HYPOXIC ADAPTATION OF THE PEPTIDERGIC INNERVATION IN THE RAT CAROTID-BODY

The abundance of substance P (SP)-, calcitonin gene-related peptide (C GRP)-, vasoactive intestinal polypeptide (VIP)-, and neuropeptide Y (N PY)-immunoreactive nerve fibers in the carotid body was compared betwe en normoxic and chronically hypoxic rats (10% O-2 and 3.0-4.0% CO2 for 3 months). The immunoreactive fibers appeared as thin processes with many varicosities, and were distributed mainly around the vasculatures . In the normoxic control carotid body, NPY fibers were more numerous than VIP, CGRP, and SP fibers. In the chronically hypoxic rats, the ca rotid body was enlarged several fold, and the mean absolute number of VIP and NPY fibers was 3.88 and 2.22 times higher than in the normoxic carotid body, respectively, although that of SP and CGRP fibers was n ot changed. When expressed as density per unit area of the parenchyma, the density of SP and CORP fibers in the chronically hypoxic carotid body decreased significantly to under 50%, the density of VIP fibers i ncreased significantly 1.80 times, and the density of NPY fibers were unchanged. Immunoreactivity for four neuropeptides was not found in th e glomus cells of normoxic or chronically hypoxic carotid bodies. Thes e results suggest that altered peptidergic innervation of the chronica lly hypoxic carotid body is one feature of hypoxic adaptation. Because these neuropeptides are vasoactive in nature, altered carotid body ci rculation may contribute to modulation of the chemosensory mechanisms by chronic hypoxia. (C) 1998 Elsevier Science B.V. All rights reserved .