Influence of P4 Implant Treatments on the Subsequent Incidence of Regular Estrous Cyclicity
After removal of the last implants at 8 mo of age, subsequent patterns of estrous cyclicity were determined by daily vaginal lavage for the next 4 wk. Rats that displayed prolonged cycles (6 or more days) of variable duration were considered to be irregularly cyclic, whereas those displaying more than 15 consecutive days of vaginal cornification were classified as persistent-estrous.
Plasma concentrations of LH and FSH were measured by double-antibody RIAs, as previously described, employing reagents provided by the National Hormone and Pituitary Program, NlDDK (Baltimore, MD). LH and FSH values are expressed in terms of the reference standards NIDDK rat LH-RP-1 and rat FSH-RP-1, respectively. The intra- and interassay coefficients of variation were 3.2% and 7.9%, respectively, for LH and 8.9% and 10.9%, respectively, for FSH. Serum concentrations of E2 and P4 were measured by specific RIAs as previously reported. Prior to RIA, samples were extracted with diethyl ether, and P4 and E2 fractions were isolated by Celite (Celite Corporation, Lompoc, CA) column chromatography. The intra- and interassay coefficients of variation were 5.4% and 6.9%, respectively, for E2 and 5.7% and 7.2%, respectively, for P4.
Comparisons of the numbers of resting follicles among the treatment groups were performed by one-way ANOVA, followed by Duncan’s multiple range test when appropriate. Two-way ANOVA was employed to compare the plasma patterns of LH and FSH during 0800-2000 h of the day in female rats implanted with P4 and those with empty implants. The incidences of regular cyclicity in each group were compared by chi-square test. A confidence level of p < 0.05 was considered statistically significant.