ABERRANT HYPOTHALAMIC-PITUITARY-OVARIAN AXIS IN THE WATANABE HERITABLE HYPERLIPIDEMIC RABBIT

The WHHL rabbit has a defective low density lipoprotein receptor and is a model for familial hypercholesterolemia. WHHL rabbits are less fecund than NZW rabbits, the strain into which the defect has been inbred. This lower fecundity could be related to impaired ovarian steroidogenesis due to reduced intracellular availability of cholesterol. Here we compare the WHHL and NZW rabbits with regard to oocyte morphology and fertilization rates after stimulation with equine chorionic gonadotropin. We also compare hypothalamic-pituitary-ovarian axis function by measuring baseline and gonadotropin releasing hormone-stimulated plasma estradiol, progesterone, and gonadotropin levels, both before and after simvastatin inhibition of de novo cholesterol synthesis. WHHL rabbit oocytes remained encased in cumulus and had a lowered fertilization rate (9/50 vs. 83/87, P < 0.05). WHHL rabbits had lower baseline estradiol levels (7.1 +/- 0.72 vs. 10.2 +/- 0.94, P < 0.05) and had higher baseline follicle stimulating hormone (P < 0.05) and luteinizing hormone (P < 0.05) levels. Simvastatin lowered luteal progesterone concentrations only in WHHL rabbits (P < 0.05). We conclude that the hypothalamic-pituitary-ovarian axis in WHHL rabbits is abnormal. The reduced availability of intracellular cholesterol for progesterone synthesis by inhibition of de novo cholesterol biosynthesis leads to a significant reduction in plasma progesterone concentrations in the WHHL. These findings have implications for women with familial hypercholesterolemia, particularly regarding treatment with inhibitors of de novo cholesterol synthesis.