Carotid body (CB) hyperactivity promotes
hypertension in response to chronic intermittent
hypoxia (CIH). The plasma concentration of
adrenaline is reported to be elevated in CIH and our previous work suggests that
adrenaline directly activates the CB. However, a role for chronic
adrenergic stimulation in mediating CB hyperactivity is currently unknown. This study evaluated whether beta-blocker treatment with
propranolol (Prop) prevented the development of CB hyperactivity, vascular sympathetic nerve growth and
hypertension caused by CIH. Adult male Wistar rats were assigned into 1 of 4 groups: Control (N), N + Prop, CIH and CIH + Prop. The CIH paradigm consisted of 8 cycles h-1, 8 h day-1, for 3 weeks.
Propranolol was administered via
drinking water to achieve a dose of 40 mg kg-1 day-1. Immunohistochemistry revealed the presence of both β1 and β2-adrenoceptor subtypes on the CB type I cell. CIH caused a 2-3-fold elevation in basal CB single-fibre chemoafferent activity and this was prevented by chronic
propranolol treatment. Chemoafferent responses to
hypoxia and mitochondrial inhibitors were attenuated by
propranolol, an effect that was greater in CIH animals.
Propranolol decreased respiratory frequency in normoxia and
hypoxia in N and CIH.
Propranolol also abolished the CIH mediated increase in vascular sympathetic nerve density. Arterial blood pressure was reduced in
propranolol groups during
hypoxia.
Propranolol exaggerated the fall in blood pressure in most (6/7) CIH animals during
hypoxia, suggestive of reduced sympathetic tone. These findings therefore identify new roles for β-
adrenergic stimulation in evoking CB hyperactivity, sympathetic vascular hyperinnervation and altered blood pressure control in response to CIH.