Pulsatile Luteinizing Hormone Release during Pregnancy in the Rat

The present studies were designed to characterize LH release during pregnancy in the rat. Unanesthetized animals with jugular cannulae were bled for 3 h between 1000–1300 h on days 6–8, 14–16 or 22 of gestation (50 lμ whole blood/5 min). Plasma estradiol and progesterone values both increased from days 6–8 to days 14–16. However, while plasma estradiol levels increased further between days 14–16 and day 22, plasma P levels had declined 86%. The percent coefficients of variation obtained for alterations in blood LH levels at each stage of pregnancy were all significantly greater than intraassay variation, indicating that LH release was pulsatile at each stage. Although there were no significant differences in mean blood LH levels, pulse amplitude, or frequency between days 6–8 and 14–16, the individual patterns of LH release clearly varied between these 2 groups, and most notably within the 14–16 day group. Fifty-three percent (9 of 17) of the LH records in rats on days 14–16 were nonpulsatile compared to ...