Use of trifluoroperazine isolates a [(3)H]Ifenprodil binding site in rat brain membranes with the pharmacology of the voltage-independent ifenprodil site on N-methyl-D-aspartate receptors containing NR2B subunits.

The use of trifluoroperazine in a well washed rat brain membrane preparation revealed [(3)H]ifenprodil binding to a single high affinity state with the pharmacology of N-methyl-D-aspartate (NMDA) receptors containing NR2B subunits. Inhibition of [(3)H]ifenprodil binding in the presence of trifluoroperazine by 10 NR1a/NR2B selective agents was highly correlated with their inhibition at rat NR1a/NR2B receptors expressed in Xenopus ooctyes and [(3)H]TCP binding to rat brain NR2B subunit containing NMDA receptors but not with their inhibition of [(3)H]DTG binding. Allosteric interactions with polyamines, Mg(2+), Zn(2+), glutamate, glycine, and their antagonists were consistent with NMDA receptors with NR2B subtype pharmacology. The rank order of polyamine inhibition was spermine > spermidine > 1,5-(diethylamino)piperidine > arcaine > agmatine > putrescine. Both spermidine and MgCl(2) shifted the inhibition curve of ifenprodil to the right in a parallel manner, but Mg(2+) did not appear to be additive to spermidine. Glutamate increased and glycine decreased the binding. Conversely, CPP decreased the binding, and MDL 105,519 increased the binding in an agonist reversible manner. The increase with MDL 105,519 and glutamate appeared to be additive as did the decrease with glycine and CPP. Changes in the buffer pH between 6.5 and 8.0 did not affect the affinity of NR2B agents. Cirazoline but not clonidine inhibited the binding. MK-801 and agents from various other pharmacological classes did not significantly inhibit [(3)H]ifenprodil binding. [(3)H]Ifenprodil binding in the presence of trifluoroperazine appears to be selective for the voltage-independent ifenprodil site on NMDA receptors containing the NR2B subunit.

Inhibition of gastrin-stimulated cell proliferation by the CCK-B/gastrin receptor ligand CI-988.

The gastrointestinal hormone gastrin functions as a trophic factor for oxyntic mucosa as well as a secretagogue for gastric acid. In preclinical toxicology studies CI-988, a peptoid cholecystokinin (CCK) ligand with nanomolar affinity for the CCK-B/gastrin receptor, caused gastric gland degeneration and mucosal atrophy in cynomolgus monkeys, perhaps consistent with an expected pharmacological outcome of inhibition of the trophic effect of gastrin on stomach mucosa. Because of the expense and difficulty associated with experimental use of non-human primates, we investigated the effects of CI-988 on signal transduction pathways associated with gastrin-stimulated cell proliferation using the AR42J rat pancreatic tumour cell line as a model. The AR42J cell line was selected because it is known to express the CCK-B/gastrin receptor and because it is responsive to the growth promoting effects of gastrin in vitro. Gastrin-17 at 1 nM stimulated proliferation of AR42J cells 26% and 104% above control after 24 and 96 hours, respectively. CI-988 at 1 nM had no apparent effect on basal cell proliferation rates, but decreased gastrin-17 stimulated cell proliferation 13% and 47%, respectively, after 24 and 96 hours of treatment, consistent with competitive antagonism at the gastrin receptor. Because the trophic effect of gastrin towards AR42J cells has been linked to intracellular calcium ([Ca2+]i) mobilization and/or cyclic AMP, the effect of CI-988 on these second messengers were also investigated. Gastrin-17 at 10 nM stimulated both ([Ca2+]i) and cAMP, while CI-988 alone at 100 nM had no effect, but blocked the gastrin-stimulated increases in both mediators. Therefore, using the AR42J pancreatic tumour cell line as a model, the dipeptoid CCK-B/gastrin receptor ligand CI-988 behaves as an antagonist towards gastrin receptor-stimulated signal transduction pathways and cell proliferation in vitro.

Histological, chemical, and crystallographic analysis of four calcium phosphate cements in different rabbit osseous sites.

Four calcium phosphate cement formulations were implanted in the rabbit distal femoral metaphysis and middiaphysis. Chemical, crystallographic, and histological analyses were made at 2, 4, and 8 weeks after implantation. When implanted into the metaphysis, part of the brushite cement was converted into carbonated apatite by 2 weeks. Some of the brushite cement was removed by mononuclear macrophages prior to its conversion into apatite. Osteoclastlike cell mediated remodeling was predominant at 8 weeks after brushite had converted to apatite. The same histological results were seen for brushite plus calcite aggregate cement, except with calcite aggregates still present at 8 weeks. However, when implanted in the diaphysis, brushite and brushite plus calcite aggregate did not convert to another calcium phosphate phase by 4 weeks. Carbonated apatite cement implanted in the metaphysis did not transform to another calcium phosphate phase. There was no evidence of adverse foreign body reaction. Osteoclastlike cell mediated remodeling was predominant at 8 weeks. The apatite plus calcite aggregate cement implanted in the metaphysis that was not remodeled remained as poorly crystalline apatite. Calcite aggregates were still present at 8 weeks. There was no evidence of foreign body reaction. Osteoclastlike cell remodeling was predominant at 8 weeks. Response to brushite cements prior to conversion to apatite was macrophage dominated, and response to apatite cements was osteoclast dominated. Mineralogy, chemical composition, and osseous implantation site of these calcium phosphates significantly affected their in vivo host response.