Postsynaptic alpha 2-adrenoceptors have been reported to exist in various tissues, including vascular smooth muscle. In order to investigate the possibility of their mediating a positive inotropic change and clarify the influence of the thyroid on their responsiveness, we examined the effects of clonidine, a known alpha 2-agonist, on the isolated left atria and femoral vascular beds of rats whi...

In the dog saphenous vein (DSV), phenylephrine (PE) responses through alpha-1 adrenoceptors receptors are antagonized by both alpha-1 and alpha-2 receptor antagonists. Furthermore, pretreatment with chloroethylclonidine (CEC) eliminates prazosin binding but reduces rauwolscine binding by half (). In new functional experiments, the effects of preincubation with phenoxybenzamine (PBZ), an irrever...

Gonadal hormones regulate the expression of alpha1-adrenoceptor subtypes in several tissues. The present study was carried out to determine whether or not cyproterone acetate, an anti-androgenic agent, regulates the alpha1-adrenoceptor subtypes that mediate contractions of the rat vas deferens in response to noradrenaline. The actions of subtype selective alpha1-antagonists were investigated in...

PURPOSE This study sought to identify and characterize subtypes of alpha 2-adrenoceptors in rabbit ciliary body. METHODS Radioligand binding assays were performed with the alpha 2-agonist ligand [125I]-p-iodoclonidine ([125I]PIC) and the antagonist ligand [3H]rauwolscine. RESULTS Both [125I]PIC and [3H]rauwolscine bound to a single population of receptors in membrane preparations of rabbit ...

The present study was designed to verify our previous hypothesis that carteolol, a 1/ 2-adrenoceptor-blocking agent, is a nonconventional partial agonist of cardiac 1-adrenoceptors. To this purpose, we characterized the effects of carteolol in guinea pig myocardial preparations and measured the affinities of carteolol for highand low-affinity sites of 1-adrenoceptors labeled by CGP12177 [( )4-(...