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Synthesis and aromatization of 19-norandrogens in the stallion testis.
Abstract: The results of the measurement of 19-nortestosterone in the testiscular artery and vein of the stallion, the very low levels of this steroid in the peripheral blood of geldings and the similar patterns of increase in the peripheral levels of 19-nortestosterone and testosterone after hCG stimulation, show that 19-nortestosterone, like testosterone, is essentially synthesized in the testis. This testicular origin was confirmed by the ability of testicular tissue to synthesize 19-norandrogens from [4-14C]androgens in vitro. 19-Nortestosterone was 50% conjugated in the peripheral blood and almost entirely conjugated after biosynthesis in vitro. The sequence of appearance of steroids in the peripheral blood after a single injection of 10,000 IU hCG suggests that, in the equine testis, 19-norandrogens are produced by a specific C10-19 desmolase (estrene synthetase), stimulable by hCG. 19-Nortestosterone was aromatized into estradiol-17 beta by stallion testicular microsomes. The affinity of the aromatase for 19-nortestosterone was very low compared to that for testosterone. At low and presumably physiological levels, and at a high testosterone/19-nortestosterone ratio, testosterone did not inhibit 19-nortestosterone aromatization by more than 53%. Thus, 19-nortestosterone may be aromatized in vivo in the testis in spite of the endogenous concentrations of androgens. However, the low velocity of 19-nortestosterone aromatization by testicular microsomes at roughly physiological concentrations suggests that 19-norandrogen aromatization may only participate slightly in the testicular estrogen production. These results suggest that in the equine testis, two aromatizing enzyme systems may exist: one which aromatizes both androgens and 19-norandrogens, and a minority system more specific for 19-norandrogens.
Publication Date: 1989-04-01 PubMed ID: 2724957DOI: 10.1016/0022-4731(89)90387-7Google Scholar: Lookup The Equine Research Bank provides access to a large database of publicly available scientific literature. Inclusion in the Research Bank does not imply endorsement of study methods or findings by Mad Barn.
- Journal Article
Summary
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This research reveals the processes of 19-norandrogen synthesis and aromatization in the horse’s testis. It points to a potential existence of two aromatizing enzyme systems within equine testis; one that aromatizes both androgens and 19-norandrogens, and another that primarily targets 19-norandrogens.
Synthesis and Aromatization of 19-norandrogens
- This study confirms that 19-nortestosterone, much like testosterone, originates in the testis of stallions (male horses). This claim is upheld by measures of 19-nortestosterone in the testicular artery and vein.
- 19-nortestosterone levels were found to be quite low in the peripheral blood of neutered male horses, or geldings. However, they exhibited similar patterns of increase with testosterone after hCG stimulation, further validating its testicular origin.
- In vitro tests show the ability of testicular tissue to synthesize 19-norandrogens from androgens, marking the testis as the primary site for this conversion process.
Function and Activity of 19-norandrogens
- Upon biosynthesis, 19-nortestosterone was found to be almost entirely conjugated, with half of it conjugated in the peripheral blood post-synthesis.
- The researchers noticed that 19-norandrogens are produced by a specific C10-19 desmolase (estrene synthetase) in the equine testis, which could be stimulated by hCG. This finding came from tracking the sequence of steroid appearance in the peripheral blood after a hCG injection.
Aromatization and Competition with Testosterone
- The study shows 19-nortestosterone being converted (aromatized) into estradiol-17 beta by testicular microsomes. However, this conversion having an notably low affinity compared to testosterone.
- Even at low presumed physiological levels and a high testosterone to 19-nortestosterone ratio, testosterone only suppressed the conversion of 19-nortestosterone to essentially not more than half (53%). This suggests that the process can occur in vivo despite high androgen concentrations.
- Notwithstanding, the slow speed of 19-nortestosterone aromatization at roughly physiological concentrations suggests that this conversion may only have a small role in testicular estrogen production.
Implications
- These results imply the existence of two aromatizing enzyme systems within the equine testis: one that transforms both androgens and 19-norandrogens and another one that is more specific to 19-norandrogens. However, further investigation is needed to confirm this idea.
Cite This Article
APA
Dintinger T, Gaillard JL, Zwain I, Bouhamidi R, Silberzahn P.
(1989).
Synthesis and aromatization of 19-norandrogens in the stallion testis.
J Steroid Biochem, 32(4), 537-544.
https://doi.org/10.1016/0022-4731(89)90387-7 Publication
Researcher Affiliations
- Laboratoire de Biochimie, UA CNRS 609, Caen, France.
MeSH Terms
- Animals
- Aromatase / metabolism
- Chorionic Gonadotropin / pharmacology
- Estradiol / metabolism
- Horses / metabolism
- Kinetics
- Male
- Nandrolone / biosynthesis
- Nandrolone / metabolism
- Testis / drug effects
- Testis / metabolism
- Testosterone / metabolism
Citations
This article has been cited 1 times.- Pan MM, Kovac JR. Beyond testosterone cypionate: evidence behind the use of nandrolone in male health and wellness. Transl Androl Urol 2016 Apr;5(2):213-9.
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