Diabetes and derived complications, especially diabetic nephropathy and neuropathy annually cause great morbimortality worldwide. 5-hydroxytryptamine (5-HT) acts as a modulator of renal sympathetic input and vascular tone. In this line, 5-HT₂ receptor blockade has been linked with reduced incidence and progression of diabetic microvascular alterations. In this work, we aimed to determine, in diabetic rats, whether 5-HT₂ blockade ameliorates renal function and to characterize the serotonergic modulatory action on renal sympathetic neurotransmission. Diabetes was induced in male Wistar rats by alloxan administration (150 mg/kg, s.c.), and sarpogrelate (30 mg/kg·day, p.o.; 5-HT₂ antagonist) was administered for 14 days (DM-S). Normoglycemic and diabetic (DM) animals were maintained as aged-matched controls. At 28th day, DM-S animals were anesthetized and prepared for the in situ autoperfusion of the kidney. Renal vasoconstrictor responses were induced electrically or by i.a. noradrenaline (NA) administration. The role of 5-HT and selective 5-HT agonist/antagonist were studied on these renal vasopressor responses. Sarpogrelate treatment decreased renal sympathetic-induced vasopressor responses, reduced renal hypertrophy and kidney damage markers increased in DM. Intraarterial 5-HT inhibited the sympathetic-induced renal vasoconstrictions, effect reproduced by 5-CT, AS-19, L-694,247 and LY 344864 (5-HT_1/5/7, 5-HT₇, 5-HT_1D and 5-HT_1F receptor agonists, respectively). Blocking 5-HT_1D/1F/7 receptors completely abolished the 5-CT sympatho-inhibition. NA vasoconstrictions were not altered by any of the 5-HT agonists tested. Thus, in experimental diabetes, chronic sarpogrelate treatment reduces renal damage markers, kidney hypertrophy and renal sympathetic hyperactivity and modifies serotonergic modulation of renal sympathetic neurotransmission, causing a sympatho-inhibition by prejunctional 5-HT_1D/1F and 5-HT₇ activation.

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.

Background and Purpose: In male rats, the serotonergic system modulates sympathetic outflow at vascular levels, causing sympatho‐inhibition and sympatho‐excitation, mainly via 5‐HT_1D/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‐HT_1/5/7) and L‐694,247 (5‐HT_1D), whereas the selective 5‐HT_2A/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‐HT_1A/1B/1F, 5‐HT_2B/2C, 5‐HT₄, 5‐HT_5A 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‐HT_1D receptor activation, whereas pre and/or postjunctional 5‐HT₃ and prejunctional 5‐HT_2A 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.

The vascular 5-HT sympatho-modulation may involve inhibitory or potentiating pathways: nitric oxide (NO), endothelium-dependent hyperpolarization (EDH)-K⁺ channels, prostanoids, angiotensin II (Ang-II), or endothelin. Compared to males, female rats show differences in the serotonergic sympatho-regulation; therefore, we aimed to study the involvement of indirect pathways via 5-HT_1D-mediated inhibition and 5-HT_2A/3-mediated potentiation of vascular noradrenergic neurotransmission in females. An i.v. bolus of different inhibitors/blockers of modulators/mediators (NO, K⁺ channels, prostanoids, Ang-II, or endothelin) was administered prior to the infusion of the agonists, L-694,247 (5-HT_1D), TCB-2 (5-HT_2A), or 1-PBG (5-HT₃), in female pithed rats. In these conditions, the vascular sympathetic outflow was electrically stimulated to assess the vasopressor responses. The L-694,247 vascular sympatho-inhibition was abolished by a non-selective K⁺ channel blocker, tetraethylammonium. The 1-PBG sympatho-excitatory vascular effect was not modified by any of the inhibitors tested, whereas TCB-2 sympatho-potentiation was blocked solely by losartan (Ang-II type 1 receptor antagonist). Moreover, Ang-II levels were increased after TCB-2 infusion in females. The EDH pathway mediates the 5-HT_1D-induced sympatho-inhibition, while the 5-HT_2A-evoked sympatho-excitatory effect is associated with Ang-II. In contrast, the 5-HT₃ sympatho-potentiation does not involve any indirect pathway. These findings advance current understanding of the complex interactions between 5-HT and vascular homeostasis in female rats.

Background and purpose: Serotonin modulates vascular tone both directly and indirectly through autonomic and sensory nerves innervating blood vessels. Perivascular sensory nerves release calcitonin gene-related peptide (CGRP), a potent vasodilator strongly implicated in migraine pathophysiology. In male rats, the serotonergic system inhibits CGRPergic vasodepressor responses via 5-HT _1B/1F and 5-HT ₇ receptors. Since both serotonergic and CGRPergic pathways exhibit marked sex differences, the present study investigated the 5-HT receptor (sub)types involved in the 5-carboxamydotryptamine (5−CT, 5-HT _1/5/7 receptor agonist) modulation of vascular CGRPergic neurotransmission in rats, focusing on sex-dependent differences. Methods: Male and female Wistar rats (14–16 weeks old) were pithed and pretreated with an i.v. continuous infusion of hexamethonium and methoxamine, followed by administration of 5-HT-related drugs. Mean blood pressure (MBP) and heart rate (HR) were continuously recorded throughout the experiments. Vasodepressor CGRPergic responses were elicited by electrical stimulation of the sensory outflow (0.1–5 Hz) or i.v. α-CGRP (0.1–1 μg/kg). Results: Basal MBP and HR were lower in females than in males, whereas the methoxamine-induced increase in MBP was greater in females. The electrically evoked vasodepressor responses, as well as their inhibition by 5−CT, were similar in both sexes. In males, the inhibitory effect of 5−CT was reproduced by 5-HT _1B , 5-HT _1F , and 5-HT ₇ receptor agonists (CP-93,129, LY344864, and AS-19, respectively) and persisted in the presence of the 5-HT _5A receptor antagonist SB699551. In contrast, in females, 5-CT-induced inhibition was mimicked by 5-HT _1F and 5-HT ₇ receptor agonists and was not affected by administration of SB699551. None of the other 5-HT receptor agonists (5-HT _1A/1B/1D ) modified the CGRPergic vasodilator responses in females. Only AS-19 reduced the vasodepressor responses elicited by exogenous α-CGRP in females. Conclusion: 5−CT inhibits perivascular sensory CGRPergic neurotransmission in both male and female rats. Unlike males, where the 5−CT effect is mediated by prejunctional 5-HT _1B/1F/7 receptors, in females, this inhibitory effect is mediated by prejunctional 5-HT _1F and pre and/or postjunctional 5-HT ₇ receptors. These findings provide novel insights into sex-specific serotonergic modulation of neurovascular function.