Vascular angiotensin AT1 receptor neuromodulation in fetal programming of hypertension.

Fetal stress increases the susceptibility to cardiovascular diseases in adult age, including hypertension, a process known as fetal programming of hypertension (FPH). This study intends to investigate the interplay between vascular sympathetic nervous system (SNS) and RAS, namely the neuromodulatory role exerted by Angiotensin II (Ang II) receptor-1 (AT1) in FPH, and respective contribution for hypertension. METHODS: 6-month old Sprague-Dawley offspring from mothers fed ad-libitum (CONTROL) or with 50% intake during the second half of gestation (maternal undernutrition, MUN) were used. Sympathetic neurotransmission was studied in mesenteric/tail arteries and mesenteric veins by electrically-evoked [3H]-noradrenaline release experiments using RAS drugs. AT1 receptors in sympathetic nerves of mesenteric arteries were investigated by immunohistochemistry and Laser Scanning Confocal Microscopy. RESULTS: Ang II facilitated noradrenaline release in the vessels studied from MUN and CONTROL rats. Losartan induced a tonic facilitation only in MUN vessels. Sympathetic innervation was larger in MUN versus CONTROL vessels. AT1 receptors on sympathetic nerves were present in higher amounts in MUN versus CONTROL vessels. CONCLUSIONS: Findings support that FPH is associated with a vascular hyper-sympathetic activation, involving a tonic facilitation of prejunctional AT1 receptors by endogenous Ang II, which can justify, at least in part, the development of hypertension.

Effect of fetal undernutrition and postnatal overfeeding on rat adipose tissue and organ growth at early stages of postnatal development.

Intrauterine and perinatal life are critical periods for programming of cardiometabolic diseases. However, their relative role remains controversial. We aimed to assess, at weaning, sex-dependent alterations induced by fetal or postnatal nutritional interventions on key organs for metabolic and cardiovascular control. Fetal undernutrition was induced by dam food restriction (50 % from mid-gestation to delivery) returning to ad libitum throughout lactation (Maternal Undernutrition, MUN, 12 pups/litter). Postnatal overfeeding (POF) was induced by litter size reduction from normally fed dams (4 pups/litter). Compared to control, female and male MUN offspring exhibited: 1) low birth weight and accelerated growth, reaching similar weight and tibial length by weaning, 2) increased glycemia, liver and white fat weights; 3) increased ventricular weight and tendency to reduced kidney weight (males only). Female and male POF offspring showed: 1) accelerated growth; 2) increased glycemia, liver and white fat weights; 3) unchanged heart and kidney weights. In conclusion, postnatal accelerated growth, with or without fetal undernutrition, induces early alterations relevant for metabolic disease programming, while fetal undernutrition is required for heart abnormalities. The progression of cardiac alterations and their role on hypertension development needs to be evaluated. The similarities between sexes in pre-pubertal rats suggest a role of sex-hormones in female protection against programming.

MAO activity in serotonergic endings of rat major cerebral arteries.

The present work studies the existence of monoamine oxidase (MAO) activity in serotonergic endings present in rat major cerebral arteries. Enzymatic activity was appraised in vivo by serotonin (5-HT) accumulation or 5-hydroxyindole acetic acid (5-HIAA) disappearance with time after systemic administration of MAO inhibitors. Pargyline (75 mg/Kg, ip) brought about significant 5-HT increase and 5-HIAA decrease in major cerebral arteries 30 and 60 min after its administration. Clorgyline (75 mg/Kg, ip) also induced 5-HT enhancement and 5-HIAA decline in these arteries 30 and 60 min after its injection. However, treatment with deprenyl (75 mg/Kg, ip) only evoked a significant 5-HT increase at 60 min. When either clorgyline (5 mg/Kg, ip) or deprenyl (5 mg/Kg, ip) were administered 5-HT and 5-HIAA levels remained unaffected. Two weeks after performing electrolytical lesion of dorsal raphe nucleus and 60 min after clorgyline (75 mg/Kg, ip) injection 5-HT and 5-HIAA levels appeared significantly reduced in cerebral arteries and striatum when compared to sham-lesioned controls. These results suggest that MAO-A isoform acting on endogenous 5-HT is present in rat major cerebral arteries and is located in nerve endings of fibers arising from dorsal raphe nucleus.

Local treatments of dorsal raphe nucleus induce changes in serotonergic activity in rat major cerebral arteries.

BACKGROUND AND PURPOSE: Rat major cerebral arteries seem to receive serotonergic fibers originating from the dorsal raphe nucleus (DRN), but little is known about their function. The aim of our present work was to establish a functional relationship between this brain stem nucleus and the cerebral blood vessels by studying the effects of several treatments in the DRN on cerebrovascular serotonergic activity. METHODS: Serotonin, clomipramine, 8-OH-DPAT, and WAY-100635 were administered in DRN. A stereotaxically localized electrode allowed the electrical stimulation of this brain stem nucleus. Serotonergic activity was appraised in major cerebral arteries, striatum, and hippocampus from 5-hydroxytryptophan accumulation after aromatic L-amino acid decarboxylase inhibition with NSD-1015. RESULTS: Serotonin significantly decreased serotonergic activity in major cerebral arteries and striatum without affecting it in hippocampus. This reduction was blocked by previous injection of WAY-100635 in DRN. Local administration of 8-OH-DPAT or clomipramine elicited an effect similar to that of serotonin, whereas that of WAY-100635 did not modify serotonergic activity in either of the tissues. Electrical stimulation of DRN significantly increased serotonergic activity in major cerebral arteries and striatum but not in hippocampus. CONCLUSIONS: These results confirm the presence of a serotonergic innervation in rat major cerebral arteries functionally related to DRN. 5-HT(1A) receptor activation partly mediates the action of serotonin in DRN. A serotonergic tone acting on these somatodendritic receptors was not clearly found.

Cervical gangliectomy does not affect in vitro tryptophan hydroxylase activity in rat brain base arteries.

The presence of a serotonergic innervation in rat cerebral arteries of peripheral origin was explored. Superior cervical ganglia removal did not change tryptophan hydroxylase activity measured in cell-free extracts of brain base vessels. A low enzyme activity was detected in the ganglia. These results suggest that rat cerebral arteries do not receive a serotonergic innervation from the superior cervical ganglia.

In vivo tryptophan hydroxylase activity in rat major cerebral arteries is decreased by dorsal raphe nucleus lesions.

The in vivo presence of tryptophan hydroxylase activity in rat major cerebral arteries as well as the possible origin of the structure containing it were explored. Enzyme activity was appraised by accumulation of 5-hydroxytryptophan after inhibition of aromatic L-amino acid decarboxylase. Decarboxylase inhibition evoked a significant increase in 5-hydroxytryptophan levels in rat cerebral arteries, striatum, hippocampus, hypothalamus, and plasma but had no effect on aorta. p-Chlorophenylalanine reduced 5-hydroxytryptophan accumulation in the cerebral vessels and brain nuclei, whereas alpha-methyltyrosine did not modify it except in hypothalamus, where it was enhanced. alpha-Methyltyrosine significantly reduced noradrenaline levels in cerebral arteries and L-dopa accumulation after inhibition of the decarboxylase in striatum. Dorsal raphe nucleus lesioning significantly diminished 5-hydroxytryptophan formation in cerebral arteries, striatum, and hypothalamus, without affecting it in hippocampus. Lesion of median raphe nucleus reduced 5-hydroxytryptophan accumulation in hippocampus and in hypothalamus but not in cerebral blood vessels or striatum. Superior cervical ganglia removal decreased noradrenaline levels in cerebral blood vessels without affecting 5-hydroxytryptophan accumulation. These results indicate the presence of a functionally active tryptophan hydroxylase in rat cerebral arteries associated with fibers originating from dorsal raphe nucleus. This supports that rat major cerebral arteries receive serotonergic innervation from central origin.

Different influence of superoxide anions and hydrogen peroxide on endothelial function of isolated cat cerebral and pulmonary arteries.

1. Exogenous superoxide dismutase (SOD) or catalase did not modify isolated cat middle cerebral arterial basal tone. Catalase but not SOD reduced ACh relaxation. 2. H2O2 induced endothelium-independent relaxation which was abolished by catalase. 3. 3-Amino-1,2,4-triazole (AT) evoked endothelium-dependent contractions and diminished ACh relaxation. 4. Diethyldithio carbamic acid (DETC) induced endothelium-independent relaxation and did not modify ACh vasodilatation. 5. ACh relaxation of cat isolated pulmonary arteries was unaffected by SOD, catalase or AT, and diminished by DETC. 6. Endothelial catalase but neither SOD nor superoxide anions is involved in EDRF cerebral vasodilatation and H2O2 participates in ACh relaxation. In pulmonary arteries, only endothelial SOD activity plays a role.

Serotonergic activity in rat cerebral arteries depends on dorsal raphe nucleus but not on median raphe nucleus.

The effect of Chlorimipramine and Muscimol on serotonergic activity in rat cerebral arteries and in dorsal and median raphe nuclei were used to study the presence of a serotonergic innervation in the cerebral blood vessels functionally dependent on the brainstem nuclei activity. Serotonergic activity was appraised in rat cerebral arteries from 5-hydroxyindoleacetic acid (5-HIAA) disappearance rate or 5-hydroxytryptophan (5-HTP) accumulation after inhibiting monoamine oxidase (MAO) or aromatic amino acids decarboxylase, respectively. In dorsal and median raphe nuclei the decay with time of 5-HIAA after MAO inhibition was used to estimate serotonergic activity. Chlorimipramine significantly reduced serotonergic activity in cerebral blood vessels and in both raphe nuclei. 5-HIAA basal levels in these blood vessels were not altered by treatment with the drug. Muscimol evoked only a decrease in the serotonergic activity of the median raphe nucleus. These results suggest that rat cerebral arteries receive serotonergic fibers functionally active arising mainly from dorsal raphe nucleus.

Tryptophan hydroxylase activity in rat brain base arteries related to innervation originating from the dorsal raphe nucleus.

BACKGROUND AND PURPOSE: Tryptophan hydroxylase activity was assayed in cell-free extracts of rat brain base arteries as marker of a serotonergic innervation. METHODS: Estimation of the enzymatic activity was made in untreated male Sprague-Dawley rats (n = 53) and in those who underwent destruction of the dorsal and median raphe nuclei (n = 10). RESULTS: Tryptophan hydroxylase activity was measured in rat cerebral arteries. The time-dependent 5-hydroxytryptophan production was undetectable in the absence of tryptophan or 6-methyltetrahydropterine and in the presence of 6-fluorotryptophan, and it was significantly reduced in the presence of p-chlorophenylalanine. Destruction of the dorsal raphe nucleus but not the median raphe nucleus brought about a significant reduction in enzyme activity. CONCLUSIONS: These results suggest that rat cerebral arteries receive a serotonergic innervation arising from the dorsal raphe nucleus.

Effects of L-arginine analogues in isolated cat cerebral arteries.

The possible contribution of nitric oxide (NO) to the endothelium-dependent relaxation of isolated cat cerebral arteries was studied by examining the effects of the L-arginine (L-ARG) analogues L-canavanine and NG-nitro-L-arginine (L-NOARG) on acetylcholine-induced relaxation. L-canavanine (100 microM) as well as L-NOARG (10 microM) decreased significantly the relaxant response of acetylcholine, their effect being significantly reversed by L-arginine (10 microM) but not by D-arginine (10 microM). In resting conditions, L-NOARG (10 microM) elicited a contraction of 314 +/- 42 mg in arteries endowed with endothelium that was significantly diminished by endothelium removal to 88 +/- 35 mg, and by (10 microM) L-arginine to 135 +/- 54 mg. L-canavanine (100 microM) induced contractions in arteries with and without endothelial cells which were not statistically different. The results suggest that the endothelium of cat cerebral arteries has the ability to synthesize nitric oxide from L-arginine and to release it, even in the absence of a stimulus such as that of acetylcholine. L-NOARG seems to be a specific and powerful inhibitor of nitric oxide synthesis.

Different influence of endothelium in the mechanical responses of human and cat isolated cerebral arteries to several agents.

The present work was undertaken to elucidate the role of the vascular endothelium in the changes of isometric tension elicited by different compounds in isolated cylinders of human and cat cerebral arteries and cat pulmonary arteries. Endothelium removal by rubbing significantly reduced the relaxing response to acetylcholine (ACh) of isolated segments of all the arteries. The same treatment did not modify the contraction elicited by 5-hydroxytryptamine (5-HT) in the human and cat cerebral segments but increased the contractile effect of the amine in cat pulmonary arteries. The mechanical responses to vasopressin, ATP and adenosine in isolated segments of cat cerebral arteries were unaffected after removing the endothelial layer. L-Arginine, but not D-arginine (10(-5) M), enhanced significantly the relaxation induced by increasing doses of ACh in unrubbed cat cerebral arteries whereas it did not modify the response to ACh in rubbed ones. However, L-arginine had no effect on the dose-response curve to 5-HT in both kinds of preparation and did not change the tone in precontracted unrubbed cat cerebral segments. These results suggest that the endothelium of the cerebrovascular bed plays a minor role in regulating the mechanical response induced by several vasoactive agents, although it retains its ability to produce an endothelium-derived relaxing factor.

Response of isolated cat middle cerebral artery to platelets: effect of endothelium removal.

1. Platelets induced an endothelium-independent contraction in isolated cat middle cerebral artery under resting conditions. In precontracted segments they evoked an endothelium-dependent contraction followed by a relaxation. 2. The contraction induced by serotonin was unaffected by endothelium removal either in the absence or in the presence of a previous tone. 3. The contractile response to platelets and serotonin under resting tension was blocked in the same way by ketanserin, methysergide or cyproheptadine. 4. After adding the platelets, serotonin could be measured in the bath medium. 5. These results suggest that the endothelium plays a minor role in the contraction induced by platelets, which is partly due to serotonin release.

Lesion of the dorsal raphe nucleus induces supersensitivity to serotonin in isolated cat middle cerebral artery.

Simultaneous lesions of dorsal and median raphe nuclei were induced after 15 days postjunctional supersensitivity to serotonin in isolated segments of cat middle cerebral artery. The same result was obtained when only the dorsal raphe nucleus was destroyed. The lesion of the median raphe nucleus brought about an increased contractile response to serotonin only at the three first doses used. The contractile response to noradrenaline was unaffected by these treatments. These results suggest the existence of a serotonergic innervation of the cat middle cerebral artery whose main origin might be the dorsal raphe nucleus.

Regional differences in cerebrovascular cholinergic innervation in goats.

The presence and distribution of a cerebrovascular cholinergic system were studied in goats. Regional cerebral blood flow was measured in the parietal cerebral cortex, caudate nucleus, and white matter by the hydrogen clearance technique in unanesthetized goats. Intravenous low doses of physostigmine, but not of neostigmine, significantly increased regional blood flow without changing mean arterial blood pressure or behavior. Increases of blood flow were greater in cerebral cortex and caudate nucleus than in white matter although the vasodilation induced by hypercapnia was similar in the three regions. Intracerebral microvessels were isolated from cerebral cortex, caudate nucleus, and white matter to evaluate choline acetyltransferase activity as a marker for perivascular cholinergic nerves. The enzyme level was higher in vessels from cerebral cortex and caudate nucleus than in vessels from white matter, which is in accordance with the functional data. These results suggest the presence of a cholinergic perivascular innervation system in intracerebral microvessels. Such innervation has a nonhomogeneous distribution throughout the brain and might be implicated in the local regulation of cerebral blood flow.

Evidence for the direct effect of vasopressin on human and goat cerebral arteries.

The effects of vasopressin on the cerebral circulation were studied in conscious goats and in isolated human and goat cerebral arteries. Infusion of 1 to 12 mU of vasopressin into the internal maxillary artery of unanesthetized goats caused dose-dependent reductions in cerebral blood flow, a decrease of 36 +/- 4.7% (mean +/- S.E.) occurring with the highest dose. Cumulative application of vasopressin (10(-12) to 10(-6) M) markedly constricted human and goat cerebral arteries in vitro, the effect being more prominent in human vessels. (1-Deaminopenicillamine, 4-valine)-8-D-arginine-vasopressin, a competitive antagonist of the pressor effects of vasopressin, partially inhibited the cerebral vasoconstriction produced by vasopressin in vivo and in vitro without affecting the vasoconstrictor responses to norepinephrine, 5-hydroxytryptamine and potassium chloride. The results indicate that low concentrations of vasopressin produce constriction of cerebral vessels by direct excitatory effects on specific receptor sites. This effect should be considered in certain pathophysiological states in which vasopressin is released in amounts that could interfere with the proper blood supply to the brain.

Cerebrovascular responses to CO2 after inhibition of sympathetic activity.

The effects of inhalation of 10% CO2 in air on cerebral blood flow (CBF) and cerebrovascular resistance (CVR) were examined in 13 unanesthetized goats before and after impairment of the sympathetic activity present in cerebral vessels. Under control conditions, inhalation of CO2 increased CBF from 112 +/- 10.2 (SE) to 191 +/- 17.2 ml X min-1 X 100 g-1 and decreased CVR from 0.91 +/- 0.02 to 0.55 +/- 0.03 Torr X ml-1 X min X 100 g. After treatment with reserpine CO2 increased CBF to levels similar to those before treatment, but values for CVR were significantly lower. Inhalation of CO2 1-2 days after removal of both superior cervical sympathetic ganglia produced a larger increase in CBF and a greater drop in CVR, whereas at 6-20 days after ganglionectomy the effects of CO2 were analogous to those measured before the operation. The results suggest that the existence of an intact tonic adrenergic activity is a factor in the level of CVR achieved in hypercapnic acidosis.

Reduction of cerebrovascular reactivity during hypercapnia.

The effects on cerebral blood flow of alpha- or beta-adrenergic receptor stimulation of cerebral vessels were examined in 13 unanesthetized goats before and during hypercapnia produced by inhalation of 10% CO2 in air. This procedure increased the PCO2 from 34 to 52 and was accompanied by a fall in pH from 7.39 to 7.26. Electrical stimulation of the cervical sympathetic nerve and injections of norepinephrine and tyramine into the internal maxillary artery produced reductions in cerebral blood flow that were abolished or reduced in hypercapnia. The increase in cerebral blood flow in response to beta-adrenergic stimulation with isoproterenol was also reduced. Hypercapnia caused a similar depression of the constrictor and dilatory effects of the nonadrenergic drugs vasopressin and diazoxide. The results show a decreased response of cerebral vessels to adrenergic and nonadrenergic stimuli in hypercapnia. The findings do not suggest any difference between the refractoriness of cerebral vessels in hypercapnia and that described in other vascular beds.