Hypothyroid-induced changes in autonomic control have a central serotonergic component

Area of Science:

• Neuroendocrinology
• Autonomic Neuroscience
• Cardiovascular Physiology

Background:

• Hypothyroidism is associated with autonomic dysfunction.
• Serotonergic pathways play a role in cardiovascular regulation.
• The specific impact of hypothyroidism on central serotonergic control of cardiovascular function is not fully understood.

Purpose of the Study:

• To investigate the effects of hypothyroidism on cardiovascular responsiveness to central serotonergic agonists.
• To examine the role of the parasympathetic nervous system in these altered responses.

Main Methods:

• Three experiments were conducted in euthyroid and hypothyroid rats.
• Cardiovascular responses to phenylephrine and nitroprusside were assessed (Exp I).
• Responses to intracerebroventricular administration of serotonin 5-HT2 (DOI) and 5-HT1A (8-OH-DPAT) agonists were evaluated, with and without atropine administration (Exp II and III).

Main Results:

• Hypothyroid rats showed reduced pressor and pulse pressure responses, and enhanced bradycardia to DOI, which were atropine-sensitive.
• Hypothyroid rats exhibited larger decreases in mean arterial pressure, heart rate, and body temperature in response to 8-OH-DPAT compared to euthyroid controls.
• General cardiovascular responsiveness to phenylephrine and nitroprusside was not significantly impaired in hypothyroid rats.

Conclusions:

• Hypothyroidism alters autonomic control, leading to differential cardiovascular responses to central serotonergic agonists.
• Parasympathetic nervous system activity is involved in the blunted response to DOI in hypothyroid rats.
• Changes in central serotonergic activity likely contribute to the deranged autonomic control observed in hypothyroidism.