Pulsatile luteinizing hormone release during pregnancy in the rat

Area of Science:

• Reproductive Endocrinology
• Neuroendocrinology
• Mammalian Reproduction

Background:

• Luteinizing hormone (LH) plays a critical role in reproductive processes.
• Understanding LH secretion patterns during pregnancy is essential for comprehending reproductive physiology.

Purpose of the Study:

• To characterize the pulsatile release of LH during different stages of pregnancy in the rat.
• To investigate changes in LH secretion patterns and hormone levels (estradiol, progesterone) across gestation.

Main Methods:

• Unanesthetized rats were cannulated and blood samples collected over 3-hour periods on days 6-8, 14-16, and 22 of gestation.
• Plasma concentrations of LH, estradiol, and progesterone were measured.
• LH release patterns were analyzed for pulsatility, pulse amplitude, and frequency.

Main Results:

• Plasma estradiol and progesterone levels increased from early to mid-gestation, with estradiol further rising by day 22, while progesterone declined significantly.
• LH release was pulsatile at all stages, though patterns varied, with a higher incidence of non-pulsatile release observed on days 14-16 compared to days 6-8.
• On day 22 of gestation, a marked increase in mean LH levels was observed, primarily due to an increased LH pulse frequency, with all rats exhibiting pulsatile LH secretion.

Conclusions:

• LH secretion is pulsatile throughout rat pregnancy.
• The characteristics of LH pulsatile release undergo significant alterations during gestation, particularly by day 22.
• These dynamic changes in LH secretion are linked to the hormonal milieu of pregnancy.