Identification and characterization of opioid and somatostatin binding sites in the opossum kidney (OK) cell line and their effect on growth

Opioids and somatostatin analogs have been implicated in the modulation of renal water handling, but whether their action is accomplished through central and/or peripheral mechanisms remains controversial. In different cell systems, on the other hand, opioids and somatostatin inhibit cell proliferation. In the present study, we have used an established cell line, derived from opossum kidney (OK) proximal tubules, in order to characterize opioid and somatostatin receptors and to investigate the action of opioids and somatostatin on tubular epithelial tissue. Our results show the presence of one class of opioid binding sites with kappa₁ selectivity (K_D 4.6 ± 0.9 nM, 57,250 sites/cell), whereas delta, mu, or other subtypes of the kappa site were absent. Somatostatin presents also a high affinity site on these cells (K_D 24.5 nM, 330,000 sites/cell). No effect of either opioids or somatostatin on the activity of the Na⁺/P_i cotransporter was observed, indicating that these agents do not affect ion transport mechanisms. However, opioid agonists and somatostatin analogs decrease OK cell proliferation in a dose-dependent manner; in the same nanomolar concentration range, they displayed reversible specific binding for these agents. The addition of diprenorphine, a general opioid antagonist, reversed the effects of opioids, with the exception of morphine. Furthermore, morphine interacts with the somatostatin receptor in this cell line too, as was the case in the breast cancer T47D cell line. Our results indicate that in the proximal tubule opioids and somatostatin do not affect ion transport, but they might have a role in the modulation of renal cell proliferation either during ontogenesis or in kidney repair. © 1996 Wiley-Liss, Inc.     

Tissue distribution, autoradiography, and metabolism of 4-(2'-methoxyphenyl)-1-[2' -[N-2"-pyridinyl)-p-[(18)F]fluorobenzamido]ethyl]piperazine (p-[(18)F]MPPF), a new serotonin 5-HT(1A) antagonist for positron emission tomography: An In vivo study in rats

The in vivo behavior of 4-(2'-methoxyphenyl)-1-[2'-[N-(2"-pyridinyl)-p-[(18)F]fluorobenzamido ]ethyl]-piperazine (p-[(18)F]MPPF), a new serotonin 5-HT(1A) antagonist, was studied in awake, freely moving rats. Biodistribution studies showed that the carbon-fluorine bond was stable in vivo, that this compound was able to cross the blood-brain barrier, and that a general diffusion equilibrium could account for the availability of the tracer. The great quantity of highly polar metabolites found in plasma did not contribute to the small amounts of metabolites found in hippocampus, frontal cortex, and cerebellum. Exvivo p-[(18)F]MPPF and in vitro 8-hydroxy-2-(di-n-[(3)H]propylamino)tetralin autoradiography were compared both qualitatively and quantitatively. Qualitative evaluation proved that the same brain regions were labeled and that the p-[(18)F]MPPF labeling is (a) in total agreement with the known distribution of 5-HT(1A) receptors in rats and (b) characterized by very low nonspecific binding. Quantitative comparison demonstrated that the in vivo labeling pattern obtained with p-[(18)F]MPPF cannot be explained by differences in regional blood flow, capillary density, or permeability. The 5-HT(1A) specificity of p-[(18)F]MPPF and binding reversibility were confirmed in vivo with displacement experiments. Thus, this compound can be used to evaluate parameters characterizing 5-HT(1A) binding sites in the brain.     

The influence of simvastatin, atorvastatin and high-cholesterol diet on acetylcholinesterase activity, amyloid beta and cholesterol synthesis in rat brain

OBJECTIVE: There is evidence to suppose that cholesterol-lowering medicine might confer protection against dementia, probably via modulation of cholesterol synthesis in the brain. The aim of the present study was to investigate the potential influence of statins and cholesterol diet on selected parameters relevant to Alzheimer's disease pathophysiology. METHODS: For 15 days, rats were orally administered simvastatin (10 or 20mg/kg b.wt.), atorvastatin (10 or 20mg/kg b.wt.), or aqua (control group); and one group was fed high-cholesterol (2%) diet. At the end of experiments brain (and plasma) cholesterol, lathosterol, hydroxymethylglutaryl-coenzyme A reductase protein, acetylcholinesterase activity, amyloid beta (40 and 42) and cholesterol synthesis rate (using the incorporation of deuterium from deuterated water) were determined and statistically compared to those of aqua. RESULTS: Both statins were able to lower cholesterol in the plasma, but none elicited an effect on total brain cholesterol. Significant reductions of brain lathosterol and cholesterol synthesis rate were observed after simvastatin and atorvastatin treatment. Acetylcholinesterase activity, amyloid beta and hydroxymethylglutaryl-coenzyme A reductase levels remained unaffected by the two drugs. CONCLUSIONS: This study brings additional evidence of a role for statins in cholesterol synthesis in the brain. Our data question the relationship between amyloid beta, acetylcholinesterase activity and cholesterol synthesis in the rat brain as well as the assumption about no exchange between peripheral and brain cholesterol pools.