Immunohistochemical demonstration of vasopressin nerve fibers in the cerebral artery

Selective cerebral vascular dysfunction in Mn-SOD-deficient mice

We tested the hypothesis that the mitochondrial form of superoxide dismutase [manganese superoxide dismutase (Mn-SOD)] protects the cerebral vasculature. Basilar arteries (baseline diameter ∼140 μm) from mice were isolated, cannulated, and pressurized to measure vessel diameter. In arteries from C57BL/6 mice preconstricted with U-46619, acetylcholine (ACh; an endothelium-dependent vasodilator) produced dilation that was similar in male and female mice and abolished by an inhibitor of nitric oxide synthase. Vasodilation to ACh was not altered in heterozygous male or female Mn-SOD-deficient (Mn-SOD+/−) mice compared with wild-type littermate controls (Mn-SOD+/+). Constriction of the basilar artery to arginine vasopressin, but not KCl or U-46619, was increased in Mn-SOD+/− mice ( P < 0.05), and this effect was prevented by tempol, a scavenger of superoxide. We also examined responses of cerebral (pial) arterioles (branches of the middle cerebral artery, control diameter ∼30 μm) to ACh in anesthetized mice using a cranial window. Responses to ACh, but not nitroprusside (an endothelium-independent agonist), were reduced ( P < 0.05) in cerebral arterioles in Mn-SOD+/− mice, and this effect was prevented by tempol. Thus these are the first data on the role of Mn-SOD in cerebral circulation. In the basilar artery, ACh produced nitric oxide-mediated dilation that was similar in male and female mice. Under normal conditions in cerebral arteries, responses to ACh were not altered but constrictor responses were selectively enhanced in Mn-SOD+/− mice. In the cerebral microcirculation, there was superoxide-mediated impairment of responses to ACh.

Vasopressin contributes to dynorphin modulation of hypoxic cerebrovasodilation

Because pial artery dilation during a 20- or 40-min hypoxic exposure was less than that observed during a 5- or 10-min exposure, stimulus duration determines the vascular response to hypoxia. Dynorphin (Dyn) modulates hypoxic pial dilation and contributes to decremented dilation during longer hypoxic exposures. This study was designed to determine whether vasopressin (VP) contributes to Dyn modulation of hypoxic pial dilation in newborn pigs equipped with a closed cranial window. Moderate (M) and severe (S) hypoxia (arterial PO2 approximately 35 and 25 mmHg, respectively) had no effect on cerebrospinal fluid VP during a 5-min exposure but increased its concentration during longer exposure periods. The VP antagonist [beta-mercapto-beta,beta-cyclopentamethylenepropionyl1,O-Me-Tyr2, Arg8]vasopressin (MEAVP) had no influence on pial dilation during the 5-min exposure but potentiated the 20- and 40-min M and S hypoxic exposure dilations: 21 +/- 2 vs. 29 +/- 3% and 23 +/- 2 vs. 33 +/- 2% for 20- and 40-min S hypoxic dilation before and after MEAVP. Topical VP during 5 min of hypoxia elicited dilation that was reversed to vasoconstriction during 20 min of S and 40 min of M and S hypoxia. Similarly, during 5 min of hypoxia, Dyn elicited dilation that was reversed to vasoconstriction during longer hypoxic periods. MEAVP blunted this Dyn-induced vasoconstriction. These data show that VP modulates hypoxic pial dilation in a stimulus duration-dependent manner and that VP contributes to the reversal of Dyn from a dilator to a constrictor during prolonged hypoxia. Finally, these data suggest that VP contributes to Dyn modulation of hypoxic cerebrovasodilation.

A clinical review of the adaptive role of vasopressin in migraine

Vasopressin is a naturally available neuropeptide that subserves important vasomotor, antinociceptive, behavior control, fluid and electrolyte balance, platelet aggregation and blood coagulation functions. This review focuses on the clinical phenomena of migraine that are likely to influence vasopressin bioavailability or efficacy as well as the modulating influence of vasopressin itself. As part of a complex homeostatic adjustment to stress and pain, the intricacies of vasopressin metabolism may have particular relevance to the pathophysiology of migraine.

Role of endothelin in pial artery vasoconstriction and altered responses to vasopressin after brain injury

Pial artery constriction following fluid-percussion injury to the brain is associated with elevated cerebrospinal fluid (CSF) vasopressin concentration in newborn pigs. It has also been observed that fluid-percussion injury reverses the function of vasopressin from that of a dilator to a constrictor. Endothelin-1 (ET-1), a purported mediator of cerebral vasospasm, can be released by several stimuli, including vasopressin. The present study was designed to investigate the role of ET-1 in pial artery constriction and in the reversal of vasopressin from a dilator to a constrictor, which is observed after fluid-percussion injury. Brain injury of moderate severity (1.9-2.3 atm) was produced in anesthetized newborn pigs that had been equipped with a closed cranial window. Endothelin-1 elicited pial dilation at low concentrations and vasoconstriction at higher concentrations. Fluid-percussion injury reversed the process of dilation to that of constriction at the low ET-1 concentration and potentiated this constriction at high ET-1 concentrations (10% +/- 1%, -8% +/- 1%, and -15% +/- 1% vs. -6% +/- 1%, -17% +/- 1%, and -26% +/- 2% for 10(-12), 10(10),10(-8) M ET-1 before and after fluid-percussion injury, respectively). Vasopressin modestly increased CSF ET-1 concentration before fluid-percussion injury. Fluid-percussion injury markedly increased CSF ET-1 concentration and the ability of vasopressin to release ET-1 (20 +/- 2, 26 +/- 3, and 40 +/- 4 pg/ml vs. 93 +/- 6, 141 +/- 9, and 247 +/- 31 pg/ml for control, 40 pg/ml vasopressin, and 400 pg/ml vasopressin before and after fluid-percussion injury, respectively). An ET-1 antagonist, BQ 123 (10(-6) M) blunted pial artery constriction following fluid-percussion injury (146 +/- 5 microns -127 +/- 6 microns vs.144 +/- 5 microns-136 +/- 4 microns). The BQ 123 also blocked the reversal of vasopressin's function from that of a dilator to a constrictor after fluid-percussion injury (8% +/- 1%, 21% +/- 3%, and -5% +/- 1%, -14% +/- 2% vs. 8% +/- 1%, 21% +/- 2% and 4% +/- 1%, 2% +/- 1% for 40 and 4000 pg/ml vasopressin before and after fluid-percussion injury in the absence and presence of BQ 123, respectively). The BQ 123 blocked the constrictor component to ET-1, whereas it had no effect on the dilator component. These data show that ET-1 contributes to pial constriction after fluid-percussion injury. These data also indicate that vasopressin-induced release of ET-1 contributes to the reversal of vasopressin from a dilator to a constrictor following fluid-percussion injury. Furthermore, these data indicate that elevated CSF vasopressin and ET-1 interact in a positive feedback manner to promote pial artery constriction following fluid-percussion injury.

Cerebral oxygenation during cardiopulmonary resuscitation with epinephrine and vasopressin in pigs

BACKGROUND AND PURPOSE

Administration of vasopressin during cardiopulmonary resuscitation (CPR) improves vital organ blood flow compared with epinephrine, but the effect of vasopressin on cerebral oxygenation and cerebral venous hypercarbia during CPR has not previously been studied.

METHODS

Fourteen pigs were allocated to receive either epinephrine (0.2 mg/kg) or vasopressin (0.4 U/kg) after 4 minutes of ventricular fibrillation and 3 minutes of CPR. Cerebral blood flow was determined by radiolabeled microspheres, and arterial and cerebral venous blood gases were measured.

RESULTS

Cerebral blood flow, measured before and 90 seconds and 5 minutes after drug administration, was 9 (3; 12), 25 (19; 27), and 18 (10; 23) mL/min per 100 g (median and 25th and 75th percentiles, respectively) in the epinephrine group and 12 (5; 16), 51 (48; 70), and 53 (45; 63) mL/min per 100 g in the vasopressin group (P<.05 at 90 seconds, P<.01 at 5 minutes between groups). Five minutes after drug administration, cerebral venous Pco2 was 63 (59; 68) mm Hg in the epinephrine group and 47 (43; 55) mm Hg in the vasopressin group (P<.01); at the same time cerebral venous pH was 7.18 (7.17; 7.20) and 7.26 (7.22; 7.36) (P<.01) in the epinephrine and vasopressin groups, respectively. Cerebral oxygen extraction ratio, calculated before and 90 seconds and 5 minutes after drug administration, was 0.42 (0.32; 0.57), 0.47 (0.41; 0.57), and 0.56 (0.56; 0.64) in the epinephrine group and 0.43 (0.38; 0.45), 0.38 (0.25; 0.44), and 0.35 (0.33; 0.49) in the vasopressin group (P<.05 at 90 seconds and 5 minutes).

CONCLUSIONS

Compared with epinephrine, vasopressin not only increases cerebral blood flow but also improves cerebral oxygenation and decreases cerebral venous hypercarbia when administered during CPR in pigs.

Effects of vasopressin on regional cerebral blood flow in dogs

Vasopressin may regulate the regional cerebral blood flow (rCBF) via two balancing effects: increased flow from the vessels dilated by nitric oxide from the endothelium, and decreased flow from the vessels contracted by direct stimulation of smooth muscle. The effect on the rCBF in anesthetized dogs following the intracisternal or intraarterial administration of vasopressin was investigated by laser flowmetry with the device placed on the dura over the parietal cortex. The intracisternal injection of 1 nmol vasopressin significantly increased the rCBF to 145.3 +/- 27.3% of base line. In contrast, the intravertebral arterial injection of vasopressin had no significant effect on the rCBF. This can be explained by a difference in the affected vasculature; mainly large vessels in the subarachnoid space vs. whole vascular system supplied by the vertebral artery. The intracisternal injection of 10 mumol of NG-monomethyl-L-arginine (L-NMMA) reduced the rCBF; pretreatment with this agent significantly suppressed the elevation in rCBF induced by vasopressin. The intraarterial injection of L-NMMA reduced the rCBF more than its intracisternal administration. It also suppressed the rCBF induced by vasopressin.

Differing effects of vasopressin on regional cerebral blood flow of dogs following intracisternal vs. intra-arterial administration

We investigated the differential effect of the intracisternal and intraarterial administration of vasopressin on the regional cerebral blood flow (rCBF) in the parietal cortex of dogs. Regional CBF, velocity and blood volume were assayed by laser flowmetry. The intracisternal injection of 1 nmol vasopressin significantly increased the rCBF and velocity, without affecting blood volume. However, the intravertebral arterial injection of 1 nmol vasopressin significantly decreased the rCBF and velocity. This discrepancy can be explained by a difference in the affected vasculature; large blood vessels in the subarachnoid space vs. whole cerebral vascular system. The intracisternal and intraarterial injection of the nitric oxide inhibitor NG-monomethyl-L-arginine reduced the rCBF from the base line, and significantly suppressed the rCBF elevation induced by vasopressin. The effect of vasopressin may be considered as the summation of the increased flow from the dilated large vessels via the release of nitric oxide from the endothelium, and of the decreased flow from the contracted small vessels.

Regional differences in the vasodilator response to vasopressin in canine cerebral arteries in vivo

BACKGROUND AND PURPOSE

The aim of this study was to investigate the regional differences in the in vivo vasodilator responses to vasopressin, which is thought to stimulate the release of nitric oxide from the endothelium, in canine cerebral arteries by angiography.

METHODS

Angiograms were performed through a catheter inserted directly into the right vertebral artery and were taken periodically after the infusion of vasopressin. The diameters of various segments of the major arteries were measured using a computerized image analysis system.

RESULTS

The bolus administration of vasopressin (10 pmol to 1 nmol) into the vertebral artery produced a long-lasting, dose-dependent vasodilation in the major cerebral arteries centering around the circle of Willis. One nanomole of vasopressin appeared to be the optimal dose for producing maximal vasodilation. The internal diameters of the basilar, posterior communicating, and internal carotid arteries experienced the most dilation (approximately 150% that of control) 2 minutes after the infusion of 1 nmol of vasopressin, followed by those of the middle cerebral, the intracranial portion of the vertebral, and the anterior spinal arteries (approximately 130% that of control). The extracranial portion of the vertebral artery (109.8 +/- 4.8% that of control, n = 4) was less sensitive to 1 nmol of vasopressin. Pretreatment with an intracisternal injection of 10 mumol of NG-monomethyl L-arginine suppressed the vasodilator effect of vasopressin and substance P, whereas it did not affect the response to vasoactive intestinal peptide.

CONCLUSIONS

These results suggest that the arteries composing the circle of Willis at the base of the brain are more sensitive to nitric oxide release induced by vasopressin compared with other intracranial and extracranial arteries.

Role of nitric oxide in the cerebral vasodilatory responses to vasopressin and oxytocin in dogs

We angiographically assessed the vasodilatory effects of vasopressin and oxytocin on the basilar arteries in dogs. Intracisternal bolus injections of vasopressin (100 pmol and 1 nmol) and oxytocin (1 and 10 nmol) produced dose-dependent increases in the internal diameter of the basilar arteries without affecting mean arterial blood pressure. The maximal dilatations of the basilar arteries induced by 1 nmol vasopressin and 10 nmol oxytocin were 142.3 +/- 19.9 and 136.8 +/- 25.5% of the baseline, respectively. When the same peptides were injected into the vertebral artery, the maximal dilatations were similar, but the duration of response was shorter. Pretreatment with intracisternal injection of 10 mumol NG-monomethyl-L-arginine (L-NMMA), which inhibits the synthesis of nitric oxide from L-arginine, suppressed the vasodilatory responses induced by intracisternal injection of vasopressin and oxytocin and by intraarterial injection of vasopressin. Calcitonin gene-related peptide also caused dilatation of the basilar artery when injected into the cisterna magna, but its effect was not blocked by L-NMMA. L-NMMA reduced the basal diameter of the basilar artery in a dose-dependent manner; L-arginine produced dose-dependent increases in diameter. The vasoconstriction induced by L-NMMA was reversed by high concentrations of L-arginine. These results suggest that vasopressin and oxytocin dilate the basilar arteries via the release of nitric oxide from both the intraluminal and the extraluminal sides and that synthesis and release of nitric oxide in the vascular wall contribute to maintenance of basal vascular tonus.

Triphasic response of rat intracerebral arterioles to increasing concentrations of vasopressin in vitro

To determine how vasopressin affects the vascular tone of the smaller cerebral arterioles, we carried out an in vitro study of isolated and cannulated intracerebral arterioles of rats. We found that increasing concentrations of vasopressin induced a triphasic response of vasodilation (10(-12)-10(-11) M), vasoconstriction (10(-10)-10(-8) M), and vasodilation stabilizing to control diameter (10(-7)-10(-6) M) and that the maximum constriction was twice the maximum dilation in these smaller arterioles [21.2 +/- 13.1% (mean +/- SD) decrease in diameter vs. 11.2 +/- 5.7% increased]. Pretreatment of the arterioles with NG-monomethyl-L-arginine (10(-4) M), a specific inhibitor of endothelium-derived relaxing factor, abolished the vasopressin-induced vasodilation and significantly increased the vasoconstriction. These results suggest that these arterioles were maintained in a dilated state by an endothelium-derived relaxing factor activated by vasopressin. Both vasodilation and vasoconstriction were found to be mediated through vasopressin V1 receptors in a study of arterioles pretreated with d(CH2)5Tyr(Me)arginine vasopressin (10(-6) M), a vasopressin V1 receptor antagonist. These results support the hypothesis that vasopressin may constrict smaller cerebral arterioles while simultaneously dilating larger cerebral arteries. Our results also suggest that vasopressin may aggravate cerebral ischemia in pathological conditions, such as subarachnoid hemorrhage, when the arteriolar response to vasopressin shifts from vasodilation to vasoconstriction due to increased vasopressin levels in plasma and CSF and impaired endothelium-derived relaxation.

Effects of vasopressin and oxytocin on canine cerebral circulation in vivo

In vivo experiments on the vasoactive effects of vasopressin and oxytocin on cerebral circulation were carried out in anesthetized dogs, using an electromagnetic flowmeter to measure vertebral blood flow and angiography to measure the internal diameter of the basilar artery. Direct bolus infusion of 1 pmol to 1 nmol of vasopressin or 10 pmol to 10 nmol of oxytocin into a femoral-vertebral artery shunt produced a dose-dependent decrease in vertebral artery blood flow without significantly affecting mean arterial blood pressure. Vasopressin was more potent than endothelin and neuropeptide Y, which have also been demonstrated to induce long-lasting decreases in vertebral artery blood flow. However, direct bolus infusion of vasopressin (100 pmol and 1 nmol) or oxytocin (1 nmol and 10 nmol) into the vertebral artery dilated major vessels including the vertebral, anterior spinal, and basilar arteries, as well as the circle of Willis and its main branches, while endothelin (1 nmol) and neuropeptide Y (5 nmol) caused no change in the diameters of major cerebral arteries. The V1 antagonist d(CH2)5tyrosine(methyl) arginine vasopressin suppressed the effects of both vasopressin and oxytocin. Vasopressin was over 10 times as potent as oxytocin in both assays. The vasodilatory effect of vasopressin, which may be mediated by an endothelium-dependent mechanism, was functionally damaged in dogs after experimental subarachnoid hemorrhage. These data suggest regional differences in the sensitivity and responsiveness of vasculature to vasopressin and oxytocin, and specifically that both peptides act through V1 receptors to decrease the resistance of large vessels and increase the resistance of small vessels.

Autotransplantation of peripheral cholinergic neurons into the brains of Alzheimer model rats

Current hypotheses regarding Alzheimer's disease implicate cholinergic function. In this study, peripheral cholinergic neurons in the vagal nodosal ganglion were transplanted into the brains of Alzheimer model rats. Eighteen Sprague-Dawley strain rats were divided into three groups: 1) unoperated control rats, 2) rats that had undergone bilateral destruction of the nucleus basalis of Meynert (NBM) (Alzheimer model), and 3) the transplantation group in which the vagal nodosal ganglion was transplanted into the cerebral neocortex one week after the bilateral destruction of the Meynert nucleus. Seven weeks after the transplantation rat behaviour was assessed using psychological tests (spontaneous activity, passive avoidance response and the Hebb-Williams maze test). The Alzheimer model rats had a statistically significant increase in spontaneous activity in comparison with controls (P less than 0.01). The transplant rats showed some amelioration of this abnormal increase in spontaneous activity observed in the Alzheimer model rats. All of the control rats showed conditioned passive avoidance responses, while only one Alzheimer model rat retained is shocked-conditions behaviour before 24 hours (P less than 0.01). Three of the six transplanted rats showed complete improvement in the passive avoidance response test. In the Hebb-Williams maze test, the rats with NMB lesions made more errors than the control rats. The transplanted rats had a lower number of errors than NBM-lesioned rats but still more than the controls. Histological examination revealed many cholinergic cells in the transplanted tissue, especially in the area adjacent to the cerebral cortical surface. The present results indicate that autotransplantation of peripheral cholinergic cells ameliorates abnormal behaviour in Alzheimer model rats.

Blood-brain transfer of L-phenylalanine declines after peripheral but not central nervous administration of vasopressin

To determine whether a previously reported effect of vasopressin on blood-brain transfer of leucine extends to other large neutral amino acids, we measured the regional blood-brain transfer of L-phenylalanine with the integral technique. Intravenous co-injection of L-phenylalanine and arginine vasopressin (30 nmol to 10 pmol) resulted in a decrease of the permeability-surface area (PaS) product of phenylalanine of between 11 and 39%. In addition, the peptide elicited a decrease of the cerebral blood flow of between 11 and 56% combined with a drastic decrease of the cardiac output (32-64%) and an elevation of the blood pressure to approximately 150% of control values. However, we found no changes of the cardiac output, the blood pressure, or the PaS product of phenylalanine after microdialysis (30 min, 5 microliters min-1) of arginine vasopressin (15 mumol L-1) into the dorsal hippocampus, but cerebral blood flow was decreased. The results support the hypothesis that arginine vasopressin receptors at the blood-brain barrier are involved in the regulation of large neutral amino acid transfer from blood to brain and indicate that these receptors are located at the luminal membrane of the endothelial cells.