Gestational changes in calcitonin gene-related peptide, nerve growth factor, and its receptors in rat dorsal root ganglia

In dorsal root ganglia (DRG) cell cultures, levels of calcitonin gene-relat ed peptide (CGRP) are increased in the presence of ovarian hormones and ner ve growth factor (NGF). In addition, injection of ovariectomized rats with ovarian hormones led to an increase in levels of two NGF receptors, TrkA an d p75(NTR), in DRG. Thus, we hypothesized that increased levels of ovarian hormones during pregnancy may elevate the synthesis of CGRP and NGF recepto rs in the DRG. DRG harvested from rats on specific days of pregnancy, on Da y 2 postpartum, and after ovariectomy were subjected to radioimmunoassay, W estern blot analysis, and NGF immunoassay to determine levels of CGRP, TrkA and p75NTR, and NGF, respectively. CGRP levels in rat DRG were significant ly higher during pregnancy than at Day 2 postpartum or in ovariectomized ra ts. Levels of both TrkA and p75NTR in DRG increased during pregnancy and re mained elevated at Day 2 postpartum, but CGRP levels declined. Levels of NG F reached a statistically significant peak at Day 18 of gestation, and were not significantly reduced at Day 2 postpartum. Increased levels of ovarian steroid hormones during pregnancy may be involved in the synthesis of CGRP , however, the postpartum decreases in CGRP synthesis appear to be unrelate d to NGF and its receptors.