α1-Adrenoceptor Subtypes in Rat Epididymis and the Effects of Sexual Maturation1

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Abstract
We have characterized the expression of α1-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 α1a-, α1b-, and α1d-adrenoceptor transcripts were present in both caput and cauda epididymis from adult rats. Ribonuclease protection assays further indicated that the expression of these α1-adrenoceptor transcripts differed with age and epididymal region analyzed. Prazosin (nonselective α1 antagonist), 5-methyl urapidil (α1A-selective), and BMY 7378 (α1D-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 (pKi) values for the high-affinity sites, indicated a predominant population of α1A-adrenoceptor subtype in caput and cauda epididymis from adult animals. Differences in pKi values in caput and cauda epididymis from immature and adult animals also suggested that the relative amount of α1-adrenoceptors, at the protein level, is modulated by sexual maturation. Taken together, the changes in α1-adrenoceptor expression during sexual maturation may suggest specific roles for these receptors in epididymal function.

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