Regulation of Calcitonin Gene-Related Peptide Expression in Dorsal Root Ganglia of Rats by Female Sex Steroid Hormones1

Abstract

Calcitonin gene-related peptide (CGRP), a potent vasodilator primarily synthesized in dorsal root ganglia (DRG) neurons, has been shown to decrease vascular resistance and thus regulate blood flow to a variety of organs in rats. Serum CGRP levels in the human have been reported to increase with pregnancy and decrease postpartum. It has been suggested that female sex steroid hormones play a role in cardiovascular function, but the mechanisms are unknown. In this study, we examined the effects of estradiol-17beta (E(2)) and progesterone (P(4)) on the expression of CGRP in DRG in adult rats both in vivo and in vitro. Ovariectomized (ovx) animals were injected s.c. with 5 microg E(2), 4 mg P(4), or 5.0 microg E(2) + 4 mg P(4) in 0.5 ml sesame oil or with 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 neurons from adult female rats were used to assess the effects of varying doses of 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 CGRP 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) caused a significant increase in CGRP mRNA at 24 h (1.8-fold) and in i-CGRP levels 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 studies, either E(2) or P(4) alone or the two in combination were without effect on CGRP expression in cultured DRG neurons at all the doses tested. However, in the presence of NGF, both CGRP mRNA and peptide levels were significantly 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 maximal effects achieved at 1.0 nM (E(2)) and 100 nM (P(4)) at 24 h of incubation. In summary, both E(2) and P(4), either alone or in combination, stimulate CGRP peptide synthesis in DRG neurons through increasing CGRP mRNA. The effects of these steroid hormones are mediated through amplifying the NGF-induced synthesis of CGRP in these neurons. Thus, we propose that the cardiovascular 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.

Increased levels of calcitonin gene-related peptide in serum accelerate fracture healing following traumatic brain injury

“…Numerous studies confirm the involvement of CGRP in the bone metabolism and pathophysiology of brain damage (4,5). Osteoblastic cells are equipped with receptors of CGRP, and cyclic adenosine monophosphate (cAMP) production in human osteoblastic cells can be enhanced by CGRP by as much as 30-50-fold (17), leading to changes in cell morphology and function.…”

“…CGRP is also capable of inhibiting bone resorption in vitro and inducing hypocalcemia in vivo (4). Moreover, during hematencephalon formation, the secretion of CGRP markedly increases (5), indicating that CGRP may be released directly by the injured brain tissue. The present study aimed to determine whether CGRP is one of the unidentified humoral factors that cause enhanced osteogenesis in patients with TBI and to identify the downstream pathway that is activated by increased CGRP expression.…”

Up-regulation of calcitonin gene-related peptide receptors underlying elevation of skin temperature in ovariectomized rats

“…In the present study, the endogenous CGRP level in the circulation was significantly lower in OVX rats than in sham-operated rats, suggesting that ovarian hormone deficiency following ovariectomy decreases the plasma CGRP level. It has been reported that both estrogen and progesterone, which are ovarian hormones, stimulate CGRP peptide synthesis in dorsal root ganglia neurons through increasing CGRP mRNA (Gangula et al 2000a). Plasma CGRP levels in rats and humans have been reported to increase with pregnancy and decrease postpartum (Stevenson et al 1986, Saggese et al 1990, Gangula et al 2000b.…”

Effects of 17β-Estradiol and the Japanese Herbal Medicine Keishi-bukuryo-gan on the Release and Synthesis of Calcitonin Gene-Related Peptide in Ovariectomized Rats

“…They further showed that the effects are inhibited by treatment with k252a, an inhibitor of the tyrosine kinase A (trkA), which has a high affinity for the NGF receptor, suggesting that the release of CGRP from the nerve endings is influenced by NGF. Furthermore, it has been reported that estrogen up-regulates expression of trkA mRNA in sensory neurons, where estrogen receptors and NGF receptor are co-localized (20,21). Together, these findings suggest that the number of VR-1 receptors may be decreased by attenuating the endogenous effect of NGF due to decrease in the activity of the trkA domain in the NGF receptor following estrogen deficiency with ovariectomy.…”

“…On the other hand, regarding the involvement of estrogen on CGRP synthesis in dorsal root ganglia, it is suggested that CGRP mRNA expression is up-regulated (20) or contrarily down-regulated (22) by estrogen through its receptors, although estrogen receptors obviously exist in the dorsal root ganglia (22). In addition, our present result indicated that CGRP concentrations in dorsal root ganglia and the spinal cord and the mRNA expression in the dorsal root ganglia were not affected by estrogen deficiency and estrogen replacement in OVX rats.…”