PROGESTIN CONTENT AND BIOSYNTHETIC POTENTIAL OF THE CORPUS-LUTEUM OF THE AFRICAN ELEPHANT (LOXODONTA-AFRICANA)

The aim of this study was to examine the progestin content and biosynt hetic potential of the corpus luteum of the African elephant (Loxodont a africana). Luteal tissue was collected from nonpregnant and early, m id- and late pregnant elephants (n = 2 per group) shot in the Kruger N ational Park. Pieces of individual corpora lutea (2-3 per animal; 23 i n total) were stored directly in ethanol before hormone analysis. Matc hing tissue pieces were incubated for 2 h with [H-3]pregnenolone (2 x 10(5) c.p.m.), after which tissue plus medium were also stored in etha nol. Progesterone and 17 alpha-hydroxyprogesterone immunoreactivity in tissue extracts were determined by enzymeimmunoassay and radioimmunoa ssay, respectively, before and after reverse phase HPLC. Progesterone immunoreactivity predominated over that of 17 alpha-hydroxyprogesteron e in all corpora lutea examined but concentrations of both hormones we re very low (73-374 ng g(-1) and 3-93 ng g(-1), respectively after HPL C). There were no obvious differences in hormone concentrations in cor pora lutea from animals at different reproductive stages. Progesterone and 17 alpha-hydroxyprogesterone immunoreactivity assayed before HPLC was 10-30 times higher than that measured after chromatographic separ ation. HPLC consistently revealed two large immunoreactive peaks assoc iated with relatively nonpolar compounds, which together accounted for most (at least 75%) of an progesterone immunoreactivity measured. Lar ge amounts of radioactivity with the same retention times as these pea ks were also detected after HPLC in samples incubated with [H-3]pregne nolone. Analysis of conversion products from four corpus luteum incuba tions indicated that between 52% and 84% of [H-3]pregnenolone had been converted; 19-33% was accounted for by progesterone, and 12-50% by th e two substances represented by the unidentified peaks. Subsequent GCM S analysis identified the two immunoreactive peaks as 5 alpha-pregnane -3 alpha-ol-20-one and 5 alpha-pregnane-3,20-dione (5 alpha-dihydropro gesterone). These results indicate that the major progestins contained within and biosynthesized by corpora lutea of African elephants are 5 alpha-reduced metabolites, and that progesterone and 17 alpha-hydroxy progesterone are quantitatively of minor importance.