Sterol carrier protein-X (SCPx) is a unique 58 kDa peroxisomal protein which has both 3-oxoacyl coenzyme A thiolase and lipid transfer activity. SCPx is part of a family of proteins which includes the cholesterol transport protein sterol carrier protein-2 (SCP2; 13.2 kDa). Previous studies from this laboratory have demonstrated a shift in hepatic sterol carrier protein expression (SCP2 to SCPx) following the onset of diabetes. We suggest a similar change in SCP expression occurs in the ovary as this tissue responds to the enhanced fatty acid load associated with diabetes. Furthermore, we hypothesize that reduced steroid production in the diabetic female rat is related to an increase in SCPx expression and decreased SCP2 expression and is not necessarily a result of a change in the mRNA levels of the steroidogenic enzymes, P450 side chain cleavage (P450scc) or 3β-hydroxysteroid dehydrogenase (3β-HSD). Rats (day 3 pregnant) were injected with streptozotocin (STZ, 65 mg/kg; iv) to induce a diabetic (D) state. Ovarian P450scc and 3β-HSD mRNA levels were examined on day 12 following STZ (D-rats, n=12) or vehicle injection (non-D rats, n=6) by Northern blot analysis. SCPx steady-state mRNA levels were measured using an SCPx-specific riboprobe (280 bp protected fragment) in a ribonuclease protection assay (RPA). Ovarian mRNA levels were quantified by densitometric analysis following Northern or RPA analysis. As expected, serum progesterone levels were reduced in the diabetic animals (108.6 ± 5.1 ng/ml, non-D vs. 74.3 ± 8.9 ng/ml, D-rats) in association with reduced fetal weight and growth. SCPx mRNA levels in the diabetic animals were increased 4.2-fold compared to control SCPx mRNA levels. In contrast, ovarian SCP2 protein levels were markedly reduced in the diabetic animals with serum triglyceride levels >1000 mg/dL. Ovarian P450scc and 3β-HSD mRNA levels were increased 3-fold in the diabetic animals relative to the non-D animals. Results of this study confirm that SCPx mRNA levels are elevated following diabetes onset and that P450scc and 3β-HSD mRNA levels do not reflect the reduced steroid hormone profile associated with diabetes. These results are consistent with the possibility that reduced steroid levels in the diabetic animals reflects a loss of cholesterol transport capacity as SCPx/3-oxoacyl coenzyme A thiolase expression is enhanced.