Effects of 5-hydroxytryptophan on arterial blood pressure, body temperature and tissue monoamines in the rat

Sleep quality, sleep duration, and their association with hypertension prevalence among low-income oldest-old in a rural area of China: A population-based study

OBJECTIVE

The relationship among sleep quality, sleep duration and hypertension prevalence is controversial in different age groups and genders. This study aimed to investigate sleep quality, sleep duration and their association with hypertension prevalence among low-income oldest-old in a rural area of China.

METHODS

A cross-sectional survey was conducted in a representative sample of 1066 adults aged 80-99 years in 2017. Logistic regression analysis was performed.

RESULTS

Among males, sleep durations of <6 h and 6-<7 h were significantly associated with hypertension prevalence, with odds ratios (ORs) of 3.15 (95% confidence interval (CI) 1.37 to 7.23) and 2.38 (95% CI 1.22 to 4.63), respectively. Among females, only the sleep duration of <6 h was associated with increased OR of hypertension of 3.49 (95% CI 1.50 to 8.09). Poor sleep quality was associated with hypertension for both genders (OR_men 1.67, 95% CI 1.12 to 2.49; OR_women 1.91, 95% CI 1.29 to 2.82). For women, a combination of poor sleep quality and any group of sleep duration, except for 7-<8 h, was associated with higher hypertension prevalence. For men, only the combination of poor sleep quality and short sleep duration (<7 h) was associated with high hypertension prevalence.

CONCLUSION

Short sleep duration and poor sleep quality are associated with hypertension prevalence of oldest-old. The prevention of hypertension in older adults should be investigated from the perspective of sleep improvement.

Hypothermia induced by hyperbaric oxygen is not blocked by serotonin antagonists

Exposure to HBO causes hypothermia, bradycardia, head weaving, resting tremor, piloerection, and straub tail in rats. These physiological and behavioral responses can also be evoked by selective activation of serotonin1A (5-HT1A) receptors. The purpose of the current study was to determine if hypothermia caused by HBO is due to increased activation of 5-HT1A receptors. The levels of brain biogenic amines were measured in brain regions of Sprague-Dawley (SD) rats exposed to HBO. Exposure to HBO caused an increase in the levels of 5-hydroxyindoleacetic acid (5-HIAA) in the striatum (92%, p < 0.05) and occipital-temporal cortex (116%, p < 0.05), but not in other brain regions. Exposure to HBO did not change the levels of tryptophan, serotonin (5-HT), other biogenic amines, or their metabolites. It is hypothesized that the Fawn Hood (FH) rat, which is reported to be resistant to hypothermia induced by 8-hydroxy-2-(di-n-propylamino)tetralin (8-OH-DPAT), has an abnormality of 5-HT1A receptor activity. Although the FH rat was more resistant to hypothermia induced by HBO than the SD rat, we were not able to confirm that this rat was resistant to hypothermia induced by 8-OH-DPAT. The 5-HT receptor antagonists, 1-(1H-Indol-4-yloxy)-3-[(1-methylethyl)amino]-2-propanol (Pindolol), 1-(2-methoxyphenyl)-4-[4-(2-phthalimido)butyl] piperazine hydrobromide (NAN-190), and methysergide, did not block hypothermia induced by HBO in SD rats. A series of control experiments were used to confirm that the antagonists blocked hypothermia induced by serotonin agonists.(ABSTRACT TRUNCATED AT 250 WORDS)

Serotoninergic stimulation of aldosterone secretion in vivo: role of the hypothalamo-pituitary adrenal axis

The control of aldosterone secretion in vivo by serotonin was studied in conscious rats. Serial blood samples were taken from indwelling arterial cannulae before and after i.p. administration of 1 ml (4 g/l) 5-hydroxytryptophan (5-HTP), the precursor of serotonin (5-HT), or saline, and analysed for 5-HTP, serotonin, 5-hydroxyindoleacetic acid, plasma renin activity (PRA), corticosterone, aldosterone, sodium and potassium concentration. The relative contribution of the hypothalamo-pituitary adrenal axis was investigated in animals pretreated with the synthetic glucocorticoid dexamethasone. 5-HTP caused a significant increase in all parameters within 45 min except for plasma sodium and potassium. Saline administration showed no significant effect. Dexamethasone pretreatment significantly impaired the corticosterone and aldosterone response to 5-HTP, although the aldosterone response was merely attenuated. No other parameter was affected by dexamethasone pretreatment. The results show that administration of 5-HTP, which increases serum serotonin levels, stimulates PRA, corticosterone and aldosterone secretion. Dexamethasone pretreatment inhibits the aldosterone response, though not completely, suggesting that the stimulatory action of 5-HTP involves the release of ACTH, which stimulates corticosterone and aldosterone secretion by the adrenal cortex. The failure of dexamethasone to block the aldosterone response completely, suggests the involvement of other mechanisms such as the renin-angiotensin system or a direct action of serotonin on the adrenal zona glomerulosa.

Effect of central serotonin depletion on blood pressure and the renin system in rats

In the present study we examined the effect of depletion of central nervous system serotonin by 5,7-dihydroxytryptamine on blood pressure in male Wistar rats. We also analyzed the relationship between the serotonergic and renin-angiotensin systems. Blood pressure was determined before and after intracisternal administration of 5,7-dihydroxytryptamine, 200 micrograms in saline with 1 mg/ml ascorbic acid (n = 9). Control rats (n = 8) received intracisternal vehicle. Before sacrifice, blood and cerebrospinal fluid samples were obtained. The brain was dissected in several areas. Serotonin, norepinephrine, angiotensinogen, and reninlike concentrations were determined in the brain parenchyma; angiotensinogen concentration was evaluated in cerebrospinal fluid and plasma samples; plasma renin activity was also measured. Treatment produced a significant decrease in blood pressure (-10 mm Hg; p less than 0.025) and, simultaneously, a high depletion of serotonin stores in the studied central areas (p less than 0.001), except in the cerebral cortex. Reninlike concentration was increased in the medulla oblongata (p less than 0.005) and the brainstem (p less than 0.02) after 5,7-dihydroxytryptamine treatment. Angiotensinogen concentration was decreased in the hypothalamus and elevated in the spinal cord. Angiotensinogen concentration in cerebrospinal fluid, plasma angiotensinogen concentration, and plasma renin activity did not change with treatment. Serotonin concentration in the cerebrospinal fluid remained unchanged, while the 5-hydroxyindoleacetic acid level was diminished (-47%; p less than 0.001). Intracisternal administration of 5,7-dihydroxytryptamine produced a hypotensive effect in normal rats and several modifications of the renin-angiotensin complex, suggesting a relationship between the monoaminergic and peptidergic systems.

The inhibitory action of 5-hydroxytryptamine on gastric secretory function in rats

The inhibitory action of 5-hydroxytryptamine (5-HT) on gastric function was studied in vagotomized rats. 5-HT (0.6, 1 or 5 mgkg-1, s.c.) dose-dependently reduced gastric acid secretion evoked by histamine, pentagastrin or methacholine. Pepsin secretion induced by pentagastrin or methacholine was also depressed by 5-HT. Basal secretion of both acid and pepsin was not significantly affected by any of the three 5-HT doses. Indomethacin pretreatment, which significantly decreased gastric mucosal prostaglandin E2 content, did not modify the inhibitory effects of 5-HT on histamine-induced acid secretion, nor did phentolamine or propranolol. This study suggests that 5-HT inhibits gastric secretory function through mechanisms other than by sympathetic influence or increased prostaglandin synthesis. The inhibitory action appears not to be vagus-dependent. Other mechanisms of action are discussed.

Brain serotonin and blood pressure regulation: studies using in vivo electrochemistry and direct tissue assay

Hypotensive responses to tryptophan and 5-hydroxytryptophan infusions were studied in normotensive male Sprague-Dawley rats. Results showed that 5-hydroxytryptophan but not tryptophan lowered pressure in a dose dependent way in direct relation to the production of brain serotonin and 5-HIAA. Intrinsic release of serotonin from brain was also studied during periods of induced hypertension and hypotension. Brain monoamine responses to blood pressure changes induced by intravenous phenylephrine and nitroprusside were measured in dorsal raphe nucleus and nucleus tractus solitarius by in vivo electrochemistry. Results showed that 5-HIAA was increased during drug induced hypertension and during reflex hypertension which followed a period of hypotension. These changes were blocked by sinoaortic denervation indicating that these central serotonergic neurons are responding to increased pressure sensed by baroreceptors. Therefore, serotonin has a role in blood pressure regulation as a pharmacologic agent and as a neurotransmitter in homeostatic control of pressure.

The hypotensive action of 4-(5,6-dimethyl-2-benzofuranyl) piperidine HCl (CGP 6085 A) in spontaneously hypertensive rats

CGP 6085 A, [4-(5,6-dimethyl-2-benzofuranyl)piperidine HCl], has been found to be a mild to moderately potent hypotensive agent. One hour following CGP 6085 A administration (10 mg/kg, i.p.), a maximal reduction in blood pressure of approximately 20-30 mm Hg is observed in spontaneously hypertensive rats. The maximal reduction in blood pressure was observed at a dose of 3 mg/kg. CGP 6085 A blocks 5-HT uptake in the brainstem when assessed in vivo by use of the serotonin depletor, H 75/12 (3-hydroxy-4-methyl-alpha-ethyl-phenylethylamine). The maximal inhibitory effect on 5-HT uptake occurred at 10 mg/kg CGP 6085 A. The reduction in blood pressure correlates well with the ability of the drug to inhibit 5-HT uptake as assayed by H 75/12, with a correlation coefficient of 0.71 for SH rats. However, since the drug has not been widely characterized, alternate explanations for the cardiovascular pharmacological properties of CGP 6085 A are also proposed.

Behavioral and 5-HT antagonist effects of ritanserin: a pure and selective antagonist of LSD discrimination in rat

The newly synthesized compound and putative 5-HT2 antagonist ritanserin, but not the structurally related compound R 56413, resembles pirenperone in that it acts as a pure antagonist in an LSD-saline drug discrimination assay in the rat. Ritanserin exceeded pirenperone in terms of behavioral specificity; the lowest effective dose of ritanserin in antagonizing LSD was one order of magnitude higher than that of pirenperone, but the compound depressed rate of operant responding only at doses that were about 1000-fold higher than those at which pirenperone was effective. Ritanserin exerted effects in an open field test which were reminiscent of anxiolytic drug activity in the rat; its effects were greater than those of pirenperone, R 56413 and the benzodiazepines chlordiazepoxide and diazepam. The results of experiments on antagonism of 5-HT-induced hypothermia and of the 5-HTP-induced head-twitch response fail to support the possibility that the putative anxiolytic effects of ritanserin in the rat can be ascribed simply to a pharmacologically defined action at 5-HT receptors.

Cardiovascular responses to centrally administered serotonin in conscious normotensive and spontaneously hypertensive rats

Serotonin (5-HT, 1-10 micrograms), injected into the lateral ventricle of the urethanized, and conscious normotensive and spontaneously hypertensive rats produced a dose-dependent increase in blood pressure. In conscious rats, there was mainly a decrease in heart rate while variable changes in heart rate were elicited by intraventricular (i.c.v.) administration of 5-HT in anesthetized animals. These pressor responses and bradycardia caused by 5-HT in conscious rats were reduced by pretreatment with i.c.v. methysergide (25 micrograms). Microinjection of 5-HT (2.5-5 micrograms) directly into the medial hypothalamus and the anterior hypothalamus/preoptic area of conscious normotensive rats caused a pressor response accompanied by variable changes in heart rate. The present results indicate that urethane can affect the HR response to 5-HT injected i.c.v. without having a marked influence on the pressor response. These findings, which show that 5-HT produced a rise in BP independent of the anesthetized or conscious state and of normotension or hypertension, further confirm the idea that 5-HT plays a pressor role in the central regulation of the cardiovascular system.

Altered serotonin and norepinephrine metabolism in rat dorsal raphe nucleus after drug-induced hypertension

The effect of drug-induced hypertension on neurotransmitter release from dorsal raphe nucleus was studied by in vivo electrochemical electrodes in urethane anesthetized male Sprague-Dawley rats. Carbon paste electrodes were stereotaxically placed into dorsal raphe nucleus and neurotransmitter release was estimated electrochemically. Blood pressure was recorded from a femoral arterial catheter. Voltammograms taken from dorsal raphe nucleus showed two distinct peaks corresponding to norepinephrine and 5-hydroxyindole acetic acid (5-HIAA). After basal blood pressure and neurotransmitter release were monitored for 30 min, blood pressure was raised 50 mmHg by continuous intravenous infusion of L-phenylephrine hydrochloride. Drug infusion was discontinued after 50 min, but blood pressure and neurotransmitter release were measured for an additional 2 hr. Results showed that the 5-HIAA response increased immediately after the initiation of hypertension and remained elevated. By contrast, norepinephrine release initially decreased, then returned to the basal level and then rose in parallel with 5-HIAA to a level above baseline as drug-induced hypertension was discontinued. The same experimental protocol was used to study the electrochemical response to drug-induced hypotension. Blood pressure was lowered 20 mmHg by intravenous infusion of sodium nitroprusside dihydrate. During hypotension, no changes were seen in either transmitter response. However, as reflex hypertension appeared following discontinuation of the sodium nitroprusside infusion, the 5-HIAA response increased and the norepinephrine response decreased. These results show that drug-induced and reflex hypertension reduce norepinephrine release and increase serotonin turnover in dorsal raphe nucleus in anesthetized normotensive rats. These reciprocal changes appear to be a part of the neural response to hypertension.

Effects of LM 5008, a selective inhibitor of 5-hydroxytryptamine uptake, on blood pressure and responses to sympathomimetic amines

LM 5008 (4-[2-(3-indolyl)ethyl]piperidine) (10, 20 and 50 mg kg-1) had no significant effect on pressor responses to noradrenaline or tyramine in rats anaesthetized with urethane. Desmethylimipramine (1 mg kg-1) blocked the response to tyramine but chlorimipramine (5 mg kg-1) had no significant effect on responses to noradrenaline or tyramine. In the rabbit, anaesthetized with chloralose, LM 5008 (5 mg kg-1) had no effect on pressor responses to noradrenaline, tyramine or angiotensin II, while desmethylimipramine (0.25 mg kg-1) inhibited responses to tyramine and potentiated those to noradrenaline. LM 5008 (10 mg kg-1) had no effect on resting blood pressure of conscious normotensive or DOCA-saline hypertensive rats. Tranylcypromine (5 mg kg-1) produced a fall in blood pressure in conscious normotensive and in DOCA hypertensive rats. Treatment with a combination of LM 5008 (10 mg kg-1) and tranylcypromine (5 mg kg-1) resulted in the appearance of a behavioural hyperactivity syndrome, but blood pressure was not different from that of animals treated with tranylcypromine alone. These results further demonstrate the selectivity of LM 5008 for 5-hydroxytryptamine as opposed to catecholamine uptake.

Alpha-Adrenergic and 5-hydroxytryptaminergic receptor stimulants as new antihypertensive drugs, with observations on involvement of opiate receptors

Cardiovascular actions of central alpha-adrenergic and 5-hydroxytryptaminergic stimulants are discussed in terms of overall effects, correlation of various activities, receptor activation and side-effects. The involvement of opiate receptors in their actions is also examined.

Central serotonergic participation on blood pressure regulation

1. The changes on blood pressure induced by pharmacological handling of serotonergic systems were studied in normotensive anesthetized rats. Administration of 5-hydroxytryptophan (5-HTP) (5, 10 and 30 mg/kg i.v.) produced a dose-dependent decrease in mean blood pressure without significative effect on heart rate. 2. Inhibition of either peripheral L-aminoacid DOPA decarboxylase or monoamine oxydase enzymes increased this hypotensive effect. 3. Methysergide, a serotonergic antagonist, prevented the hypotension induced by 5 OH-TP in animals whose peripheral decarboxylase was inhibited. 4. Fenfluramine, a serotonergic releasing drug, produced a decrease in both blood pressure and heart rate. These effects were prevented by inhibiting fenfluramine uptake or by serotonin (5-HT) receptor blockade. 5. The hypotensive action induced by 5-HTP was not affected when opioid, dopaminergic or histaminergic receptors were blocked. 6. In animals injected intracisternally with a serotonergic neurotoxine a selective destruction of serotonergic terminals of spinal cord was obtained. 7. In these animals the dose-response curve relating hypotensive effect induced by a direct serotonergic agonist showed a significative shift to the left when compared with control group, suggesting the existence of supersensitivity. 8. Our results show that increases in central serotonergic activity produce a hypotensive effect in normotensive anesthetized rats. The receptor involved in this action could be localized in spinal cord.

Comparison of the cardiovascular responses to intracerebroventricular administration of tryptamine, 5-hydroxytryptamine, tryptophan and 5-hydroxytryptophan in rats

General characteristics of the cardiovascular responses to intracerebroventricular (i.c.v.) injection of tryptamine, 5-hydroxytryptamine (5-HT), tryptophan and 5-hydroxytryptophan (5-HTP) were compared. Relatively small doses of tryptamine and 5-HT (0.005-0.1 microM) produced considerable, long-lasting and dose-dependent pressor effects, which sometimes were followed by prolonged depressor effects. Tryptophan (0.02-0.5 microM) and 5-HTP (0.02-0.2 microM) caused variable and usually slight, but long-lasting, vascular responses or no vascular response A large dose of tryptamine (0.5 microM) evoked variable vascular effects, while the same dose of 5-HT and 5-HTP evoked marked and prolonged depressor effects. The vascular responses to the drugs were accompanied by variable changes in heart rate. Tryptamine, 5-HT and 5-HTP, in the majority of rats, produced a bradycardia. The present study provides evidence that the cardiovascular response to i.c.v. administration of tryptamine is similar to that of 5-HT, supporting the idea that tryptamine, in addition to 5-HT, participates in the central physiological regulation of the rat cardiovascular system. The role of tryptophan and 5-HTP by themselves in this regulation, if any is of secondary importance.

Pressor effects of dorsal raphe stimulation and intrahypothalamic application of serotonin in the spontaneously hypertensive rat

Electrical stimulation of the dorsal raphe nucleus or direct microinjection of serotonin into the preoptic region of the anterior hypothalamus produces a transient rise in arterial blood pressure in both spontaneously hypertensive rats (SRH) and Wistar--Kyoto (WKY) controls. SRHs are more responsive to raphe stimulation but are somewhat less responsive to serotonin injections when compared to WKYs. The serotonin antagonist metergoline blocks the pressor response to serotonin in both strains. These results suggest that the central serotonergic neuronal system play a similar, but not identical, role in blood pressure modulation in hypertensive and normotensive rats.

Contrasting effects of clonidine and 5-hydroxytryptophan on spinal sympathetic pathways

The effects of clonidine HCI were compared with those of 5-HTP on transmission through two spinal sympathetic pathways, segmental spinal reflex pathways and descending intraspinal excitatory pathways, in unanesthetized spinal cats. Evoked sympathetic discharges were recorded from upper thoracic preganglionic rami. Clonidine (5-50 microgram/kg) produced a parallel, dose-dependent depression of transmission through each pathway. The intraspinal pathway was five time more sensitive than the spinal reflex pathway (ED50's, 6 and 30 microgram/kg), and the spinal reflex pathway could not be depressed by more than 60% even by higher doses. In contrast, 5-HTP was more effective in depressing the spinal reflex than the intraspinal pathway (ED50's 32 and 44 mg/kg), and both pathways could be depressed completely. Small doses of tolazoline or yohimbine rapidly antagonized the effects of clonidine but not 5-HTP. Clonidine and 5-HTP appear to depress the excitability of sympathetic preganglionic neurons by activating alpha2- and 5-HT receptors, respectively. Each mechanism may contribute independently to regulation of the sympathetic outflow.

Studies of carbachol-induced wet-dog shake behavior in rats

Intraventricular administration of carbachol chloride evoked wet-dog shakes (WDS) in rats in a dose-related manner. WDS induced by carbachol at the dose of 20 microgram were antagonized by scopolamine, atropine, cyproheptadine, morphine, clonidine, phentolamine, haloperidol, and L-5-hydroxytryptophan (5-HTP). Methergoline, propranolol, bicuculline, and aminooxyacetic acid had no effect on carbachol-induced shaking behavior. The present experiments show the existence of different types of shaking behavior, not exclusively related to the stimulation of central 5-HT structures.

Failure to produce blood pressure changes following pharmacological or surgical depletion of brain serotonin in the spontaneously hypertensive rat

Spontaneously hypertensive (SH) and normotensive (Wistar-Kyoto, WKY) rats were examined for blood pressure changes following depletion of CNS serotonin (5-HT) by 3 separate techniques: (1) p-chlorophenylalanine, (2) 5,7-dihydroxytryptamine, and (3) a lesion of the dorsal and median raphe nuclei. All of these procedures failed to alter blood pressure in either hypertensive or normotensive rats, despite marked reductions (75-85%) in forebrain 5-HT. Moreover, treatment of 10 day-old hypertensive rat pups with intracisternal injections of 5,7-DHT (10 microgram) failed to alter the development of hypertension despite a 75-80% decrease in spinal cord 5-HT. These findings, which show that 5-HT depletion does not alter blood pressure in the SH or the WKY rat, do not lend support to the idea that 5-HT is involved in the regulation of blood pressure or in the development and maintenance of hypertension in the SH rat.

Review of the role of the central serotonergic neuronal system in blood pressure regulation

Alterations in the dynamics of brain serotonin biosynthesis can lead to changes in cardiovascular function. It appears that the activation of cerebral serotonin receptors produces a pressor effect in normotensive rats but produces a depressor effect in normotensive cats or dogs. On the other hand, reductions in the levels of serotonin can prevent the onset of hypertension in some experimental hypertensive models and lower the blood pressure of organisms with established hypertension. The ability of brain serotonin to modulate arterial blood pressure may be mediated by the influences of the serotonergic neuronal systems on efferent sympathetic activity. Finally, the reduction in sympathetic outflow produced by increasing brain serotonin levels in dogs protects the heart against ventricular fibrillation and may, therefore, constitute a reasonable adjunct in the management of high-risk, cardiac-arrest patients.

Changes in body temperature after administration of amino acids, peptides, dopamine, neuroleptics and related agents

Drugs may alter body temperature by acting on any component of the thermoregulatory system. These components include heat production, heat conservation and heat loss effectors and their efferent pathways, thermosensors and their afferent pathways and neurons within the central nervous system that coordinate thermoregulatory effector activities. A thermostat is often thought to be involved although thermoregulation can be explained by models that do not incorporate a thermostat. An action on a particular component can be assessed by determining the effect of a drug on body temperature over a range of environmental temperatures and by observation and measurement of associated changes in effector activities. A scheme for such assessment is presented along with examples of its use. The study of drug-induced changes in body temperature has expanded greatly within the past decade. The primary purpose of this review is to provide a readily available source of information on interactions between certain drugs and the thermoregulatory system. Extensive tables are presented of body temperature changes after administration of amino acids, peptides, dopamine and related agents, phenothiazine neuroleptics and also phenothiazines that lack neuroleptic activity, butyrophenones, diphenylbutylpiperidines such as pimozide and miscellaneous neuroleptics. The information tabulated includes the species used, route of administration and dose of drugs, the environmental temperature at which the experiments were performed, the number of tests, the direction and magnitude of body temperature change and remarks on the presence of special conditions, such as age or lesions, or on the influence of other drugs, such as antagonists, on the response to the primary drug. Most of the cited literature was published since 1965.

The involvement of serotonergic neurons in the central nervous system as the possible mechanism for slow head-shaking behavior induced by methamphetamine in rats

Following the IV administration of d-methamphetamine (MA), rats showed slow head shaking (SHS) and stereotyped gnawing (SG) behaviors in a dose-dependent manner. Methysergide, cyrpoheptadine, and p-chlorophenylalanine given intracerebroventricularly (ICV) or systemically significantly blocked SHS behavior induced by 10 mg/kg MA. Combined administration of L-5-hydroxytryptophan and peripheral decarboxylase inhibitor (Ro 4-4602) enhanced SHS behavior. Tyrosine hydroxylase inhibitor (H44/68) blocked SG behaviors, but dopamine-beta-hydroxylase inhibitors (FLA 63 and U-14, 624) and combined administration of L-3,4-dihydroxyphenylalanine and Ro-4-4602 enhanced it. These drugs did not affect SHS behavior. Phentolamine, phenoxybenzamine, clonidine, isoproterenol, and propranolol given ICV or systemically showed no effect on either SHS or SG behaviors. These results suggest that SHS behavior is produced by the activation of seronergic neurons in the central nervous system and are consistent with the view that SG behaviors are mediated through the release of dopamine. Some neuroleptics inhibited SHS as well as SG behaviors, but the older of inhibitory activity of neuroleptics onSHS behavior was quite different from their effects on SG behaviors induced by MA or apomorphine.

Bulbospinal tryptaminergic neurones. A search for the role of bulbospinal tryptaminergic neurones in the control of sympathetic activity

1. The possible role of bulbospinal tryptaminergic neurones in the control of sympathetic activity has been investigated in anaesthetised cats. 2. Depletion of spinal cord stores of 5-hydroxytryptamine was achieved by systemic administration of p-chlorophenylalanine or by intraspinal microinjections of 5,6-dihydroxytryptamine. 3. Blood pressure was little changed by these treatments, neither was the pattern of ongoing activity in sympathetic nerves (arterial pulse rhythmicity and respiratory modulation), the influence of pulmonary afferent nerves on this activity (determined by an airway occlusion technique), the sympatho-inhibitory influence of the carotid sinus baroreceptors, nor the sympatho-inhibitory or -excitatory influences of somatic afferent nerves. 4. Since both p-chlorophenylalanine and 5,6-dihydroxytryptamine treatment caused extensive disruption of the bulbospinal tryptaminergic neurones, it was concluded that these play no significant role in the mediation of the responses tested in anaesthetised cats in the present study.

Effect of midbrain raphé lesions or intracisternal 6-hydroxydopamine administration on D, L-5-hydroxytryptophan-14C metabolism after peripheral decarboxylase inhibition

Brain and blood 14C-5-hydroxyindole metabolism was studied in normal, raphé-lesioned and 6-hydroxydopamine (60HDA)-treated rats given L-(-)-alpha-hydrazino-3, 4-dihydroxy-alpha-methylhydrocinnamic acid (MK-486) (50 mg/kg) intraperitoneally and 5-hydroxytryptophan (5-HTP)-14C (5 muCi, 0.51 mCi/mmol) intravenously. Raphé lesioning and 60HDA treatment caused significant decrements in brain 5-hydroxytryptamine (5-HT)-14C and 5-hydroxyindoleacetic acid (5-HIAA)-14C levels and 5-HT concentrations compared to those in normal controls. In normal and 60HDA-treated rats there were decreased brain dopamine levels, possibly a consequence of non-specific metabolism of 5-HTP in brain. Blood 5-HIAA-14C levels were significantly decreased in 60HDA-treated but not raphé-lesioned rats. As increased brain 5-HT turnover was observed in raphé-lesioned rats, this may have prevented a decrease in blood 5-HIAA-14C levels. The results suggest that changes in blood 5-HIAA-14C following MK-486 and 5-HTP-14C may be related to changes in brain 5-HT-14C metabolism.

Effect of intracerebroventricular 5,6-dihydroxytryptamine on blood pressure of spontaneously hypertensive rats

The effects of intracerebroventricular injections of 5,6-DHT on the development and maintenance of hypertension in spontaneously hypertensive rats has been investigated. 5,6-DHT, injected into 6 week old rats, retarded the development of hypertension for at least 6 weeks; this effect was not accompanied by inhibition of the pressor response produced by stimulation of the total peripheral sympathetic outflow. 5,6-DHT, injected into 14-15 week old rats with established hypertension, produced a short-lived fall in blood pressure. These findings suggest that central 5-HT neurones are involved in the development of hypertension in spontaneously hypertensive rats.

Prolonged effects of p-chlorophenylalanine on the blood pressure of conscious normotensive and DOCA/saline hypertensive rats

1. In deoxycorticosterone acetate (DOCA) saline hypertensive rats a single dose of p-chlorophenylalanine methylester (PCPAME) (400 mg/kg i.p.) produced a significant fall in blood pressure (20-43 mmHg) which lasted for at least 8 days and was accompanied by a parallel depletion of brain stem 5-hydroxytryptamine (5-ht) but not of noradrenaline (NA). 2. In normotensive rats single doses of PCPAME (200 and 400 mg/kg i.p.) produced a significant hypotension (15-20 mmHg) after a latent period of 5 days. An initial pressor response (12 mmHg) was observed at the higher dose level only on day 3. 3. The hypotensive response to PCPAME (200 mg/kg i.p.) in normotensive rats was not modified by pretreatment with 5,6-dihydroxytryptamine (5,6-DHT; 50 mug i.c.v.) or 6-hydroxydopa (6-ohda; 3 X 250 mug intracerebroventricularly). 4. It is concluded that the hypotensive response to PCPAME in normotensive rats in independent of brain stem depletion of 5-HT and is probably not mediated by the formation of a false transmitter substance acting via central noradrenergic inhibitory pathways. The mechanism involved in the antihypertensive response to PCPAME in DOVA/saline hypertensive rats has yet to be defined.

Time and dose influences on the behavioral effects of L-DOPA and 5-hydroxytryptophan after inhibition of extracerebral decarboxylase

The influence of time and dose factors on the locomotor activity and gross behavioral effects of l-3,4-dihydroxyphenylalanine (L-DOPA) and 5-hydroxytryptophan (5-HTP) were assessed a albino mice pretreated with the peripheral decarboxylase inhibitor, MK-486, L-DOPA caused stereotyped behaviors and a decrease in orienting responses and locomotor activity, followed at the highest dose by increased locomotor activity. 5-HTP caused a dose-dependent increase in orienting responses and locomotor activity followed after 90 min by a dose-dependent decrease in locomotor activity. Administration of MK-486 and L-DOPA followed in the same animal by 5-HTP resulted in a diminution of the effects seen after either drug alone. This apparent antagonism may result from competition between the two amino acids at sites of membrane transport in the brain.