Effect of low density and high density lipoproteins on progesterone secretion by dispersed corpora luteal cells from rats treated with aminopyrazolo-(3,4-d)pyrimidine.

Immature female rats, superovulated and treated daily for 3 days with 4-aminopyrazolo-(3,4-d)pyrimidine (APP), showed a marked reduction in plasma cholesterol levels, which is reflected by reduced levels of very low density, low density (LDL), and high density (HDL) lipoproteins. Luteal cells from non-APP-treated rats released 2444 +/- 212 ng progesterone/mg protein in 4 h, which slowly increased to 2806 +/- 327 after 20 h. Luteal cells from APP-treated animals showed a similar pattern at about half the level of progesterone production. In the presence of 100 ng LH/ml, progesterone levels were stimulated 2-fold in both APP-treated and nontreated controls. The addition of either human HDL or LDL to any of the preparations markedly increased the progesterone level. These results support the hypothesis that APP treatment reduces the ability of dispersed luteal cells to secret progesterone. This effect is partially overcome by the addition of either HDL or LDL to the incubation media in vitro, suggesting that rat luteal tissue can use either human HDL or LDL as a source of cholesterol. However, about 5 times as much human LDL-derived cholesterol was required to stimulate equivalent increases in progesterone compared to human HDL cholesterol.