Influence of alpha-receptor blockade on the time-dependent change in the effect of furosemide

Selective and sustained occupancy of prostatic alpha1-adrenoceptors by oral administration of KMD-3213 and its plasma concentration in rats

This study examined the ex-vivo occupancy by KMD-3213 of alpha1-adrenoceptors in the prostate and other tissues of rats in terms of tissue selectivity and duration of occupancy in relation to plasma concentration. Oral administration of KMD-3213 (0.2-20.2 micromol kg(-1), 0.5 h) dose-dependently decreased [3H]prazosin binding sites (Bmax) in the prostate (42-74%) and submaxillary gland (54-88%) compared with the control value. In contrast, there was only a slight change in the Bmax values in the spleen and cerebral cortex of KMD-3213-treated rats. The alpha1-adrenoceptor occupancy in the prostate and submaxillary gland was increased, with plasma free concentration of KMD-3213 at 0.5 h after oral administration of KMD-3213 (0.6-20.2 micromol kg(-1)). The receptor occupancy in these tissues was much greater than that in the spleen, heart or cerebral cortex. After oral administration of KMD-3213 (6.1 micromol kg(-1)), the alpha1-adrenoceptor occupancy in the prostate and submaxillary gland occurred rapidly, in parallel with the rise in the plasma concentration of the drug, and it lasted for at least 24 h, despite a remarkable decrease in the plasma concentration. It is concluded that KMD-3213 may produce fairly selective and sustained occupancy of alpha1-adrenoceptors in the prostate, a target organ for treatment of bladder outlet obstruction in patients with benign prostatic hyperplasia.

Analysis of alpha1-adrenoceptor subtypes in rabbit aorta and arteries: regional difference and co-existence

This study was done to determine the alpha1-adrenoceptor subtypes and to characterize the functional role of alpha1D-adrenoceptors in the following rabbit arteries: thoracic and abdominal aorta, mesenteric, renal and iliac arteries. In all arteries, selective alpha1D-adrenoceptor antagonist BMY 7378 (8-(2-(4-(2-methoxyphenyl)-1-piperazinyl)ethyl)-8-azaspirol(4,5) decane-7,9-dione dihydrochloride) dose dependently shifted the concentration-response curves for norepinephrine to the right. Schild plots of the results obtained from the inhibition by BMY 7378 for norepinephrine yielded a straight line with a slope of unity in thoracic (pA2 6.54+/-0.02) and abdominal (pA2 6.73+/-0.03) aorta. Slopes of Schild plots obtained from the inhibition by BMY 7378 for norepinephrine were significantly different from unity in mesenteric, renal and iliac arteries. Slopes of Schild plots for BMY 7378 were not different from unity in chloroethylclonidine-treated thoracic (pA2 6.49+/-0.14) and abdominal (pA2 6.61+/-0.11) aorta. Slopes of Schild plots for BMY 7378 were significantly different from unity in chloroethylclonidine-treated mesenteric, renal and iliac arteries. On the other hand, in Ca2+-free physiological saline solution (Ca2+-free PSS) slopes obtained from Schild plots for BMY 7378 were not different from unity in thoracic (pA2 6.41+/-0.09) and abdominal (pA2 6.28+/-0.07) aorta and mesenteric (pA2 6.55+/-0.06), renal (pA2 6.24+/-0.10) and iliac (pA2 6.64+/-0.13) arteries. BMY 7378 inhibited [3H]prazosin binding to thoracic (pKi 6.44+/-0.08) and abdominal (pKi 6.59+/-0.02) aorta with low potency, and mesenteric (pKi High 8.66+/-0.28, pKi Low 6.34+/-0.14), renal (pKi High 8.71+/-0.33, pKi Low 6.45+/-0.03) and iliac artery (pKi High 8.60+/-0.24, pKi Low 6.56+/-0.13). These results suggest that alpha1D-adrenoceptors play a significant role for contractile responses in renal and iliac artery, but play virtually no role in thoracic and abdominal aorta and that an alpha1-adrenoceptor subtype, which is pharmacologically distinguishable from the alpha1A-, alpha1B- and alpha1D-adrenoceptor subtype, may co-exist in mesenteric artery.

Binding and functional characterization of alpha1-adrenoceptor subtypes in the rat prostate

The alpha1-adrenoceptor subtypes of rat prostate were characterized in binding and functional experiments. In binding experiments, [3H]tamsulosin bound to a single class of binding sites with an affinity (pKD) of 10.79+/-0.04 and Bmax of 87+/-2 fmol mg(-1) protein. This binding was inhibited by prazosin, 2-(2,6-dimethoxy-phenoxyethyl)-aminomethyl-1,4-benzodioxane hydrochloride (WB4101), 5-methylurapidil, alpha-ethyl-3,4,5,-trimethoxy-alpha-(3-((2-(2-methoxyphenoxy)ethyl)-amin o)-propyl)benzeneacetonitrile fumarate (HV723) and oxymetazoline with high efficacy, resulting in a good correlation with the binding characteristics of cloned alpha1a but not alpha1b and alpha1d-adrenoceptor subtypes. In functional studies, noradrenaline and oxymetazoline produced concentration-dependent contractions. These contractions were antagonized by tamsulosin, prazosin, WB4101 and 5-methylurapidil with an efficacy lower than that exhibited by these agents for inhibition of [3H]tamsulosin binding. The relationship between receptor occupancy and contractile amplitude revealed the presence of receptor reserve for noradrenaline, but the contraction induced by oxymetazoline was not in parallel with receptor occupation and developed after predicted receptor saturation. From these results, it is suggested that alpha1A-adrenoceptors are the dominant subtype in the rat prostate which can be detected with [3H]tamsulosin, but that the functional subtype mediating adrenergic contractions has the characteristics of the alpha1L-adrenoceptor subtype, having a lower affinity for prazosin and some other drugs than the alpha1A-adrenoceptor subtype.