HOME HELP FEEDBACK SUBSCRIPTIONS ARCHIVE SEARCH TABLE OF CONTENTS		QUICK SEARCH:   [advanced] Author: Keyword(s): Year:  Vol:  Page:

This Article Full Text (PDF) Alert me when this article is cited Alert me if a correction is posted Services Email this article to a friend Similar articles in this journal Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via HighWire Citing Articles via Google Scholar Google Scholar Articles by Gustafsson, J.-A. Articles by Ingelman-Sundberg, M. Search for Related Content PubMed PubMed Citation Articles by Gustafsson, J.-A. Articles by Ingelman-Sundberg, M. Social Bookmarking                      What's this?

Regulation and Properties of a Sex-specific Hydroxylase System in Female Rat Liver Microsomes Active on Steroid Sulfates

I. GENERAL CHARACTERISTICS

From the ¹ From the Department of Germfree Research and Department of Chemistry, Karolinska Institutet, Stockholm, Sweden

The general characteristics and gonadal hormonal regulation of a new, sex-specific hydroxylase system present in female rat liver microsomes and active on steroid sulfates but not on free steroids is described. The substrate studied was 5-[4-¹⁴C]androstane-3,17ß-diol 3,17-disulfate which was converted to 5-[4-¹⁴C]androstane-3,15ß,17ß-triol 3,17-disulfate.

The 15ß-hydroxylase system could not be detected in liver microsomes from male rats and was at least 3000 times more active in female rats. The spectral dissociation constant (K_s) of 5-androstane-3,17ß-diol 3, 17-disulfate was 9.52 µm for male liver microsomes and 23.8 µm for female liver microsomes, whereas the apparent K_m value calculated for female liver microsomes was 25.8 µm.

Incubations carried out in the presence of carbon monoxide led to more than 98% inhibition of the 15ß-hydroxylase system, whereas presence of SKF 525-A in a concentration of 10^-3 m inhibited the 15ß-hydroxylase activity by 60%.

Treatment of female rats with phenobarbital and 3-methylcholanthrene led to a significant decrease in the activity of the 15ß-hydroxylase system, whereas treatment with 16-cyanopregnenolone did not significantly affect the enzyme activity.

Postpubertal gonadectomy did not significantly affect the 15ß-hydroxylase activity in female rats and did not lead to the appearance of detectable enzyme levels in liver microsomes from male rats. On the other hand, neonatal castration of male rats resulted in completely feminized levels of 15ß-hydroxylase in the adult animals and this feminization was totally inhibited by one single dose of 1.45 µmoles of testosterone propionate administered on the day after neonatal testectomy. Treatment of postpubertally castrated male rats with estradiol benzoate led to an at least transient, partial feminization of the liver with a 15ß-hydroxylase activity of about 30% of that present in normal female rats. When postpubertally castrated female rats were treated with testosterone propionate, the activity of the 15ß-hydroxylase system was suppressed.

The 15ß-hydroxylase activity was also studied in male and female rats 0, 10, 20, 30, 35, 40, 45, and 55 days of age and in rat fetuses. The 15ß-hydroxylase activity was not measurable until at 20 days of age and at this time no sexual difference in enzyme activity was apparent. Already at 30 days of age, however, female rats tended to hydroxylate more effectively than male rats and after this time the 15ß-hydroxylase activity increased rapidly in female rats so that it had almost reached adult levels at 40 days of age. During the same period the hydroxylase activity decreased successively in male rats and from 45 days and onward it was no longer detectable.

It is speculated that the physiological role of the highly sexspecific 15ß-hydroxylase system is to ascertain efficient hepatic deactivation of potential androgenic compounds in female rats.

CiteULike    Complore    Connotea    Del.icio.us    Digg    Reddit    Technorati    What's this?

This article has been cited by other articles:

				C. Buggs, N. Nasrin, A. Mode, P. Tollet, H.-F. Zhao, J.-A. Gustafsson, and M. Alexander-Bridges IRE-ABP (Insulin Response Element-A Binding Protein), an SRY-Like Protein, Inhibits C/EBP{alpha} (CCAAT/Enhancer-Binding Protein {alpha})-Stimulated Expression of the Sex-Specific Cytochrome P450 2C12 Gene Mol. Endocrinol., September 1, 1998; 12(9): 1294 - 1309. [Abstract] [Full Text]