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Circulating blood progesterone is pulsatile throughout the rat oestrous cycle
1Department of Physiology and Biophysics, University of Illinois, Urbana.
Acta Endocrinologica
|September 1, 1987
Summary
Progesterone (P4) levels in female rats fluctuate pulsatilely throughout the estrous cycle. Early proestrus showed the lowest P4 levels and pulse frequency, while day 1 showed the highest mean P4 levels.
Area of Science:
- Reproductive Endocrinology
- Chronobiology
- Animal Physiology
Background:
- Circulating progesterone (P4) plays a critical role in regulating the mammalian estrous cycle.
- Understanding the dynamic patterns of P4 secretion is essential for comprehending reproductive physiology.
Purpose of the Study:
- To investigate the pulsatile secretion patterns of circulating progesterone (P4) in intact cycling female rats throughout their estrous cycle.
- To quantify variations in P4 pulse frequency and amplitude across different phases of the estrous cycle.
Main Methods:
- Intact cycling female rats were cannulated via the jugular vein for sequential blood sampling.
- Blood samples (80-100 µL) were collected at 10-minute intervals for 6 hours under unanesthetized conditions.
- Plasma P4 concentrations were measured using radioimmunoassay, and data were analyzed using PULSAR software.
Main Results:
- Progesterone (P4) exhibited pulsatile secretion throughout the rat estrous cycle.
- Mean circulating P4 levels were lowest during early proestrus (EP) and highest during diestrus 1 (D1).
- P4 pulse frequency was significantly reduced in D1, while pulse amplitude was lower in EP.
Conclusions:
- Progesterone secretion in female rats is characterized by pulsatile dynamics that vary across the estrous cycle.
- Specific phases, such as early proestrus and diestrus 1, exhibit distinct patterns of P4 pulse frequency and amplitude.
- These findings contribute to a deeper understanding of the hormonal regulation of the rat estrous cycle.