Effects of catecholamines on thermoregulation in pigeons

Area of Science:

• Neuroendocrinology
• Physiology

Background:

• The role of catecholamines in thermoregulation is complex and species-specific.
• Understanding the specific adrenoceptor subtypes involved in avian thermoregulation is crucial for physiological research.

Purpose of the Study:

• To investigate the effects of various catecholamines and adrenergic receptor antagonists on cloacal temperature in unanaesthetized pigeons.
• To elucidate the specific adrenoceptor pathways (alpha and beta) mediating the thermoregulatory responses to catecholamines in avian species.

Main Methods:

• Injections of catecholamines (noradrenaline, adrenaline, dopamine, isoprenaline), phenoxybenzamine, and propranolol into the cerebral ventricles of unanaesthetized pigeons.
• Monitoring of cloacal temperature changes in response to the administered substances.

Main Results:

• Noradrenaline, adrenaline, and dopamine induced hypothermia, mediated by alpha-adrenoceptors, as evidenced by blockade with phenoxybenzamine but not propranolol.
• Isoprenaline also caused hypothermia, which was unaffected by phenoxybenzamine or propranolol, suggesting a non-alpha/beta adrenoceptor-mediated mechanism.
• Phenoxybenzamine alone caused a slight, sustained increase in cloacal temperature, potentially by blocking tonic noradrenergic hypothermic tone.

Conclusions:

• Hypothermia induced by noradrenaline, adrenaline, and dopamine in pigeons is primarily mediated through alpha-adrenoceptor activation.
• The hypothermic effect of isoprenaline appears to involve a different receptor mechanism, not directly linked to alpha or beta-adrenoceptors.
• Adrenergic signaling, particularly via alpha-adrenoceptors, plays a significant role in the central control of thermoregulation in pigeons.