S Giovanazzi | Search PubMed

PubMed1992

Heterogeneity of binding sites for ICI 198,615 in human lung parenchyma.

We have identified and characterized two different subclasses of binding site for the novel peptido-leukotriene (LT) antagonist, [3H]ICI 198,615, in membranes from human lung parenchyma using a receptor-ligand assay. This novel compound is representative of a new class of LT receptor antagonists and it has been demonstrated to be several orders of magnitude more potent and selective than most other LT antagonists described to date. The binding of [3H]ICI 198,615 is rapid, specific and saturable. Equilibrium was reached within 5-10 min. Non linear fitting of dissociation time courses has revealed the presence of two different components (K(off)1 = 8.3 +/- 6.8 x 10(-4) sec-1 and K(off)2 = 0.79 +/- 1.66 x 10(-3) sec-1) of the kinetic curves, suggesting heterogeneity of the binding sites. Computer analysis of equilibrium binding data obtained at 25 degrees results in a model with two classes of binding sites, a high affinity-low capacity class with Kd1 = 0.024 +/- 0.014 nM and Bmax1 = 0.015 +/- 0.004 pmol/mg protein and a low affinity-high capacity class with Kd2 = 6326 +/- 3859 nM and Bmax2 = 473 +/- 383 pmol/mg protein. In competition studies, LTD4 was also found to interact with two classes of binding site (Kd1 = 0.016 +/- 0.008 nM and Kd2 = 15195 +/- 8965 nM). On the contrary, LTE4 and LTC4 were found to interact with a homogeneous class of sites only with Kd = 7466 +/- 4629 nM and Kd = 428 +/- 73 nM, respectively. Furthermore, we have evaluated the effect of a number of LT antagonists on the binding of [3H]ICI 198,615. Ro 24-5913 (Kd = 3.0 +/- 2.1 nM), FPL55712 (Kd = 4945 +/- 2868 nM), LY171883 (Kd = 19628 +/- 12365 nM), SKF 104353 (Kd = 74.2 +/- 46 nM) and its enantiomer SKF 104373 (Kd = 13627 +/- 6813 nM) were found to interact with a single class of binding sites. The present studies indicate a heterogeneity of binding sites for ICI 198,615 in membranes from human lung parenchyma and that ICI 198,615 is a very potent and selective antagonist of LTD4 receptors in this tissue.

Asthma↗

PubMed1992

Decrease in rat brain calcitonin binding sites and adenylyl-cyclase activity during ageing.

In order to investigate the effects of ageing on the cerebral receptors for calcitonin (CT), we used an in vitro autoradiographic method to study the distribution of the binding sites for eel CT (eCT) in young and old rat brain. The inhibitory action of eCT on adenylyl-cyclase (AC) activity upon isolated brain cell membranes was also evaluated. The results show area-specific reduction of binding particularly in the hypothalamus and pons medulla of the old rat. The inhibitory action of eCT on AC activity was significantly reduced in the same areas, whereas in the striatum and mesencephalon no changes were observed. The parallel decrease of binding of eCT and of the inhibitory action of eCT on AC in ageing may represent a functional decline of neuronal activities during ageing.

1-Methyl-3-isobutylxanthine↗

PubMedDate not supplied

Effects of prostaglandins and PAF on the contractility of the bovine ciliary muscle.

The present study has investigated the effect of prostaglandins and PAF on the contractility of the bovine ciliary muscle, a tissue involved in the control of aqueous outflow. The results show that the prostaglandins tested (PGI2, its stable analogue Iloprost, PGE2, PGE1, and PGF2 alpha) as well as PAF, were able to contract the ciliary muscle, although with different potencies and efficacies. PGI2 and Iloprost displayed parallel dose-effect curves with upper plateaus that did not differ significantly; however, PGI2 was slightly more potent than Iloprost. This is at variance with what is observed at the level of the platelet prostacyclin receptor. PGF2 alpha was equipotent with the PGEs tested, with a maximal effect not different from either PGI2 or PGEs. PAF was the most efficacious of the compounds tested.

Animals↗