Modulation of Ca2+ channels by opioid receptor antagonists in mesenteric arterial smooth muscle cells of rats in hemorrhagic shock

Effects of nociceptin and nocistatin on uterine contraction

The presence and effects of nociceptin (N/OFQ) and nocistatin (NST) in the central nervous system have been reasonably well described, but less data are available on their peripheral functions. Besides their presence in several peripheral organs (white blood cells, airway, liver, skin, vascular and intestinal smooth muscles, ovary, and testis), they have been found in the pregnant myometrium in both rat and human. The level of their precursor prepronociceptin is elevated in the preterm human myometrium as compared with full-term samples, whereas it gradually increases toward term in the pregnant rat uterus. Both N/OFQ and NST inhibit myometrial contractions, an effect which can be enhanced by naloxone and blocked by Ca²⁺-dependent K⁺ channel (BK(Ca)) inhibitors. Both compounds increase the myometrial cAMP level which may be responsible for the activation of this channel and subsequent intracellular hyperpolarization. NST releases calcitonin gene-related peptide from the sensory nerve ends, which explains its cAMP-elevating effect. In contrast with the nervous system, where they behave as antagonists, N/OFQ and NST are able to potentiate the uterine-relaxing effect of each other in both rat and human tissues. Further studies are required to clarify the roles of N/OFQ and NST in the regulation of the myometrial contractions and the perception of pain during delivery.

Nocistatin inhibits pregnant rat uterine contractions in vitro: roles of calcitonin gene-related peptide and calcium-dependent potassium channel

The endogenous neuropeptide nociceptin/orphanin FQ, translated from the prepronociceptin gene, exerts a contraction-inhibitory effect on the rat uterus. As nocistatin has been reported to cause functional antagonism of the pro-nociceptive effects of nociceptin, we set out to investigate its effects on the pregnant rat uterus and to elucidate its signalling pathway. The expression of prepronociceptin mRNA in the uterus and nocistatin levels in the uterus and the plasma were confirmed by RT-PCR and radioimmunoassay. The uterine levels of prepronociceptin mRNA and nocistatin were significantly increased by the last day of pregnancy, while the plasma nocistatin levels remained unchanged. In the isolated organ bath studies nocistatin inhibited the prostaglandin- and the KCl-evoked contractions in the uterus dose-dependently. This latter effect was decreased by preincubation with capsaicin. Incubation with calcitonin gene-related peptide after capsaicin treatment caused an elevation in the contraction-inhibitory effect of nocistatin. The effect of nocistatin was also decreased by the Ca(2+)-dependent K(+) channel inhibitor paxilline, against spontaneous uterine contractions. Nociceptin potentiated the action of nocistatin. Naloxone decreased the effect of nocistatin administered either alone or in combination with nociceptin. In Ca(2+)-poor environment, this effect of naloxone was suspended. Enzyme immunoassay for the uterine intracellular cAMP levels partially confirmed the results of in vitro contractility studies. We conclude that nocistatin, generated locally in the uterus, exerts an inhibitory effect, the mechanism being mediated in part by Ca(2+)-dependent K(+) channels, the elevation of cAMP levels and sensory neuropeptides.

Hemorrhagic shock-induced vascular hyporeactivity in the rat: relationship to gene expression of nitric oxide synthase, endothelin-1, and select cytokines in corresponding organs

BACKGROUND

Our previous work observed that vascular hyporeactivity to norepinephrine (NE) developed after hemorrhage and the response was not the same in the 4 arteries examined. To evaluate possible mechanisms involved, the present study investigated the gene expression of iNOS, eNOS, IL-1beta, IL-6, TNF-alpha, and endothelin-1 in the corresponding organs, and the roles of nitric oxide (NO) and endothelin (ET).

MATERIALS AND METHODS

LAnesthetized rats (n=7/time point/group) were hemorrhaged to a mean arterial pressure of 50 mmHg for 60 min. The vascular reactivity of the superior mesenteric (SMA), celiac (CA), left renal (LRA), and left femoral arteries (LFA) to NE was measured at baseline, at the end of the hypotensive period (E), and at 1, 2, and 4 h later in the three groups (hemorrhage, hemorrhage+NG-nitro-L-arginine methyl ester (L-NAME), an NO synthase inhibitor, or hemorrhage+PD142893, an ET receptor antagonist). Gene expression in ileum, left kidney, liver, and skeletal muscle was determined by quantitative RT-PCR at these times.

RESULTS

Vascular reactivity of SMA, CA, LRA, and LFA to NE decreased as much as 98% over 4 h compared with baseline. This loss of responsiveness in CA and LFA was more severe than in SMA and LRA. Gene expression of iNOS, eNOS, IL-1beta, IL-6, TNF-alpha, and endothelin-1 in the corresponding organs of select vasculatures increased markedly over baseline levels and the fold increase in mRNA levels of these enzymes and mediators in liver and skeletal muscle was higher than in ileum and left kidney. For example, at 4 h, iNOS expression was over 16-fold higher than baseline in liver and skeletal muscle, but 5- and 7-fold higher in ileum and kidney, respectively. L-NAME or PD142893 partially attenuated the decreased vascular reactivity induced by hemorrhagic shock and attenuated the changes in gene expression observed.

CONCLUSION

These findings suggest that the differential expression of NOS, cytokines, and endothelin-1 in different organs are associated with the development of vascular hyporeactivity after hemorrhagic shock and may account, at least in part, for the vascular bed diversity observed.