Expression of 4-ene steroid 5 alpha-reductase messenger ribonucleic acid in the rat epididymis during postnatal development.

The regulation of epididymal 5 alpha-reductase mRNA is multifactorial and segment-specific. To further investigate the regulation of the message for the enzyme, the expression of 5 alpha-reductase mRNA in the rat epididymis was studied as a function of postnatal development. Developmental changes in 5 alpha-reductase mRNA concentrations were assessed by probing Northern blots with the full-length cDNA for rat steroid 5 alpha-reductase. In the first experiment the effect of postnatal age on 5 alpha-reductase mRNA concentrations in the caput-corpus and cauda epididymides was studied. Male rats, taken at 1-week intervals between the ages of 7-91 days, were used. In both epididymal regions, the mRNA for 5 alpha-reductase was present at all ages examined; it appeared in the immature animal at least 2 weeks before detectable 5 alpha-reductase enzyme activity. In the caput-corpus epididymidis, mRNA levels for 5 alpha-reductase decreased by half between postnatal days 7 and 21, rose 5-fold by day 56, and then remained constant through day 91. No change with postnatal age, however, was observed in the cauda epididymidis. In the second experiment, the longitudinal distribution of 5 alpha-reductase mRNA on postnatal days 21, 42, 49, 56, 77, and 91 was studied. The mRNA levels for 5 alpha-reductase increased remarkably, by 6- to 7-fold, in the initial segment of the caput epididymidis between postnatal days 21 and 42 and stayed constant thereafter. However, no significant change comparable to that found in the initial segment was observed in the adjacent proximal caput region or in any of the other epididymal segments. Thus, the 5-fold rise in 5 alpha-reductase mRNA concentrations that occurred in the caput-corpus epididymidis in the first experiment can be attributed solely to changes in the initial segment. We conclude that steady state concentrations of epididymal 5 alpha-reductase mRNA vary dramatically at different postnatal ages and are highly specific with respect to epididymal segment.