LOCALIZATION AND MEASUREMENT OF CORTICOSTATIN-I IN NONPREGNANT AND PREGNANT RABBIT-TISSUES DURING LATE-GESTATION

Corticostatin-I (CSI) is the most potent of the corticostatic peptides isolated from rabbit lungs and neutrophils. CSI was localized in cells by immunohistochemistry using highly specific polyclonal antisera raised against the synthetic peptide. Western blot showed a single 4-kilodalton band, indicating that the antibody employed was specific for CSI in spleen, intestine, adrenal, and lung, but no CSI band was observed in liver. CSI was localized to macrophages in spleen, adult lung, placenta, and adult duodenum. CSI was found in epithelial cells of the upper half of the villi of the small intestine, but not in the Paneth cells. In the adrenal, CSI staining was observed only in the zona fasciculata and zona reticularis, and no immunostaining was observed in kidney, liver, heart, or ovary. CSI was measured in the maternal and fetal tissues of the pregnant rabbit on days 24, 27, and 30 of gestation and in nonpregnancy tissues. First, the peptide was extracted using mild acid conditions, purified by HPLC, and then quantitated by RIA. Immunoreactive CSI was highest in lung, spleen, intestine, and adrenal. In the brain, CSI was found in higher amounts in the pituitary, hypothalamus, and thalamus, with peak values observed at 27 days gestation. The largest amounts were found in the pituitary and hypothalamus of the nonpregnant animal. Rabbit lung had large amounts of immunoreactive CSI, with rising values in both maternal and fetal lung with progressing gestation. Again, the highest amounts were found in the lung of the nonpregnant rabbit. The adrenal contained large amounts of immunoreactive CSI, and the fetal adrenal concentrations declined with progressing pregnancy, whereas the maternal adrenal values were much lower and showed a small decline at 27 and 30 days gestation. The placenta had large amounts of immunoreactive CSI, which increased with progressing gestation. In fetal and maternal plasma, there were small amounts of ACTH, which remained constant in the maternal circulation, but increased in the fetal circulation with progressing gestation. Immunoreactive CSI was present in plasma in a much higher concentration, which decreased in the fetal compartment but increased in the maternal compartment with progressing gestation. The data presented indicate that CSI is localized to a large number of tissues in the rabbit, as visualized by immunoperoxidase staining, and that in a number of tissues it is found in macrophages. After HPLC purification from tissues, CSI was measured by RIA and found in all tissues examined except liver, kidney, heart, and ovary. Large amounts were measured during gestation in a number of fetal and maternal tissues and in plasma, and the changes in concentration with advancing gestation suggest a putative physiological role for corticostatic peptides during pregnancy.