Cytosolic glucocorticoid receptors in the developing rat heart

Area of Science:

• Cardiology
• Endocrinology
• Developmental Biology

Background:

• Glucocorticoid hormones significantly impact cardiac function.
• Neonatal glucocorticoid treatment in rats alters heart function for weeks, implying neonatal cardiac glucocorticoid receptors (GRs) are involved.
• However, the presence of GRs in neonatal rat hearts has not been previously confirmed.

Purpose of the Study:

• To identify and characterize glucocorticoid receptors in neonatal rat heart cytosol.
• To investigate the effect of early-life hydrocortisone acetate administration on GR binding in the neonatal rat heart.

Main Methods:

• Glucocorticoid receptor binding assays were performed on neonatal rat heart cytosol using [3H] dexamethasone.
• Competition assays and Scatchard analysis were employed to characterize receptor binding.
• Rats received a single hydrocortisone acetate injection on post-natal day 2, with GR binding assessed in 12–14-day-old hearts.

Main Results:

• Saturable, specific, high-affinity glucocorticoid receptor binding was detected in neonatal rat heart cytosol.
• Despite altered cardiac function in treated 12–14-day-old rats, hydrocortisone acetate injection on post-natal day 2 did not alter cytosol GR binding in these hearts.

Conclusions:

• Glucocorticoid receptors are present in the neonatal rat heart cytosol.
• Early-life glucocorticoid exposure may alter cardiac function through mechanisms other than direct modulation of GR binding levels in the neonatal period.
• Permanent organizational effects on cardiac tissue due to neonatal glucocorticoid exposure are postulated.