Mark E. Goldman

Endogenous inhibitors of 4'-[3H]chlorodiazepam (Ro 5-4864) binding to 'peripheral' sites for benzodiazepines.

‘Peripheral’ binding sites for benzodiazepines are under neural or homonal control in the pineal gland, olfactory bulb, and kidney. These observations prompted a search for an endogenous substance which could modulate these sites under physiological conditions. Acidified methanol extracts from several tissues (e.g. stomach, kidney, lung) were found to inhibit the binding of [3H]Ro 5‐4864 to ‘peripheral’ binding sites, but did not significantly affect the binding of [3H]diazepam to ‘brain’ benzodiazepine receptors. Fractionation of a crude extract prepared from antral stomach by either ultrafiltration or gel filtration chromatography yielded high (M r > 10000) and low (M r < 1000) M r fractions which competitively inhibited [3H]Ro 5‐4864 binding to ‘peripheral’ sites. These observations suggest the presence of endogenous substances in several rat tissues which may represent physiologically important ligands for ‘peripheral’ binding sites for benzodiazepines.

Differentiation of [3H]phencyclidine and ( + )-[3H]SKF-10,047 binding sites in rat cerebral cortex

SKF‐10,047 Sigma receptor Phencyclidine Phencyclidine receptor Psychotomimetic activity

TL 333, a benzhydro[g]quinoline, stimulates both D-1 and D-2 dopamine receptors: Implications for the selectivity of LY 141865 towards the D-2 receptor

TL 333, (trans-N-ethyl-6,7-dihydroxyoctahydrobenzo[g]-quinoline), stimulates both D-1 and D-2 dopamine receptors. In contrast, LY 171555 (the active enantiomer of the selective D-2 agonist LY 141865) and LY 149632 stimulate only D-2 receptors. The structural differences between TL 333, LY 171555 and LY 149632 are discussed with regards to understanding the basis for the selective D-2 agonist activity of LY 171555 or LY 149632.

Inhibition of [3H]nitrendipine binding by phospholipase A2

Phospholipase A2 from several sources inhibited [3H]nitrendipine binding to membranes from brain, heart and ileal longitudinal muscle. The enzymes from bee venom and Russells viper venom were most potent, having IC50 values of approximately 5 and 14 ng/ml, respectively, in all three membrane preparations. Inhibition of binding by bee venom phospholipase A2 was time- and dose-dependent. Mastoparan, a known facilitator of phospholipase A2 enzymatic activity, shifted the bee venom phospholipase A2 dose-response curve to the left. Pretreatment of brain membranes with bee venom phospholipase A2 (10 ng/ml) for 15 min caused a 2-fold increase in the Kd without changing the Bmax compared with untreated membranes. Extension of the preincubation period to 30 min caused no further increase in the Kd but significantly decreased the Bmax to 71% the value for untreated membranes. [3H]Nitrendipine, preincubated with bee venom phospholipase A2, was recovered and found to be fully active, indicating that the phospholipase A2 did not modify the ligand. It is concluded that phospholipase A2 acts on the membrane at or near the [3H]nitrendipine binding site and that phospholipids play a key role in the interactions of 1,4 dihydropyridine calcium channel antagonists with the dihydropyridine binding site.