Rat brain norepinephrine release during progesterone-induced LH secretion

Area of Science:

• Neuroendocrinology
• Reproductive Biology
• Pharmacology

Background:

• Progesterone administration to ovariectomized, estrogen-primed rats induces luteinizing hormone (LH) release.
• Norepinephrine (NE) surges in plasma precede LH release, suggesting a role for noradrenergic pathways.

Purpose of the Study:

• To investigate the role of central noradrenergic activity in mediating progesterone-induced LH surges.
• To determine the source and mechanism of plasma NE changes associated with LH release.

Main Methods:

• Administration of progesterone to rats, with or without reserpine or phenoxybenzamine pretreatment.
• Measurement of plasma and hypothalamic norepinephrine (NE) levels.
• Assessing arteriovenous concentration differences of NE across the brain.

Main Results:

• Progesterone induced plasma NE surges and LH release; reserpine blocked both.
• Phenoxybenzamine blocked LH release but not NE surges, indicating NE is not solely responsible for LH release.
• Progesterone decreased hypothalamic NE while increasing plasma NE, with brain being the primary source of circulating NE.

Conclusions:

• Central noradrenergic activity, originating in the brain, is crucial for the progesterone-induced LH surge.
• Plasma NE changes reflect enhanced central noradrenergic activity rather than peripheral effects.