Diabetes-related changes in cAMP-dependent protein kinase activity and decrease in relaxation response in rat...

Area of Science:

• Vascular Physiology
• Endocrinology
• Biochemistry

Background:

• Endothelium-derived hyperpolarizing factor (EDHF)-type relaxation is impaired in streptozotocin (STZ)-induced diabetic rats.
• This impairment may involve reduced cyclic adenosine monophosphate (cAMP) action due to increased phosphodiesterase (PDE) activity.
• Cyclic adenosine monophosphate-dependent protein kinase (PKA) is crucial for cAMP-mediated cellular signaling and vasorelaxation.

Purpose of the Study:

• To investigate the activity and expression of cAMP-dependent protein kinase (PKA) in the superior mesenteric arteries of STZ-induced diabetic rats.
• To determine the role of PKA in impaired vasorelaxation observed in diabetes.
• To explore potential imbalances in PKA subunit expression contributing to altered vascular function.

Main Methods:

• Comparison of superior mesenteric artery rings from age-matched control and STZ-induced diabetic rats.
• Assessment of relaxation responses to cilostamide (a PDE3 inhibitor) and cAMP analogs (8-bromo-cAMP, db-cAMP).
• Measurement of PKA activity and expression levels of PKA catalytic (Cat-alpha) and regulatory (RII-beta) subunits.

Main Results:

• Relaxation to cilostamide and cAMP analogs was significantly weaker in diabetic rat arteries.
• PKA activity was significantly lower in db-cAMP-treated mesenteric arteries from diabetic rats.
• mRNA and protein levels of PKA catalytic subunit Cat-alpha were decreased, while PKA regulatory subunit RII-beta increased in diabetic rats.

Conclusions:

• Impaired vascular relaxation in STZ-induced diabetic rats is attributable to both increased PDE activity and decreased PKA activity.
• Decreased PKA activity may result from an imbalance in the expression of its catalytic and regulatory subunits.
• These findings highlight a novel mechanism involving PKA dysfunction in diabetic vascular complications.