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The central oxytocin pulse generator: a pacemaker for luteolysis
J A McCracken1, E E Custer, J C Lamsa
1Worcester Foundation for Biomedical Research, Shrewsbury, MA 01545, USA.
Advances in Experimental Medicine and Biology
|January 1, 1995
Summary
Oxytocin (OT) release is regulated by ovarian hormones. Estrogen and progesterone withdrawal trigger OT pulses, influencing uterine prostaglandin F2a (PGF2a) release for corpus luteum regression.
Area of Science:
- Reproductive Endocrinology
- Neuroendocrinology
- Ovine Physiology
Background:
- Oxytocin (OT) is secreted in pulses from the neurohypophysis and corpus luteum (CL) in sheep.
- Large OT bursts during luteolysis appear to regulate uterine prostaglandin F2a (PGF2a) pulses.
Purpose of the Study:
- To differentiate the neurohypophyseal and CL contributions to OT secretion during luteolysis.
- To investigate the roles of estrogen (E) and progesterone (P) in regulating OT pulses.
Main Methods:
- Ovariectomized sheep received E and/or P infusions to mimic the estrous cycle.
- Intact cycling sheep underwent CL surgical excision during the luteal phase.
- OT pulses were measured via RIA and uterine biometry.
Main Results:
- Exogenous E infusion increased OT pulse frequency in ovariectomized sheep.
- Progesterone withdrawal in ovariectomized sheep and CL removal in intact sheep both induced high-frequency OT pulses.
- These responses were dose- and time-dependent on hormone levels and withdrawal.
Conclusions:
- Estrogen and progesterone withdrawal are key regulators of the central OT pulse generator.
- The central OT pulse generator, potentially amplified by CL-derived OT, triggers PGF2a release for corpus luteum regression.
- Ovarian steroids interact with the posterior pituitary to terminate the reproductive cycle.