Analysis of thoracic duct flow waves using fast Fourier transform in sheep

We measured the lymph flow of the thoracic duct using an ultrasound transit-time flowmeter and then analyzed the obtained flow signals by fast Fourier transform. We found that the wave form included a low frequency component (approximately 0.1 Hz) as well as high frequency components which represented cordiac pulsation and respiratory movement. The low frequency component signified an intrinsic thoracic duct pulsation. When venous outflow pressure was increased, the frequency of the thoracic duct pulsation increased, whereas the frequencies of cardiac pulsation and respiratory movement were unchanged. These findings suggest that thoracic duct pulsation is independent of cardiac pulsation and respiratory movement.

Electrical stimulation-induced alpha1- and alpha2-adrenoceptors-mediated contraction in isolated dog thoracic ducts

The electrical stimulation-induced responses of isolated dog thoracic ducts were investigated using an organ bath technique. Electrical stimulation (0.7 ms in pulse width, 25 V in nominal voltage, 10 s in duration time, 1-32 Hz at frequency) produced frequency-related contractions in the lymphatic preparations. The contractions were abolished by pretreatment with tetrodotoxin (10(-7) M), guanethidine (10(-7), 10(-6) M), and bretylium (10(-7), 10(-6) M). Cocaine (10(-6) M) significantly potentiated the electrical stimulation-induced contractions. Phentolamine (10(-8)-10(-5) M), prazosin (10(-8)-10(-5) M), bunazosin (10(-6), 10(-5) M), yohimbine (10(-8)-10(-6) M) and rauwolscine (10(-8)-10(-6) M) also dose-dependently reduced the contractions. On the other hand, propranolol (10(-8)-10(-6) M), atropine (10(-6) M), hexamethonium (10(-6) M), aspirin (3 x 10(-5) M), N(omega)-nitro-L-arginine methyl ester (L-NAME) (3 x 10(-5) M) and L-NAME (3 x 10(-5) M) + L-arginine (10(-4) M) caused no significant effect on electrical stimulation-induced contractions. No significant difference in the electrical stimulation-induced responses was observed between the lymphatic preparations with and without an intact endothelium. The electrical stimulation caused only a small contraction with no relaxation in the thoracic duct preparation precontracted with 10(-8) M U46619. The small contraction was abolished by 10(-5) M phentolamine. These findings suggest that there exists alpha1- and alpha2-adrenoceptors-mediated excitatory innervation, but no NO-ergic inhibitory nerve fiber in dog thoracic ducts.

Lymphatic drainage reduces intestinal edema and fluid loss

Lymphatic vessels are important in removing excess fluid from the intestine and transporting the fluid to veins in the neck. However, in some diseases, neck vein pressure is increased and the high pressure may slow lymph flow. This study was to test the hypothesis that lymphatic clearance of fluid from the intestine may be increased by draining the lymphatics. Inflatable cuffs were used to increase neck vein pressure and portal venous pressure in anesthetized sheep. The lymphatic vessel from one segment of small intestine was cannulated and drained. The lymphatic vessel to a control segment of intestine was left intact. After 90 min. we found significantly less fluid in the lumen of the drained vs. control segments (7.4 +/- 3.1 (SD) ml vs 11.5 +/- 4.7 ml per gram dry tissue, respectively). Also we found significantly less tissue fluid in the drained vs control segments (5.3 +/- 0.3 ml/g vs 6.0 +/- 0.4 ml/g). The findings support the hypothesis that external diversion of lymph in the presence of an elevated central venous pressure reduces edema formation.

Lymph flow pattern in the intact thoracic duct in sheep

1. To study the lymph flow dynamics in the intact thoracic duct, we applied an ultrasound transit-time flow probe in seven anaesthetized and four unanaesthetized adult sheep (approximately 60 kg). In unanaesthetized non-fasting animals we found that lymph flow in the thoracic duct was always regular pulsatile (pulsation frequency, 5.2 +/- 0.8 min-1) with no relation to heart or respiratory activity. At baseline the peak level of the thoracic duct pulse flow was 11.6-20.7 ml min-1 with a nadir of 0-3.6 ml min-1. Mean lymph flow was 5.4 +/- 3.1 ml min-1. The flow pattern of lymph in the thoracic duct was essentially the same in the anaesthetized animals. 2. In both the anaesthetized and unanaesthetized animals, the lymph flow response to a stepwise increase in the outflow venous pressure showed interindividual variation. Some were sensitive to any increase in outflow venous pressure, but others were resistant in that lymph flow did not decrease until outflow venous pressure was increased to higher levels. This resistance was also observed in the high lymph flow condition produced by fluid infusion in the anaesthetized animal and mechanical constriction of the caudal vena cava in the unaesthetized animals. Pulsation frequency of the thoracic duct flow initially increased and then decreased with a stepwise increase in the outflow venous pressure. This initial increase might be a compensatory response to maintain lymph flow against elevated outflow venous pressure. 3. To test the effect of long-term outflow venous pressure elevation in unanaesthetized sheep, outflow venous pressure was increased by inflation of a cuff around the cranial vena cava for 1, 5 or 25 h. The cuff was inflated to a level where lymph flow was reduced. Lymph flow remained low or decreased further during the entire cuff-inflation period. We calculated the lymph debt caused by the outflow venous pressure elevation and the amount 'repaid' when venous pressure returned to normal. Lymph debt for 25 h was 6400 ml but only 200 ml was repaid. Since we observed no visible oedema formation in the lower body of the sheep, the non-colloidal components of the lymph must have been reabsorbed into the bloodstream, most likely in the lymph nodes.

Drainage of CSF through lymphatic pathways and arachnoid villi in sheep: measurement of 125I-albumin clearance

We investigated lymphatic drainage pathways of the central nervous system in conscious sheep and quantified the clearance of a cerebrospinal fluid (CSF) tracer into lymph and blood. In the first group of studies, 125I-HSA was injected into the lateral ventricles of the brain or into lumbar CSF and after 6 h, various lymph nodes and tissues were excised and counted for radioactivity. Multiple lymphatic drainage pathways of cranial CSF existed in the head and neck region defined by elevated 125I-HSA in the retropharyngeal/cervical, thymic, pre-auricular and submandibular nodes. Implicated in spinal CSF drainage were mainly the lumbar and intercostal nodes. In a second group of experiments, multiple cervical vessels and the thoracic duct were cannulated and lymph diverted from the animals. Transport of tracer through arachnoid villi was taken from recoveries in venous blood. Following intraventricular administration, the 6 h recoveries of 125I-HSA in the lymph (sum of cervical and thoracic duct) and blood were 8.2% +/- 3.0 and 12.5% +/- 4.5 respectively and at 22 h, 25.1% +/- 6.9 and 20.8% +/- 4.1 respectively. When 125I-HSA was injected into lumbar CSF, the 6 h recoveries of tracer in thoracic duct and blood were 11.6% +/- 2.7 and 16.3% +/- 3.7 respectively. Total lymph and blood recoveries were not significantly different in any experiment. We conclude that the clearance of 125I-HSA from the CSF is almost equally distributed between lymphatic and arachnoid villi pathways.

Thoracic duct function in fetal, newborn, and adult sheep

We measured thoracic duct lymph flow rate versus outflow pressure in 7 chronically catheterized adult sheep and in 6 newborn lambs and compared our results to data previously obtained from 10 fetal sheep. In fetal sheep the thoracic duct lymph flow rate was 34.5 +/- 17.2 ml/hr or 11.7 +/- 6.0 ml/kg/hr. Fetal thoracic duct lymph flow deviated from baseline between 8 and 12 torr outflow pressure and lymph stopped at 18 +/- 2.5 torr. In newborn lambs the thoracic duct lymph flow rate was 49.5 +/- 22.0 ml/hr or 7.4 +/- 2.5 ml/kg/hr. The range of outflow pressures over which newborn lymph flow deviated from baseline was between 15 and 18 torr and lymph flow stopped at 26.2 +/- 6.4 torr. Adult sheep thoracic duct lymph flow rate was 130 +/- 74 ml/hr or 2.3 +/- 1.3 ml/kg/hr. Adult lymph flow deviated from baseline between 25 and 35 torr and stopped at an outflow pressure of 41.7 +/- 6.7 torr. The ability of the thoracic duct to return lymph against an outflow pressure improves with maturation. However, lymph flow rate corrected for body weight is greatest in immature animals. The higher corrected lymph flow rate in conjunction with the decreased ability to pump against an outflow pressure may help account for immature animals predisposition for edema.

[The valvular apparatus and tissue organization of the endothelium of the thoracic duct]

The structure of ostial valves and valves located along the thoracic duct and of its branches ostial valves and right lymphatic duct ostial valves were studied in 30 experimental outbred dogs and 46 cats. Cryodestruction of thoracic duct was performed in 28 outbred cats. 1, 3, 7 and 14 days later perfusive fixation with intercellular borders impregnation was carried out with simultaneous examination of intact regions of intravalvular segments, cisterna chyli and area of thoracic duct trunks connection with valvular surfaces. Tissue organization in ageing was studied using the intervalvular segment of old animals. Specimens were studied by means of scanning electron microscopy and film preparations of endothelium. Valves, located along the thoracic duct length are bicuspid formations, while ostial ones are falciform and cuneiform respectively in 80 and 20%. Endotheliocytes of cuspids are characterized with high content of microfilaments bundles in the cytoplasm and low content of microvesicles. Cells of the valvular free margin cross the cuspid edge and have adaptive changes preventing their desquamation: fusiform shape, long basal processes and bundles of microfilaments in the cytoplasm. Peculiar "pericyte-like" cells alike with myofibroblasts lie deep in the cuspid thickness close to the sinusal venous side. Fascicles of the duct smooth myocytes reach the base of the valve. Besides, in the ostial valve stroma there is elastic membrane, better displayed along the cuspid venous side. Increased polymorphism and changes of the endotheliocytes metric characteristics were demonstrated in the zones of turbulent lymph flow. Analysis of the newly formed endothelium tissue mosaics allows to reveal mechanisms of monolayer repair: spreading and migration of endotheliocytes on the first day, their proliferation within three days, desquamation of newly formed endotheliocytes and spreading of adjacent cells on later stages.

Increased abdominal lymph flow increases lung lymphatic outflow pressure in sheep

We tested the hypothesis that increased lymph flow from the abdominal organs would increase the pressure within the thoracic duct at the thoracic duct-lung lymphatic junction. Cannulas were placed into the thoracic duct via the caudal mediastinal (lung) node efferent lymphatics in 4 sheep. After the sheep recovered from the surgery, we monitored the thoracic duct pressure with pressure transducers. To increase lymph flow from the lower body, we infused Ringers solution (59 +/- 19 [mean +/- SD] ml/kg body weight in 30 min.) intravenously into the sheep and we inflated a balloon in the inferior vena cava. This technique causes substantial increases in lymph flow from the lower body (mainly from the liver and intestines) through the thoracic duct. During the infusions, the thoracic duct pressure increased significantly from 4.1 +/- 2.9 cm H2O (baseline) to 6.8 +/- 1.7 cm H2O. The neck vein pressure (pressure at the outflow of the thoracic duct) did not increase from baseline (3.0 +/- 2.6 cm H2O). Thus our results support the hypotheses that increased flow through the thoracic duct causes increased thoracic duct pressure.

Regeneration of the endothelium in the canine and feline thoracic duct

Recent improvements in microsurgical techniques on lymphatic vessels facilitated the treatment of lymphoedema. But it is becoming clear that a successful treatment of lymphatic disease has to be based on knowledge of ongoing processes. Particularly, one of the important and unclear issue is cellular mechanisms of lymphatic regeneration. The regeneration of endothelial and the smooth muscle cells of the thoracic duct has been experimentally tested in vivo. The canine and feline thoracic duct was cryo-injured using 3 mm-based copper rod. Damaged endothelial cells remained attached to the substrate and lost unthrombogenecy within 48 hr. Adjacent EC restored the defect within 3 days by migration and proliferation. We observed that on the first day, the endothelial monolayer included some elongated multinuclear cells with blind silver lines whereas, on the third day, they were replaced by a population of smaller ECs with numerous mitoses. Organization of the monolayer was restituted within 7 days. The newly formed endothelium was similar to regenerating endothelium of arteries. In general, the clot that appeared at the zone of injury on the second day was dissolved by the third day. Occasionally, the dense polymorphic clot adhered to the wall and caused a delay in reendothelisation. Complete restitution of the tunica media which involved migration and proliferation mechanisms accompanied the endothelium regeneration.

Direct lymphatic drainage from the esophagus into the thoracic duct

The lymphatic vessels from around the esophagus which drain into the thoracic duct were identified macroscopically and histologically in 106 cadavers. Direct lymphatic drainage to the duct was macroscopically demonstrated by 84 vessels in 46 cases (43.4%). In 23 cases (19.8%), large collecting vessels arose from the thoracic esophagus and opened directly into the duct. In most of these cases (15/23) these lymphatic connections were found at the levels of the 1st-3rd or 6th-8th thoracic vertebrae. Histologic study revealed that two vessels originated from the fine lymphatic plexus in the esophageal adventita, which showed monocytic infiltration. In 11 of the 23 cases, an intercalated node was found along the thoracic duct. The results suggest that lymph drains rapidly into the systemic circulation via the thoracic duct. In view of the clinical applications in esophageal carcinoma, previous accounts of the extramural esophageal lymphatics concerned in direct drainage are discussed.

[The contractile activity of the lymphatic vessels in rats after head-down tilt exposure]

After antiorthostatic attitude of rats during 12 days, the contractile activity of their isolated lymphangions of the thoracic duct was studied. The amplitude of contractions was found to be decreased as well as the effects of serotonine, histamine, and acetylcholine, whereas that of adrenaline increased. The latter finding suggests enhancing of the activity of lymphatic vessels' adrenergic structures in antiorthostatic.

Chylothorax

The management of chylothorax requires a thorough understanding of the anatomy and pathophysiology of the major thoracic lymphatics, prompt diagnosis, and (with rare exception) conservative management, including evacuation of the pleural space, nutritional support, and measures to reduce chyle production. A minority of chylothoraces will fail to resolve with these measures. Surgical intervention is then required to prevent chronic metabolic deterioration and death.

Pharmacologic properties of Daflon 500 mg

AIMS AND METHODS

Some pharmacologic activities of a micronized flavonoid complex consisting of 90% diosmin + 10% hesperidin (Daflon 500 mg*) have been investigated by use of various experimental models: (1) interference with mechanisms of edema (synthesis of arachidonic acid derivatives, microvascular hyperpermeability induced by bradykinin, ischemia, or streptozotocin), (2) interference with lymphatic drainage (thoracic duct fistula in the dog).

RESULTS

Daflon 500 mg inhibited prostaglandin E2 (PGE2) and thromboxane A2 (TxA2) synthesis during a one-month oral daily treatment (100 mg.kg-1.day-1) in the rat, after induction of chronic inflammation by subcutaneous implantation of sponge fragments. Microvascular hyperpermeability induced by bradykinin or ischemia in the rat cremaster muscle was reduced after an oral treatment with Daflon 500 mg (100 mg.kg-1 twice daily). Microvascular hyperpermeability of the streptozotocin-induced diabetic rat was antagonized when Daflon 500 mg (300 mg.kg-1 once daily) was given orally as a preventive treatment. In the anesthetized dog, an increase in lymphatic flow, correlated with administered doses, was observed after IV injection of Daflon 500 mg. Lymphatic flow was maximal twenty minutes after injection of the drug (12.5 mg.kg-1) and was three times higher than the basal flow.

CONCLUSION

The protective effect of Daflon 500 mg against the formation of perivascular edema and its therapeutic value in the treatment of venous stasis could be explained by its inhibitory activity on the inflammatory process or ischemia-induced hyperpermeability and by its stimulatory effect on the pulsatile activity of lymphatic vessels.

Chylothorax: an update

Chylothorax is occasionally found in malignant disease and following sympathectomy, but is seen more frequently after cardiothoracic surgery. The varied anatomy of the thoracic duct, limited individual experience and a lack of appreciation of the factors indicating surgical intervention have led to controversy regarding its optimal management. This article reviews historical aspects, clinical features and guidelines for conservative and surgical management.

Maximal lymph flow in the ovine fetus

OBJECTIVE

This study was designed to determine the maximal left thoracic duct lymph flow rate in late-gestation ovine fetuses.

STUDY DESIGN

Chronically catheterized sheep fetuses (n = 8) with indwelling left thoracic lymph duct and vascular catheters were studied > or = 5 days after surgery at 136 +/- 1 (SE) days' gestation. To increase lymph flow rate, 4 L of warm lactated Ringer's solution were infused intravenously into the fetus over 4 hours, because this causes mild edema as determined ultrasonographically.

RESULTS

During a 1-hour preinfusion period lymph flow rate was 0.53 +/- 0.06 ml/min. During the infusion increases occurred in fetal arterial (7.6 +/- 1.0 mm Hg) and venous (2.4 +/- 0.3 mm Hg) pressures (p < 0.001). Lymph flow rate increased and reached a plateau after 1 hour at 339% +/- 30% of preinfusion values (p < 0.001). When the infusion was terminated, fetal arterial and venous pressures rapidly returned to preinfusion levels. Lymph flow rate gradually decreased during the first 30 minutes and stabilized at 97% +/- 17% above control during the subsequent 30 minutes. Analysis of lymph flow rate as a function of outflow pressure revealed that the increases in flow occurred because of an upward shift in the plateau flow rate with no change in the stop-flow pressure.

CONCLUSIONS

(1) Fetal left thoracic duct lymph flow rate can increase significantly above basal values and therefore is an important safety factor against fetal edema formation. (2) The maximal lymph flow rate appears to be 3.4 times normal when venous pressure is elevated and two times normal when venous pressure is normal.

Evaluation of thoracic duct healing after experimental laceration and transection

Healing of the thoracic duct (TD) was evaluated clinically and histologically in six healthy dogs. A 2.5 cm longitudinal laceration of the caudal TD was created in three dogs and the caudal TD was completely transected in three other dogs. The site of the defect was identified by placing one 4-0 stainless steel suture in the tissue adjacent to the TD defect. All dogs developed a chylous effusion confirmed by biochemical analysis. By five days after surgery in dogs with TD lacerations, and by 10 days after surgery in dogs with TD transections, thoracic effusion had ceased. Lymphangiography, performed seven days after resolution of thoracic effusion, showed TD patency only in the dogs with TD lacerations. The TD did not appear to be patent in dogs with TD transections. Histologically, in dogs with TD lacerations, one moderately dilated lymphatic vessel was seen at the surgical site in one animal and the thoracic duct and other lymphatics in the two other dogs appeared normal. Minimal perivascular accumulations of neutrophils, macrophages, and lymphocytes were present adjacent to two lymphatics in one animal. A mild increase in fibrous connective tissue and neovascularization was present in the adjacent subpleura. In dogs with complete transections, three to six dilated lymphatics were present at the transection site. Mild thickening of the tunica media was present in one thoracic duct, associated with a "J"-shaped area of condensed collagen, presumed to be a collapsed thoracic duct in one animal. Mild to moderate accumulations of macrophages, lymphocytes, and moderate neovascularization was present in the surrounding tissue, separating it from the underlying connective tissue.(ABSTRACT TRUNCATED AT 250 WORDS)

Intestinal lymphatic pressure increases during intravenous infusions in awake sheep

Intravenous fluid infusions cause increased venous pressure and increased lymph flow throughout the body. Together the increased lymph flow and increased venous pressure (the outflow pressure to the lymphatic system) should increase the pressure within the postnodal intestinal lymphatics. To test this, we measured the pressure in postnodal intestinal lymphatics and the neck vein pressure in five awake sheep. At baseline, the neck vein pressure was 1.2 +/- 1.5 (SD) cmH2O and the lymphatic pressure was 12.5 +/- 1.7 cmH2O. When we infused Ringer solution intravenously (10% body weight in approximately 50 min), the neck vein pressure increased to 17.3 +/- 0.9 cmH2O and the lymphatic pressure increased to 24.6 +/- 3.8 cmH2O (both P < 0.05). In two additional sheep, the thoracic duct lymph flow rate increased from 0.8 +/- 0.4 ml/min at baseline to 5.5 +/- 2.0 ml/min during the infusions. Our results show that postnodal intestinal lymphatic pressure may increase substantially during intravenous fluid infusions. This is important because increases in postnodal lymphatic pressure may slow lymph flow from the intestine.

Long-term vascular volume expansion maintains elevated thoracic duct lymph flow

OBJECTIVE

To investigate the mechanisms responsible for edema seen during pregnancy, we tested whether lymph vessels are able to pump high volumes over long periods of time.

STUDY DESIGN

In six chronically catheterized nonpregnant ewes, we examined left thoracic duct lymph flow rate and fluid balance responses to the administration of a balanced isotonic solution at a rate of 1 L/hr for 20 hours. Because estrogen administration decreases lymphatic contractility against outflow pressure, we also administered conjugated estrogens (Premarin) during the last 3 hours of the fluid infusion (experimental time 17 to 20 hours).

RESULTS

After volume loading for 16 hours, the mean +/- SEM lymph flow rate, blood volume, and arterial pressure rose 100% +/- 26%, 20% +/- 2.3%, and 16% +/- 8.1%, respectively. Vascular compliance decreased significantly and, as evidenced by a lack of body weight changes, interstitial fluid volume failed to change (p < 0.05, analysis of variance). The transcapillary oncotic pressure difference increased by 2 mm Hg; venous pressure increased by 5.2 mm Hg. These data suggest that transcapillary forces favored fluid movement into the interstitium. Lymph flow rate remains elevated after blood volume expansion to a level similar to that described during pregnancy in sheep. A transient decrease in urinary output (approximately 20%) occurred with no changes in lymph flow rate, arterial pressure, or blood volume.

CONCLUSION

Lymph flow rate is able to compensate for the increased capillary filtration observed during prolonged blood volume expansion.

Increased venous pressure causes increased thoracic duct pressure in awake sheep

The lymph from most organs drains through the thoracic duct and into veins in the neck. We hypothesized that increases in neck vein pressure (Pnv) are reflected through the thoracic duct to the lung lymphatic-thoracic duct junction. To test this, we cannulated the lung lymphatics in the direction of flow in four sheep. We advanced each cannula until it entered the thoracic duct. Thus the pressure at the tip of the lymphatic cannula (Px) was the pressure at the outflow of the lung lymphatics. We also placed a balloon into the superior vena cava. One to two days later, we measured Px in the awake sheep as we inflated the balloon and increased Pnv in steps to 25-45 cmH2O. We found no significant differences in Px and Pnv. Furthermore, Px closely followed Pnv after each step increase in Pnv. These results support our hypothesis that increases in Pnv cause increases in the outflow pressure to lung lymphatics.

Left thoracic duct lymph flow responses to angiotensin II or atrial natriuretic factor infusion in the ovine fetus

In the ovine fetus it is known that left thoracic duct lymph flow rate relative to body weight is four to five times adult levels, but it is not known whether the circulating hormones modulate fetal lymph flow. To explore this, we intravenously infused either angiotensin II (10 to 400 ng/min, n = 8) or atrial natriuretic factor (500 to 1000 ng/min, n = 8) into chronically catheterized fetal sheep for 30 minutes. Significant increases occurred in fetal arterial (p less than 0.0001) and venous (p = 0.018) pressures during the angiotensin II infusion, and thoracic duct lymph flow rate underwent a dose-dependent increase (r = 0.888, p = 0.0033). With termination of the angiotensin II infusion, fetal vascular pressures rapidly returned to control levels, and lymph flow fell from 18.8% +/- 10.1% (mean +/- SE) above control to 13.7% +/- 7.7% below preinfusion levels (p less than 0.01). During the atrial natriuretic factor infusion, fetal arterial pressure and circulating blood volume decreased significantly (p less than 0.01), whereas thoracic duct lymph flow was unchanged. After termination of the atrial natriuretic factor infusion, fetal arterial pressure returned toward control, blood volume remained reduced, and lymph flow rate underwent a transient rise to 35.6% +/- 15.7% (p less than 0.05) above control levels. These data suggest that angiotensin II and atrial natriuretic factor have significant but opposite effects on fetal thoracic duct lymph flow rate, with angiotensin II stimulating and atrial natriuretic factor suppressing lymph flow.

In vitro effects of a thromboxane A2-analogue U-46619 and noradrenaline on contractions of the human thoracic duct

A piece of a human thoracic duct removed at operation was investigated in organ baths. The duct was cut in 8 ring segments each about 1mm long and isometric tension recorded. The segments were exposed to a potassium rich (124mM) Krebs buffer solution. In only two of the segments were contractions induced (7.2 and 1.0mN, respectively). Noradrenaline and the thromboxane mimetic U-46619 induced tonic and phasic contractions. At a noradrenaline concentration of 10(-5)M the phasic contractions had a frequency of 5 min-1. The highest frequency, 9 min-1, was recorded with 3 x 10(-10)M of U-46619 present in the bath. Noradrenaline had a mean Emax of 50% of the previous K+ (124mM)-induced contraction, and the mean pEC50-value was 6.7. The Emax and pEC50-values of U-46619 were 142% and 9.5, respectively. Postjunctional alpha-adrenoceptors and thromboxane A2-receptors may play a role in the contractility of the human thoracic duct.