells) makes them a good biological model for studying the physiological significance of "peripheral type" benzodiazepine binding sites.

The 5-hydroxytryptamine-releasing properties of two epimer quinoline derivatives

Two epimer quinoline derivatives, PK 5078 and PK 7059, have been shown to be potent at releasing 5-HT from blood platelets. Moreover PK 5078 was also a potent and selective inhibitor of the uptake of 5-HT, being about 20 times as active as clomipramine. Both drugs, like p-chloroamphetamine, released 5-HT but did not inhibit MAO-A. Whilst p-chloroamphetamine seemed to be active on the cytoplasmic pool of 5-HT and reserpine on the vesicular pool, PK 5078 and PK 7059 were effective first on the vesicular pool and then on the cytoplasmic pool. The quinoline derivatives were devoid of the typical side-effects of amphetamine-like drugs, i.e. hyperactivity, anorexia and group toxicity. For these reasons PK 5078 and PK 7059 can be considered to be a new type of selective 5.HT-releasing drug.

Labelling of "peripheral-type" benzodiazepine binding sites in the rat brain by using [3H]PK 11195, an isoquinoline carboxamide derivative: kinetic studies and autoradiographic localization

PK 11195 [1-(2-chlorophenyl)-N-methyl-N-(1-methylpropyl)-3-isoquinolinecarboxamide] is a new ligand for the "peripheral-type" benzodiazepine binding sites, chemically unrelated to benzodiazepines. It displaces with a very high potency (IC50 congruent to 10(-9) M) [3H]-RO5-4864 (a benzodiazepine which specifically labels the peripheral-type sites) from its binding sites. [3H]PK 11195 binds to a membrane fraction from rat brain cortex and rat olfactory bulb in a saturable and reversible manner with a very high affinity (KD = 10(-9) M). The number of maximal binding sites was ten times greater in the olfactory bulb than in the brain cortex. The order of potency of several compounds as displacers at 25 degrees C (PK 11195 greater than RO5-4864 greater than diazepam greater than dipyridamole greater than clonazepam) demonstrates that [3H]PK 11195 binds to the peripheral-type benzodiazepine binding sites. The KD value for the [3H]PK 11195 binding is not affected by temperature changes, whereas RO5-4864 and diazepam affinities decrease with increasing temperatures. Autoradiographic images of [3H]PK 11195 binding to rat brain sections show that binding sites are mainly localized in the olfactory bulb, median eminence, choroid plexus, and ependyma. This ligand could be a useful tool to elucidate the physiological and pharmacological relevance of these binding sites.

"Peripheral type" benzodiazepine binding sites in rat adrenals: binding studies with [3H]PK 11195 and autoradiographic localization

PK 11195 [1-(2-chlorophenyl)-N-methyl-N-(1-methylpropyl)-3-isoquinolinec arboxamide] is a compound chemically unrelated to benzodiazepines with a high affinity for the "peripheral type" binding sites for benzodiazepines (Le Fur et al., 1983a). [3H]PK 11195 binds to the adrenal membranes with a high affinity (KD congruent to 3 nM) in a specific, reversible and GABA-independent manner. Binding is also characterized by very high Bmax (34 pmol/mg protein). These binding sites are the "peripheral type" benzodiazepine binding sites as demonstrated by the potency order of displacement of the [3H]PK 11195 bound: PK 11195 greater than R05-4864 greater than diazepam greater than dipyridamole greater than clonazepam. The biochemical characteristic of the binding to rat adrenal sections has also been studied. In these conditions the affinity for [3H]PK 11195 is ten times smaller, but the potency order of displacing agents was the same, demonstrating the identity of the section binding sites. Using tritium sensitive film these sites have been visualized in adrenal sections. [3H]PK 11195 binding sites are localized in the adrenal cortex with some spare labelling in the medulla.

Peripheral benzodiazepine binding sites: effect of PK 11195, 1-(2-chlorophenyl)-N-methyl-N-(1-methylpropyl)-3-isoquinolinecarboxamide. I. In vitro studies

[3H] RO5-4864 binding sites have been characterized in kidney, heart, brain, adrenals and platelets in the rat. In all these organs the following order of potency in the RO5-4864 displacement was found: RO5-4864 greater than diazepam greater than clonazepam indicating that they correspond to the "peripheral type" of benzodiazepine binding sites. PK 11195, an isoquinoline carboxamide derivative, displaces [3H] RO5-4864 from its binding sites in all the organs. PK 11195 was as potent as RO5-4864 in the platelets, heart, adrenals, kidney and several brain regions (midbrain, hypothalamus, medulla + pons and hippocampus. However it was 5 to 10 times more effective in cortex and striatum. In conclusion PK 11195 might represent a new tool to elucidate the physiological relevance of "peripheral type" benzodiazepine binding sites and might help to discriminate the hypothetical subclasses of these binding sites.