Yasuaki Kawai

The response of lymphatic smooth muscles to vasoactive substances

A study was made of the isotonic response of bovine mesenteric lymphatics to several physiological vasoactive substances. Contractions of lymphatic smooth muscles were induced by serotonin (5-HT), prostaglandin F2α (PGF2α), noradrenaline (NA), histamine, dopamine and acetylcholine (ACh). The smooth muscles were particularly sensitive to 5-HT. Excepting PGF2α no other substances could equal 5-HT in the magnitude of the maximum response. The majority of 5-HT receptors seemed to be the D receptors. The decreasing order of the contractile responses was as follows: 5-HT>PGF2α>NA>histamine>dopamine>ACh. The contractile response to ACh was observed only in specimens involving valvular region. It was very likely that, in the lymphatics, there were 2 kinds of receptors for catecholamines, i.e. α and β receptors, and the stimulation of the former induced smooth muscle contraction and that of the latter relaxation. A difference was noticed between the responses of valvular and intervalvular segments to NA. Relaxations of lymphatic smooth muscles were induced not only by isoproterenol but also by adenosine and adenine nucleotides. The decreasing order of the relaxant responses was as follows: ISP>adenosine >ATP>ADP>cyclic AMP≧AMP. The relaxant responses to adenine nucleotides tended to reduce with decrease in the number of high energy phosphates.

Effects of isocarbacyclin, a stable prostacyclin analogue, on monkey isolated cerebral and peripheral arteries

1 The effects of isocarbacyclin (TEI 7165), a stable prostacyclin analogue, were examined in monkey isolated cerebral and peripheral arteries. 2 Addition of TEI 7165 (0.1 nm‐10 μm) produced a dose‐dependent relaxation in cerebral arteries pre‐contracted with 1 μm 5‐hydroxytryptamine (5‐HT). High concentrations (more than 1 μm) of TEI 7165 elicited a transient contraction followed by a sustained relaxation. 3 TEI 7165 also elicited a dose‐dependent relaxation in the peripheral (except popliteal) arteries. The maximum relaxation induced by 10 μm TEI 7165 was greater (P < 0.05) in the mesenteric artery than in the cerebral artery. The negative logarithm of the EC50 value for the mesenteric, 7.6 ± 0.3, was greater (P < 0.05) than that for the cerebral artery, 6.4 ± 0.3. The decreasing order of potency for the TEI 7165‐induced relaxation was as follows: mesenteric > renal > cerebral > coronary > popliteal. 4 Removal of the endothelium did not significantly affect TEI 7165‐induced relaxations. 5 The transient contraction produced by high concentrations of TEI 7165 was not observed in cerebral arteries precontracted with 1 nm U46619, a stable analogue of thromboxane A2 (TXA2). Furthermore, the TEI 7165‐induced contraction was markedly suppressed (P < 0.05) by treatment with 10 nm S1452, a TXA2 blocking agent. 6 These results suggest that TEI 7165 causes an endothelium‐independent relaxation in monkey cerebral and peripheral arteries, and that there is a marked regional difference in the TEI 7165‐induced relaxations. A high concentration of TEI 7165 also produces a transient contraction which is probably through activation of TXA2 (TP‐) receptors.

Dual effects of histamine on spontaneous activity in isolated bovine mesenteric lymphatics

The mode of action of histamine on spontaneous contractions is isolated bovine mesenteric lymphatics was investigated by recording isometric tensions. Histamine at lower concentrations between about 5 x 10(-8) and 10(-6) M caused a dose-dependent deceleration of the rhythm of spontaneous contractions. Higher concentrations of histamine (more than about 5 x 10(-6) M) produced a dose-related acceleration of the rhythm in association with a slight elevation of basal tone in 115 of 173 preparations. In 58 of 173 lymphatic preparations, histamine at concentrations ranging from about 5 x 10(-8) to 10(-5) M caused only the positive chronotropic effect. The histamine-induced positive and negative chronotropic effects were unaltered by pretreatment with alpha- and beta-adrenergic antagonists but were dose-dependently antagonized by pretreatment with H1- or H2-blockers (diphenhydramine or cimetidine). The specific H1- and H2-agonists, 2-pyridylethylamine (2PEA) and dimaprit caused dose-related positive and negative chronotropic effects, respectively, on spontaneous contractions of isolated bovine mesenteric lymphatics. The effect of 2PEA was significantly blocked by pretreatment with 10(-6) M diphenhydramine, whereas the effect of dimaprit was suppressed by 10(-6) M cimetidine. These results suggest that both H1- and H2-receptors are located on the plasma membrane of smooth muscle cells in bovine mesenteric lymphatics, and that the excitations of H1- and H2-receptors respectively produce an acceleration and a deceleration of the rhythm of spontaneous contractions in lymphatic smooth muscles.

Histochemical studies of the adrenergic innervation of canine cerebral arteries.

The glyoxylic acid method was used to examine the adrenergic innervation of the major cerebral arteries of the circle of Willis in dogs. Fluorescent nerve fibers were observed in whole-mount preparations of the part of the internal carotid artery lying in the cavernosus sinus, the anterior, middle and posterior cerebral arteries, the posterior communicating artery and the basilar artery. Adrenergic nerve fibers were most abundant in the proximal portions of the anterior, middle and posterior cerebral arteries as well as in the posterior communicating artery. The distal smaller arteries were less densely innervated than larger ones. The basilar artery contained a moderate number of fluorescent fibers while the internal carotid artery lying in the cavernosus sinus had a very sparse innervation. The peak wavelengths of the excitation and emission spectra of the fluorescence were analyzed by means of a microepifluorescence spectrophotometer and were about 415 and 465 nm, respectively. These values suggest that the fluorescent fibers are adrenergic ones containing norepinephrine.

Demonstration of both β1- and β2-adrenoceptors mediating negative chronotropic effects on spontaneous activity in isolated bovine mesenteric lymphatics

The pharmacological classification of beta-adrenoceptor subtypes in isolated bovine mesenteric lymphatics was studied by using various beta-adrenoceptor agonists and antagonists. Isoproterenol (ISP) (10(-10)-10(-8) M) produced dose-dependent negative chronotropic effects on the rhythm of spontaneous contractions in the lymphatic preparation. The ISP-induced effects were dose-dependently blocked by pretreatment with 10(-8)-10(-7) M metoprolol (a selective beta 1 antagonist) as well as 10(-8)-10(-7) M propranolol (a beta 1 and beta 2 antagonist). Dobutamine (a selective beta 1 agonist) caused a dose-dependent negative chronotropic effect, which was significantly blocked by pretreatment with 10(-8) M metoprolol. Salbutamol and procaterol (selective beta 2 agonists) also produced dose-dependent negative chronotropic effects, which were dose-dependently inhibited by pretreatment with 10(-8)-10(-7) M propranolol, but not by 10(-7) M metoprolol. The decreasing order of the relative potency was as follows: ISP greater than procaterol greater than salbutamol greater than dobutamine. These results suggest that bovine mesenteric lymphatics contain both beta 1- and beta 2-adrenoceptors and that both subtypes can produce a negative chronotropic effect on the rhythm of spontaneous contractions, when stimulated.

Contractile and relaxant responses of the canine isolated spinal artery to vasoactive substances

1 Effects of vasoactive substances were investigated in the canine isolated spinal branch of the intercostal artery (SBICA). 2 Addition of angiotensin II (AII), vasopressin, noradrenaline (NA), adrenaline, 5‐hydroxytryptamine (5‐HT), and dopamine each produced concentration‐dependent contraction in the SBICA, whereas prostaglandin F2α, histamine, and tyramine caused only slight contraction. The decreasing order of the potency of contractile agents was AII ≫ vasopressin = NA > 5‐HT > adrenaline ≫ dopamine. 3 Although the pD2 value for phenylephrine (5.31 ± 0.36) was smaller than that for NA (6.48 ± 0.13), there was no significant difference in Emax value between these two agonists in the SBICA. On the other hand, xylazine produced only a slight contraction, the pD2 value being 3.59 ± 0.08. Phentolamine (10−8–10−6m) and prazosin (10−8–10−6m) competitively inhibited the NA‐induced contraction, while yohimbine (10−8–10−6m)did not. 4 Acetylcholine (ACh), sodium nitroprusside (SNP), ATP, ADP, and adenosine caused concentration‐dependent relaxations in SBICA following contraction with NA. On the other hand, isoprenaline up to 10−4m did not produce any relaxation. The decreasing order of potency of the relaxant agents was ACh > SNP ≫ ATP = ADP = adenosine. 5 The ACh‐induced relaxation was competitively inhibited by atropine and was abolished by mechanical removal of the endothelium. Aspirin (5 × 10−5m) did not affect the relaxant response to ACh, while oxyhaemoglobin (10−5m) and methylene blue (10−5m) produced significant attenuation. 6 These results suggest that NA produces contraction of the isolated canine SBICA which is mainly mediated via α1‐adrenoceptors and that ACh causes a relaxation of the SBICA due to release of endothelium‐derived relaxing factor (EDRF) from the endothelial cells.

The mode of ATP-induced vasoconstriction in the canine internal carotid artery.

The mode of the ATP-induced vasoconstriction in the internal carotid artery was studied from the physiological and pharmacological points of view. ATP caused dose-dependent vasoconstrictions in the canine internal carotid artery. The ATP-induced vasoconstriction was not affected by pretreatment with phenoxybenzamine, propranolol, atropine, cyproheptadine, or tetrodotoxin. Verapamil suppressed the contractile response. ATP produced no vasoconstriction in a calcium-free Krebs solution containing 1 mM EGTA nor augmentation of Ca2+-induced contraction in potassium-depolarized tissues. These results suggest that an increase of potential-dependent Ca2+ influx into the arterial smooth muscle may play a major role in the ATP-induced vasoconstriction.

Age-dependent changes of postischemic reperfusion in rat skin

Ischemia-reperfusion plays a certain role in causing skin damage associated with pressure sores. In this study, changes in cutaneous hemodynamics during reperfusion were investigated in young and older rats. After cessation of 1-hour or 2-hour ischemia, the skin blood flow increased transiently (postischemic hyperemia) and quickly returned to the baseline in young and older rats. After 4-hour ischemia, however, the postischemic hyperemia was reduced in both groups, and the skin blood flow decreased below the baseline for a few hours in older rats. The skin blood flow tolerated well the repeated exposures to 1-hour ischemia in both groups. In 2-hour ischemia experiments, the postischemic hyperemia was preserved after the second ischemic period in young rats but not in older rats. These results suggest that the tolerance of skin microcirculation to ischemia-reperfusion may decrease with increasing age.