Developmental and stress induced changes in peptide and catecholamine content of the paraaortic paraganglia
Abstract: The paraaortic body (PAB) is the largest extra-adrenal paraganglion and during the perinatal period it contains a substantial amount of catecholamines (CAs). The PAB also contain peptides, whose function in the PAB is not clear. The main object of this thesis was to examine peptides in the PAB, to describe their perinatal development and response to different stimuli. The effect of tumor transition on the expression of peptides was also studied. Enkephalin- (ENK), galanin- (GAL), and neuropeptide Y- (NPY) like immunoreactivities (LI) were demonstrated in paraganglion cells as well as in adrenal medullary cells of fetal or newborn animals of three species; i.e. the rabbit, guinea-pig and pig. However, NPY-LI was not detected in these cells of the pig. In addition, coexistence of NPY/GAL, NPY/ENK, and GAL/ENK was observed within the paraganglion cells of the guinea pig. The coexistence of these peptides was also demonstrated on the subcellular level, since both GAL- and NPY-LI as well as noradrenaline (NA) and adrenaline were present in the chromaffin granule fraction after ultracentrifugation of adrenal gland homogenate on a sucrose density gradient. This strongly suggests that both peptides are stored in chromaffin granules together with CAs. A higher number of peptides is expressed in paraganglion cells, which have undergone tumor transition. In a human paraganglioma, immunoreactivities to ENK, dynorphin, somatostatin, and calbindin were the most frequently expressed peptides, whereas immunoreactivities, to GAL, NPY, and cholecystokinin were less frequent. The PAB is prominent in the fetal and newborn rabbit, why this species was chosen for the subsequent developmental studies. During the perinatal period, the highest content of GAL- and NPY-LI in the rabbit PAB was found at birth and after birth both decreased. In contrast, the content of ENK-LI showed a progressive increase with age, as did the content of the CAs. This suggests that the expression of these peptides is regulated differently. In the adrenal gland, there was a progressive increase with age in the content of all peptides as well as of the CAs. At birth, the PAB content of all these peptides was higher than in the adrenal glands. This is the first report describing the perinatal development of GAL- and NPY-LI in paraganglia and, for GAL-LI, also in the adrenal gland. The PAB content of the peptides did not change in response to asphyxia, insulin-induced hypoglycemia or reserpine, with the exception of an increased content of ENK-LI by 60 minutes of asphyxia. Also in the adrenal gland, ENK-LI tended to increase after asphyxia, whereas the adrenaline content was reduced. The only peptide for which its adrenal content was reduced by insulin-induced hypoglycemia was ENK-LI. The reduction of ENK-LI was strikingly parallel to the reduction of the CAs and was significant at all times between 1.5 and 4 hours after insulin administration (20 U/kg). Reserpine (15 mg/kg) reduced the CA content in both the PAB and adrenal glands three hours after administration, whereas no change in peptide content was observed. The present results demonstrates that there is a relatively homogenous expression of peptides in the three species studied, with the exception for NPY-LI in the pig, and that these peptides can occur in the same chromaffin cells, where they can be localized within the same chromaffin granule as the CAs. During the perinatal period they appear to be regulated differently in the PAB, where the highest amounts of GAL- and NPY-LI are found at birth, whereas the PAB content of ENK-LI increases postnatally. The possible role of these peptides in the PAB has not been established, since the PAB content of these peptides was unchanged in response to all stimuli used.
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