Biphasic Change in Correlation between Ovarian Lipid Peroxides and Progestational Activity during Pseudopregnancy Induced in Immature Rats.

Abstract

ABSTRACT. We measured ovarian lipid peroxide (LP) levels and plasma progestins, progesterone (P 4 ) and 20α-dihydroprogesterone, throughout pseudopregnancy in gonadotropin-primed immature rats. Plasma P 4 fluctuated, with two peaks on days 5 (PSP5) and 8 of pseudopregnancy, and then declined to the basal level by PSP12. Ovarian LP increased from PSP1 to PSP4, decreased temporarily until PSP8, and then rose gradually until PSP14. From PSP1 through PSP7, ovarian LP was positively correlated with total progestins according to the Spearman ranked correlation coefficient (r=+0.829, p<0.05). In contrast, a negative correlation between ovarian LP and plasma P 4 was apparent (r=-0.816, p<0.05) from PSP8 to PSP14. These results show the biphasic correlation of LP with luteal progestational activity depending on the luteal stage.-KEY WORDS: lipid peroxide, progestin, pseudopregnancy, rat.J. Vet. Med. Sci. 61(9): 1039-1042, 1999 Animal and tissue preparation: Immature female rats of the Wistar-Imamichi strain were used in this study. They were kept in an air-and light-conditioned room (temperature, 23 ± 3°C; lights on, 0500-1900 hr). Superovulation and pseudopregnancy were induced by the earlier method [21,22] with a little modification. Twenty six-day-old animals weighing 50-73 g were injected with eCG (50 IU, sc) at 1700 hr followed by hCG (50 IU, ip) 46 hours later. These animals ovulated 34.2 ± 9.0 (mean ± SEM, n=5) ova the next morning. On vaginal smear examination, the rats exhibited proestrus on the 28th, estrus on the 29th day, and diestrus thereafter for 12.9 ± 0.3 (n=24) days. The first diestrous day was designated as day 1 of pseudopregnancy (PSP1) in this report. The rats were killed by decapitation on each day from PSP1 to PSP14 except for PSP2. Systemic blood plasma was kept at 20°C until the steroid assay. Ovaries were kept at 80°C until assay of the LP level.Determination of plasma progestins and ovarian LP: Plasma P4 and 20α-OHP were extracted with n-hexan and isolated by column chromatography. They were then determined in duplicate by radioimmunoassay [6,14,16]. The working range of assays was 12.5-1000 pg for both progestins.LP levels in ovarian homogenates were measured by the thiobarbituric acid test [27]. Values were expressed as nmol of malondialdehyde (MDA) per ovary.Statistical analyses: All data on progestins and LP were expressed as the mean ± SEM (n=6). They were analysed by ANOVA and Student's t-test. Correlation coefficients and, in some cases, the Spearman ranked correlation coefficients of ovarian LP were evaluated with several parameters of luteal progestational activity (P4, 20α-OHP, sum of P4 and 20α-OHP, or the ratio of 20α-OHP to P4). Differences between experimental groups were considered Superoxide radicals (SOR) and other reactive oxygen species have been assumed to play pathological roles in inflammation, cancer and radiation damage. Recent evidence has demonstrated their physiological roles, for example in the regulation of ovarian corpus luteum (CL) function [2,9]. SOR and related...