IMMUNOEXPRESSION OF AQUAPORIN-1 IN THE EFFERENT DUCTS OF THE RAT AND MARMOSET MONKEY DURING DEVELOPMENT, ITS MODULATION BY ESTROGENS, AND ITS POSSIBLE ROLE IN FLUID RESORPTION

Recent data suggest that estrogens play a role in regulating fluid res orption from the efferent ducts, though the biochemical mechanisms inv olved are unknown. The present study has used immunocytochemistry to l ocalize a water channel protein, Aquaporin-1 (AQP-1), to the efferent ducts of male rats and marmoset monkeys from perinatal life through to adulthood and has then investigated its potential hormonal regulation in neonatal/peripubertal life, via administration of a GnRH antagonis t (GnRHa) or diethylstilbestrol (DES) to rats. AQP-1 was immunoexpress ed intensely in the apical brush border of the epithelium lining the e fferent ducts at all ages studied, from late fetal life through pubert y to adulthood. In the marmoset, but not the rat, AQP-1 was also expre ssed in the epithelium of the rete testis. Once the cell types within the efferent duct epithelium had differentiated, it was clear that onl y nonciliated cells of the rat localized AQP-1. When gonadotropin secr etion was suppressed in rats by neonatal administration of GnRHa, immu noexpression of AQP-1 at age 18 and 25 days was virtually unchanged in intensity, though the efferent ducts were reduced in size. In contras t, when DES was administered neonatally to rats (up to day 12), immuno expression of AQP-1 was reduced at day 10, virtually abolished at day 18, reduced markedly at day 25 and to a small extent at day 35; these findings were confirmed by Western blot analysis at day 18. The DES-in duced decrease in immunoexpression of AQP-1 was accompanied by pronoun ced distension of the efferent ducts and rete, consistent with reduced fluid resorption. The epithelial cells of the efferent ducts in DES-t reated rats were cuboidal rather than columnar in shape as in controls and were reduced significantly in height compared with controls at al l ages through to adulthood. These findings suggest that estrogens may play a role in regulating fluid resorption from the efferent ducts du ring fetal/neonatal development and/or a role in the gross and functio nal development of the efferent ducts and rete testis. The present dat a also suggest that AQP-1 is one of the elements involved in the regul ation of fluid resorption in the efferent ducts. The importance of flu id flow in fetal/neonatal development of the excurrent duct system of the male is also suggested by these observations.