Characterization of cephalic arteriovenous LH differences by continuous sampling in ovariectomized sheep

Area of Science:

• Reproductive Endocrinology
• Neuroendocrinology
• Sheep Physiology

Background:

• Ovariectomized sheep exhibit characteristic large episodic pulses of luteinizing hormone (LH) secretion.
• Previous methods of blood sampling lacked the resolution to accurately capture rapid arteriovenous LH changes during these pulses.

Purpose of the Study:

• To determine the temporal pattern of LH secretion pulses in ovariectomized sheep.
• To investigate the role of head tissues in modulating circulating LH concentrations.
• To assess the impact of gonadotropin-releasing hormone (GnRH) administration on LH release patterns.

Main Methods:

• Development of a continuous blood sampling system for simultaneous arterial and jugular venous collection at 20-second intervals.
• Measurement of LH concentrations in collected blood samples.
• Administration of synthetic GnRH pulses via arterial cannulae in anesthetized ewes.

Main Results:

• A continuous sampling system successfully resolved arteriovenous LH differences during episodic pulses.
• Individual spontaneous LH pulses in ovariectomized sheep were detected to last 2-6 minutes.
• Venous LH concentrations exceeded arterial levels during pulses, indicating release from the head, followed by periods of net removal by head tissues.
• Exogenous GnRH administration induced variable LH discharges, sometimes exceeding spontaneous levels.

Conclusions:

• Spontaneous pulsatile LH discharge in ovariectomized sheep is likely driven by episodic hypothalamic secretion of GnRH.
• LH secretion episodes are brief, lasting 2-6 minutes.
• Circulating LH profiles are influenced by both secretion dynamics and extravascular sequestration within head tissues.