Estrogen metabolism in the Asian elephant (Elephas maximus)

Abstract

Estradiol-17P metabolism was studied in two female Asian elephants (Elephas maximus). In an initial study, 500 pCi of tritiated estradiol-17P was injected iv into a single animal, and 0, 30 and 60 min serum samples were collected as well as all excreted urine and feces for 24 hr. In a second study, 1.5 mg unlabeled estradiol-17P was injected iv into a second animal and 0, 5 , 15, 30, and 60 min serum samples and a 30 min urine sample were collected postinjection. Analyses of samples from both studies demonstrated a rapid conversion of free estradiol to conjugated forms in the serum. The first (5 min) serum sample following the injection of unlabelled estradiol contained unconjugated estradio1:conjugated estradio1:conjugated estrone at a ratio of 60:29:10, respectively, and at 30 min a ratio of 33:43:24. The urinary estrogen metabolites were in the conjugated form with an estradio1:estrone ratio of 60:40. No radiolabeled estrogen was found in the fecal samples during the 24 hr following administration of the radiolabeled estradiol. These data indicate a rapid clearance of circulating free estradiol in the elephant, with a major metabolite in the serum and urine being estradiol Conjugate. 0 1992 Wiley-Liss, Inc.

Excretion and metabolic fate of radiolabeled estradiol and testosterone in the cockatiel (Nymphicus hollandicus)

“…Although fecal monitoring has been used in other avian species to measure daily changes in sex steroid production [Bishop and Hall, 1991;Yamaguchi and Ishii, 1991;Cockrem and Rounce, 1994;Lee et al, 1995], the present data are the first to demonstrate that daily fecal/urine measurements reflect primarily the excretion products of estradiol and testosterone produced during the previous 24 hr. These results are unlike mammalian studies in which radiolabeled steroid excretion has been relatively slow and overall recovery has been low [Shille et al, 1984;Loskutoff et al, 1987;Ziegler et al, 1989;Hindle and Hodges, 1990;Czekala et al, 1992;Shideler et al, 1993]. The present report reveals a recovery of 75% of each radiolabeled steroid administered within 24 hr after radiolabel injection.…”

Hormone Secretion in the Asian Elephant (Elephas maximus): Characterizationof Ovulatory and Anovulatory Luteinizing Hormone Surges

“…Alternatively, it is possible that the elephant ovary secretes estrogen metabolites other than estradiol, as has been shown for progestogens, for which the most abundant circulating forms are 5␣-reduced compounds, not progesterone [25][26][27]. There is evidence that circulating estradiol may predominate in a conjugated form, rather than a free steroid form, in both Asian [28] and African [29] elephants. However, incubation of Asian elephant serum with ␤-glucuronidase/aryl sulfatase to hydrolyze estrogen conjugates before analysis did not provide any clearer evidence of cyclic follicular activity (unpublished results).…”

Estrogen and LH dynamics during the follicular phase of the estrous cycle in the Asian elephant

“…It is notable that such a clear pattern emerges using a urinary estrogen conjugate assay when earlier attempts to assess estrogen dynamics using serum analyses failed to show any relationship with elephant reproductive status [for reviews see Hodges, 1998;Brown, 2000]. One possible reason for the inconclusive serum results is that the free steroid is quickly metabolized to estradiol and estrone conjugates in the bloodstream [Czekala et al, 1992]. Thus, techniques to measure circulating estradiol would have excluded the identification of a conjugated form due to the extraction process.…”

“…The lack of a reliable serum indicator of follicular activity led to the investigation of urinary estrogen analysis as a possible alternative, the biological relevance of which was based on radiolabel infusion studies that showed circulating estrogen conjugates are excreted primarily (95%) in the urine of Asian [Czekala et al, 1992] and African [Wasser et al, 1996] elephants. However, urinary estrogen data have also been inconsistent, likely because of sampling frequency limitations.…”