SR-BI is present at relatively high levels on the membranes of hepatocytes
and steroidogenic tissues, including the adrenal gland, testes, and
ovaries, where it mediates the uptake and transport of cholesteryl ester
from high density lipoproteins. It has been demonstrated that transgenic
animals which do not produce SR-BI are healthy, with the exception that
the females are infertile. SR-BI KO females have abnormal HDLs, ovulate
dysfunctional oocytes and are infertile. Surgical, genetic and
pharmacologic methods were used to show that the fertility of SR-BI KO
females (or their transplanted oocytes) can be restored in the absence of
ovarian and/or extraovarian SR-BI expression by manipulations that modify
the structure, composition and/or abundance of their abnormal plasma
lipoproteins. These manipulations included inactivation of the
apolipoprotein A-I gene and administration of the cholesterol-lowering
drug PROBUCOL.TM.. In the absence of treatment, female animals which do
not express SR-BI have dramatically reduced levels of offspring, even
though they are otherwise healthy and the males normal. Studies
demonstrate that they do not produce viable eggs and have a defect
involving implantation of normal eggs.