CALCITONIN-GENE-RELATED PEPTIDE IS A DEPRESSOR IN N-G-NITRO-L-ARGININE METHYL ESTER-INDUCED HYPERTENSION DURING PREGNANCY

Inhibition of nitric oxide production with N-G-nitro-L-arginine methyl ester (L-NAME) increases blood pressure and fetal mortality in pregna nt rats. We previously reported that administration of calcitonin gene -related peptide (CGRP) reduces the blood pressure and fetal death pro duced by L-NAME. To determine the hemodynamic role of endogenous CGRP in this setting, CGRP(8-37), a CGRP receptor antagonist, was used. In addition, CGRP mRNA and peptide levels were determined in dorsal root ganglia. L-NAME or control rats had intravenous (for drug administrati on) and arterial (for continuous mean blood pressure monitoring) cathe ters surgically placed and were studied in the conscious unrestrained state. Baseline blood pressure was higher in the L-NAME than the contr ol rats on days 19, 20, and 21 or pregnancy and postpartum day 1. Vehi cle administration did not change blood pressure in any group, and CGR P(8-37) (100 mu g) did not change blood pressure in control groups. Ho wever, CGRP(8-37) administration to the L-NAME rats further increased blood pressure (P<.05) on days 19 (8+/-1), 20 (12+/-2), and 21 (7+/-1) of gestation but was without effect on postpartum day 1. Furthermore, CGRP mRNA or peptide levels in dorsal root ganglia were not different between the L-NAME and control rats at any of the time points studied . These data indicate that in experimental preeclampsia, CGRP is playi ng a compensatory vasodilator role to attenuate the elevated blood pre ssure. The mechanism of this effect appears to be an enhanced vascular responsiveness to CGRP that is attenuated after the birth of pups.