Long-term hypoxia increases the number of norepinephrine-containing glomus cells in the rat carotid body: a correlative immunocytochemical and biochemical study.

A group of adult rats was divided into two subgroups: one was submitted to long-term normobaric hypoxia (10% O2, two weeks) while the other (control group) was kept in the same room, breathing air. Animals from each subgroup were used to study either the norepinephrine content of the carotid body by high pressure liquid chromatography or to localize norepinephrine-containing structures using an immunocytochemical procedure (peroxidase-labelled antibodies on cryostat sections). The biochemical study showed, as expected, a large increase in carotid body norepinephrine content (19-fold) and turnover (ten-fold) in hypoxic rats. The immunocytochemical study revealed only a few norepinephrine-immunopositive glomus cells in sections through the carotid body of normoxic rats, whereas the carotid body of hypoxic rats showed a very large number of norepinephrine-positive glomus cells. This increase was quantified, using an image analyser, and it was found to constitute a 61-fold increase in the number of immunopositive profiles per section and a 29-fold increase in the immunopositive profile area/section area ratio. It is concluded that long-term hypoxia increases rat carotid body norepinephrine content by inducing norepinephrine synthesis in glomus cells in which this amine was not detectable previously, before hypoxia.