Arginine vasopressin regulation in pre- and postpubertal male rats by the androgen metabolite 3beta-diol

Abstract

Arginine vasopressin (AVP) is a nonapeptide expressed in several brain regions. In addition to its well-characterized role in osmoregulation, AVP regulates paternal behavior, aggression,circadian rhythms, and the stress response. In the bed nucleus of the stria terminalis (BST), AVP gene expression is tightly regulated by gonadal steroid hormones. However, the degree by which AVP is regulated by gonadal steroid hormones in the suprachiasmatic nucleus (SCN) and medial amygdala (MeA) is unclear. Previous studies have shown that AVP expression in the brain of gonadectomized rats is restored with testosterone, 17beta-estradiol, and 5alpha-dihydrotestosterone(DHT) replacement. In addition, we have demonstrated that 3beta-diol, a metabolite of DHT,increased AVP promoter activity in a neuronal cell line and that the effects of 3beta-diol on AVP promoter activity were mediated by estrogen receptor-beta. To test whether 3beta-diol has a physiological role in the regulation of central AVP expression in vivo, we gonadectomized pre- and postpubertal male rats and followed with once daily injections of estradiol benzoate (EB),DHT-propionate, 3beta-diol-dipropionate, or vehicle. The SCN, BST, and MeA were analyzed for AVP mRNA expression using in situ hybridization. In the BST, intact juveniles had significantly fewer AVP-expressing cells than adults. GDX abolished all AVP mRNA expression in the BST in both age groups, whereas treatment with EB restored >80% and DHTP <10% of the AVP expression. Interestingly, 3beta-diol-proprionate was more effective at inducing AVP expression in juveniles than in adults, suggesting that the regulation of AVP by 3beta-diol might be age dependent [corrected].

Fig. 1.

Diagram depicting the metabolic pathway of testosterone. Enzymes are shown in italics. Double-sided arrow illustrates the bidirectional catalysis of 5α-dihydrotestosterone (DHT) to 5α-androstane-3α,17β-diol (3α-diol). 3αHSD, 3α-hydroxysteroid oxidoreductase; 17βHSD7, 17β-hydroxysteroid dehydrogenase; 6α-triol, 5α-androstane-3β,6α-17β-triol; 7α-triol, 5α-androstane-3β,7α,17β-triol; CYP7B1, cytochrome P450, family 7, subfamily B, polypeptide 1.

Fig. 2.

Effects of gonadal steroid hormones on total number of arginine vasopressin (AVP) mRNA-expressing cells in the bed nucleus of the stria terminalis (BST; A) and medial amygdala (MeA; B) of adult and juvenile rats. Rats were gonadally intact or gonadectomized and treated with vehicle (safflower oil), estradiol benzoate (EB), 5α-dihydrotestosterone proprionate (DHTP), or 3β-diol proprionate (3β-diol-P). ND, not detectable. *Significant difference within treatment groups (P < 0.05).

Fig. 3.

Photomicrographs showing representative regions of AVP mRNA-expressing cells in the BST in gonadally intact adult (left) and juvenile (right) rats. Cells were considered positive for AVP when the number of silver grains on top of the cells was 3 times higher than background. Insets show individual cells at higher magnification (×40). Scale bar, 10 μm.

Fig. 4.

Photomicrographs showing representative regions of AVP mRNA-expressing cells in the MeA in gonadally intact adult (left) and juvenile (right) rats. Cells were considered positive for AVP when the number of silver grains on top of the cells was 3 times higher than background. Insets show individual cells at higher magnification (×40). Scale bar, 10 μm.

Fig. 5.

Effects of gonadal steroid hormones on the relative density of silver grains representative of AVP mRNA-expressing cells in the suprachiasmatic nucleus (SCN) of adult and juvenile rats. Rats were gonadally intact or gonadectomized and treated with vehicle (safflower oil), EB, DHTP, or 3β-diol-P.