The effect of intraventricularly administered GnRH on plasma β-endorphin levels of the rat

Abstract

This study investigates the effects of intraventricularly administered gonadotropin-releasing hormone (GnRH) on plasma β-endorphin levels in female proestrous rats.

Adult female Wistar rats (220-250 g) were implanted with an indwelling cannula in the third ventricle. Approximately 20 days later, the animals which had established a regular 4-day cycle were implanted with two indwelling catheters, one intracarotid and one intra-jugular, on the morning of proestrus. A single injection of 100 ng GnRH dissolved in 5 μl distilled water or 5 μl of saline (control) was infused slowly through the cannula in the third ventricle. Blood was withdrawn via the intracarotid catheter just before the infusion (12.30 h) andat 14.00, 15.30, 16.30 and 17.30 h for the determination of plasma β-endorphin levels.

The results indicated that intracerebroventricular infusion of GnRH causes a significant decline of plasma β-endorphin levels at all time points. It is postulated that GnRH possibly causes desensitization of GnRH receptors, due to the continuous GnRH supply to the pituitary via the blood circulation.

Key Words:

• β-Endorphin
• Opioids
• GnRH
• GnRH Receptors
• Pituitary
• Desensitization

Additional information

Notes on contributors

O. Guiba-Tziampiri

Joyce Laing works in the Department of Child and Family Psychiatry, Playfield House, Cupar, Fife, and is a Consultant Art Therapist to Psychiatric Hospitals and Prisons and Chairwoman of the Scottish Society of Art and Psychology.