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₁-Adrenoceptor Subtypes in Rat Epididymis and the Effects of Sexual Maturation¹

^a Section of Experimental Endocrinology, Department of Pharmacology, Universidade Federal de São Paulo-Escola Paulista de Medicina, 04044-020 São Paulo, Brazil

We have characterized the expression of ₁-adrenoceptor in epididymis from rats in different stages of sexual maturation: 40 (immature), 60 (young adult), and 120 (adult) days of age. Plasma testosterone levels were low in the immature animals but increased significantly in the 60- and 120-day-old animals. These changes were followed by a progressive increase in rat body weight and in caput and cauda epididymis relative weight. Reverse transcription polymerase chain reaction assay indicated that _1a-, _1b-, and _1d-adrenoceptor transcripts were present in both caput and cauda epididymis from adult rats. Ribonuclease protection assays further indicated that the expression of these ₁-adrenoceptor transcripts differed with age and epididymal region analyzed. Prazosin (nonselective ₁ antagonist), 5-methyl urapidil (_1A-selective), and BMY 7378 (_1D-selective) displaced [³H]prazosin binding curves in caput and cauda epididymis from 40- and 120-day-old rats. The potency order for these antagonists, as calculated from the negative logarithm of the inhibition constant (pK_i) values for the high-affinity sites, indicated a predominant population of _1A-adrenoceptor subtype in caput and cauda epididymis from adult animals. Differences in pK_i values in caput and cauda epididymis from immature and adult animals also suggested that the relative amount of ₁-adrenoceptors, at the protein level, is modulated by sexual maturation. Taken together, the changes in ₁-adrenoceptor expression during sexual maturation may suggest specific roles for these receptors in epididymal function.

First decision: 30 July 2001.

¹ This study was supported in part by Fundação de Amparo à Pesquisa do Estado de São Paulo, Brazil (FAPESP, grant 96/1777-1) and T.W. Fogarty International, USA (subcontract UNC 5-53284); a Master fellowship supported by FAPESP (D.B.C.Q.); and a Researcher fellowship supported by Conselho Nacional do Desenvolvimento Científico e Tecnológico, Brazil (M.C.W.A. and C.S.P.). Part of this work was presented at the 24th annual meeting of the American Society of Andrology, Louisville, KY, 1999.

² Correspondence: Maria Christina W. Avellar, Department of Pharmacology, Section of Experimental Endocrinology, UNIFESP-Escola Paulista de Medicina, Rua 03 de maio 100, INFAR, Vila Clementino, 04044-020 São Paulo, Brazil. FAX: 55 11 5576 4448; avellar.farm{at}infar.epm.br

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