Impaired capsaicin-induced decrease in heart rate and coronary flow in isolated heart of diabetic rats

Area of Science:

• Cardiovascular Physiology
• Neuroendocrinology
• Diabetology

Background:

• Insulin-deficient diabetes mellitus is associated with sensory neuropathy.
• Diabetic neuropathy can affect autonomic functions, including cardiovascular regulation.
• Capsaicin's effects on cardiovascular parameters are mediated by sensory nerves.

Purpose of the Study:

• To investigate the impact of diabetic sensory neuropathy on capsaicin-induced cardiovascular responses.
• To explore the role of endothelin-1 in mediating capsaicin's effects in diabetic rats.
• To assess nerve conduction velocity in the femoral nerve of diabetic rats.

Main Methods:

• Langendorff-perfused hearts from streptozotocin-induced diabetic rats (4 and 8 weeks) were used.
• Heart rate and coronary flow were measured before and after capsaicin (0.1 microM) administration.
• Endothelin-1 (0.1 nM) effects and femoral nerve conduction velocity were assessed.

Main Results:

• Baseline heart rate and coronary flow decreased with diabetes duration.
• Capsaicin reduced heart rate and coronary flow in normal and 4-week diabetic rats, but not in 8-week diabetic rats.
• Endothelin-1 consistently reduced heart rate and coronary flow, while nerve conduction velocity decreased with diabetes duration.

Conclusions:

• Diminished capsaicin responses in diabetes indicate sensory neuropathy.
• This neuropathy is linked to reduced endothelin-1 release from sensory nerve endings.
• Post-receptor mechanisms for endothelin-1 effects remain intact despite diabetes.