Is SDZ NVI-085 an alpha 1-adrenoceptor subtype-selective agonist?

Functional evidence for an alpha 1B-adrenoceptor mediating contraction of the mouse spleen

alpha 1-Adrenoceptor agonists ((-)-adrenaline = (-)-noradrenaline > > L-phenylephrine > methoxamine > (-)-(4a R, 10a R)-3,4,4a,5,10,10a-hexahydro-6-methoxy-4-methyl-9-methylthio-2 H-naphth[2,3-b]-1,4-oxazine (SDZ NVI 085) > cirazoline) evoked contraction of isolated mouse spleen strips, whereas oxymetazoline and indanidine were nearly inactive. Splenic contractions elicited by (-)-noradrenaline were inhibited by chloroethylclonidine (3 x 10(-6) - 6 x 10(-5) M) and partially attenuated by SZL-49 (10(-7) -10(-6) M), but remained resistant to (+/-)-isradipine (10(-9) -10(-7) M). The contractions were competitively antagonized by low concentrations of the alpha 1B-adrenoceptor-selective antagonist, spiperone (pA2 = 8.29), but by relatively high concentrations of the alpha 1A-adrenoceptor-selective receptor antagonists, tamsulosin (pA2 = 8.62), 5-methyl-urapidil (pA2 = 7.03), (+)-niguldipine (pA2 = 6.26) and the alpha 1D-adrenoceptor-selective antagonist, 8-[2-[4-(2-methoxyphenyl)-1-piperazinyl]ethyl]-8-azaspiro-[4.5]dec ane-7, 9-dione (BMY 7378) (pA2 = 6.76). Functional antagonist affinities at mouse spleen alpha 1-adrenoceptors were consistent with those at guinea-pig splenic alpha 1B-adrenoceptors, but not with those of either rat vas deferens alpha 1A- or rat aortic alpha 1D-adrenoceptors. Antagonist affinities at mouse spleen alpha 1-adrenoceptors correlated also best with published antagonist data on cloned and expressed alpha 1b-adrenoceptors but less well with those for either alpha 1a- or alpha 1d-adrenoceptors. The results provide pharmacological evidence that the alpha 1-adrenoceptor mediating smooth muscle contraction of mouse spleen is the B subtype.

SDZ NVI 085, an alpha 1A-adrenoceptor agonist with 5-HT2A receptor antagonist properties

(+/-)-SDZ NVI 085 (3,4,4a,5,10,10a-hexahydro-6-methoxy-4-methyl-9- methylthio-2H-naphth [2,3-b]-1,4-oxazine hydrochloride), an alpha 1-adrenoceptor agonist, produced a concentration-dependent relaxation (pIC50 of 7.2 +/- 0.1) in the isolated caudal artery of rat precontracted with serotonin (5-hydroxytryptamine, 5-HT, 1 microM). (+/-)- SDZ NVI 085 had no effect upon caudal arteries precontracted with vasopressin or U46619 (9,11-dideoxy-11 alpha, 9 alpha-epoxymethano-prostaglandin F2 alpha). In other studies, (+/-)-SDZ NVI 085 shifted 5-HT concentration-effect curves to the right, in a concentration-dependent manner, and Schild regression gave a pA2 estimate of 8.0 (slope of 1.0). Experiments using pharmacological resultant analysis indicated a syntopic interaction of (+/-)-SDZ NVI 085 with ketanserin (a 5-HT2 receptor antagonist) toward 5-HT-induced contractions. It is concluded that (+/-)-SDZ NVI 085 behaves as a reversible competitive 5-HT2A receptor antagonist, a property which may be of importance regarding its pharmacological effects in vivo.

Comparison of guinea-pig, bovine and rat alpha 1-adrenoceptor subtypes

1. To elucidate a possible role of species differences in the classification of alpha 1-adrenoceptor subtypes, we have characterized the alpha 1-adrenoceptors in guinea-pig spleen, kidney and cerebral cortex and in bovine cerebral cortex using concentration-dependent alkylation by chloroethylclonidine and competitive binding with 5-methlurapidil, methoxamine, (+)-niguldipine, noradrenaline, oxymetazoline, phentolamine, SDZ NVI-085, tamsulosin and (+)-tamsulosin. Rat liver alpha 1B-adrenoceptors were studied for comparison. Chloroethylclonidine-sensitivity and (+)-niguldipine affinity were also compared at cloned rat and bovine alpha 1a-adrenoceptors. 2. Chloroethylclonidine concentration-dependently inactivated alpha 1-adrenoceptors in all five tissues. While chloroethylclonidine inactivated almost all alpha 1-adrenoceptors in rat liver and guinea-pig kidney and brain, 20-30% of alpha 1-adrenoceptors in guinea-pig spleen and bovine brain were resistant to alkylation by 10 microM chloroethylclonidine. With regard to concentration-dependency guinea-pig kidney and brain were approximately 10 fold less sensitive than guinea-pig spleen or rat liver. 3. In rat liver, all drugs tested competed for [3H]-prazosin binding with steep and monophasic curves. Drug affinities were relatively low and resembled most closely those of cloned rat alpha 1b-adrenoceptors. 4. In guinea-pig spleen, all drugs tested competed for [3H]-prazosin binding with steep and monophasic curves. Drug affinities were relatively low and resembled most closely those of cloned rat alpha 1b-adrenoceptors. 5. In guinea-pig kidney most drugs tested competed for [3H]-prazosin binding with steep and monophasic curves and had relatively low drug affinities close to those of cloned rat alpha 1b- and alpha 1d-adrenoceptors. However, noradrenaline and tamsulosin had consistently biphasic competition curves recognizing 36-39% high and 61-64% low affinity sites. 6. In guinea-pig cerebral cortex, all drugs tested competed for [3H]-prazosin binding with shallow and biphasic curves. While most drugs recognized approximately 25% high affinity sites, tamsulosin and noradrenaline recognized approximately 50% high affinity sites. Drug affinities at the high and low affinity sites except those for tamsulosin and noradrenaline resembled those at cloned alpha 1a- and alpha 1b-adrenoceptors, respectively. 7. In bovine cerebral cortex all drugs tested except for noradrenaline competed for [3H]-prazosin binding with shallow and biphasic curves. All drugs recognized approximately 70% high affinity sites. Drug affinities at the high and low affinity sites resembled those at cloned alpha 1a- and alpha 1b-adrenoceptors, respectively. Noradrenaline competition curves in bovine cerebral cortex were steep and monophasic. 8. When cloned rat and bovine alpha 1a-adrenoceptors transiently expressed in COS cells were studied in a direct side-by-side comparison, both species homologues had similar chloroethylclonidine-sensitivity and (+)-niguldipine affinity. 9. We conclude that properties of bovine alpha 1A- and alpha 1B-adrenoceptors are very similar to those of other species such as rat. alpha 1-Adrenoceptor subtypes in guinea-pigs resemble alpha 1A- and alpha 1B-adrenoceptors in other species but chloroethylclonidine sensitivity and competition binding profiles of noradrenaline and tamsulosin are not compatible with previously established alpha 1-adrenoceptor subtype classification.

The alpha 1-adrenoceptor agonist, SDZ NVI-085, behaves as a potent, competitive antagonist of 5-hydroxytryptamine-induced contraction of rat aorta

In this study we investigated the actions of SDZ NVI-085 ((-)-(4aR,10aR)-3,4,4a,5,10,10a-hexahydro-6-methoxy-4-methyl -9-(methylthio)-2H- naphth[2,3-b)-1,4-oxazine hydrogen malonate), previously classified and employed as a selective alpha 1-adrenoceptor agonist, in the rat isolated aorta assay. It was shown that, in addition to its alpha 1-adrenoceptor agonistic action, SDZ NVI-085 behaves as a competitive antagonist of 5-hydroxytryptamine (5-HT)-induced contraction of rat aorta (pKB = 8.13 +/- 0.08). The structurally related alpha 1-adrenoceptor agonist, SK & F 89748-A (l-1,2,3,4-tetrahydro-8-methoxy-5-(methylthio)-2-naphthalenamine hydrochloride), produced inhibition of the 5-HT response only at the highest concentration tested (1 microM) with an associated pA2 value of 6.0 +/- 0.1. These findings suggest that the affinity of SDZ NVI-085 for 5-HT2 receptors is considerably higher than for alpha 1-adrenoceptors, which may have implications for its use as a pharmacological tool.