| dc.description.abstract |
Both testosterone and its aromatizedmetabolite, oestradiol-17b, are known to act centrally on the secretion ofGnRH, but the major site of aromatization is not clear as aromatase activitiesare found in numerous tissues including brain and testis. Here, we tested theimportance of central aromatization of testosterone using a non-steroidalaromatase inhibitor, fadrozole. To distinguish between testicular andnon-testicular sites, five intact and five testosterone-infused castrated rams(600 g kg <emph type="7">-1 per 24 h for 3 days) were given fourinjections of fadrozole (i.m; 500 g kg <emph type="7">-1 ) at 48,52, 64 and 68 h relative to the start of testosterone infusion. Control rams(n = 5) received vehicle only. Fadrozoletreatment decreased plasma oestradiol-17b concentrations and increased the LHpulse frequency in both intact rams and testosterone-treated castrates,suggesting that non-testicular sites of aromatization are important in thecontrol of pulsatile LH secretion. To test the importance of centralaromatization, intact rams (n = 5) were infusedinto the third ventricle with vehicle (artificial cerebrospinal fluid) or withfadrozole (20 and 200 g kg <emph type="7">-1 per day). After twoweeks, the same two doses of fadrozole were infused intravenously instead ofintracerebrally. Central infusion of fadro-zole did not affect plasmaoestradiol concentrations but increased LH pulse frequency. Only the highestdose increased LH pulse frequency when infused intravenously. In conclusion,central aromatization is involved in the control of pulsatile LH secretion inmale sheep. |
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