The Effects of Hypophysectomy and Administration of Pituitary Hormones on Luteal Function and Uptake of High Density Lipoproteins by Luteinized Ovaries and Adrenals of the Rat

The role of plasma lipoproteins and hypophyseal hormones in the maintenance of progesterone secretion by the rat corpus luteum was investigated. In the first experiment, rats were treated daily from days 1–6 of pregnancy with 5 mg/kg 4-aminopyrozolopyramidine (4APP), a blocker of hepatic lipoprotein secretion, or with 5 mg/kg 4APP and 1 or 2 mg ovine PRL or 0.1 ml 0.5% phosphoric acid (4APP vehicle). The administration of 4APP reduced serum cholesterol and progesterone levels on days 2–6 of pregnancy and ovarian progesterone on day 6. The reduced progesterone secretion had no effect on embryo implantation. PRL, in the doses used, was incapable of abrogating the effects of 4APP on circulating or ovarian progesterone levels. Ovaries and adrenals, but not kidneys, of pseudopregnant rats exhibited specific and saturable uptake of porcine high density lipoprotein (HDL). Time-course studies indicated that the uptake of HDL was rapid in ovaries compared to that in adrenals. Ovaries from rats not only exhibited u...