1 The subtype of a1-adrenoceptor mediating contractions of human prostate to noradrenaline was characterized by use of a range of competitive and non-competitive antagonists. 2 Contractions of the prostate to either noradrenaline (pD2 5.5), phenylephrine (pD2 5.1) or methoxamine (pD2 4.4) were unaltered by the presence of neuronal and extraneuronal uptake blockers. Noradrenaline was about 3 and 10 times more potent than phenylephrine and methoxamine respectively. Phenylephrine and methoxamine were partial agonists. 3 Pretreatment with the alkylating agent, chlorethylclonidine (10-4 M) shifted the noradrenaline concentration-contraction curve about 3 fold to the right and depressed the maximum response by 31%. This shift is 100 fold less than that previously shown to be produced by chlorethylclonidine under the same conditions on OlB-adrenoceptor-mediated contractions. 4 Cumulative concentration-contraction curves for noradrenaline were competitively antagonized by WB 4101 (pA2 9.0), 5-methyl-urapidil (pA2 8.6), phentolamine (pA2 7.6), benoxathian (pA2 8.

1 The a,-adrenoceptor subtype mediating contraction of the rat epididymal vas deferens and rat spleen has been investigated by use of a,-adrenoceptor antagonists that have shown selectivity between the different cloned receptor subtypes. 2 In the rat epididymal vas deferens the potency of noradrenaline and phenylephrine was increased in the presence of neuronal and extra-neuronal uptake blockers, cocaine and fl-oestradiol, but these did not alter that of methoxamine. The order of potency of the agonists in the presence or absence of uptake blockade was noradrenaline>phenylephrine>methoxamine. In the rat spleen the potency of these agonists was not altered in the presence of cocaine and f-oestradiol, and their order of potency was the same as in the vas deferens.3 The non subtype selective a,-adrenoceptor antagonist prazosin (up to 1 x lo-7 M) was found to antagonize contractions to noradrenaline in the vas deferens competitively (pA2 9.2), but only in a non competitive manner in the spleen. Contractions to phenylephrine in the spleen however were competitively antagonized by prazosin (up to 1 x l0-' M) with a pA2 of 9.2. This suggests that there is an a,-and a non a,-adrenoceptor response to noradrenaline in the rat spleen.4 Pretreatment with chlorethylclonidine (l0-' M for 30 min) did not alter the noradrenaline contractions in the vas deferens, but contractions to noradrenaline and phenylephrine in the spleen were shifted 30 and 300 fold to the right of the control curve, respectively. This suggests that only the contractions in the spleen were mediated by aIB-adrenoceptors. 5 The noradrenaline contractions in the vas deferens were competitively antagonized by WB 4101 (pA2 9.6), 5-methyl-urapidil (pA2 8.7), phentolamine (pA2 8.3), benoxathian (pA2 9.4), spiperone (pA2 7.5), indoramin (pA2 8.4) and BMY 7378 (pA2 6.7), consistent with the affinities of these antagonists in binding studies on tissue aA-adrenoceptors. These values correlated best with their published affinities on the expressed aic-adrenoceptor clone and poorly with those at either the expressed alb-or aXdadrenoceptor clones. Therefore the classical xA-adrenoceptor appears to be the same as the expressed ,lc-adrenoceptor clone.6 The phenylephrine contractions in the spleen were competitively antagonized by WB 4101 (pA2 8.1), 5-methyl-urapidil (pA2 7.1), phentolamine (pA2 7.3), benoxathian (pA2 7.4), spiperone (pA2 7.9), indoramin (pA2 7.5) and BMY 7378 (pA2 7.4), consistent with the affinities of these antagonists in binding studies on tissue alB-adrenoceptors. The pA2 values correlated best with the published affinities of these compounds on the expressed alb-adrenoceptor clone and poorly with those at either the expressed Cld-or alc-adrenoceptor clones. Therefore the alB-adrenoceptor appears to be the same as the expressed alb-adrenoceptor clone.7 The results provide pharmacological evidence that the a,-adrenoceptor mediating noradrenaline contractions in the epididymal portion of the rat vas deferens is the X1A-(alC) subtype and that contracti...

1 CGRP receptors mediating vasorelaxation of the rat isolated pulmonary artery and inhibition of contractions of the rat isolated prostatic vas deferens were investigated using CGRP agonists, homologues and the antagonist CGRP . 2 In the pulmonary artery, human (h)a-CGRP-induced relaxation of phenylephrine-evoked tone was abolished either by removal of the endothelium or by N G -nitro-L-arginine (10 75 M). The inhibitory e ect of N G -nitro-L-arginine was stereoselectively reversed by L-but not by D-arginine (10 74 M). Thus, CGRP acts via nitric oxide released from the endothelium. 3 In the endothelium-intact artery, ha-CGRP, hb-CGRP and human adrenomedullin (10 710 ± 3610 77 M), dose-dependently relaxed the phenylephrine-induced tone with similar potency. Compared with ha-CGRP, rat amylin was around 50 fold less potent, while [Cys(ACM 2,7 )] ha-CGRP (10 77 ± 10 74 M) was at least 3000 fold less potent. Salmon calcitonin was inactive (up to 10 74 M). 4 Human a-CGRP 8-37 (3610 77 ± 3610 76 M) antagonized ha-CGRP (pA 2 6.9, Schild plot slope 1.2+0.1) and hb-CGRP (apparent pK B of 7.1+0.1 for ha-CGRP 8-37 10 76 M) in the pulmonary artery. Human b-CGRP 8-37 (10 76 M) antagonized ha-CGRP responses with a similar a nity (apparent pK B 7.1+0.1). Human adrenomedullin responses were not inhibited by ha-CGRP 8-37 (10 76 M). 5 In the prostatic vas deferens, ha-CGRP, hb-CGRP and rat b-CGRP (10 710 ± 3610 77 M) concentration-dependently inhibited twitch responses with about equal potency, while rat amylin (10 78 ± 10 75 M) was around 10 fold less potent and the linear analogue [Cys(ACM 2,7 )] ha-CGRP was at least 3000 fold weaker. Salmon calcitonin was inactive (up to 10 74 M). 6 The antagonist e ect of ha-CGRP 8-37 (10 75 ± 3610 75 ) in the vas deferens was independent of the agonist, with pA 2 values against ha-CGRP of 6.0 (slope 0.9+0.1), against hb-CGRP of 5.8 (slope 1.1+0.1), and an apparent pK B value of 5.8+0.1 against both rat b-CGRP and rat amylin. Human b-CGRP 8-37 (3610 75 ± 10 74 M) competitively antagonized ha-CGRP responses (pA 2 5.6, slope 1.1+0.2).The inhibitory e ect of ha-CGRP on noradrenaline-induced contractions in both the prostatic and epididymal vas deferens was antagonized by ha-CGRP 8-37 (pA 2 5.8 and 5.8, slope 1.0+0.2 and 1.0+0.3, respectively). 7 The e ects of ha-CGRP and ha-CGRP 8-37 in both rat pulmonary artery and vas deferens were not signi®cantly altered by pretreatment with peptidase inhibitors (amastatin, bestatin, captopril, phosphoramidon and thiorphan, all at 10 76 M). The weak agonist activity of [Cys(ACM 2,7 )] ha-CGRP in the vas deferens was not increased by peptidase inhibitors. 8 These data demonstrate that two di erent CGRP receptors may exist in the rat pulmonary artery and vas deferens, a CGRP 1 receptor subtype in the rat pulmonary artery (CGRP 8-37 pA 2 6.9), while the lower a nity for CGRP 8-37 (pA 2 6.0) in the vas deferens is consistent with a CGRP 2 receptor.

This work reports the results of the first functional characterization of the alpha 1c-adrenoceptor subtype. The most functionally important alpha 1-adrenoceptor type in the human prostate appears to be the alpha 1c subtype. This finding may aid the development of prostate-selective adrenoceptor pharmacotherapy.

3 The novel ax-adrenoceptor antagonist RS 17053 had a relatively high affinity for the aAadrenoceptors mediating contraction of the rat epididymal vas deferens (pA2 9.5) compared with the alB-adrenoceptors in the rat spleen (pA2 7.2) or the aID-adrenoceptors in the rat aorta (pKB 7.1), in agreement with its selectivity for the expressed a,.-clone. However, RS 17053 had over 100 fold lower affinity for the aIA-adrenoceptors mediating contraction of the rat portal vein (pKB 7.1) and human prostate (pKB 7.1) compared with its affinity for the alA-adrenoceptors in the rat epididymal vas deferens or the expressed aa-clone. 4 The difference in affinity of RS 17053 between the rat epididymal vas deferens and rat portal vein cannot be explained by a species difference in the receptor. Therefore RS 17053 may distinguish between subtypes of the aIA-adrenoceptor in the rat portal vein and human prostate compared with those in the rat epididymal vas deferens or the expressed ala-clone.