Antisense inhibition of thyrotropin-releasing hormone reduces arterial blood pressure in spontaneously hypertensive rats

Thyrotropin-releasing hormone (TRH) plays an important role in central cardiovascular regulation. Recently, we described that the TRH precursor gene overexpression induces hypertension in the normal rat. In addition, we published that spontaneously hypertensive rats (SHR) have central extrahypothalamic TRH hyperactivity with increased TRH synthesis and release and an elevated TRH receptor number. In the present study, we report that intracerebroventricular antisense (AS) treatment with a phosphorothioate oligonucleotide against the TRH precursor gene significantly diminished up to 72 hours and in a dose-dependent manner the increased diencephalic TRH content, whereas normalized systolic blood pressure (SABP) was present in the SHR compared with Wistar-Kyoto (WKY) rats. Although basal thyrotropin was higher in SHR compared with WKY rats and this difference disappeared after antisense treatment, no differences were observed in plasma T4 or T3 between strains with or without AS treatment, indicating that the effect of the AS on SABP was independent of the thyroid status. Because the encephalic renin-angiotensin system seems to be crucial in the development and/or maintenance of hypertension in SHR, we investigated the effect of antisense inhibition of TRH on that system and found that TRH antisense treatment significantly diminished the elevated diencephalic angiotensin II (Ang II) content in the SHR without any effect in control animals, suggesting that the Ang II system is involved in the TRH cardiovascular effects. To summarize, the central TRH system seems to be involved in the etiopathogenesis of hypertension in this model of essential hypertension.

Expression of TRH and TRH-like peptides in a human glioblastoma-astrocytoma cell line (U-373-MG)

The human glioblastoma-astrocytoma cell line U-373-MG shows morphological features typical of its neuroectodermal origin. Cells showed positive immunostaining for the glial fibrillary acidic protein. We used this cell culture for studying the putative production of TRH and TRH-related peptides. In a cell extract and conditioned medium, cation and anion exchange chromatography and HPLC revealed the presence of TRH and acidic TRH-like peptides which were identified, at least in part, as pGlu-Glu-ProNH(2). These findings demonstrated that U-373-MG cells are able to produce and release these peptides. Further evidence of TRH synthesis was obtained by amplification using RT-PCR of a 396 bp fragment that corresponds to the TRH precursor mRNA. Our results therefore suggest that the U-373-MG cell line may be a useful model for studying the regulation of TRH and TRH-related peptide production and the interaction of these peptides with other classical neurotransmitter systems. In fact, pilocarpine (a muscarinic cholinergic agonist) enhanced and nicotine (a nicotinic cholinergic agonist) decreased TRH and TRH-related compound production by this cell line. These data also point out that glia may produce substances with neuromodulatory action.

Parathyroid hormone-related protein expression in vascular smooth muscle of spontaneously hypertensive rats: evidence for lack of response to angiotensin II

OBJECTIVE

We studied the expression of parathyroid hormone (PTH)-related protein in vascular smooth muscle cells of spontaneously hypertensive rats (SHR) using Wistar-Kyoto (WKY) and Sprague-Dawley rats as normotensive controls.

METHODS

Aortae from 4- and 18-week-old SHR versus age-matched WKY and Sprague-Dawley rats were excised to obtain total RNA or smooth muscle cells. The cells were subcultured in Dulbecco's Modified Eagle's Medium containing 10% fetal calf serum, then serum-deprived for 72 h and stimulated with 0.1 micromol/I angiotensin II. PTH-related protein, c-myc and angiotensin II type qa receptor (AT1aR) messenger (m)RNA levels were measured by Northern blot, using total RNA extracted by phenol/chloroform. The effects of PTH-related protein(1-34)NH2 intravenous injections on arterial blood pressure and the heart rate were studied in anesthetized SHR and WKY rats.

RESULTS

The Northern blots showed a significantly higher abundance of PTH-related protein mRNA in aortae of SHR versus WKY rats in the prehypertensive state but no significant difference in adult animals. In cultured aortic smooth muscle cells, angiotensin II induced a four- to sixfold increase in PTH-related protein mRNA levels in smooth muscle cells from normotensive animals, but failed to elicit a significant response in smooth muscle cells derived from SHR in either the prehypertensive or the hypertensive state. This lack of response to angiotensin II in SHR smooth muscle cells was not due to decreased expression or responsiveness of the AT1aR, since SHR smooth muscle cells had more AT1aR mRNA than Sprague-Dawley smooth muscle cells, and angiotensin II-induced activation of c-myc was faster and greater in smooth muscle cells derived from 4- or 18-week-old SHR than in Sprague-Dawley smooth muscle cells. In contrast, PTH-related protein(1-34)NH2 induced a long-lasting dose-dependent hypotensive and tachycardic response in both SHR and WKY rats, indicating that SHR retained responsiveness to the vasodilator.

CONCLUSIONS

PTH-related protein gene expression in response to angiotensin II is impaired in SHR arteries. A deficiency in this potent local vasodilator may contribute to the development and/or maintenance of arterial hypertension in this model.

Central overexpression of the TRH precursor gene induces hypertension in rats: antisense reversal

Extrahypothalamic TRH participates in cardiovascular regulation and spontaneous hypertension of the rat. To investigate whether an increase in central TRH activity produces hypertension we studied the effect of the preTRH overproduction induced by I.C.V. transfection with a naked eukaryotic expression plasmid vector which encodes preTRH (pCMV-TRH). Northern blot analysis and RT-PCR showed that pCMV-TRH was transcribed in vitro and in vivo. At 24, 48, and 72 hours, pCMV-TRH (100 microg) in a significant and dose-dependent manner increased 37%, 84%, and 49%, respectively, the diencephalic TRH content and SABP (42+/-3, 50+/-2, and 22+/-2 mm Hg, respectively) with respect to the vector without the preTRH cDNA insert (V[TRH(-)]) as measured by RIA and the plethysmographic method, respectively, in awake animals. In addition, using immunohistochemistry we found that the increase of TRH was produced in circumventricular areas where the tripeptide is normally located. To further analyze the specificity of these effects we studied the actions of 23-mer sense (S), antisense (AS), and 3'self-stabilized sense (Ss) and antisense (ASs) phosphorothioate oligonucleotides against the initiation codon region. Only ASs inhibited the increase of TRH content and SABP induced by pCMV-TRH treatment. In addition, pCMV-TRH-induced hypertension seems not to be mediated by central Ang II or serum TSH. To summarize, central TRH overproduction in periventricular areas induced by I.C.V. transfection produces hypertension in rats which is reversed by specific antisense treatment. This model may help in testing effective antisense oligodeoxynucleotides against other candidate genes.

Thyrotropin-releasing hormone hyperactivity in the preoptic area of spontaneously hypertensive rats

Thyrotropin-releasing hormone (TRH) plays an important role in central cardiovascular regulation through the activation of different neurotransmitter systems at distinct extrahypothalamic sites. To study possible alterations in the TRH system in the hypertensive state, we measured TRH concentration in cerebrospinal fluid and TRH content of the preoptic area in spontaneously hypertensive rats (SHR) and Wistar-Kyoto rats (WKY) by radioimmunoassay. In addition, we also measured the density of the TRH receptor in this area by a rapid filtration technique using [3H]methyl-TRH. We found a significant increase in both the TRH content (634 +/- 61 versus 350 +/- 26 pg/mg protein, SHR versus WKY; P < .01, n = 5) and density of TRH receptors without changes in affinity (Bmax, 5.0 +/- 0.1 versus 3.3 +/- 0.1 fmol/mg protein, P < .01, n = 4). An increase in TRH concentration was also found in the cerebrospinal fluid of SHR (30 +/- 3 versus 21 +/- 2 pg/mL, P < .01, n = 5), suggesting increased TRH release in the central nervous system. Northern blot analysis indicated a threefold augmented abundance of TRH precursor mRNA in the preoptic area of SHR. A polyclonal antibody raised against TRH injected peripherally or intracerebroventricularly lowered arterial blood pressure in SHR but not in WKY. In addition, long-term treatment with enalapril (5 mg/kg twice daily), which was effective in inhibiting serum angiotensin-converting enzyme activity by more than 50%, decreased arterial blood pressure and preoptic area TRH content of SHR, whereas another vasodilator, diltiazem (10 mg/kg every 8 hours), failed to produce a similar change.(ABSTRACT TRUNCATED AT 250 WORDS)

Corticotropin-releasing hormone differentially modulates the interleukin-1 system according to the level of monocyte activation by endotoxin

The interleukin-1 (IL-1) system is constituted by IL-1 alpha and IL-1 beta and IL-1 receptor antagonist (IL-1ra) that bind the same IL-1 receptors. Hypothalamic-pituitary-adrenal axis hormones are major mediators of the neuroendocrine control over immune function. Corticotropin-releasing hormone (CRH) is produced in peripheral inflammatory sites; its direct effects on inflammatory cytokine synthesis, however, remain unclear. We have studied the effects of CRH (0.1-100 nM) on IL-1 beta and IL-1ra expression by human peripheral monocytes in culture activated with different doses of lipopolysaccharide (LPS). In the absence of LPS, CRH up-regulated IL-1ra and IL-1 beta messenger RNA expression as well as protein synthesis. No significant changes were observed with low doses of LPS (1 ng/ml). In contrast, in combination with high doses of LPS (1 microgram/ml), CRH caused inhibition of IL-1ra and IL-1 beta transcription and secretion. The CRH effects were blocked by its antagonist alpha-helical CRH and mediated by intracellular cAMP. These data indicate that CRH modulates the IL-1 system; depending on the state of activation of the monocyte, CRH exerts an inhibitory control on the activated cell and a stimulatory action on the resting monocyte.

Synenkephalin processing in embryonic rat brain

Synenkephalin (proenkephalin 1-70) is produced and secreted as an intact molecule or as a part of precursors in the adult brain and adrenal medulla, respectively. However, it is cleaved to low molecular weight peptides in proliferating immune cells. Considering that the pre-proenkephalin gene is expressed in the embryonic rat brain during the cell proliferation stage, we studied the processing of synenkephalin in embryonic rat brains (E18) and compared it with the processing in adult rat brains. IR-synenkephalin was measured by RIA using a C-terminally directed antiserum. Adult rat brains contained higher concentrations of immunoreactive (IR)-synenkephalin (2,612 + 264) than embryonic rat brain (1,361 + 100) (results in fmol/mg proteins, n = 5). Gel filtration chromatography (Sephadex G-50) showed that in the extracts of adult rat brain, 50% of the IR-synenkephalin eluted in the position of the authentic peptide (8 kDa) and the rest of the immunoreactivity corresponded to partially processed peptides of 4.0 and 2.5 kDa. In embryonic rat brains synenkephalin was processed to intermediate peptides of 2.5, 1.7 and mainly to a low molecular weight peptide of 1.0 kDa. The concentration of this last peptide, which was further characterized by affinity column and HPLC, represented 45% of the total immunoreactivity. IR-met-enkephalin in embryonic rat brains (analyzed before and after enzymatic digestion with trypsin and carboxypeptidase B) corresponded principally to non-processed or partially processed products. However, these were cleaved to free met-enkephalin in adult rat brains.(ABSTRACT TRUNCATED AT 250 WORDS)

Superinduction of mitogen-stimulated interferon-gamma production and other lymphokines by Sendai virus

We observed that Sendai virus preinduction of peripheral blood mononuclear cells and subsequent mitogenic stimulation resulted in: (i) Superproduction of interferon-gamma, (IFN-gamma) (ii) an increase in interleukin-2 (IL-2) synthesis that correlates with DNA synthesis when stimulated with phytohemagglutinin (PHA) or pokeweed mitogen (PWM) after treatment with the Sendai virus, while stimulation with Protein A from Staphylococcus aureus was not affected, and (iii) enhanced tumor necrosis factor-alpha (TNF-alpha) production in response to bacterial lipopolysaccharide (LPS). Treatment of monocyte cultures with LPS and cycloheximide or actinomycin-D inhibited the superinduction phenomenon. When cycloheximide was added at the viral induction time, the inhibition of TNF-alpha superproduction and DNA synthesis was still observed. These results suggest that Sendai virus lymphocyte superinduction is specific for a particular stimulatory pathway, not dependent on mRNA accumulation, and probably mediated by induction of an activating protein.

Low lymphocyte interferon-gamma production and variable proliferative response in anorexia nervosa patients

Interferon-gamma (IFN-gamma) production by peripheral blood mononuclear cells (PBMC) in 14 patients with anorexia nervosa (AN) was significantly lower than in 14 age-matched healthy controls. Follow-up samples in four patients displayed low levels, except in two when they recovered the IFN-gamma production as the hormonal cycles were restored. A large interindividual variation for the lymphocyte proliferative response was observed in 30 AN patients. DNA synthesis of PBMC was normal in 8 patients (27%), significantly increased in 6 (20%) (P < 0.001), and significantly decreased in 16 (53%) (P < 0.001). IFN-gamma inhibition was reversed by culturing a control lymphocyte population with monocytes from patients with AN. This was not observed in cultures of control monocytes and AN lymphocytes. IL-2 receptor (TAC subunit) was assessed and no difference was found in the number of TAC-positive cells between patients and controls. These results point out impaired production of the immunomodulator cytokine IFN-gamma as a major functional defect of AN peripheral lymphocytes.

Early complete maturation of proenkephalin processing induced by dexamethasone in the adrenal gland of neonatal rats

We have previously found that proenkephalin processing is incomplete in the neonatal rat adrenal medulla and have postulated that immaturity of either the nervous input to the gland or the endocrine hypothalamus-pituitary-adrenal axis might be involved in the failure of the gland to yield free met-enkephalin. Therefore, we investigated whether cholinergic and glucocorticoid agonists may act in vivo on neonatal proenkephalin processing; reserpine, a strong activator of precursor cleavage, was also tested. Acute administration of nicotine, pilocarpine and reserpine to 24-hour-old rats increased the content of enkephalin-containing peptides (ECP) after 72 h (4-day-old rats) and activated the posttranslational processing of proenkephalin to high, intermediate and low molecular weight peptides respectively, although free met-enkephalin was not produced. Chronic treatment with nicotine and pilocarpine neither modified the concentration of ECP nor were able to induce free metenkephalin production. Chronic administration of dexamethasone increased ECP levels in the adrenal of 4-day-old rats and caused proenkephalin processing to intermediate- and low-molecular-weight products including the production of free met-enkephalin. These results indicate that only dexamethasone was able to induce the production of met-enkephalin in the adrenal of neonatal rats, suggesting an involvement of the hypothalamus-pituitary-adrenal axis in the proteolytic maturation of proenkephalin during the ontogeny of rat adrenal medulla.

Interaction between thyrotrophin-releasing hormone and the muscarinic cholinergic system in rat brain

TRH increases the pressor response to acetylcholine through an increment in muscarinic receptors. As chronic atropinization produces a similar effect, we hypothesized that both phenomena may be related. The effect of chronic atropine treatment on the TRH content of several brain areas in Wistar rats was studied. Atropine produced significant increases in TRH content in the preoptic and septal areas, while decreases were observed in the hypothalamus and hypophysis. The concentration of TRH in cerebrospinal fluid rose significantly in atropine-treated rats compared with controls. A similar effect was observed with eserine, an acetylcholinesterase inhibitor. Finally, perfusion of brain preoptic area slices from normal rats with Krebs-Ringer solution in the presence of pilocarpine increased basal TRH release significantly and this effect was blocked by atropine. These results are compatible with a muscarinic control on the activity of the central TRH system.

Central bradykininergic system in normotensive and hypertensive rats

1. The kinin antagonist des-Arg9-[Leu8]bradykinin, injected into the lateral ventricle, caused a long-lasting, dose-dependent reduction in arterial blood pressure and heart rate in spontaneously hypertensive rats but not in normotensive Wistar-Kyoto rats; the antagonist also blocked the pressor response to ventricularly infused bradykinin in both strains. 2. Bradykinin content was increased in the hypothalamus and septum and decreased in the dorsal medulla of spontaneously hypertensive rats when compared with those of normotensive Wistar-Kyoto rats, whereas similar bradykinin contents were observed in the pineal gland, hypophysis and rostroventrolateral medulla of both rat strains. 3. Increased concentrations of bradykinin and its precursor kininogen were found in the cerebrospinal fluid of spontaneously hypertensive rats. 4. Bradykinin receptor numbers, measured as the binding of [125I-Tyr1]bradykinin to nervous tissue, were found to be increased in the dorsal medulla and hypophysis, and to be decreased in the pineal gland, of spontaneously hypertensive rats. 5. Therefore, the central kinin system may participate, by both pre- and post-synaptic mechanisms, in the maintenance of hypertension in spontaneously hypertensive rats.

Brain amines in glucocorticoid-induced hypertension in the rat

A two week administration of the glucocorticoid betametasone to male Wistar rats produced a mild hypertensive state. The brain of these rats showed some significant changes in amine and metabolite content with respect to normotensive controls. Epinephrine and metanephrine were increased in the rostral ventrolateral medulla and in the preoptic area. Epinephrine also increased in the septal area. Normetanephrine decreased in the rostral ventrolateral medulla. Dopamine and homovanillic acid increased in septal and preoptic areas. Dopamine alone increased in rostral ventrolateral medulla. Serotonin and 5-hydroxyindole-3-acetic acid increased in the septal area and dorsal medulla. These changes suggest significant alterations in the aminergic activity of the brain circuitry known to regulate cardiovascular functions; the changes may play a basic role in the development and maintenance of glucocorticoid-induced hypertension.

The cholinergic system participates in thyrotropin-releasing hormone (TRH) regulation

The effect of chronic atropine treatment was studied on thyrotropin releasing hormone (TRH) content of several brain areas in Wistar rats. Atropine produced TRH increases in the septal area, preoptic area and the hypophysis; this was observed when rats were killed immediately after the last dose, while a decrease was observed only in the hypophysis 48 h after the last atropine dose. TRH concentration in cerebrospinal fluid rose significantly after atropine withdrawal with respect to controls. Treatment with eserine, an acetylcholinesterase inhibitor, produced the same effect. These results indicate cholinergic participation in central TRH regulation.

The inhibitory effect of the muscarinic agonist pilocarpine on lymphocyte activation involves the IL-2 pathway and the increase in suppressor cell function

The inhibition of lymphocyte DNA synthesis by the cholinergic muscarinic agonist pilocarpine (5 x 10(-4) M) was not reversed by addition of exogenous recombinant Interleukin-2 (100-1000 IU/ml). Pilocarpine did not inhibit Interleukin-2 (IL-2) production by human peripheral blood mononuclear cells but decreased the number of interleukin-2 receptor bearing cells (TAC positive cells). Furthermore, pilocarpine increased the CD8:CD4 T lymphocyte ratio enhancing the suppressor cell function. All these effects were blocked by the muscarinic antagonist atropine (1 x 10(-6) M). As described for the specific lymphocyte nicotinic stimulation, the pure cholinergic muscarinic stimulation inhibits lymphocyte proliferation by enhancing suppressor activity.

Glucocorticoid-induced hypertension in rats: role of the central muscarinic cholinergic system

Betamethasone was administered on alternate days to rats, and the role of the central cholinergic system in the development of hypertension assessed. After 15 days of treatment the systolic blood pressure of treated rats was significantly higher than that of control rats. Peripheral administration of atropine but not of methyl atropine reduced systolic pressure in glucocorticoid-treated rats and had no effect in controls. Therefore, [3H]quinuclidinyl benzylate binding, sodium-dependent high-affinity choline uptake and choline acetyltransferase studies were performed in the septal area, anteroventrolateral medulla (AVLM), anterior hypothalamic preoptic area (AH/PO) and hypothalamus. The density of muscarinic receptors was increased in the hypothalamus and AVLM of treated rats without significant changes in affinity. Choline acetyltransferase activity significantly decreased in the AVLM and increased in the AH/PO. In addition, a decrease in the hypothalamus and an increase in the AH/PO of sodium-dependent high-affinity choline uptake was observed in glucocorticoid-treated rats. These results suggest the presence of an enhanced muscarinic cholinergic activity in several brain nuclei in rats with glucocorticoid-induced hypertension. This activation could be due to pre- and post-synaptic hypersensitivity.

Lesions of the medial septal nucleus produce a long-lasting inhibition of T lymphocyte proliferation

The influence of the central cholinergic system on the immune system was studied in Wistar rats by lesioning the medial septal nucleus. This lesion inhibited T cell proliferation of splenocytes and thymocytes induced by the mitogens concanavalin A (Con A), phytohemagglutinin (PHA) and pokeweed mitogen (PWM) up to 25 days and did not affect proliferation at 40 days after lesioning. In contrast, the response to the B cell mitogen lipopolysaccharide from E. coli (LPS) was not affected at any time. These findings suggest a regulatory role of the cholinergic medial septal nucleus on T lymphocyte proliferation.

Cholinergic hyperactivity in the lateral septal area of spontaneously hypertensive rats: depressor effect of hemicholinium-3 and pirenzepine

In the lateral septal area of spontaneously hypertensive rats, but not in Wistar-Kyoto rats, the selective M1 antagonist, pirenzepine, and the depletion of acetylcholine storage, by hemicholinium-3 (HC-3), decreased blood pressure. The selective M1 agonist McNeil-A-343, produced a pressor response only after treatment of the lateral septal area with HC-3 in spontaneously hypertensive rats. Carbachol, at doses that mainly affect M2 muscarinic receptors, caused no cardiovascular changes in either strain, pointing to the main intervention of the M1 subtype of muscarinic receptor in the hypertensive condition. In addition, increases in the density of binding sites for [3H]QNB and in Vmax of sodium-dependent, HC-3-inhibitable, high affinity uptake of choline were demonstrated, without significant changes of the activity of choline acetyltransferase in the lateral septal area of spontaneously hypertensive rats. These results suggest that a hyperactivity of the cholinergic system of this area could play a role in the development and/or maintenance of hypertension in spontaneously hypertensive rats.

Effects of sodium o-iodobenzoate on acid-base parameters and survival in dogs with hemorrhagic shock

Sodium o-iodobenzoate (OISB) produces an increase in P50 (PO2 at 50% of oxyhemoglobin saturation) and survival when infused at the time of initiation of prolonged hemorrhagic shock in dogs. Acid-base parameters improved during treatment, and plasma lactic acid concentrations showed smaller rises than in nontreated control animals. Erythrocyte 2,3-diphosphoglycerate (2,3-DPG) rose in prolonged hemorrhagic shock in the control group and conversely decreased in OISB-treated dogs. OISB did not require red cell integrity, since its effects were still more marked in hemolyzed blood. The therapeutic benefit of OISB, appears to be related to a direct effect of the agent on the hemoglobin molecule.

Release of acetylcholine from isolated canine renal tissue

Slices of canine kidney were incubated with [3H]choline and Ringer-Krebs solution for 30 min. Secretion of [3H]acetylcholine ([3H]ACh) was evoked by either 1) an electrical field stimulation (0.5-1 Hz, 2 ms, 20 V) or 2) high-potassium (57 mM) superfusion for 3 min to depolarize nerve terminals. With these stimulatory schedules, the 3H release mainly consists of [3H]-ACh. The ACh release is Ca2+ dependent and blocked in presence of a Mg2(+)-rich medium. Thus suppression of ongoing neuronal activity by tetrodotoxin and blockade of nicotinic receptors by hexamethonium reduced the electrically evoked ACh release. With both stimulatory procedures, the secretory response was modified by pilocarpine and atropine. In addition, the release of [3H]ACh produced by electrical field stimulation was inhibited by neostigmine, indicating the presence of functional presynaptic receptors in cholinergic putative terminals. Activation of these receptors depresses ACh secretion. The disruption of extrinsic renal nerves 7 days before did not diminish [3H]ACh release caused by K+ stimulation and, conversely, increased [3H]ACh released by electrical field stimulation. These data support the presumed existence of cholinergic nerve terminals in the canine kidney that can release ACh under suitable conditions of stimulation.

Serotonin inhibition of tumor necrosis factor-alpha synthesis by human monocytes

Serotonin inhibited in a concentration dependent way (10(-3) M to 10(-10) M) the LPS induced Tumor Necrosis Factor-alpha synthesis both, when added to the monocyte cultures from the beginning and when added together with the activating stimulus 8 hours before the end of the culture. The inhibitory effect was specifically blocked by the 5-HT1 and 5-HT2 serotonin antagonist methysergide and the 5-HT2 receptor antagonist ketanserin. This indicates that only the 5-HT2 receptor family (5-HT2 or 5-HT1C) may be involved in the inhibitory effect. Serotonin seems to play an important immunomodulatory role in macrophage functions.

Pineal hyperactivity in spontaneously hypertensive rats: muscarinic regulation of indole metabolism

1. Choline acetyltransferase activity and [3H]quinuclidinyl benzylate-binding sites were detected in the pineal gland of normotensive Wistar-Kyoto rats and of spontaneously hypertensive rats. 2. In vitro, muscarinic activation by pilocarpine increased the pineal metabolic production of hydroxyindole derivatives up to 5-hydroxytryptamine and produced a less marked stimulation of melatonin biosynthesis. 3. Electrical field stimulation of pineal gland slices caused similar metabolic effects. 4. Muscarinic blockade with atropine inhibited the effects on hydroxyindole metabolism. 5. [3H]Quinuclidinyl benzylate-binding sites, indicative of muscarinic receptors, were more numerous, and basal 5-hydroxytryptamine and melatonin levels were higher, in the pineal gland of spontaneously hypertensive rats compared with Wistar-Kyoto rats. 6. The atropine-sensitive metabolic effects of pilocarpine and electrical field stimulation on the pineal gland were increased in spontaneously hypertensive rats compared with Wistar-Kyoto rats.

Differential association of endogenous proenkephalin-derived peptides with membranes of microsomes from rat striatum, adrenal medulla and heart ventricle

Proenkephalin-derived peptides, in common with other prohormones, are associated with membranes of microsomes and secretory granules in the bovine adrenal medulla. Post-translational processing of the precursor molecule varies depending upon the tissue. The relationship between post-translational events in different tissues was examined by studying the membrane association of endogenous proenkephalin-derived peptides in the crude microsomal fraction of rat adrenal medulla, brain striatum and heart ventricle. [Met]-Enkephalin and synenkephalin (proenkephalin(1-70)) immunoreactivities were quantified by radioimmunoassay after sequential enzymatic digestion with trypsin and carboxypeptidase B. Between 60 and 75% of total immunoreactive peptides present in intact microsomes of the three tissues were associated with membranes and specifically released with 2 M KSCN (pH 7.4). Analysis of the chromatographic profile of materials present in the soluble and associated fractions produced the following results. In the three tissues the materials associated with microsomal membranes corresponded to peptides larger than 3-5 kDa and displayed synenkephalin and [Met]-enkephalin immunoreactivity. Adrenal and heart microsomes showed a continuous pattern of membrane-associated proenkephalin-derived peptides of high, intermediate and low molecular weights containing the synenkephalin and [Met]-enkephalin sequences. These tissues, however, presented quantitative differences, as the highest concentrations belonged to materials larger and smaller than 12.5 kDa in adrenal and heart microsomes respectively. On the other hand, brain striatal microsomes displayed a discontinuous pattern of associated materials, with the absence of some products of high and intermediate molecular weight. Only in the soluble fraction of striatal microsomes were peptides detected of high and intermediate molecular weight containing the [Met]-enkephalin but not the synenkephalin sequence.(ABSTRACT TRUNCATED AT 250 WORDS)

Proenkephalin system in human polymorphonuclear cells. Production and release of a novel 1.0-kD peptide derived from synenkephalin

In the hematopoietic system a pluripotent stem cell generates precursors for lymphoid and myeloid lineages. Proenkephalin-derived peptides were previously detected in differentiated lymphoid cells. We have studied whether the proenkephalin system is expressed in a typical differentiated cell of the myeloid lineage, the neutrophil. Human peripheral polymorphonuclear cells contain and release proenkephalin-derived peptides. The opioid portion of proenkephalin (met-enkephalin-containing peptides) was incompletely processed, resulting in the absence of low molecular weight products. The nonopioid synenkephalin (proenkephalin 1-70) molecule was completely processed to a 1.0-kD peptide derived from the COOH-terminal. This molecule was characterized in neutrophils by biochemical and immunocytochemical methods. The chemotactic peptide FMLP and the calcium ionophore A23187 induced the release of the proenkephalin-derived peptides, and this effect was potentiated by cytochalasin B. The materials secreted were similar to those present in the cell, although in the supernatant a higher proportion corresponded to more processed products. The 1.0-kD peptide was detected in human, bovine, and rat neutrophils, but the chromatographic pattern of synenkephalin-derived peptides suggests a differential posttranslational processing among species. These findings demonstrate the existence of the proenkephalin system in human neutrophils and the production and release of a novel 1.0-kD peptide derived from the synenkephalin molecule. The presence of opioid peptides in neutrophils suggests their participation in the inflammatory process, including a local analgesic effect.

Interaction of angiotensin II with the cholinergic and noradrenergic systems in the rat pineal gland: regulation of indole metabolism

The pineal gland, angiotensin, and noradrenergic and cholinergic systems are involved in the regulation of tissue indole metabolism. Angiotensin II increased noradrenaline release and the production of hydroxy- and methoxyindoles by pineal slices. Electrical field stimulation (EFS) of pineal slices released angiotensin II and reproduced many of the actions of exogenous angiotensin II on serotonin and melatonin biosynthesis and release. Both sarcosine-isoleucine-angiotensin II ([Sar, Ile]-ANG II) and atropine blocked, and nadolol increased, the effect of EFS and exogenous angiotensin II on serotonin production. Nadolol blocked both the EFS-induced and the angiotensin II-induced production of melatonin. Atropine and [Sar, Ile]-ANG II did not modify melatonin biosynthesis in electrically stimulated slices, but the muscarinic receptor antagonist increased the stimulatory effect of angiotensin II. These data showed that EFS released angiotensin II and noradrenaline from pineal slices and that a close functional connection exists between the peptide and acetylcholine. The stimulation of serotonin biosynthesis and release by these two neurotransmitters was negatively regulated by noradrenaline acting through beta-adrenergic receptors.

Evidence for cholinergic innervation in dog renal tissue

Denervation procedures that affect the sympathetic system of the kidney, as demonstrated by norepinephrine depletion of renal tissue, increased urine volume, fractional sodium excretion, and free water clearance in anesthetized water-loaded dogs. These increases were reduced by atropine, which also blocked the increase above those basal functional levels produced by acetylcholine in both innervated and denervated kidneys. An in vitro tubular cell preparation of innervated kidneys corresponding to the outer cortex showed [3H]quinuclidinyl benzilate (QNB) binding parameters characteristic of muscarinic receptors. Denervation did not change either [3H]QNB binding parameters or the ability of inner and outer cortex cells to perform the hemicholinium-3-inhibitable, sodium-dependent choline uptake and conversion of [3H]choline to [3H]acetylcholine. This cell membrane behavior is similar to that observed in tissues where cholinergic neuronal structures are present, suggesting the existence of a cholinergic innervation of the kidney, independent of the integrity of vessel-traveling nerves. Similarly, the finding of choline acetyltransferase in renal tissue, unaffected by sympathetic denervation, seems to confirm the presence of cholinergic nerve terminals. The cholinergic system may thus contribute to the regulation of tubular reabsorption of sodium and water in some conditions.

Muscarinic effects on the hydroxy- and methoxyindole pathway in the rat pineal gland

[3H]Quinuclidinyl benzylate ([3H]QNB)-binding sites, showing similar properties to cholinergic muscarinic receptors in other tissues, were disclosed in the rat pineal gland. Functionality of these receptors was demonstrated, as in-vitro muscarinic activation by pilocarpine increased the pineal metabolic production of the hydroxyindole derivatives 5-hydroxytryptophan and serotonin, with a slight effect on melatonin biosynthesis. Electric-field stimulation of pineal slices caused similar metabolic effects. These effects were inhibited by muscarinic blockade with atropine and enhanced by neostigmine inactivation of acetylcholinesterase. These results suggest that acetylcholine is the neurotransmitter involved. Cholinergic activity may, therefore, regulate indole metabolism in the pineal gland.

Association of endogenous synenkephalin containing peptides with intracellular membranes of bovine adrenal medulla

The association of endogenous synenkephalin and met-enkephalin containing peptides with the membrane of bovine chromaffin granules and physicochemical characteristics of this association were studied. The associated materials were only released at a non physiological pH range and this effect was enhanced with growing salt concentrations (0.5, 1.0 and 2.0 M KSCN). A higher peptide dissociation occurred with membrane solubilizing agents (SDS greater than Triton X-100 greater than digitonin). In microsomes the materials dissociated with 2 M KSCN (pH 7.4) corresponded to peptides larger than 12.0 kDa, while in granules corresponded to molecules smaller than 8.5 kDa, displaying synenkephalin and met-enkephalin immunoreactivities. These data suggest that some sequence of the C-terminal portion of synenkephalin may be responsible for the association of proenkephalin derived peptides with microsome and granule membranes.

Mitogenic activation of the human lymphocytes induce the release of proenkephalin derived peptides

Several reports indicate that enkephalins participate in lymphocyte proliferation and several events of the immune response. It has been proposed that peptides involved in these processes may originate in the nervous system or endocrine glands. We have found that human peripheral blood lymphocytes (PBL) activated with a mitogenic agent contain and release proenkephalin derived peptides. The kinetics of met-enkephalin and cryptic products of proenkephalin in PBL activated with phytohemaglutinin (PHA) were studied. Peptides were released to the supernatant of stimulated PBL, reaching the highest values after 18 to 24 hours. The material secreted corresponds to high, intermediate and low molecular weight peptides derived from proenkephalin, displaying met-enkephalin and synenkephalin (proenkephalin 1-70) immunoreactivity. Therefore, an intrinsic lymphocytic proenkephalin system is induced by PHA and may play an important role in the regulation of the immune response.

The muscarinic agonist pilocarpine inhibits DNA and interferon-gamma synthesis in peripheral blood mononuclear cells

Lymphocyte basal DNA synthesis and proliferative responses to phytohemagglutinin (PHA) showed a dose-dependent (5 X 10(-5)-5 X 10(-3) M) inhibition by the muscarinic agonist pilocarpine, in contrast to the basal enhancing effect produced by the M2 muscarinic-nicotinic agonist carbachol. The effect of pilocarpine was reversed by both atropine (1 X 10(-6) M) and pirenzepine (1 X 10(-7)-1 X 10(-8) M), M1-M2 and M1 muscarinic antagonists, respectively. The effect of pilocarpine may thus be specific for the M1 muscarinic receptor. Pilocarpine also inhibited interferon-gamma (IFN-gamma)-PHA induced production, but was unable to reverse the pokeweed mitogen (PWM)-induced DNA synthesis. Distinct immunoregulatory activities are suggested for cholinergic muscarinic receptors M1 and M2.

Ketanserin in the treatment of essential hypertension. A double blind trial against metoprolol followed by one-year open treatment

The present study was designed to compare the antihypertensive potencies of ketanserin and metoprolol in a double-blind trial and to study ketanserin long-term efficacy in a one-year open trial, plain or combined with metoprolol, according to diastolic blood pressure (DBP) normalization. Thirty-four patients were randomly assigned to two groups, one (n = 17) received ketanserin, 80 mg/day, and the other, (n = 17) metoprolol, 200 mg/day. After 3 mo. double blind treatment, all patients received plain ketanserin, or combined with metoprolol if ketanserin failed to normalize DBP. A significant effect was demonstrated after 3 mo. double blind treatment, for both drugs, in both standing and supine DBP (p less than 0.001). In the one-year follow-up, all patients received ketanserin and were divided in: I (n = 15) previously treated with the same drug; II (n = 2) plus metoprolol, in whom ketanserin had failed to decrease DBP; and III (n = 15) previously treated with metoprolol. In group I the blood pressure lowering effect of ketanserin remained constant during the one-year follow-up. In group II a trend in the decrease of parameters was observed. In group III, supine DBP diminished from 92.5 +/- 2 mmHg during treatment with metoprolol to 86.0 +/- 2 at 12 mo., after treatment with ketanserin (p less than 0.05). In groups I and III, 24/30 of patients normalized their DBP during one-year ketanserin open treatment. Ketanserin appears as a new alternative in the treatment of mild and moderate essential hypertension.

Serotonin and melatonin synthesis in peripheral blood mononuclear cells: stimulation by interferon-gamma as part of an immunomodulatory pathway

Serotonin and melatonin inhibit phytohemagglutinin- (PHA) induced interferon-gamma (IFN-gamma) production by lymphocytes. In this paper, it is shown that IFN-gamma-increased tryptophan uptake by lymphocytes and macrophages led to an enhanced production of serotonin. When IFN-gamma and serotonin were added together to a lymphocyte culture, N-acetyl serotonin and melatonin production was increased, whereas the path to 5-hydroxy-indoleacetic acid remained unchanged. Therefore, the stimulated IFN-gamma production of serotonin and melatonin by lymphocytes and macrophages and the inhibition of IFN-gamma synthesis by these indoleamines suggest a hypothesis for an immunoregulatory circuit.

Immunomodulation by indoleamines: serotonin and melatonin action on DNA and interferon-gamma synthesis by human peripheral blood mononuclear cells

Different concentrations of indoleamines, serotonin and melatonin, inhibited phytohemagglutinin stimulated DNA synthesis. Thus, 10(-3) to 10(-4) M of either indoleamine acted at the optimal phytohemagglutinin concentration, while 10(-3) to 10(-7) M acted at suboptimal phytohemagglutinin levels. The serotonin effect was reversed by the serotonergic S1-S2 receptor antagonist methysergide but not by the S2 antagonist ketanserin. This indicates that only the S1 receptor is involved in the inhibitory effect. Inhibition of lymphoproliferation by indoleamines was also exerted on pokeweed mitogen and protein A from Staphylococcus aureus stimulations. Serotonin and melatonin also inhibited phytohemagglutinin and protein A from Staphylococcus aureus induction of interferon-gamma synthesis. The initial uptake of Ca2+ was not affected by indoleamines, suggesting that it is not the mechanism of their inhibitory effects. As interferon-gamma induced tryptophan uptake by T lymphocyte- and macrophage-depleted populations, and tryptophan is the metabolic precursor of serotonin and melatonin, a new immunoregulatory circuit is postulated.

Adrenal proenkephalin-derived peptides during postnatal development in spontaneously hypertensive rats

Adrenal enkephalin and enkephalin-containing peptides were studied during postnatal development in normotensive (WKY) and spontaneously hypertensive rats (SHR). The effect of chronic treatment with the ganglionic blocker chlorisondamine (5 mg/kg) was also assessed. Free enkephalin immunoreactivity and total enkephalin immunoreactivity, as determined by enzymatic digestion of large enkephalin containing fragments, were quantitated in the adrenal glands at 11 days and 7, 16, and 24 weeks of age. Both total and free metenkephalin were significantly diminished in the adrenal of SHR when compared to WKY at all ages tested. The analysis of the chromatographic profile showed that SHR displayed reduced levels of high and low molecular weight materials at 11 days and 16 weeks of age; however intermediate compounds were high in the glands of these animals. Similar increased values for free met-enkephalin were found in adrenals of WKY and SHR after ganglionic blocker treatment, which means that the relative increase was larger in SHR than WKY; while for total enkephalin the relative increase and the concentration reached in SHR was about half of those presented in WKY. These and other results presented suggest that the basic alteration of the adrenal proenkephalin system of SHR may be due to a genetic reduction of proenkephalin levels. Otherwise, the free enkephalin decrease could be related to changes in nervous input to the adrenal gland.

Differential release of enkephalin and enkephalin-containing peptides from perfused cat adrenal glands

We have compared the enkephalin-like material derived from proenkephalin released from perfused cat adrenal glands stimulated with pilocarpine (5 X 10(-4)M) and nicotine (5 X 10(-6) M). In addition, two doses of acetylcholine (10(-5) and 10(-4) M) and 50 mM K+ were tested. Free Met-enkephalin immunoreactivity and total Met-enkephalin immunoreactivity, as determined by enzymatic digestion of large enkephalin-containing fragments, were coreleased with catecholamines. Free Met-enkephalin immunoreactivity represented 13% of total immunoreactivity for nicotinic stimulation, 46% for pilocarpine, 33% for 10(-5) M acetylcholine, 22% for 10(-4) M acetylcholine, and 16% for 50 mM K+. Analysis of the perfusate by gel filtration showed that 80% of the total Met-enkephalin immunoreactivity whose release was induced by pilocarpine was eluted in fractions corresponding to fragments of low molecular weight, whereas these fractions accounted only for 10% of the total Met-enkephalin immunoreactivity whose release was induced by nicotine. HPLC analysis of low-molecular-weight peptide fractions revealed that Met-enkephalin, Met-enkephalin-Arg-Gly-Leu, and Met-enkephalin-Arg-Phe represented 69% of total Met-enkephalin immunoreactivity whose release was induced by pilocarpine. These results indicate that selective activation of muscarinic receptors is followed by release of low-molecular-weight material, whereas nicotine application also yielded high-molecular-weight peptides. Furthermore, increasing the acetylcholine concentration from 10(-5) to 10(-4) M and using 50 mM K+ increased proportionally the high-molecular-weight peptide secretion. Results are discussed in relation to the existence of a heterogeneous population of granules either in the same cell or in different cells, containing proenkephalin-derived peptides. (ABSTRACT TRUNCATED AT 250 WORDS)

Angiotensin converting enzyme activity in the amygdaloid complex in a neurogenic hypertensive model

The bilateral destruction of the ventral noradrenergic pathway induced by 6-hydroxydopamine (6-OHDA) administration into the ventral pons led to an increase in arterial blood pressure (ABP) and norepinephrine depletion in the amygdaloid complex, nucleus accumbens, septal area and olfactory bulb. Specific angiotensin converting enzyme (ACE) activity was significantly increased only in the amygdaloid complex (Control: 4.56 +/- 0.95; Vehicle: 4.08 +/- 1.07; 6-OHDA: 11.76 +/- 1.84). A significant correlation between arterial blood pressure and specific ACE activity levels in the amygdaloid complex was observed (r: 0.775; p less than 0.002). These results suggest that an increase in specific ACE activity of the amygdaloid complex after norepinephrine depletion could play a role in the development of hypertension in this model.

Low TRH-TSH responses in human essential hypertension

Thirty female and male essential hypertensive patients and eighteen normotensive controls were submitted to the TRH-TSH conventional test (200 ug intravenously, bolus injection of TRH). Supramaximal doses of 400 and 600 ug were repeated with a week interval to each subject. Hypertensives showed a significant lower response to both conventional and supramaximal TRH doses. Hypothalamic-pituitary-thyroid axis abnormalities, secondary to TRH-receptor alterations, could account for this result.

Angiotensin II regulates interferon-gamma production

An extensive literature links the immune responses to neuroendocrine regulation. We have examined the effects of the neuropeptide hormone angiotensin II on the production of the immunomodulatory lymphokine interferon-gamma (IFN-gamma). Angiotensin II (10(-6)-10(-8) M) stimulated (three- to fivefold) the IFN-gamma production in human blood lymphocytes obtained from normal individuals. At 10(-9) M angiotensin II stimulation disappeared and was reestablished at physiological concentrations of the neuropeptide (10(-10)-10(-11) M). Stimulation by angiotensin II was compared with the classical effect of the lectin phytohemagglutinin, and it was seen that both actions are mediated by external calcium (as they are blocked by EGTA 2.5 mM) and that the stimuli follow different kinetics, reaching the steady state at 6 h with angiotensin II and later (18 h) when the lectin was used. The effect of angiotensin II over the IFN-gamma production was blocked by its analog sarcosine 1-isoleucine 8-angiotensin II, showing the specificity of angiotensin II action. These findings demonstrate a selective biological regulation of IFN-gamma production by angiotensin II and suggest another regulation pathway of immune responses.

Serotonin mediates cardiovascular responses to acetylcholine, bradykinin, angiotensin II and norepinephrine in the lateral septal area of the rat brain

The infusion of acetylcholine, bradykinin, angiotensin II, norepinephrine and serotonin into the lateral septal area produced a dose-dependent increase of arterial blood pressure and heart rate. A pattern of inhibition of these cardiovascular responses, produced by pretreatment of the lateral septal area with phentolamine, 6-hydroxydopamine, methysergide and 5,7-dihydroxytryptamine was disclosed. These results suggest that the effects of acetylcholine, bradykinin and partially of angiotensin II, depend on the release of norepinephrine and the actions of this neurotransmitter in turn depend on the integrity of the serotonergic system in the lateral septal area.

Muscarinic M1 receptors in the lateral septal area mediate cardiovascular responses to cholinergic agonists and bradykinin: supersensitivity induced by chronic treatment with atropine

The infusion of pilocarpine, acetylcholine, bradykinin and the selective M1 muscarinic agonist McNeil-A-343 into the lateral septal area produced a dose-dependent increase of arterial blood pressure and heart rate. The M1 muscarinic agonist carbamylcholine that causes a rise in arterial blood pressure when injected into the anterior lateral ventricles did not produce any cardiovascular effects when infused into the lateral septal area. Chronic treatment with atropine induced supersensitivity to the muscarinic agonists and a significant increase in the number of muscarinic receptors. In this study bradykinin failed to produce any significant change in cardiovascular activity. Pirenzepine, a M1 muscarinic blocking agent, inhibited completely the effect of both muscarinic agonists and bradykinin on cardiovascular activity. In fact, in vitro studies shows that the displacement of the binding of [3H]QNB by pirenzepine is compatible with the presence of the M1 subtype of muscarinic receptor in the lateral septal area, where it may play a major role on cardiovascular regulation.

Interaction between acetylcholine and bradykinin in the lateral septal area of the rat brain: involvement of muscarinic receptors in cardiovascular responses

The lateral septal area was used as a model to study the interaction between acetylcholine (Ach) and bradykinin on arterial blood pressure, since both mediators are present in this region. In the lateral septal area, the administration of the peptide or Ach produced a long-lasting, sympathetic-mediated increase of arterial blood pressure which was blocked by atropine. Pretreatment of the lateral septal area with hemicholinium-3, which depletes stores of acetylcholine, partially blocked the pressor effect of bradykinin but not that of Ach. Captopril--an inhibitor of kininase II--enhanced the pressor effects of bradykinin and Ach. Synaptosomal studies showed that bradykinin increased sodium-dependent, high-affinity uptake of choline and the conversion of [3H]choline to [3H]acetylcholine. Competition experiments using the highly specific muscarinic antagonist [3H]quinuclidinyl benzilate, demonstrated that bradykinin displaced the muscarinic antagonist from its receptor-ligand complexes. These results suggest that in the lateral septal area acetylcholine and bradykinin interact in a positive feed-back which amplifies pressor responses.

Saralasin blocks the effect of angiotensin II and extracellular fluid saline expansion on the Na-K-ATPase inhibitor release in rats

A low molecular weight substance which behaves like ouabain as inhibitor of brain membrane Na-K-ATPase and 3H-ouabain binding was found in plasma after saline expansion of extracellular fluid or angiotensin II infusion into the third brain ventricle in the rat. Intracerebroventricular infusion of angiotensin II antagonist, saralasin, blocks the increase of the Na-K-ATPase inhibitor produced by infusion of angiotensin II into the third ventricle or extracellular fluid saline expansion.

Increase in muscarinic receptors in rat intestine by thyrotropin releasing hormone (TRH)

The effect of Thyrotropin Releasing Hormone (TRH) on the contractile activity elicited by acetylcholine and electric stimulation in the rat ileus terminalis was investigated. TRH did not show any intrinsic contractile activity but, after a 30 minute latency period, the peptide caused a shift to the left of the dose-response curve for both acetylcholine and electric stimulation. The binding of 3H-quinuclidinylbenzilate (3H-QNB) assayed on ileum slices disclosed that the addition of TRH increased the number of muscarinic cholinergic receptors without changes in affinity when incubation was performed at pH 7.8, but no effect TRH was demonstrated at pH 7.4. Therefore, in spite of its neural and direct actions on intestine motor activity, TRH may affect the acetylcholine induced contraction by increasing the number of muscarinic receptors at a specific pH.

Thyrotropin-releasing hormone increases the number of muscarinic receptors in the lateral septal area of the rat brain

Stereotactic injection of acetylcholine (0.5-2 micrograms) into the lateral septal region of the rat brain produces a long-lasting sympathetic-mediated increase of the arterial blood pressure. This effect is mediated by muscarinic receptors since 1 microgram atropine abolishes this response. In this same brain region, TRH (0.5-4 micrograms) did not elicit any significant change in the arterial blood pressure, but potentiated the effect of acetylcholine. This phenomenon is apparently due to an increase of the number of muscarinic receptors in the lateral septal area of the rat brain.

Neurogenic hypertension after depletion of norepinephrine in anterior hypothalamus induced by 6-hydroxydopamine administration into the ventral pons: role of serotonin

Destruction of the ventral noradrenergic pathway elicited by administration of 6-hydroxydopamine (6-OHDA, 5 micrograms into each side of the ventral pons) reduced the content of norepinephrine (NE) in the anterior hypothalamus (-80%) and induced an increase in arterial blood pressure (ABP) and in heart rate. These hypertensive rats, showed hypersensitivity to the hypotensive effect of NE (0.5-2 micrograms) and clonidine (0.75-1.5 micrograms) administered into the anterior hypothalamic preoptic (AH/PO) region. Methysergide (1-2 micrograms) and, to a lesser extent, ketanserin (1-2 micrograms) administered into the anterior hypothalamic preoptic region also reduced the arterial blood pressure in these rats treated with 6-OHDA. Bilateral administration of 5,7-dihydroxytryptamine (5,7-DHT, 8 micrograms) into the median forebrain bundle decreased the content of serotonin (5-HT) in the hypothalamus (-85%) without change in arterial blood pressure but largely prevented the development of hypertension after treatment with 6-OHDA in the ventral pons. These results suggest that neurogenic hypertension is produced after the removal of NE tonic depressor activity in the anterior hypothalamus and that serotonergic mechanisms play a major role in the development of the increased arterial blood pressure in this preparation.