In vitro and in vivo effects of vitamin D (calcitriol) administration on the normal neonatal and prepubertal prostate

Purpose: Although many studies have investigated the role of calcitriol in the growth regulation of normal and cancerous prostates, little is known about its role in early prostatic development. The interactions between calcitriol and androgens, and their actions on the normal prostate have similarly been proposed but not evaluated. Previous studies in our laboratory have revealed that in utero administration of 1,25-dihydroxycholecalciferol or calcitriol can influence prostate growth and differentiation throughout the life of the animal. We further examined the influence of calcitriol on the normal prostate in vitro and in vivo by focusing on early stages of prostatic development. Materials and Methods: The effects of calcitriol on the growth of the normal human neonatal prostatic epithelial cell line 267B-1 was determined in the presence and absence of dihydrotestosterone (DHT). We also examined the effect of calcitriol on the growth of maturing rat prostates in vivo. Before puberty 4 groups of rats 27 to 38 days old were treated with vehicle (controls) or calcitriol. When the rats reached adulthood at age 100 to 110 days a control group and a calcitriol group were sacrificed. The other 2 groups were given exogenous DHT for 5 days. For the animals to become adapted to DHT they were kept alive for 1 additional week and sacrificed at about age 120 days. Results: In vitro studies demonstrated that 267B-1 cells possess vitamin D receptors and their growth was inhibited by calcitriol with an IC₅₀ (concentration resulting in 50% cytotoxicity) of 30 μM. Proliferation of these neonatal prostate cells was also inhibited by calcitriol in the presence of DHT in vitro. Our studies indicate that, although calcitriol was administered at the apparently important prepubertal period, there was no difference in prostatic weights between the control and calcitriol treated rats. Exogenous administration of DHT decreased prostatic weight of control rats but in rats treated with 1,25-dihydroxycholecalciferol DHT did not have any significant effect on prostatic weight. No statistically significant differences were observed in seminal vesicle weights among the different groups of animals. Analysis of the nuclear matrix protein composition of the prostatic tissue showed differences in composition between the DHT, and calcitriol and DHT treated rat prostates. Conclusions: These studies indicate that calcitriol administered just before puberty does not significantly influence prostatic growth in the presence of endogenous or exogenous administered DHT, and has an inhibitory effect on neonatal prostate epithelial cell growth in vitro in the presence and absence of DHT. Treatment with calcitriol and DHT also results in differences in nuclear matrix protein composition. Prepubertal administration of calcitriol may inhibit the exogenous DHT action in decreasing epithelial growth and stimulating stromal proliferation in the rat prostate.