Showing papers by "R. J. van Aarde published in 1997"

Concentrations of progesterone and the 5 alpha-reduced progestins, 5 alpha-pregnane-3,20-dione and 3 alpha-hydroxy-5 alpha-pregnan-20-one, in luteal tissue and circulating blood and their relationship to luteal function in the African elephant, Loxodonta africana.

Abstract: The 5 alpha-reduced metabolites 5 alpha-pregnane-3,20-dione (5 alpha-DHP) and 3 alpha-hydroxy-5 alpha-pregnan-20-one (5 alpha-P-3 alpha-OH) are the principal progestins biosynthesized by the African elephant corpus luteum. The aim of the present study was to determine luteal and circulating concentrations of these 5 alpha-reduced progestins in relation to progesterone (P4) and to examine whether their measurement reflects corpus luteum function. Ovarian (luteal) tissue (30 corpora lutea and 3 corpora rubra from 8 animals) and plasma samples (30 animals) were collected from pregnant and nonpregnant adult elephants shot in the Kruger National Park. Specific immunological measurement for both 5 alpha-reduced progestins and P4 was achieved by enzymeimmunoassay of tissue and plasma extracts following purification by HPLC. Mean (+/- SEM) luteal concentrations of 5 alpha-DHP and 5 alpha-P-3 alpha-OH were 79.5 +/- 9.4 micrograms/g and 196.5 +/- 24.8 micrograms/g, respectively, approximately 2-3 orders of magnitude higher than those of P4 (mean +/- SEM, 0.16 +/- 0.01 microgram/g). Whereas 5 alpha-reduced progestin concentrations tended to be lower in corpora lutea from late pregnancy compared with earlier stages and were lowest in corpora rubra, P4 levels were similar in all tissues/stages examined. The 5 alpha-reduced progestins also predominated over P4 in plasma (mean 5 alpha-DHP:P4 and 5 alpha-P-3 alpha-OH:P4 ratios 20.3 and 13.4, respectively). Similar to results for luteal tissue, plasma concentrations of 5 alpha-reduced progestins, but not of P4, were lower in late pregnancy than in earlier gestation stages and in nonpregnant animals. Moreover, plasma levels of both 5 alpha-reduced metabolites were negatively correlated with gestation age, whereas those of P4 were not. Levels of 5 alpha-reduced metabolites (without chromatography) were also measured in weekly blood samples throughout two complete ovarian cycles in one captive female. Both measurements showed a cyclic profile (similar to that of P4) with a luteal-phase elevation of 10- to 15-fold. The results indicate that 5 alpha-reduced compounds are the predominant progestins contained within and secreted by the corpus luteum of the African elephant, both during the ovarian cycle and throughout pregnancy. They also provide preliminary evidence to suggest that measurements of 5 alpha-reduced metabolites may reflect corpus luteum function more closely than those of P4.

Ligand specificity of uterine oestrogen and progesterone receptors in the subadult African elephant, Loxodonta africana.

Abstract: The ligand specificity of progesterone and oestrogen receptors in the uteri of four nonpregnant, nonlactating African elephants, killed during routine culling in the Kruger National Park, were determined. The mean (+/-SEM) Kd values of the oestrogen (0.18 +/- 0.019 x 10(-9) mol l-1, n = 12) and progesterone (0.22 +/- 0.025 x 10(-9) mol l-1, n = 12) receptors were essentially similar when [3H]promegestone was used as radioligand in the progesterone receptor assays. However, when [3H]progesterone was used as radioligand, the progesterone receptor exhibited a significantly higher Kd value (1.03 +/- 0.132 x 10(-9) mol l-1, n = 12) than that of the oestrogen receptor. The use of the different radioligands did not significantly affect the quantitative values obtained for the progesterone receptor. Both the oestrogen and the progesterone receptors displayed a high ligand specificity. The 5 alpha-reduced metabolites of progesterone exhibited a high relative binding affinity for the progesterone receptor (5 alpha-pregnane-3,20-dione: relative binding affinity = 43%; 5 alpha-pregnane-3 alpha-ol-20-one: relative binding affinity = 20%) but the synthetic antiprogestin RU 486 did not compete successfully with progesterone in competitive binding studies. However, norethindrone (relative binding affinity = 293%) competed successfully for binding to the progesterone receptor, and may have some potential in the future development of a technique to control reproductive output in the African elephant.