METABOLIC-REGULATION OF APOPROTEINS OF HIGH-DENSITY LIPOPROTEINS BY ESTROGEN AND PROGESTERONE IN THE BABOON (PAPIO SP)

To determine the metabolic regulation of the apoproteins of high-density lipoproteins (HDL) by estrogen and progesterone, 12 overiectomized and hysterectomized baboons were fed a high cholesterol, high fat diet and were divided into four groups. One of these groups was the untreated control and the remaining three groups were treated with estrogen, progesterone, or a combination of both. After 10 months of treatment, there were significant differences in HDL apolipoprotein (apo) A-I and apo A-II levels in these groups. The apo A-I level was highest in baboons treated with the combination therapy, followed by those treated with estrogen. Baboons treated with progesterone and those in the control group had similar levels of apo A-I. Baboons treated with both estrogen and progesterone and estrogen alone had significantly higher levels of apo A-I than those in the control or progesterone group. Baboons treated with hormones had higher apo A-II levels than controls, and those treated with the combination therapy had the highest level. Metabolic studies suggested that both estrogen and progesterone increased apo A-I and apo A-II production. Progesterone also increased the fractional catabolic rate of apo A-I, but not of apo A-II. On the other hand, estrogen did not affect the fractional catabolic rate of either apo A-I or apo A-II. Thus, increased apo A-I content of HDL in baboons treated with both estrogen and progesterone or estrogen alone appears to be due to increased apo A-I synthesis. Since baboons treated with both estrogen plus progesterone had higher content of apo A-I in HDL than that in animals treated with estrogen alone, some effects of progesterone on the catabolic rate of HDL apo A-I were counteracted by the estrogen. © 1990.