Role of nicotinic receptors on carotid body function in developing rats.

Abstract

Acetylcholine is an excitatory neurotransmitter in adult carotid body playing a significant role in the ventilatory response to hypoxia. We used epibatidine (Epi, 5μg/Kg i.p) as agonist and hexamethonium (Hexa, 1mg/kg i.p) as antagonist of peripheral nicotinic receptors to determine the function of nicotinic receptors in developing rats. Breathing frequency (Fr), tidal volume (VT) and minute ventilation (VE) were measured using whole body plethysmography in normoxia (21%O2) and in response to hypoxia (20 min‐12%O2) in rat pups at 1, 4, 7, 12 and 21 postnatal days before and after a single injection of Epi or Hexa. In normoxia, Epi increased significantly Fr by 4%, 21%, 30%, 40%, and 43% for P1, P4, P7, P12 and P21 respectively, p for age<0.001. In hypoxia, Epi increased Fr by 15% for P4 and 30% for P12 while Hexa decreased Fr by 13% and 31% respectively, p for age<0.01. We conclude that the functional expression of cholinergic nicotinic receptor on hypoxic ventilatory response is age‐dependent, thus presumably playing a significant role in the maturation of the carotid body response to hypoxia. Founded PF‐RSR, IRSC and Sick Kids Foundation.