Role of the activation of the nuclear enzyme poly(ADP-ribose) polymerase in the pathogenesis of periodontitis.

We have investigated the role of the activation of nuclear poly(ADP-ribose) polymerase (PARP) enzyme, a mediator of downstream nitric oxide toxicity, using a combined approach of pharmacological inhibition and genetic disruption in a ligature-induced-periodontitis model in rats and mice. Immunohistochemical analysis revealed significantly increased poly(ADP-ribose) nuclear staining (indicative of PARP activation) in the subepithelial connective tissue of the ligated side compared with the non-ligated side. Ligation-induced periodontitis resulted in marked plasma extravasation in the gingivomucosal tissue and led to alveolar bone destruction compared with the non-ligated side, as measured by the Evans blue technique and by videomicroscopy, respectively. PARP inhibition with PJ34, as well as genetic PARP-1 deficiency, significantly reduced the extravasation and the alveolar bone resorption of the ligated side compared with controls. Thus, PARP activation contributes to the development of periodontal injury. Inhibition of PARP may represent a novel host response modulatory approach for the therapy of periodontitis.

Interactions between the endothelium-derived relaxing factor/nitric oxide system and the endogenous opiate system in the modulation of cerebral and spinal vascular CO2 responsiveness.

The role of the L-arginine-nitric oxide (NO) system, the role of the endogenous morphine-like substances (endorphins), and the possible interaction between these two systems in the modulation of regional cerebral and spinal CO2 responsiveness was investigated in anesthetized, ventilated, normotensive, normoxic cats. Regional cerebral blood flow was measured with radiolabeled microspheres in hypocapnic, normocapnic, and hypercapnic conditions in nine individual cerebral and spinal cord regions. General opiate receptor blockade by 1 mg/kg naloxone intravenously alone or NO synthase blockade by 3 mg/kg N(omega)-nitro-L-arginine-methyl ester (L-NAME) intravenously alone caused no changes in regional CO2 responsiveness. Combined administration of these two blocking agents in the very same doses, however, resulted in a strong potentiation, with a statistically significant reduction of the CO2 responsiveness observed. Separation of the blood flow response to hypercapnia and hypocapnia indicates that this reduction occurs only during hypercapnia. Specific mu and delta opiate receptors were blocked by 0.5 mg kg(-1) IV beta-funaltrexamine and 0.4 mg kg(-1) IV naltrindole, respectively. The role of specific mu and delta opiate receptors in the NO-opiate interaction was found to be negligible because neither mu nor delta receptor blockade along with simultaneous NO blockade were able to decrease CO2 responsiveness. The current findings suggest a previously unknown interaction between the endothelium-derived relaxing factor/nitric oxide (EDRF/NO) system and the endogenous opiate system in the cerebrovascular bed during hypercapnic stimulation, with the phenomenon not mediated by mu or delta opiate receptors.

Hypercapnia stimulates prostaglandin E(2) but not prostaglandin I(2) release in endothelial cells cultured from microvessels of human fetal brain.

Hypercapnia-induced cerebral vasodilation involves prostanoids, in newborns. The source of these prostanoids, however, is not yet determined. In the present study we address the hypothesis that microvascular endothelial cells of human fetal cerebrum increase the synthesis of dilator prostanoids in response to high pCO(2). Cells were isolated from a 22-week-old human fetus. Indication of induced abortion was 46 XY-t(3,10) 3q-25 chromosome abnormality. Normocapnia or hypercapnia was performed during normoxic and normothermic conditions in the medium of the cell culture. After normocapnic or hypercapnic stimuli, the amounts of released prostaglandin E(2) and 6-keto-prostaglandin F(1alpha) (the stable metabolite of prostaglandin I(2)) were measured by radioimmunoassay. Endothelial cells cultured from human fetal brain microvessels express PGE(2) and 6-keto-PGF(1alpha) in different degrees. Hypercapnic stimulus induced a significant increase of PGE(2), while expression of 6-keto-PGF(1alpha) was not augmented by the same stimulus. PGE(2) of endothelial origin, therefore, could be a factor in the mediation of the hypercapnia-induced vasodilation in human fetuses.

Central opiate receptor blockade by naloxone impairs thalamic and hypothalamic autoregulation in the cat.

Experiments were carried out in order to determine the effects of centrally induced opiate receptor blockade on the autoregulation of the regional cerebral blood flow (rCBF, measured by the H2-gas clearance technique) of the anesthetized, ventilated cats. General opiate receptor blockade was induced by intracerebroventricularly (i.c.v) injected naloxone. Changes of teh lower limit of hypothalamic, thalamic and white matter blood flow autoregulation were studied by reducing the systemic mean arterial pressure (MAP) in a stepwise manner to 80 mmHg, 60 mmHg and 70 mmHg by hemorrhage. Centrally administered naloxone (10 microg/10 microl/kg, i.c.v) resulted in an abolishment of the autoregulatory mechanisms in the hypothalamic and thalamic regions but caused no such changes in the white matter. These observations suggest that 1.) intracerebral opiate receptors and/or central opioid peptiderg mechanisms play a significant role in the maintenance of the thalamic and hypothalamic blood flow autoregulation during hemorrhagic hypotension and 2.) the involvement of the endogenous opioid peptide system in rCBF autoregulatory mechanisms is regionally different.

Cerebrocortical and medullary blood flow changes after general opiate receptor blockade during hemorrhagic shock in cats.

The effect of centrally induced opiate receptor blockade on regional cerebral blood flow (rCBF) was studied in anesthetized, ventilated cats during the course of hemorrhagic shock. The blood flow of the medulla and the parietal cortex was measured with the H2-gas clearance technique. Hemorrhagic shock was produced by lowering the systemic mean arterial pressure to 60 mmHg for 120 min by blood withdrawal. Central opiate receptor blockade was induced by 10 micrograms/kg intracerebroventricularly (i.c.v.) injected naloxone at the 60th min of the bleeding period. Cortical blood flow showed no improvement after i.c.v. naloxone administration. Medullary blood flow, however, increased significantly and approached the pre-bleeding control flow values following central opiate receptor blockade. The results indicate involvement of endogenous opioid mechanisms in the regulation of rCBF during hemorrhage and may provide an explanation for the previously described beneficial effects of naloxone in hemorrhagic shock.

Endogenous opioid mechanisms in hypothalamic blood flow autoregulation during haemorrhagic hypotension and angiotensin-induced acute hypertension in cats.

The influence of naloxone-induced general opiate receptor blockade on hypothalamic blood flow autoregulation was investigated in anaesthetized, artificially ventilated, temperature controlled cats. In order to study the changes of the hypothalamic blood flow (H2-gas clearance technique) at the lower limit of autoregulation systemic arterial pressure was reduced in a stepwise manner to 100, 80, 60 and 40 mmHg, by haemorrhage. Autoregulatory mechanisms of the hypothalamic vessels remained effective and hypothalamic blood flow showed no significant reduction until the arterial pressure was reduced to 60 mmHg in the vehicle-treated control cats. General opiate receptor blockade by 1 mg kg-1 mL-1 i.v. injected naloxone resulted in a significant reduction of the autoregulatory capacity of the hypothalamic vessels: the blood flow followed passively the arterial pressure fall already from 100 mmHg mean arterial pressure. The effect of opiate receptor blockade on the upper limit of the autoregulation was studied during acute arterial hypertension, induced by angiotensin-II infusion (25 micrograms 0.1 mL-1 min-1 i.v.). Hypothalamic blood flow remained remarkably steady following angiotensin-II infusion in the saline-treated control animals. Naloxone pretreatment (1 mg kg-1 mL-1 i.v.), however, induced a significant downward shift of the upper limit of the autoregulation, and hypothalamic blood flow started to increase in the 125-145 mmHg arterial pressure range. The narrowing of the autoregulatory range following general opiate receptor blockade suggests an important role of endogenous opioid peptides in hypothalamic blood flow autoregulatory mechanisms both in hypotensive and in hypertensive conditions.

Regional heterogeneity and differential vulnerability of cerebral and spinal vascular CO2-responsiveness during graded haemorrhagic hypotension.

Regional inhomogeneity of cerebrovascular CO2-sensitivity as well as its changes at three different levels of standardized haemorrhagic hypotension were studied in ten distinct brain and spinal cord regions of anesthetized, ventilated cats. Regional cerebral blood flow was measured with radiolabelled microspheres in hypocapnic, normocapnic, and hypercapnic conditions, and CO2-responsiveness was determined from the equation of the slopes of the best fit regression lines to the obtained flow values. It was concluded that in normotensive, normoxic cats response of the cerebral and spinal vessels to PaCO2 alterations can be assigned to four major categories. The CO2-responsiveness of a brain region is not solely determined by the rate of its basal steady state blood flow: CO2-reactivity of the hypothalamus was significantly different from that of any other investigated regions with almost identical steady state flow values. Vulnerability of the cerebrovascular CO2-sensitivity during hypotension was different from region to region, with the vessels of the pons-medulla oblongata region being the most sensitive to haemorrhage. Reduced regional cerebral and spinal CO2-responsiveness during haemorrhage is not a consequence of a reduced L-arginine supply for nitric oxide generation since administration of an excess amount of the precursor L-arginine failed to restore the haemorrhage-induced reduction of regional CO2-sensitivity at the 60 mm Hg mean arterial pressure level.

Major role of nitric oxide in the mediation of regional CO2 responsiveness of the cerebral and spinal cord vessels of the cat.

The role of nitric oxide (NO) in the mediation of cerebrovascular CO2 responsiveness was studied in 10 distinct brain and spinal cord regions of the anesthetized, ventilated, temperature-controlled, normoxic cat. Regional CBF was measured with 15-micron radiolabeled microspheres in hypocapnic, normocapnic, and hypercapnic conditions. CO2 responsiveness of each region was determined from the equation of the best-fit regression lines to the obtained flow values. The effect of altered endothelial and/or neuronal NO synthesis on CO2 responsiveness was studied following either selective blockade of the NO synthase enzyme by N omega-nitro-L-arginine methyl ester (L-NAME; 3 or 30 mg/kg i.v.) or simultaneous administration of L-NAME (3 mg/kg i.v.) and a large dose of the NO precursor L-arginine (30 mg/kg i.v.). Blockade of NO synthesis by 30 mg/kg L-NAME resulted in a significant reduction of the steady-state regional blood flow values and in an almost complete abolition of the CO2 sensitivity in each region studied. Changes of the basal flow values as well as the reduction of the regional CO2 sensitivity were dose dependent. Hypothalamic, sensorimotor cortical, and cerebellar regions were the areas most sensitive to the NO blockade. Impaired CO2 responsiveness following NO synthase inhibition, however, was reversed in these regions by simultaneous administration of a large dose of intravenously injected L-arginine. These findings suggest a major role of nitric oxide in the mediation of regional cerebrovascular CO2 responsiveness in cats.