J M Stauffer | PubMed Health

PubMed2000

Large-sample confidence intervals for validity and reliability coefficients.

Large-sample confidence intervals (CI) for reliability, validity, and unattenuated validity are presented. The CI for unattenuated validity is based on the Bonferroni inequality, which relies on one CI for test-retest reliability and one for validity. Covered are four reliability-validity situations: (a) both estimates were from random samples; (b) reliability was from a random sample but validity was from a selected sample; (c) validity was from a random sample but reliability was from a selected sample; and (d) both estimates were from selected samples. All CIs were evaluated by using a simulation. CIs on reliability, validity, or unattenuated validity are accurate as long as selection ratio is at least 20% and selected sample size is 100 or larger. When selection ratio is less than 20%, estimators tend to underestimate their parameters.

Confidence Intervals↗

PubMed1995

Stimulation of progesterone secretion in dispersed cells of rat corpora lutea by antioxidants.

Antioxidants were used to investigate the role of free radicals in control of luteal steroidogenesis. Corpora lutea from pseudopregnant rats were enzymatically dispersed, the cells were incubated with antioxidants, and progesterone production was measured. Addition of the antioxidants nordihydroguaiaretic acid (NDGA), butylated hydroxytoluene (BHT), and the gonadotropin luteinizing hormone (LH) resulted in a dose-dependent increase in progesterone secretion. However, the response pattern to these treatments differed with the age of the corpora lutea, and unlike LH neither NDGA nor BHT treatment resulted in an increase in the intracellular second messenger cAMP. Nevertheless, LH and antioxidant-induced progesterone stimulation could be blocked by the addition of either aminoglutethimide or ketoconazole, cytochrome P450 side-chain cleavage (cytochrome P450 SCC) enzyme inhibitors, which prevent the conversion of cholesterol to pregnenolone and thus block steroid hormone synthesis. Also, unlike exposure to LH, exposure to antioxidants resulted in an additional increase in progesterone production in luteal tissue saturated with 25 hydroxycholesterol, a soluble cholesterol analog which serves as a substrate for cytochrome P450 SCC. This study suggests that the site of antioxidant action in affecting progesterone secretion may be at the cytochrome P450 SCC enzyme. Based on these results and on studies in other steroid hormone-producing cells, it appears that free radicals may be involved in regulating synthesis by modulating activity of cytochrome P450 SCC enzyme in rat luteal tissue.

Animals↗