Vascular smooth muscle oxygen consumption is reversibly stimulated by sera from women with preeclampsia

Vasoactive diadenosine polyphosphates in human placenta: possible candidates in the pathophysiology of pre-eclampsia?

BACKGROUND

One hypothesis of the pathophysiology of pre-eclampsia is that placentally derived, yet unidentified, vasoactive factors are released into the maternal circulation, causing hypertension.

OBJECTIVE

To determine if diadenosine polyphosphates, new potent vasoconstrictors, are present in human placenta.

METHODS AND RESULTS

Human placental tissue was homogenated and fractionated by size-exclusion chromatography, affinity chromatography, anion-exchange chromatography and reversed-phase chromatography. In fractions purified to homogeneity, diadenosine diphosphate, diadenosine triphosphate, diadenosine tetraphosphate, diadenosine pentaphosphate, diadenosine hexaphosphate and diadenosine heptaphosphate were identified by matrix-assisted laser desorption/ionization mass spectrometry, retention-time comparison and enzymatic cleavage analysis.

CONCLUSIONS

The presence of diadenosine polyphosphates in human placenta makes them possible candidates for involvement in the pathophysiology of pre-eclampsia. However, their contribution to the pathophysiology of eclampsia requires substantiation in further studies.

Oxidative degradation of bilirubin produces vasoactive compounds

Subarachnoid haemorrhage is often followed by haemolysis and concomitant oxidative stress, and is frequently complicated by pathological vasoconstriction or cerebral vasospasm. It is known that upregulation of haem oxygenase (HO-1) is induced by oxidative stress and results in release of biliverdin and bilirubin (BR), which are scavengers of reactive oxygen species (ROS). Here we report biomimetic studies aimed at modelling pathological conditions leading to oxidative degradation of BR. Oxidative degradation products of BR, formed by reaction with hydrogen peroxide (an ROS model system), demonstrated biological activity by stimulating oxygen consumption and force development in vascular smooth muscle from porcine carotid artery. Analogous biological activity was observed with vasoactive cerebrospinal fluid from subarachnoid haemorrhage patients. Three degradation products of BR were isolated: two were assigned as isomeric monopyrrole (C9H11N2O2) derivatives, 4-methyl-5-oxo-3-vinyl-(1, 5-dihydropyrrol-2-ylidene)acetamide and 3-methyl-5-oxo-4-vinyl-(1, 5-dihydropyrrol-2-ylidene)acetamide and the third was 4-methyl-3-vinylmaleimide (MVM), a previously isolated photodegradation product of biliverdin. Possible mechanisms of oxidative degradation of BR are discussed. Tentative assignment of these structures in the cerebrospinal fluid (CSF) of cerebral vasospasm patients has been made. It is proposed that one or more of the degradation products of biliverdin or bilirubin are involved in complications such as vasospasm and or pathological vasoconstriction associated with haemorrhage.

The effects of placental extracts from normotensive and preeclamptic women on vasoconstriction and oxidative metabolism

OBJECTIVE

A circulating factor derived from the placenta has been implicated in the pathogenesis of preeclampsia. The aim of this study was to determine whether placental extracts from normotensive women and women with preeclampsia increase oxidative metabolism and histamine-induced vasoconstriction in porcine carotid artery.

STUDY DESIGN

Placental extracts from normotensive women and women with preeclampsia were applied to porcine carotid artery, and oxidative metabolism was measured. Histamine-induced isometric force responses were also determined in the absence and presence of placental extracts.

RESULTS

Application of placental extracts to porcine carotid artery caused a fall in oxygen tension, which reflects increased consumption. Extracts from placentas taken from women with preeclampsia caused a greater fall than those from normotensive women (0.117 +/- 0.026 vs 0.018 +/- 0.0024 micromol oxygen per milligram; P < or =.01). Histamine-induced contractions were potentiated by extracts from preeclampsia but not from those of women without hypertension. The maximal steady-state force values were 13,137 +/- 3647, 12,921 +/- 3684, and 21,673 +/- 7189 N/m(-2) for control, normotensive, and preeclamptic samples at 10-micromol/L histamine (P < or =.05, compared with control placental extracts).

CONCLUSIONS

Placental extracts from women with preeclampsia cause a greater stimulation of porcine artery oxygen consumption and exacerbation of histamine-induced vasoconstriction than extracts from normotensive women.

The presence of an extractable substance in the CSF of humans with cerebral vasospasm after subarachnoid haemorrhage that correlates with phosphatase inhibition

The cellular events leading to cerebral vasospasm after subarachnoid haemorrhage are poorly understood, although an increase in smooth muscle myosin light chain phosphorylation has been observed. This study set out to determine if phosphatase inhibition may be involved in the pathological maintenance of tension observed during vasospasm. We found that 1 nM okadaic acid, a type 2A protein phosphatase inhibitor, elicited an increase in rate of O(2) consumption in the porcine carotid artery similar to that by cerebrospinal fluid (CSF) from vasospastic patients (CSF(V), n=5) (control 0.23+/-0.03, CSF(V) 0.84+/-0.16 and okadaic acid 0.85+/-0.02 micromol min(-1) g dwt(-1)). It was also observed that phosphatase inhibition with 1 nM okadaic acid significantly slowed relaxation after a stretch in a similar fashion to CSF(V) haemorrhage. CSF from vasospastic subarachnoid haemorrhage patients, but not from those without vasospasm, contains an extractable substance which modulates myosin light chain phosphorylation in vitro. A phosphatase preparation obtained from the porcine carotid artery dephosphorylated 63+/-2% of the phosphorylated (MLC(20)) substrate in vitro, and non-vasospastic CSF treated enzyme dephosphorylated 60+/-2.6%. Okadaic acid inhibited phosphatase dephosphorylated only 7.5+/-1% of the substrate where CSF(V) treated enzyme dephosphorylated 22+/-2.8% of the substrate. We conclude that inhibition of smooth muscle phosphatase may be involved in the mechanisms associated with cerebral vasospasm after subarachnoid haemorrhage.

The effects of anti-hypertensive therapy on the structural, mechanical and metabolic properties of the rat aorta

The vascular system exhibits altered growth, calcium responses and metabolism during hypertension. To relate such changes, we compared histological, tension and metabolic responses in the aorta from 32-week-old spontaneously hypertensive rats (SHRs), normotensive Wistar-Kyoto (WKY) rats, and SHRs treated with Verapamil (V) and ACE-inhibitor, Trandolapril (T) as well as a combination of the two treatments (C). Vascular hypertrophy was apparent in the SHRs. Contractile responses induced by 50 mmol/1 KCl and 2.5 mmol/1 Ca2+ were significantly lower in the SHR (64.4 mN/mm2 vs. 49.2 mN/mm2), but an associated increase in Ca2+ -sensitivity (EC50 of extracellular Ca2+ (mumol/1): SHR, 456 vs. WKY, 616) normalised tension generating ability. All treatments led to significant decreases in blood pressure, although only T and C treated animals became normotensive with concomitant normalisation of vascular hypertrophy. An increase in oxygen consumption was apparent in the SHR aorta, which was associated with significant differences in the activities of key metabolic enzymes. Anti-hypertensive treatment normalised many of the metabolic parameters, with the C therapy being the most efficacious. We conclude that the treatment of hypertension by combined therapy leads to a better normalisation of structural, contractile, and metabolic parameters in the SHR, than either treatment alone and that metabolic changes with the pathology are resolved with appropriate therapy.