Submitted to: Biology of Reproduction Abstracts
Publication Type: Abstract Only
Publication Acceptance Date: 4/29/2005
Publication Date: 7/20/2005
Citation: Conley, A.J., Corbin, C.J., Ford, J.J. 2005. Brain aromatase in male and female pigs: hypothalamic levels and identification of the tissue-specific form [abstract]. Biology of Reproduction. (Supplement):113. (Abstract #141) Interpretive Summary:
Technical Abstract: Aromatase cytochrome P450 (P450arom) catalyzes estrogen synthesis from androgens in gonads, placenta and brain of most mammals. Pigs are unusual in having duplicated genes encoding 3 distinct paralogous forms of P450 arom expressed tissue-specifically in the gonads, the placenta and the blastocyst. Whether or not porcine brain expresses P450arom, and which form of the enzyme might be expressed there, is unknown. The gonadal P450arom is an inefficient enzyme with novel characteristics. It is selectively inhibited by the imidazole etomidate, and catalyzes 1OH-testosterone synthesis in amounts almost equal to estradiol with potentially important physiological, and perhaps evolutionary, consequences. Therefore, studies were conducted to determine which form of P450arom was expressed in the brain of males and females, and at what level. Hypothalami were collected from post-pubertal boars (n=17) and similar aged females (n=8). Aromatase activity was determined in microsomal protein, and etomidate inhibition was examined as an indicator of which form of P450arom was primarily expressed in the brain. RT-PCR was conducted to amplify, clone and sequence partial P450arom cDNAs from transcript to verify which P450arom gene was expressed in porcine brain. Hypothalamic aromatase activity was 4-fold higher in male than female tissues, though almost 1/100 the testicular activity (1.97 +/- 0.42, 0.50 +/- 0.07 and 170 +/- 10.6 pmol/mg/hr; P < 0.05). Etomidate (1 'M) inhibited brain and testis aromatase activity by > 80%, but did not inhibit activity of recombinant placental P450arom. Sequence analysis over ~320 bp confirmed unequivocally that male and female hypothalami expressed the gonadal form of P450arom. These data show for the first time that P450arom is expressed in porcine hypothalamus, that levels are higher in males than females, and that activity is associated with expression of the gonadal form of the enzyme. This suggests that 1OH-testosterone, as well as estradiol, may be synthesized in the porcine brain, potentially influencing reproductive behavior in unique ways and perhaps stabilizing the duplicated, gonadal P450arom gene.