Nitric oxide synthase in acute alteration of nitric oxide levels after subarachnoid hemorrhage.

Objective: Subarachnoid hemorrhage (SAH) is associated with acute decreases and subsequent recovery of cerebral nitric oxide (NO) levels, but the mechanisms of these alterations are not known. In this study, we measured NO synthase (NOS) protein and kinetics to determine its involvement in the alterations of cerebral NO levels after SAH.

Methods: The endovascular rat model of SAH was used.

Agonist concentration-dependent differential responsivity of a human platelet purinergic receptor: pharmacological and kinetic studies of aggregation, deaggregation and shape change responses mediated by the purinergic P2Y1 receptor in vitro.

Platelet shape change (SC), aggregation and deaggregation responses are integral components of hemostasis that are elicited and modulated in vivo by the simultaneous activation of several membrane receptors. Selective activation of the purinergic P2Y1 receptor in vivo elicits a sustained SC and a small, transient aggregation response that is reversed rapidly by a robust deaggregation response (Platelets 2003; 14: 89). Using a kinetics-based turbidimetric approach to study the modulation of these concurrent components of human platelet responses, we demonstrate that these P2Y1 receptor-related responses and a number of their kinetic and steady-state characteristics are differentially elicited and modulated.

Diversity of signaling underlying responses mediated by selective activation of the platelet thromboxane A2 (TXA2) receptor; pharmacological and kinetic studies in vitro.

Selective activation of the platelet TXA2 receptor is sufficient to mediate concurrent aggregation, deaggregation and shape change (SC) responses without activation of known Gi-coupled receptors (Platelets 2003; 14: 89). However, Gi-coupled receptor activation strongly influences the hemostasis response in vivo. This study investigated the modulatory effects of two signaling pathways related to Gi-coupled receptor activation, stimulation of phosphoinositide 3-kinases (PI3Ks) and inhibition of adenylyl cyclase (AC), on the aggregation, deaggregation and SC components of the platelet activation response.

Different pharmacological properties of two equipotent antagonists (clozapine and rauwolscine) for 5-HT2B receptors in rat stomach fundus.

On the basis of the previously demonstrated constitutive activity in natural systems and the possibility of specific ligand-induced conformations, the aims of this study were: (i) to characterize the effects of two competitive antagonists (rauwolscine, RAU and clozapine, CLO) with very similar potencies for 5-HT(2B) receptors in a natural system (rat stomach fundus), and (ii) to evaluate a new method for detecting ligand-specific generated conformations through the study of the effects of RAU and CLO in 5-HT efficacy and in the time course of the response to the agonists. RAU and CLO behaved as competitive antagonists and showed similar potencies (pA(2) 7.56+/-0.

Concurrent responses elicited by isolated activation of platelet Gq-coupled receptors, in vitro: a novel approach for their separation and analysis.

This study tested the hypothesis that aggregation mediated by activation of a single G(q)-coupled receptor can be studied quantitatively if four concurrent but distinct components of the observed platelet response, autocrine stimulation, shape change (SC), aggregation and deaggregation, are separately measured. Responses mediated by two G(q)-coupled receptors, the TXA(2) and the P2Y(1), were assayed by a novel, kinetics-based turbidimetric approach. Blocking the autocrine stimulation with a cocktail of receptor antagonists revealed rapid and sustained SC that largely masked the aggregation.

Molecular and biochemical evidence for the presence of type III adenylyl cyclase in human platelets.

The isoform(s) of adenylyl cyclase (AC) present in human platelets has not been identified, and evidence supporting a role for AC in platelet aggregation is equivocal. We recently characterized deaggregation as an active component of the platelet aggregation response that may be an important determinant of the extent and duration of aggregation. G(i)-coupled receptors are linked to the inhibition of AC and are targets of antiplatelet drugs.