Vascular sympathetic neurotransmission and its serotonergic regulation are modified by chronic fluoxetine treatment

Sex influence on serotonergic modulation of the vascular noradrenergic drive in rats

BACKGROUND AND PURPOSE

In male rats, the serotonergic system modulates sympathetic outflow at vascular levels, causing sympatho-inhibition and sympatho-excitation, mainly via 5-HT1D/1A and 5-HT3 receptors, respectively. However, sex influence on vascular serotonergic regulation has not yet been elucidated. This study aimed to analyse the 5-HT sympatho-modulatory role in female rats, characterising the 5-HT receptors involved.

EXPERIMENTAL APPROACH

Female Wistar (14- to 16-week-old) rats were prepared for sympathetic stimulation. Mean blood pressure (MBP) and heart rate (HR) were continuously measured. Vasopressor responses were obtained by electrical stimulation of the sympathetic outflow (0.1-5 Hz) or i.v. noradrenaline (0.01-0.5 μg·kg-1). 5-HT-related drug effects on adrenergic system were determined. Age-matched male rats were used as control.

KEY RESULTS

Basal MBP in females was lower than in male rats, whereas electrical-induced increases in MBP were similar. In females, 5-HT exerted a dose-dependent inhibition on the sympathetic-evoked vasoconstrictions, that was reproduced by some agonists; 5-CT (5-HT1/5/7) and L-694,247 (5-HT1D), whereas the selective 5-HT2A/2B/2C (α-methyl-5-HT) and 5-HT3 agonist (1-PBG) increased the electrically-produced vasopressor responses. None of the other drugs tested (targeting 5-HT1A/1B/1F, 5-HT2B/2C, 5-HT4, 5-HT5A or 5-HT7) modified these vasoconstrictions. Only 1-PBG (5-HT3) modified the vasoconstrictions induced by exogenous noradrenaline.

CONCLUSIONS AND IMPLICATIONS

In female rats, vascular serotonergic sympatholytic effects are due to prejunctional 5-HT1D receptor activation, whereas pre and/or postjunctional 5-HT3 and prejunctional 5-HT2A receptor activation is involved in the potentiating effect of vascular sympathetic neurotransmission. These findings may open novel sex-differential therapeutic strategies for treating cardiovascular conditions.

A meta-analysis on the association between SSRIs and blood pressure in patients with CVD and depression

OBJECTIVE

This meta-analysis aimed to explore the association between selective serotonine reuptake inhibitors (SSRIs) and blood pressure in patients with cardiovascular disease (CVD) and depression.

METHOD

This study was registered on PROSPERO (CRD42022368655) and conducted in accordance with PRISMA 2020. The databases included PubMed, Web of Science, and EMBASE. The inclusion date was from the inception date through Oct. 26, 2022.Review Manager version 5.3 and Stata version 12.0 were used for data analysis.

RESULTS

This meta-analysis included six studies, and a total number of 149 patients with CVD and depression . In the group analysis, SSRIs treatment had no effect on the systolic blood pressure (SBP) (MD = 1.01, 95%CI:-2.88, 4.90, P = 0.61) and diastolic blood pressure (DBP) (MD = 0.64, 95%CI:-1.03, 2.31, P = 0.45). In the subgroup analysis, SSRIs treatment had no effect on SBP for patients with hypertension (MD = -8.02, 95%CI:-16.84, 0.81, P = 0.08), and patients with other CVD (MD = 3.18, 95%CI:-1.15, 7.52, P = 0.15). For patients with hypertension, SSRIs treatment significantly lowered DBP (MD = -5.75, 95%CI:-10.84, -0.67, P = 0.03). But SSRIs treatment had no impact on DBP for patients with other CVD (MD = 1.41, 95%CI:-0.36, 3.18, P = 0.12). Subgroup analysis of the treatment period and the country had no significant impact on SBP and DBP. In the sensitivity analysis, there was no significant change after omitting one study in both SBP and DBP group analysis. Egger's test showed no publication bias of SBP (P = 0.183) and DBP group analysis (P = 0.392).

CONCLUSION

SSRIs help to lower DBP in hypertensive patients with depression. The potential pathophysiological mechanisms may lie in serotonin function, sympathetic activation and genetic heterogeneity. Further clinic and experimental researches need to be conducted on SSRIs and blood pressure.

Renal Sympathetic Hyperactivity in Diabetes Is Modulated by 5-HT1D Receptor Activation via NO Pathway

Renal vasculature, which is highly innervated by sympathetic fibers, contributes to cardiovascular homeostasis. This renal sympathetic outflow is inhibited by 5-HT in normoglycaemic rats. Considering that diabetes induces cardiovascular complications, we aimed to determine whether diabetic state modifies noradrenergic input at renal level and its serotonergic modulation in rats. Alloxan diabetic rats were anaesthetized (pentobarbital; 60 mg/kg i.p.) and prepared for in situ autoperfusion of the left kidney to continuously measure systemic blood pressure (SBP), heart rate (HR), and renal perfusion pressure (RPP). Electrical stimulation of renal sympathetic outflow induces frequency-dependent increases (Δ) in RPP (23.9 ± 2.1, 59.5 ± 1.9, and 80.5 ± 3.5 mm Hg at 2, 4, and 6 Hz, respectively), which were higher than in normoglycaemic rats, without modifying HR or SBP. Intraarterial bolus of 5-HT and 5-CT (5-HT_1/5/7 agonist) reduced electrically induced ΔRPP. Only L-694,247 (5-HT_1D agonist) reproduced 5-CT inhibition on sympathetic-induced vasoconstrictions, whereas it did not modify exogenous noradrenaline-induced ΔRPP. 5-CT inhibition was exclusively abolished by i.v. bolus of LY310762 (5-HT_1D antagonist). An inhibitor of guanylyl cyclase, ODQ (i.v.), completely reversed the L-694,247 inhibitory effect. In conclusion, diabetes induces an enhancement in sympathetic-induced vasopressor responses at the renal level. Prejunctional 5-HT_1D receptors, via the nitric oxide pathway, inhibit noradrenergic-induced vasoconstrictions in diabetic rats.

Effect of sarpogrelate treatment on 5-HT modulation of vascular sympathetic innervation and platelet activity in diabetic rats

This study aimed to investigate whether the 5-HT₂ receptor blockade alters the 5-HT effect on vascular sympathetic neurotransmission and platelet activation in type 1 diabetes. 28-day diabetes was obtained by alloxan (150 mg/kg; s.c.) in male Wistar rats, administering sarpogrelate (5-HT₂ blocker; 30 mg/kg/day; p.o.) for 14 days. Blood glucose and body weight were monitored for 28 days. After 4 weeks of diabetes induction, food and drink intake, urine, plasma-platelet 5-HT, and platelet activation were determined in normoglycemic, non-treated diabetic and sarpogrelate-treated diabetic rats. Another set of diabetic rats were pithed to run the vascular sympathetic stimulation or exogenous noradrenaline administration, examining the induced vasoconstrictor responses. Sarpogrelate treatment significantly reduced drink intake and urine, whereas BW gain, hyperglycemia, and food intake were not modified in diabetic rats. The platelet activation and plasma 5-HT concentration were decreased (increasing the stored 5-HT platelet) by 5-HT₂ blockade in diabetic animals. The sympathetic-induced vasoconstrictions were higher in non-treated than in sarpogrelate-treated diabetic rats. 5-HT inhibited these vasopressor responses, reproduced exclusively by the 5-HT_1/5/7 receptor agonist, 5-CT. The 5-CT-produced inhibition was partly reversed by 5-HT_1D or 5-HT₇ antagonists (LY310762 or SB-258719, respectively), and totally annulled by the mixture of LY310762+SB-258719. Noradrenaline-caused vasoconstrictions were also decreased by 5-CT. In conclusion, our results reveal that 14-day sarpogrelate treatment improves polydipsia and polyuria, reduces platelet hyperactivation, plasma 5-HT and the vascular sympathetic tone, and changes 5-HT receptors inhibiting noradrenergic drive in diabetic rats: pre and/or postjunctional 5-HT_1D/7 are involved in the sympatho-inhibition.

Fluoxetine Treatment Decreases Cardiac Vagal Input and Alters the Serotonergic Modulation of the Parasympathetic Outflow in Diabetic Rats

Comorbid diabetes and depression constitutes a major health problem, worsening associated cardiovascular diseases. Fluoxetine's (antidepressant) role on cardiac diabetic complications remains unknown. We determined whether fluoxetine modifies cardiac vagal input and its serotonergic modulation in male Wistar diabetic rats. Diabetes was induced by alloxan and maintained for 28 days. Fluoxetine was administered the last 14 days (10 mg/kg/day; p.o). Bradycardia was obtained by vagal stimulation (3, 6 and 9 Hz) or i.v. acetylcholine administrations (1, 5 and 10 μg/kg). Fluoxetine treatment diminished vagally-induced bradycardia. Administration of 5-HT originated a dual action on the bradycardia, augmenting it at low doses and diminishing it at high doses, reproduced by 5-CT (5-HT_1/7 agonist). 5-CT did not alter the bradycardia induced by exogenous acetylcholine. Decrease of the vagally-induced bradycardia evoked by high doses of 5-HT and 5-CT was reproduced by L-694,247 (5-HT_1D agonist) and blocked by prior administration of LY310762 (5-HT_1D antagonist). Enhancement of the electrical-induced bradycardia by 5-CT (10 μg/kg) was abolished by pretreatment with SB269970 (5-HT₇ receptor antagonist). Thus, oral fluoxetine treatment originates a decrease in cardiac cholinergic activity and changes 5-HT modulation of bradycardic responses in diabetes: prejunctional 5-HT₇ receptors augment cholinergic-evoked bradycardic responses, whereas prejunctional 5-HT_1D receptors inhibit vagally-induced bradycardia.

Oral fluoxetine treatment changes serotonergic sympatho-regulation in experimental type 1 diabetes

AIMS

This study investigated whether fluoxetine treatment changes the 5-HT regulation on vascular sympathetic neurotransmission in type 1 diabetes.

MAIN METHODS

Four-week diabetes was obtained by a single alloxan s.c. administration in male Wistar rats, administering fluoxetine for 14 days (10 mg/kg/day; p.o.). Systolic blood pressure, heart rate, glycaemia, body weight (BW) evolution, creatinine, and blood urea nitrogen (BUN) were monitored. Afterward, rats were pithed to perform the vascular sympathetic stimulation. 5-HT_1A/1D/2A receptors expression was analysed by Western blot in thoracic aorta. Both i.v. norepinephrine and the electrical stimulation of the spinal sympathetic drive evoked vasoconstrictor responses.

KEY FINDINGS

Fluoxetine treatment significantly reduced the BW gain, hyperglycaemia, creatinine, and BUN in diabetic rats. The electrical-produced vasopressor responses were greater in untreated than in fluoxetine-treated diabetic rats. 5-HT decreased the sympathetic-produced vasopressor responses. While 5-CT, 8-OH-DPAT and L-694,247 (5-HT_1/7, 5-HT_1A and 5-HT_1D agonists, respectively) reproduced 5-HT-evoked inhibition, the 5-HT₂ activation by α-methyl-5-HT augmented the vasoconstrictions. The 5-CT sympatho-inhibition was reversed by 5-HT_1A plus 5-HT_1D antagonists (WAY-100,635 and LY310762, respectively), whereas ritanserin (5-HT_2A antagonist) blocked the α-methyl-5-HT potentiating effect. Norepinephrine-generated vasoconstrictions were increased or diminished by α-methyl-5-HT or 5-CT, respectively. 5-HT_1A/1D/2A receptors were expressed at vascular level, being 5-HT_1A expression increased by fluoxetine in diabetic rats.

SIGNIFICANCE

Our findings suggest that fluoxetine improves metabolic and renal profiles, changes the vasopressor responses, and 5-HT receptors modulating sympathetic activity in diabetic rats: 5-HT_1A/1D are involved in the sympatho-inhibition, while 5-HT_2A is implicated in the sympatho-potentiation, being both effects pre and/or postjunctional in nature.