A newly identified peptide, proadrenomedullin N-terminal 20 peptide, induces hypotensive action via pertussis toxin-sensitive mechanisms.

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Proadrenomedullin N-terminal 20 peptide (PAMP) and adrenomedullin (AM) are novel hypotensive peptides. Although they are derived from the same gene product, proadrenomedullin, their hypotensive mechanisms are different; PAMP inhibits the release of norepinephrine from the peripheral sympathetic nerve endings, whereas AM fosters vasodilation by elevating intracellular cAMP, possibly via activation of cholera toxin-sensitive G proteins. In PC12 cells, PAMP inhibited N-type calcium channel via activation of pertussis toxin-sensitive mechanisms. To clarify the relationship between the hypotensive effect of PAMP and pertussis toxin-sensitive mechanisms, we administered pertussis vaccine intraperitoneally into rats for 3 consecutive days. By using mesenteric artery preparation, we showed that PAMP's ability to decrease norepinephrine overflow was significantly attenuated in pertussis toxin-treated rat (-18.5 +/- 6.9%; P<.05 versus control rats). In electrically stimulated pithed rat, PAMP (20 and 40 nmol/kg) showed a hypotensive effect (-13 +/- 5 and -18 +/- 7 mm Hg, respectively; P<.05, P<.01), whereas in pertussis vaccine-treated rat it did not (-2 +/- 3 and -8 +/- 9 mm Hg, respectively; P=NS). Also, in pithed rat, plasma norepinephrine level was significantly elevated by electrical stimulation in both control (0.323 +/- 0.035 ng/mL) and pertussis vaccine-treated groups (0.355 +/- 0.079 ng/mL). After injection of PAMP (40 nmol/kg), plasma norepinephrine level significantly decreased in the control group (0.225 +/- 0.044 ng/mL; P<.01) but not in the pertussis vaccine-treated group (0.392 +/- 0.021 ng/mL; P=NS). Moreover, in conscious rats, intravenous administration of PAMP (40 nmol/kg) did not evoke hypotension after pertussis vaccine treatment, although untreated controls had significantly decreased arterial pressure (-5 +/- 2 versus -20 +/- 3 mm Hg; P<.01). In contrast to PAMP, the administration of AM (1 nmol/kg) significantly reduced the blood pressure of pertussis vaccine-treated as well as control rats (-20 +/- 5 versus -18 +/- 7 mm Hg; P=NS). These results demonstrate that the ability of PAMP to inhibit norepinephrine release from peripheral sympathetic nerve endings and to decrease blood pressure is pertussis toxin sensitive. Our findings thus suggest that despite being derived from the same gene, PAMP and AM apparently produce hypotension by activating different signaling pathways.