Local effect of serotonin on blood vessels of human skin

MICROVASCULAR

Local

RESEARCH 4,258-263

(1972)

Effect of Serotonin

on Blood

Vessels of Human

Skin

HILDECARD RAND MARICQ Veterans Administration Hospital, Lyons, New Jersey 07939, Essex County Hospital Center, Cedar Grove, New Jersey 07009, and Rutgers Medical School, Department of Psychiatry, New Brunswick, New Jersey 08903 Received August 24, 1971 The response of the nailfold vascular bed to the application of serotonin by micropuncture has been studied in 18 subjects with exceptionally transparent skin (14 schizophrenic patients and 4 normal subjects). The observations were made with the technique of in uivo capillaroscopy supplemented by photomicrography and cinephotomicrography. The results demonstrate an active vasodilator response, the intensity of which appears to be related to the initial vasoconstrictor tone of the vessels.

INTRODUCTION Dilatation of the minute blood vesselsof the human skin in responseto serotonin has beenreported by numerous investigators asreviewed by Page(1968)and Whelan (1967). It is generally believed that this dilatation is due to passivecongestion of capillaries and venules (Roddie, Shepherd, and Whelan, 1955; Bock et al., 1957; Oyvin and Shegel, 1965)secondary to constriction of larger veins (Reid, 1952; Lorincz and Pearson, 1959; Demis, Davis, and Lawler, 1960; Sttittgen and Schippel, 1961; Sharpey-Schafer and Ginsberg, 1962; Greaves and Shuster, 1967; Page, 1968). This conclusion is based on observations of skin color changes(erythema and/or cyanosis), wheal formation, constriction of subcutaneous veins and on measurementsof peripheral blood flow levels after administration of serotonin by various routes (Page and McCubbin, 1953; Roddie, Shepherd, and Whelan, 1955; Glover et al., 1958; Clendenning, De Oreo, and Stoughton, 1959; Le Messurier, Schwartz, and Whelan, 1959; Sttittgen and Schippel, 1961). Only a few investigators have had recourse to direct observation of the microvesselsunder a microscope (Demis, Davis, and Lawler, 1960),and first hand information on the local effect of serotonin on the human skin microcirculation is sparse.Serotonin administered by systemic route obviously produces effects on many organs, but, even when introduced by intradermal injection, large veins may constrict severalcentimeters away from the injection site (Reid, 1952; Lorincz and Pearson, 1959; Greaves and Shuster, 1967).On the other hand, the capillaroscopic method for direct observation of the skin using reflected light usually allows only a very limited view of the most superficial blood vessels.Stripping away the keratin layer with cellophane tape can improve the visibility, but it is not an entirely atraumatic technique. In the present study, these complicating factors have been minimized. In previous work with the nailfold capillaries, the skin in many schizophrenic patients was found to be exceptionally transparent (Maricq, 1969).Application of a drug by micropuncture Copyright 0 1972 by Academic Press, Inc. All rights of reproduction in any form reserved.

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(through a droplet deposited on the skin) in such patients allows observation of the reaction of the minute blood vesselsmore easily than in normal subjectsand injures only a single microvessel or none at all. The amount of drug introduced and the area affected is thus considerably more limited than with other techniques. The purpose of the present study was to determine the effect of serotonin in human skin at the microcirculatory level by direct observation (using subjects with exceptionally transparent skin). Although most of the subjects were schizophrenic and might, therefore, differ in reactivity from the normal (in whom the vesselscannot be observed in such detail), the direct observation of the local effect of serotonin should contribute to a better understanding of its role in the human cardiovascular system. MATERIALS AND METHODS Subjects Fourteen schizophrenic patients and 4 normal subjects,aged 13 to 60, were included in this study. One of the schizophrenic patients sufferedfrom diabetesmellitus. All other subjectswere in good general health. In the schizophrenic group, 8 patients were receiving phenothiazine drugs and 6 were not receiving medication. The normal subjects were not taking drugs. All schizophrenics had an especially transparent skin with an easily observed and extensive subpapillary plexus, characterized by a plexus visualization score(PVS) of more than 15(Maricq, 1970).The view of the microvesselsin normal subjects was much less clear than in the schizophrenic patients. Methods A droplet of serotonin solution (containing 1 mg of serotonin creatinine sulfate/ml of 0.9 % saline) was deposited on the nailfold and the drug was introduced into the skin by pricking through the solution with a very fine needle (Clay-Adams insect pins No. 00). The droplet was allowed to remain in place for 1 or 2 min and was then wiped off gently. A needleprick through a droplet of 0.9 % saline served as a control. The procedure was performed under a wide-field stereomicroscope. Immersion oil on the nailfold helped to visualize the vessels during observation and photography. (Oil was removed by alcohol before application of the drug solution). Observations through the wide-field microscope were made at magnifications 6x, 12x, and 25x. The nailfold capillary bed was photographed before and after application of serotonin and saline (1) with a 35 mm single lens reflex camera provided with bellows and a macrolens that allowed a magnification of 3.5x on the negative (Maricq, 1970) and (2) through a Leitz microscope equipped with Ultropak illuminator using a 6.5x objective and a 6x and 10x eyepiece. Cinephotomicrography was performed with a 16 mm movie camera mounted on the Leitz microscope. Electronic flash equipment was used for still photomicrography. A xenon arc lamp served as a light source for cinephotomicrography. Still pictures were obtained for all subjects, motion pictures were taken in 8 subjects (1 normal and 7 schizophrenics). Comparisons were made (I) between the states of nailfold vascular bed before and after serotonin application and (2) between the responsesof the vascular bed to serotonin and saline. Observations were made (both in vivo and in photographic records) on the following aspectsof the nailfold: (a) local skin color; (b) caliber of blood vessels;

260

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(c) appearanceor disappearanceof blood vessels;(d) rate of blood flow. The observation period ranged from approximately 10 min to 1 hr after the needle prick. RESULTS A total of 46 trials with serotonin were performed, 23 with saline control. Twelve subjectshaving the most transparent skin were examined repeatedly. Basedon any one of the four standard criteria (local erythema, increase of vesselcaliber, opening up of previously invisible blood vessels,and increasein flow rate), the responsewasjudged to be definite, slight, or nondetectable compared with the vascular picture just before the application of serotonin (Fig. 1). Table I summarizesthe results of these observations.

FIG. 1. Nailfold capillaries before (a) and 7 min after (b) introduction of serotonin.

Only once could no change be detected, but the samesubject gave a strong responsein another trial. Compared to saline controls, serotonin produced a definite vasodilator responsein 18 out of 23 trials (seeTable 1 and Fig. 2). Only one subject, the patient with schizophrenia and diabetes mellitus, had a strong vasodilator response to both saline and serotonin. Of the four standard criteria, the flow rate was most difficult to determine. Therefore observations of the blood flow were limited to 25 trials. The increase in flow rate was greatest and easiest to observe in subjects with a slow initial blood flow (Fig. 3). In instances of fast initial blood flow, increasesin flow rate were difficult to estimate, and changesin local erythema were often slight and difficult to judge. Of the 7 casescharacTABLE

Effect of serotonin Serotonin compared to saline

1

Total number of trials

Definite vasodilation

Slight vasodilator response

Nondetectable response

46 23

39 18

6 2

1 3

SEROTONIN

AND

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MICROClRCULATION

261

terized by slight or nondetectable reaction to serotonin, 6 possessed a fast initial blood flow. On the other hand, in the 12 trials characterized by a pronounced response to serotonin, 6 subjects had a definitely slow “granular” blood flow before application. Four subjects revealed a different initial vasomotor picture in separate trials; all 4 exhibited a greater response, as shown by erythema, caliber change, flow increase and opening of new channels, when the blood flow was slow initially. No qualitative differences were observed in the response to serotonin between the schizophrenic patients and the few normal subjects included in this study. Reactions were slightly less pronounced and the initial blood flow was faster in normal subjects.

FIG. 2. Nailfold capillary bed before (a) and 6 min 20 set after(b) needle prick through a drop of saline compared with nailfold capillaries in another finger of the same patient before (c) and 5 min 30 set after (d) needle prick through serotonin solution.

Most of the observations were made during the first 20 min after the needle prick, although a few trials were observed for periods up to I hr. The erythema was sometimes visible as long as 40 min after the application of serotonin. At no time was a slower than initial blood flow observed after serotonin application. The most noticeable caliber change occurred in the venules, but in some cases an arteriolar dilatation could also be observed (Fig. 4). The latter were more difficult to see because of narrower caliber and deeper location. The overall picture of the nailfold capillary bed remained remarkably clear after application of serotonin, in contrast with the effect of application of some other vasodilators that preclude sharp visualization. apparently because of edema formation (Maricq, unpublished data). 10

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FIG. 3. Strips of motion picture film taken before (a) and 2 to 3 min after (b) introduction of serotonin by needle prick (18 framesisec). FIG. 4. Nailfold vascular bed of a patient before (a), 3 min 15 set (b), and 7 min 10 set after(c) needle prick through serotonin solution. Dilatation of an arteriole (arrow) in (b) and (c) and the appearance of a large previously invisible vessel in (b) (X). The site of needle prick is shown at N.

DISCUSSION The purpose of this study was to determine the effect of serotonin on the microcirculation of human skin when applied with a procedure designed to exclude a systemic response and reaction of larger skin vessels.

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The results demonstrate an active vasodilator response of the minute vessels of human skin to serotonin when applied locally. The erythema produced by serotonin is not necessarily a passive congestion of vessels responsible for the change in skin color as previously reported. On the other hand, these results are consistent with earlier reports that the reaction to serotonin depends on the neurogenic vasomotor state (Page and McCubbin, 1953; Haddy, 1958; McCubbin, Kaneko, and Page, 1962). These direct microscopic observations point to the possibility of a vasoactive role for serotonin at the microcirculatory level in the human skin. However, since most of the subjects were schizophrenic patients (since it is difficult to examine the “average normal person” by this method), it will be important to examine other types of patients and additional healthy subjects with transparent nailfold skin. REFERENCES

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