Pregnancy and sex steroid hormones enhance circulating calcitonin gene-related peptide concentrations in rats

Calcitonin-gene-related peptide (CGRP) is a 37 amino acid neuropeptide synt hesized primarily in dorsal root ganglia (DRG) and distributed widely in th e perivascular nerves, suggesting that this peptide may play a role in the regulation of peripheral vascular tone, Since female sex steroid hormones h ave been implicated in the regulation of peripheral vascular tone during pr egnancy, we postulated that they may alter the concentration of CGRP in the circulation and thus modulate the increased blood flow observed during pre gnancy. In the present study, we measured changes in plasma concentrations of CGRP in non-pregnant, pregnant, and post-partum rats. Groups of ovariect omized rats were treated s.c. for 3 days either with 17 beta-oestradiol (2. 5 mu g per injection twice daily), progesterone (2 mg per injection twice d aily), or vehicle. Another group of adult, non-pregnant rats at dioestrus s tage of the oestrous cycle was also used in this study, Plasma concentratio ns of CGRP were higher (P < 0.05) in rats on day 19 of pregnancy (22.0 +/- 3.0 pmol/l) compared to that during delivery(5.0 +/- 2.0), post-partum day 2 (2.0 +/- 0.7) or in non-pregnant (4.9 +/- 1.6) state. Furthermore, in adu lt ovariectomized (6.0 +/- 0.6) rats, plasma CGRP concentrations were incre ased significantly (P < 0.05) by oestradiol (10.0 +/- 1.0), progesterone (9 .5 +/- 1.0) and oestradiol + progesterone (14.0 +/- 1.0). Thus, circulating concentrations of CGRP are elevated during pregnancy and by oestrogen and progesterone, suggesting that the elevated concentrations of CGRP may play an important role in vascular adaptations that occur during pregnancy.