Sex-related differences in GH secretion in rat using reverse hemolytic plaque assay

Area of Science:

• Endocrinology
• Reproductive Biology
• Cell Biology

Background:

• Sex differences in growth hormone (GH) secretion are well-documented.
• The underlying mechanisms, particularly concerning the pituitary somatotrope, remain unclear.

Purpose of the Study:

• To investigate whether enhanced GH-releasing factor (GRF)-stimulated GH release in males is due to differences in somatotrope number or secretory response.
• To compare GRF-induced GH secretion between male and female rats at the single-cell level.

Main Methods:

• Utilized the hemolytic plaque assay to quantify GH secretion from individual pituitary cells.
• Conducted time-course studies and GRF concentration-response experiments (0.01–1,000 nM) in age-matched male and female rats.
• Measured the percentage of GH plaque-forming cells and plaque areas to assess somatotrope abundance and secretory activity.

Main Results:

• Male rats had a significantly higher percentage of somatotropes (45% vs. 27% in females).
• GRF stimulated a greater concentration-dependent increase in plaque areas in males compared to females.
• Maximal GH secretion was achieved at 10 nM GRF in both sexes, but males showed significantly larger maximal plaque areas and higher sensitivity (lower EC50).

Conclusions:

• The greater number of somatotropes in males contributes to enhanced GH secretion.
• Increased secretory capacity and heightened sensitivity to GRF in male rats also play a role in sex-related GH secretion differences.
• These findings elucidate key cellular mechanisms underlying sex dimorphism in GH regulation.