Two α‐adrenergic contractions with different Ca<sup>2+</sup> activation mechanisms in response to field nerve stimulation in the circular smooth muscle of guinea‐pig vas deferens

Fukushi, Yasuo; Wakui, Makoto; Sano, Hiroshi

doi:10.1111/j.1474-8673.1988.tb00175.x

Cited by 1 publication

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“…Alhave been widely used to investigate peripheral adrenergic though recent studies have demonstrated that, in the rat, the mechanisms (Saxena, 1970;Swedin, 1971;Anstey & Birming-cauda epididymis contains postjunctional a,-, but not OC2-ham, 1978;1980;Fukushi et al, 1988;Eltze & Boer, 1992; adrenoceptors (Ventura & Pennefather, 1991;, there is no Bultman et al, 1994). Many studies have demonstrated that, in evidence indicating which a-adrenoceptor subtypes mediate the rat, this tissue contains a functionally predominant popucontractile responses of the cauda epididymis of the guinealation of OCIA-adrenoceptors (Mallard et al, 1992;Ohmura et pig.…”

Section: Introductionmentioning

confidence: 99%

α‐Adrenoceptor mediated responses of the cauda epididymis of the guinea‐pig

Haynes

Hill

1996

British J Pharmacology

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1 The subtypes of Lx-adrenoceptor mediating the contractile responses of the cauda epididymis of the guinea-pig were investigated. The ocx-adrenoceptor agonist phenylephrine, but not the LX2-adrenoceptor agonist, xylazine (up to 10 gM), elicited concentration-dependent contractions from preparations of cauda epididymis (EC50 3.4 gM). The L-type Ca2+ channel antagonist, nifedipine (10 gM), reduced the maximal response to phenylephrine (by 77%). Preincubation of tissues with the alB-adrenoceptoralkylating agent, chloroethylclonidine (50 juM, 30 min), shifted phenylephrine concentration-response curves to the right (4 fold) only when the a2-adrenoceptor antagonist idazoxan (100 nM) was included during the pre-incubation with chloroethylclonidine. 2 Xylazine (1 /IM) significantly shifted phenylephrine concentration-response curves to the left (3 fold); this effect was attenuated by idazoxan (100 nM). Both the incubation of preparations with nifedipine (10 gM) and the pre-incubation of preparations with chloroethylclonidine (50 gM, 30 min) attenuated the potentiating effects of xylazine (1 gM). Protection of a2-adrenoceptors with idazoxan (100 nM) during the chloroethylclonidine (50 gM, 30 min) incubation restored the xylazine-mediated enhancement of phenylephrine concentration-response curves. Pertussis toxin (200 ng ml-1, 24 h) attenuated the xylazine (1 gM)-mediated potentiation of phenylephrine concentration-response curves.3 Following the pre-incubation of preparations with chloroethylclonidine (50 gM, 30 min) 5-methylurapidil (10 nM to 3 gM) shifted phenylephrine concentration-response curves, in parallel, to the right with mean pKB values in the range of 8.27 (at 10 nM 5-methylurapidil) to 7.76 (at 3 gM 5-methylurapidil), the addition of idazoxan (100 nM) to the incubation medium did not significantly affect the 5-methylurapidil (10 to 300 nM) pKB values (8.41 to 7.64, respectively). In the presence of both idazoxan (100 nM) and nifedipine (10 pM), and following the pre-incubation with chloroethylclonidine (50 gM, 30 min), 5-methylurapidil (30 to 300 nM) still shifted phenylephrine concentration-response curves to the right (pKB values 7.77 to 7.36, respectively).

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