Evidence that serotonin receptors mediate the cutaneous vasoconstriction produced by 5-hydroxytryptamine in canine forelimbs

Serotonin and blood pressure regulation

5-Hydroxytryptamine (5-HT; serotonin) was discovered more than 60 years ago as a substance isolated from blood. The neural effects of 5-HT have been well investigated and understood, thanks in part to the pharmacological tools available to dissect the serotonergic system and the development of the frequently prescribed selective serotonin-reuptake inhibitors. By contrast, our understanding of the role of 5-HT in the control and modification of blood pressure pales in comparison. Here we focus on the role of 5-HT in systemic blood pressure control. This review provides an in-depth study of the function and pharmacology of 5-HT in those tissues that can modify blood pressure (blood, vasculature, heart, adrenal gland, kidney, brain), with a focus on the autonomic nervous system that includes mechanisms of action and pharmacology of 5-HT within each system. We compare the change in blood pressure produced in different species by short- and long-term administration of 5-HT or selective serotonin receptor agonists. To further our understanding of the mechanisms through which 5-HT modifies blood pressure, we also describe the blood pressure effects of commonly used drugs that modify the actions of 5-HT. The pharmacology and physiological actions of 5-HT in modifying blood pressure are important, given its involvement in circulatory shock, orthostatic hypotension, serotonin syndrome and hypertension.

Immunohistochemical study of serotonin in lesions of chronic eczema

BACKGROUND

Inflammatory mediators participate in the pathogenesis and pathophysiology of skin disease (e.g. eczema). Although some investigators have suggested that serotonin may participate in the eczematous process, there has been little substantial evidence. Our objective was to study further the participation of serotonin in the pathogenesis of chronic eczema.

METHODS

Immunohistochemical techniques were used to study the expression of serotonin in the lesions of patients with chronic eczema.

RESULTS

There was a significantly stronger expression of serotonin in the prickle cells, sweat gland cells, sebaceous gland cells, and hair roots of the lesions in patients with chronic eczema. There was no positive expression of serotonin in normal skin.

CONCLUSIONS

Serotonin is probably important in the pathogenesis of chronic eczema. We demonstrated alterations in the expression of serotonin in chronic eczema lesions, which may in turn provide new insight into the pathogenesis of chronic eczema. Serotonin, along with cytokines, T lymphocytes, B lymphocytes, and macrophages, participates in the immune response and influences the inflammatory process by means of keratinocytes.

Hemodynamic effects of prostacyclin infusions in healthy volunteers

The selective hemodynamic effects of an intravenous infusion of prostacyclin on skin and on forearm blood flow during increasing doses up to 6 ng.kg.-1 min.-1 were evaluated in 12 healthy volunteers. The highest dose raised total skin blood flow (p = 0.0001) as measured by laser Doppler with a concomitant rise in finger skin temperature (p = 0.02). Capillary perfusion as measured by transcutaneous oxygen monitoring remained relatively unaffected (p = 0.25). Cold-induced vasoconstriction and the recovery thereafter were not influenced. Diastolic blood pressure tended to decrease (p = 0.06), but there was no change in systolic blood pressure, forearm blood flow, and calculated forearm vascular resistance. The authors conclude that prostacyclin may have dissimilar vasoactive potencies in different vascular beds as shown by a pronounced increase in total skin blood flow, owing to vasodilation of shunt vessels, simultaneously with an insignificant change in nutritional skin blood flow and forearm muscle blood flow.

Effects of MDL 72222 and methiothepin on carotid vascular responses to 5-hydroxytryptamine in the pig: evidence for the presence of "5-hydroxytryptamine1-like" receptors

The present study concerns the effects of MDL 72222 (0.5 mg X kg-1, i.v.), a 5-hydroxytryptamine3 (5-HT3) receptor antagonist, and methiothepin (1.0 mg X kg-1, i.v.), an antagonist of both 5-HT2 and "5-HT1-like" receptors, on the responses to local infusions of 5-HT (2.0 micrograms X kg-1 X min-1) on the total common carotid artery blood flow and its complete distribution in anaesthetized pigs. As reported earlier, more than 80% of the carotid blood bypassed the capillary circulation via cranial arteriovenous anastomoses, while approximately 15% and 2% was distributed to the extracerebral structures and brain, respectively. The total carotid blood flow did not change or was moderately reduced by 5-HT, but the amine consistently caused a 85% reduction in arteriovenous anastomotic blood flow and a 5-fold increase in blood flow to the extracerebral tissues, mainly the skin and ears. The colour of the skin and ears changed to bright pink. Complete recovery from the effects of 5-HT was observed once the infusion was stopped. MDL 72222 and methiothepin did not themselves affect carotid haemodynamics. The responses to 5-HT were not modified by MDL 72222 except that the reduction of the total carotid blood flow by 5-HT was augmented. In contrast, methiothepin almost completely abolished both the reduction of arteriovenous anastomotic blood flow and the increase in tissue blood flow following 5-HT-infusion. The colour of the skin and ears also did not become pink.(ABSTRACT TRUNCATED AT 250 WORDS)

Inhibition of cold-induced vasoconstriction with ketanserin

The role of serotonin, thromboxane A2, and prostacyclin in cold-stimulated vasoconstriction was studied in 11 volunteers randomly pretreated with placebo, antagonists to serotonin (ketanserin, 40 mg), cyclooxygenase (ibuprofen, 800 mg), or thromboxane synthetase (ketoconazole, 400 mg). With an ambient temperature of 27 degrees, the hand and distal arm of one side were immersed in iced slush for 2 min. At the end of this time there was a fall in skin temperature from 31.2 to 12.2 degrees. Six minutes later with ketanserin treatment, temperature rose 4.5 degrees above placebo (P less than 0.05). In the noncooled side, ketanserin led to a rise in baseline temperature of 2.3 degrees (P less than 0.05), and increased plethysmographic finger flow to 2.08% delta vol/sec contrasted with 1.00% delta vol/sec in the placebo group (P less than 0.05). During cold immersion, temperature of this side fell 0.5 degrees, and flow decreased to 0.17% delta vol/sec. With ketanserin, temperature did not fall and flow was 0.85% delta vol/sec (P less than 0.05). Ketanserin accelerated recovery of temperature and flow (P less than 0.05). Plasma serotonin levels were constant. Ibuprofen and ketoconazole reduced baseline thromboxane B2 levels from 30 pg to 18 and 20 pg/ml (P less than 0.05), respectively, but did not influence temperature or flow. Results show that serotonin and perhaps alpha-adrenoreceptors, but not prostanoids, modulate resting skin flow and cold-induced vasoconstriction.