Plasma nociceptin/orphanin FQ levels in response to the hyperventilation test in healthy subjects

In vitro and in vivo studies demonstrated that nociceptin/orphanin FQ inhibits norepinephrine release, while the effects of norepinephrine on nociceptin/orphanin FQ release remain unknown. Previous studies in healthy and hypertensive subjects showed that prolonged and forced hyperventilation induces different blood pressure (BP) responses depending on changes in plasma catecholamine levels. We investigated whether the effects of hyperventilation on the sympatho-adrenergic system involve nociceptin/orphanin FQ release. Fifty-six healthy subjects (26 females, mean age 63+/-2 and 30 males, mean age 63+/-3) underwent the hyperventilation test. A hierarchical cluster analysis based on BP response to hyperventilation identified three groups of subjects: group 1 (n=20) with a decrease in BP, norepinephrine (1311.1+/-45.5 fmol/ml versus 900.0+/-55.3 fmol/ml, P<0.01) and nociceptin/orphanin FQ (13.0+/-0.7 pg/ml versus 7.9+/-0.8 pg/ml, P<0.01), group 2 (n=18) without any change in BP and norepinephrine (1133.0+/-31.5 fmol/ml versus 1176.0+/-44.6 fmol/ml), with a decrease in nociceptin/orphanin FQ (12.5+/-3.2 pg/ml versus 7.4+/-0.6 pg/ml, P<0.01) and group 3 (n=18) with an increase in BP, norepinephrine (1216.7+/-50.9 fmol/ml versus 1666.7+/-44.9 fmol/ml, P<0.01) and nociceptin/orphanin FQ values (11.5+/-1.6 pg/ml versus 19.9+/-1.5 pg/ml, P<0.01). Norepinephrine changes in response to hyperventilation in groups 1 and 3 were directly (P<0.01) correlated with those of nociceptin/orphanin FQ. Our results showed that vigorous and prolonged hyperventilation changes plasma nociceptin/orphanin FQ levels due to the direct effects of hypocapnic alkalosis or to different sympatho-adrenergic system responses.