Recent studies have suggested that alpha(2)-adrenergic agonists prevent neuronal cell death in a number of animal models, although the mechanism of alpha(2)-neuroprotection remains unclear. In a retinal ischemia model, the alpha(2)-specific agonist brimonidine (1 mg/kg i.p.) preserves approximately 80% of the electroretinogram (ERG) b-wave. The protective effect of brimonidine is completely blo...

The present study was designed to investigate the role of central adrenoceptors in the hypotensive effect of intracerebroventricular (ICV) injection of norepinephrine (NE) in conscious rabbits. Experiments were carried out on 19 adult rabbits (oryctolagus cuniculus) of either sex. A dose-dependent hypotensive response to ICV injection of NE was observed with no significant change in heart rate....

The threshold sensitivity of cardiovascular tissues to alpha-adrenergic stimulation is determined largely by the affinity of alpha-adrenergic receptors for agonists. To determine whether changes in alpha-adrenergic receptor affinity could contribute to the regulation of cardiac and vascular responsiveness, we used the alpha-adrenergic-selective radioligands, [3H]prazosin, [3H]-WB-4101, and [3H]...

It is now clearly established that alpha-2 adrenergic receptors can be subdivided in three pharmacological subtypes (alpha-2A, alpha-2B and alpha-2C) encoded by distinct genes (alpha 2C10, alpha 2C2 and alpha 2C4, respectively, in humans). Whereas the study of the regulation of the human alpha-2A adrenergic receptor and of the promoter region of the alpha 2C10 gene has being greatly helped by t...

Evidence suggests that in some species (cats, rabbits, and possibly humans) alpha-adrenoceptors in the iris dilator muscle are "atypical" in that they cannot be readily classified by conventional criteria. This study was undertaken in an attempt to characterize the alpha-adrenoceptor subtype(s) mediating sympathetically elicited mydriasis in rats. Frequency-response pupillary dilator curves wer...

Previous studies have demonstrated that glial cells in culture express several subtypes of functional adrenergic receptors. To determine if similar receptors are expressed by glia in vivo, we examined the expression of adrenergic receptors in the normal, crushed, and transected optic nerves of the rabbit and rat using quantitative receptor autoradiography. Additionally, we examined the expressi...

The mechanism of hormonally induced cell hypertrophy is unknown. Stimulation of cardiac myocytes by alpha 1-adrenergic agents, phorbol esters, and serum induces an increase in the cell size of nondividing cardiac myocytes in primary culture. Expression of the c-myc gene, known to be increased in growth factor-induced cell division, was studied in this model of cell hypertrophy. The alpha-adrene...

Approximately 60% of adult canine Purkinje fibers respond to alpha 1-adrenergic stimulation with a decrease in automaticity. Recent studies of disaggregated Purkinje myocytes have suggested that this negative chronotropic effect results from alpha 1-adrenergic activation of the Na-K pump. In this study we evaluated 1) whether Na-K pump activation is associated with the negative chronotropic eff...

We hypothesized that nitric oxide (NO), in addition to beta-adrenergic effects, may contribute to exercise-induced coronary responses after alpha-adrenergic receptor blockade. Data were analyzed as relationships between coronary sinus (CS) O(2) saturation (CS O(2)sat) or coronary blood flow (CBF) and myocardial O(2) consumption (MVO(2)). As MVO(2) increased, CS O(2)sat fell more (P < 0.05) afte...

[3H]Dihydroergocryptine, a potent alpha-adrenergic antagonist, was used to label smooth muscle membrane binding sites which have the characteristics expected of alpha-adrenergic receptors. Binding of [3H]dihydroergocryptine to rabbit uterine membranes was rapid and reversible with rate constants of 1.26 X 10(7) M-1 min-1 and 0.034 min-1 for the forward and reverse reactions, respectively. [3H]D...