Regulation of calcitonin gene-related peptide expression in dorsal root ganglia of rats by female sex steroid hormones

Calcitonin gene-related peptide (CGRP), a potent vasodilator primarily synt hesized in dorsal root ganglia (DRG) neurons, has been shown to decrease va scular resistance and thus regulate blood flow to a variety of organs in ra ts. Serum CGRP levels in the human have been reported to increase with preg nancy and decrease postpartum. It has been suggested that female sex steroi d hormones play a role in cardiovascular function, but the mechanisms are u nknown. In this study, we examined the effects of estradiol-17 beta (E-2) a nd progesterone (P-4) on the expression of CGRP in DRG in adult rats both i n vivo and in vitro. Ovariectomized (ovx) animals were injected s.c. with 5 mu g E-2, 4 mg P-4, or 5.01 mu g E-2 + 4 mg P-4 in 0.5 ml sesame oil or wi th oil only, and groups of 4 rats were killed at 0, 24, or 48 h. DRGs were then removed and analyzed for CGRP mRNA and immunoreactive (i-)CGRP content by Northern blotting and RIA, respectively. Primary cultures of DRG neuron s from adult female rats were used to assess the effects of varying doses o f E-2 (1, 10, 100 nM), P-4 (10, 100, 1000 nM), or E-2 (10 nM) + P-4 (100 nM ) in the absence or presence of nerve growth factor (NGF; 20 ng/ ml); and C GRP mRNA content in the cells and i-CGRP in the medium were quantitated at 24 or 48 h after incubation. Results of in vivo studies showed that E-2 cau sed a significant increase in CGRP mRNA at 24 h (1.8-fold) and in i-CGRP le vels both at 24 h (2.8-fold) and at 48 h (3.4-fold) in DRG of ovx rats. P-4 also stimulated expression of both CGRP mRNA and i-CGRP. In the in vitro s tudies, either E-2 or P-4 alone or the two in combination were without effe ct on CGRP expression in cultured DRG neurons at all the doses tested. Howe ver, in the presence of NGF, both CGRP mRNA and peptide levels were signifi cantly enhanced by E-2, P-4, and E-2 + P-4 in a time-dependent (2.0- to 2.8 - fold at 24 h, 3.0- to 5.0-fold at 48 h) and dose-dependent manner, with m aximal effects achieved at 1.0 nM (E-2) and 100 nM (P-4) at 24 h of incubat ion. In summary, both E-2 and P-4, either alone or in combination, stimulat e CGRP peptide synthesis in DRG neurons through increasing CGRP mRNA. The e ffects of these steroid hormones are mediated through amplifying the NGF-in duced synthesis of CGRP in these neurons. Thus, we propose that the cardiov ascular functions of female sex steroid hormones may be mediated, at least in part, by the up-regulation of neuronal CGRP synthesis, via NGF-mediated mechanisms.