Contraction of guinea pig trachea by epidermal growth factor--urogastrone

To evaluate further the action of epidermal growth factor - urogastrone (EGF-URO) in smooth muscle systems, we examined the effect of the peptide on guinea pig tracheal strips. The cumulative addition of EGF-URO to the organ bath resulted in a concentration-dependent tonic contraction without tachyphylaxis. The half-maximal contraction was obtained at 13 +/- 3 ng/mL EGF-URO (2 nM). The maximum contraction at 100 ng/mL approached 60% of that induced by 1 microM histamine. No significant difference in the EGF-URO-induced contraction was observed in the presence or absence of a functional epithelium. Preincubation with 1 microM indomethacin for 20 min abolished the action of EGF-URO. The contractile effect of EGF-URO was not affected by yohimbine, propranolol, atropine, tetrodotoxin, and esculetin. However, mepacrine caused inhibition by 37 +/- 7% (mean +/- SEM for n = 3). Verapamil (10 microM) inhibited the EGF-induced response by 62 +/- 5% (mean +/- SEM for n = 4); the response was also absent in Ca-free (1 mM EGTA) buffer. However, the response was restored after the readdition of calcium. Our results suggest that EGF-URO can modulate tracheal smooth muscle contractility via a cyclooxygenase product and raise the possibility that EGF-URO might play a role in controlling pulmonary smooth muscle tone in vivo.     

Insulin resistance does not impair contractile responses of cerebral arteries

Insulin resistance (IR) impairs endothelium-mediated vasodilation in cerebral arteries as well as K+ channel function in vascular smooth muscle. Peripheral arteries also show an impaired endothelium-dependent vasodilation in IR and concomitantly show an enhanced contractile response to endothelin-1 (ET-1). However, the contractile responses of the cerebral arteries in IR have not been examined systematically. This study examined the contractile responses of pressurized isolated middle cerebral arteries (MCAs) in fructose-fed IR and control rats. IR MCAs showed no difference in pressure-mediated (80 mmHg) vasoconstriction compared to controls, either in time to develop spontaneous tone (control: 61+/-3 min, n=30; IR: 63+/-2 min, n=26) or in the degree of that tone (control: 60 min: 33+/-2%, n=22 vs. IR 60 min: 34+/-3%, n=17). MCAs treated with ET-1 (10(-8.5) M) constrict similarly in control (53+/-3%, n=14) and IR (53+/-3%, n=14) arteries. Constrictor responses to U46619 (10(-6) M) are also similar in control (48+/-9%, n=8) and IR (42+/-5%, n=6) MCAs as are responses to extraluminal uridine 5'-triphosphate (UTP; 10(-4.5) M) (control: 35+/-7%, n=11 vs. IR: 38+/-3%, n=10). These findings demonstrate that constrictor responses remain intact in IR despite a selective impairment of dilator responses and endothelial and vascular smooth muscle K+ channel function in cerebral arteries. Thus, it appears that the increased susceptibility to cerebrovascular abnormalities associated with IR and diabetes (including cerebral ischemia, stroke, vertebrobasilar transient ischemic attacks) is not due to an enhanced vasoreactivity to constrictor agents.     

Functional identification of epithelial and smooth muscle histamine-dependent relaxing mechanisms in the bovine trachea,but not in bronchi

Theoretically, the overall effect of histamine on respiratory smooth muscle is the result of a subtle balance of contraction and relaxation. The aim of the study was to identify histamine type 2 (H2) and 3 (H3) receptor-dependent relaxing mechanisms in the contractile elements of the bovine tracheobronchial tree. In bronchial preparations, histamine induced very weak contractions, which were not exacerbated with the H2-antagonist cimetidine. Moreover, precontracted bronchial rings never relaxed in response to cumulative doses of histamine or amthamine (H2-agonist). In intact tracheal preparations, histamine induced strong contractions that were exacerbated by cimetidine (E(max): +17.2+/-6.6%) but not by thioperamide (H3-antagonist). Precontracted tracheal bundles did not relax in response to cumulative doses of the H3-agonist R-alpha-methylhistamine. The tracheal contractile response was higher in denuded compared to intact preparations (11.0+/-1.2 vs. 6.0+/-1.7 g). Cimetidine effect was dramatically potentiated in denuded tracheal strips (+40.0+/-11.7%). It is concluded that the weak response of bovine bronchi to histamine is due to a relative scarcity of H1 receptors on bronchial smooth muscle rather than to H2- or H3-dependent relaxation. In the bovine trachea, the smooth muscle possesses relaxing H2 but no H3 receptors. The epithelium exercises a relaxation, which is independent from H2 and H3 receptors.     

Changes in responsiveness of the canine basilar artery to endothelin-1 after subarachnoid hemorrhage

The effect of endothelin-1 (ET-1) on the basilar arteries from control and subarachnoid hemorrhage (SAH) dogs were examined. The maximal contraction of the basilar artery in response to ET-1 was markedly decreased in the SAH group. Treatment with 10(-8)M phorbol 12-myristate 13-acetate (PMA) reduced the contractile responses to ET-1 in the basilar arteries from control dogs. ET-1-induced contractions of the basilar arteries from control dogs were similar to those in strips from SAH dogs by the treatment with 10(-8) M PMA. Ca(2+)-induced contraction of the basilar arteries which were depolarized with isotonic K+ (64 mM) were significantly attenuated in SAH dogs. Treatment with PMA also reduced the contractile responses to Ca2+ in the basilar arteries from control dogs. These results indicate that decreased contractile responses of the basilar arteries to ET-1 and Ca2+ in the SAH group may be related to changes in the activity of the protein kinase C in vascular smooth muscle.     

Role of ET-1 receptor binding and [Ca(2+)](i) in contraction of coronary arteries from DOCA-salt hypertensive rats

Hypertension is associated with an increase in coronary artery disease, but little is known about the regulation of coronary vascular tone by endothelin-1 (ET-1) in hypertension. The present study evaluated the mechanisms mediating altered contraction to ET-1 in coronary small arteries from deoxycorticosterone acetate (DOCA)-salt hypertensive rats. DOCA-salt rats exhibited an increase in systolic blood pressure and plasma ET-1 levels compared with placebo rats. Contraction to ET-1 (1 x 10(-11) to 3 x 10(-8) M), measured in isolated coronary small arteries maintained at a constant intraluminal pressure of 40 mmHg, was largely reduced in vessels from DOCA-salt rats compared with placebo rats. To determine the role of endothelin receptor binding in the impaired contraction to ET-1, (125)I-labeled ET-1 receptor binding was measured in membranes isolated from coronary small arteries. Maximum binding (fmol/mg protein) and binding affinity were similar in coronary membranes from DOCA-salt rats compared with placebo rats. Changes in intracellular Ca(2+) concentration ([Ca(2+)](i)) were measured in freshly dissociated coronary small artery smooth muscle cells loaded with fura 2. ET-1 (10(-9) M) produced a 30 +/- 9% increase in [Ca(2+)](i) in smooth muscle cells from placebo rats, but had no effect on cells from DOCA-salt rats (2 +/- 2%). In summary, the ET-1-induced coronary artery contraction and increase in [Ca(2+)](i) are impaired in DOCA-salt hypertensive rats, whereas endothelin receptor binding is not altered. These results suggest endothelin receptor uncoupling from signaling mechanisms and indicate that impaired [Ca(2+)](i) signaling contributes to the decrease in ET-1-induced contraction of coronary small arteries in DOCA-salt hypertensive rats.     

Effects of some autonomic drugs and neuropeptides on the mechanical activity of longitudinal and circular muscle strips isolated from the carp intestinal bulb (Cyprinus carpio)

1. The mechanical responses to some autonomic drugs and neuropeptides of longitudinal muscle (LM) and circular muscle (CM) strips isolated from the carp intestinal bulb were investigated in vitro. 2. Acetylcholine and carbamylcholine caused concentration-dependent transient contraction of both LM and CM strips. Tetrodotoxin had no effect, but atropine selectively decreased the contractile responses to acetylcholine and carbamylcholine. 3. Excitatory alpha-2 and inhibitory beta adrenoceptors were present in both LM and CM strips. 4. 5-Hydroxytryptamine (5-HT) caused concentration-dependent contraction of both LM and CM strips. Tetrodotoxin, atropine and methysergide decreased the contractile responses to 5-HT. 5. Some neuropeptides (angiotensin I, angiotensin II, bombesin, bradykinin, neurotensin, somatostatin and vasoactive intestinal polypeptide) did not cause any mechanical response (contraction or relaxation) in either smooth muscle strip. 6. Substance P (SP), neurokinin A (NKA) and neurokinin B (NKB) caused contraction of both LM and CM strips. However, the time course of the contraction in LM was different from that in CM. The order of potency was NKA greater than SP greater than NKB in LM strips and NKA greater than SP much greater than NKB in CM strips. In LM strips, the contractile responses to tachykinins were unaffected by spantide and methysergide, but partly decreased by tetrodotoxin and atropine. On the other hand, the contractile responses of CM strips were unaffected by tetrodotoxin, atropine, methysergide and spantide. 7. Dynorphin (1-13) (DYN), leucine-enkephalin (L-Enk) and methionine-enkephalin (M-Enk) caused concentration-dependent contraction of both LM and CM strips. The order of potency was DYN greater than M-Enk greater than L-Enk. Naloxone selectively decreased the responses to opiate peptides. 8. The present results indicate that acetylcholine, carbamylcholine, catecholamines, 5-HT, tachykinins (SP, NKA and NKB) and opiate peptides (DYN, L-Enk and M-Enk) affect the mechanical activity of LM and CM strips isolated from the carp intestinal bulb through their specific receptors.     

Altered sensitivity to a novel vasoconstrictor endothelin-1 (1-31) in myometrium and umbilical artery of women with severe preeclampsia

We have suggested that a novel endothelin-1 with 31 amino acids [ET-1 (1-31)] plays an important role in fetal circulation, owing to a strong contractile activity on the umbilical artery. To clarify the pathophysiological significance of ET-1 (1-31) in the development of severe preeclampsia, its contractile activities on human umbilical arteries and uterine smooth muscle from patients with preeclampsia were studied. The contraction by ET-1 (1-31) was stronger in uterine smooth muscle of the patients with severe preeclampsia than that of normal subjects. On the contrary, the constriction of umbilical artery of the patients with eclampsia was significantly weaker than that of normal pregnant women. The stronger contraction of myometrium by ET-1 (1-31) in patients with severe preeclampsia observed for the first time in the present study suggests that ET-1 (1-31) might be involved in the development of preeclampsia.     

Contribution of capacitative and non-capacitative Ca2+-entry to M3-receptor-mediated contraction of porcine coronary smooth muscle

We studied the contribution of store-operated or capacitative Ca2+-entry (SOCE or CCE, respectively) through store-operated Ca2+ channels (SOCCs) and the contribution of Ca2+-entry through receptor-operated, non-selective cation channels (ROCCs or NSCCs, respectively), on the M3-receptor-mediated (270 nM Ach) contractile response of porcine coronary smooth muscle strips by means of the respective inhibitors. In the presence of L-VOCC blockade (1 microM verapamil), LOE 908 (inhibition of NSCCs) decreased the contractile response to 75+/-5% (p<0.01, n=6), 2-APB (inhibition of SOCCs) and SK and F 96365 (inhibition of SOCCs and of NSCCs) decreased the response to 45+/-4% (p<0.001, n=10) and to 23+/-2% (p<0.001, n=5), respectively (control: Ach response in the presence of verapamil alone). In the absence of L-VOCC blockade, LOE 908 reduced the Ach-response to 49+/-7% (p<0.001, n=8) and SK and F 96365 to 3+/-2% (p<0.001, n=4) of control, whereas 2-APB transiently increased the response (peak effect: 130+/-11%; p<0.05, n=8). We conclude: (1) the main source of activator Ca2+ during the M3-receptor-mediated contractile response is the Ca2+ influx through L-VOCCs; (2) however, in the presence of L-VOCC blockade, the contractile response is mainly due to Ca2+-entry through SOCCs; (3) NSCCs may be considerably involved in M3-receptor-mediated contraction as they may serve to depolarize the membrane potential and, thus, to open L-VOCCs; (4) in primary tissue of vascular smooth muscle, both, SOCE and Ca2+-entry through NSCCs are activated during M3-receptor stimulation.     

Physiological antagonism caused by adrenergic stimulation of canine tracheal muscle

We studied the simultaneous alpha- and beta-adrenergic response characteristics of canine tracheal smooth muscle in 398 strips from 67 dogs in vitro. Experiments were performed to determine the effects of beta-adrenergic blockade on the expression of the alpha-adrenoceptor contractile responses elicited by norepinephrine (NE), phenylephrine (PE), and clonidine (CLO). Maximal active tension caused by NE increased from 39.1 +/- 27.0 to 241 +/- 75.0 g/cm2 as the concentration of propranolol (PROP) was increased from 10(-6) to 10(-4) M. Augmentation of tracheal smooth muscle contraction caused by PE and CLO was also observed with progressive beta-adrenoceptor blockade; contraction to NE, PE, and CLO was blocked selectively with 3 X 10(-5) M phentolamine (PA) and phenoxybenzamine (PBZ). The beta-adrenergic relaxing properties of the same three agonists were also studied. After alpha-adrenergic blockade with PA or PBZ, all three agonists caused relaxation (NE greater than CLO greater than PE) of methacholine-induced contraction of tracheal smooth muscle that was reversed selectively with PROP. We demonstrate that NE, PE, and CLO cause simultaneous stimulation of both the alpha- and beta-adrenergic receptors in tracheal smooth muscle; the net response elicited is the result of adrenergic physiological antagonism and depends on the relative degree of alpha- and/or beta-adrenoceptor blockade.     

Muscarinic receptor reserve of airway smooth muscle and the response to isoproterenol

It has been hypothesized that the muscarinic receptor reserve for contraction of airway smooth muscle is an important determinant of the potency with which isoproterenol relaxes submaximal muscarinic contractions. The goals of this study were to inactivate, with phenoxybenzamine, a fraction of the muscarinic receptors present in canine tracheal smooth muscle, and then to determine whether this decrease in muscarinic receptor reserve altered the potency with which isoproterenol relaxed submaximal muscarinic contractions. Strips of smooth muscle were suspended from force transducers in vitro and preincubated with either vehicle (untreated) or phenoxybenzamine (10(-5) M) for 30 min. For muscarinic contractions induced by carbachol that were approximately 70-80% of maximum, the half-maximally effective concentration of isoproterenol was 2.4 +/- 0.8 x 10(-7) M for untreated strips but 5.8 +/- 1.3 x 10(-9) M for strips treated with phenoxybenzamine (n = 6, P less than 0.05). We concluded that treatment with phenoxybenzamine increased the sensitivity of a submaximal muscarinic contraction to isoproterenol. The results support the hypothesis that the muscarinic receptor reserve for contraction is an important determinant of the potency with which isoproterenol relaxes submaximal muscarinic contractions.     

Role of Cl- current in endothelin-1-induced contraction in rabbit basilar artery

Cl- efflux induces depolarization and contraction of smooth muscle cells. This study was undertaken to explore the role of Cl- channels in endothelin-1 (ET-1)-induced contraction in rabbit basilar artery. Male New Zealand White rabbits (n = 26), weighing 1.8-2.5 kg, were euthanized by an overdose of pentobarbital. The basilar arteries were removed for isometric tension recording. ET-1 produced a concentration-dependent contraction of the rabbit basilar artery in the normal Cl- Krebs-Henseleit bicarbonate buffer (123 mM Cl-). The ET-1-induced contraction was reduced by the following manipulations: 1) inhibition of Na+-K+-2Cl- cotransporter with bumetanide (3 x 10(-5) and 10(-4) M), 2) bicarbonate-free solution to disable Cl-/HCO exchanger, and 3) preincubation of rings with the Cl- channel blockers niflumic acid, 5-nitro-2-(3-phenylpropylamino)benzoic acid, and indanyloxyacetic acid 94. The ET-1-induced contraction was enhanced by substitution of extracellular Cl- (10 mM) with methanesulfonic acid (113 mM). Cl- channels are involved in ET-1-induced contraction in the rabbit basilar artery.     

Effects of age on muscarinic agonist-induced contraction and IP accumulation in airway smooth muscle.

The effects of age on carbachol-stimulated force development and [3H]inositol phosphate production was studied in tracheal rings from guinea pigs aged 1 month and 25 months of age. The pD2 for the contractile response to carbachol was significantly reduced in tracheal tissues from old animals as compared to that of the young tissues (6.49 +/- 0.04, 7.09 +/- 0.04, n = 12), respectively. In contrast, inositol phosphate formation was not altered with increasing age when stimulated by carbachol or NaF, a direct activator of G proteins. Carbachol-induced inositol phosphate accumulation was inhibited by treatment with 1 micrograms/ml pertussis toxin, suggesting that IP1 accumulation is coupled to a pertussis-toxin-sensitive protein. The pD2 values for contraction (7.09 +/- 0.09, 6.49 +/- 0.04) were significantly different from the pD2 values for IP1 accumulation (4.72 +/- 0.14, 5.10 +/- 0.18) in both young and old tissues, respectively. These data suggest that IP1 accumulation is not responsible for the decreased contractile ability in tracheal smooth muscle during aging.     

Antagonism of relaxation to isoproterenol caused by agonist interactions

The interaction of contractile agonists on the relaxation elicited with isoproterenol (ISO) was studied in 112 tracheal smooth muscle (TSM) strips from 20 dogs in vitro. Strips were contracted to the same active target tension (TT) with acetylcholine (ACh), histamine (HIS), serotonin (5-hydroxytryptamine, 5-HT), potassium chloride (KCl), or the combinations of ACh + HIS, ACh + 5-HT, HIS + KCl, HIS + 5-HT (50% TT from each agonist). Although a less potent agonist, adding HIS to cause 50% of the TT reduced the concentration of ACh to elicit the remaining 50% TT and substantially altered relaxation by ISO compared with HIS alone [concentration required to achieve 50% relaxation (RC50) = 9.2 +/- 2.4 X 10(-8) vs. 9.0 +/- 4.4 X 10(-9) M to HIS alone; P less than 0.003]. Relaxation for TSM strips contracted with ACh + HIS was comparable to that elicited from the same TT with ACh alone, although concentrations required in combination were lower than for either agonist alone. Trachealis strips contracted equivalently with KCl + HIS also had augmented contraction and attenuated relaxation (RC50 = 3.7 +/- 0.8 X 10(-8) M; P less than 0.015 vs. HIS alone). However, combinations of 5-HT + ACh and 5-HT + HIS did not alter relaxation to ISO from that elicited by the weaker agonist alone. We demonstrate that TSM relaxation depends on the combination of agonists eliciting contraction and may be inhibited substantially by interactions among contractile agonists.     

Differential effects of prostaglandin E2 on contractions of airway smooth muscle

In an in vitro muscle bath, the active tension generated by strips of canine tracheal smooth muscle responding to cumulative additions of either histamine (10(-8) to 10(-3) M) or acetylcholine (10(-9) to 10(-3) M) was measured in the absence and presence of prostaglandin E2 (PGE2) (10(-6) to 10(-5) M). When contractile responses of equal magnitude were compared, the contractions elicited by acetylcholine were resistant to the inhibitory effects of PGE2, relative to comparable contractions elicited by histamine. To assess the role of adenylate cyclase in determining the different responses to histamine and acetylcholine in the presence of PGE2, we assayed adenylate cyclase activity in membranes prepared from canine tracheal smooth muscle and found that acetylcholine, but not histamine, decreased PGE2-stimulated adenylate cyclase activity by 48 +/- 2% (mean +/- SE; n = 5). However, in other experiments, we found that even large pharmacological increases in tissue adenosine 3',5'-cyclic monophosphate (cAMP) content only partially inhibited muscarinic tone. Also, exogenously applied analogues of cyclic AMP inhibited contractions induced by histamine more effectively than comparable contractions induced by acetylcholine. We concluded that acetylcholine decreased adenylate cyclase activity in membranes prepared from canine tracheal smooth muscle and that this effect may have contributed to, but did not completely account for, the relative resistance of muscarinic contractions to the inhibitory effects of PGE2.     

Tyrosine kinase inhibitors and the contractile action of epidermal growth factor-urogastrone and other agonists in gastric smooth muscle.

We examined the effects of the tyrosine kinase (TK) inhibitors, genistein, and tyrphostin (RG-50864) on the contractile action of epidermal growth factor - urogastrone (EGF-URO), transforming growth factor-alpha (TGF-alpha), and other agonists in two smooth muscle bioassay systems (guinea pig gastric longitudinal muscle, LM, and circular muscle, CM). We also studied the inhibition by tyrphostin of EGF-URO stimulated protein phosphorylation in identical smooth muscle strips. The selective inhibition by genistein and tyrphostin of EGF-URO and TGF-alpha induced contraction, but not of carbachol- and bradykinin-mediated contraction, occurred at much lower concentrations (genistein, less than 7.4 microM (2 micrograms/mL); tyrphostin, less than 20 microM (4 micrograms/mL)) than those used in previously published studies with these TK inhibitors. In LM tissue, the IC50 values were for genistein 1.1 +/- 0.1 microM (0.30 micrograms/mL; mean +/- SEM) and 3.6 +/- 0.5 microM (0.74 micrograms/mL) for tyrphostin, yielding a molar potency ratio (GS: TP) of 1:3 in the longitudinal preparation. In CM tissue, the IC50 values were 3.0 +/- 0.3 microM (0.81 micrograms/mL) for genistein and 2.4 +/- 0.2 microM (0.49 micrograms/mL) for tyrphostin, yielding a molar potency ratio (GS:TP) of 1.0:0.8 in the circular strips. The inhibition by genistein and tyrphostin of EGF-URO and TGF-alpha mediated contraction was rapid (beginning within minutes) and was reversible upon washing the preparations free from the enzyme inhibitors. In intact tissue strips studied under bioassay conditions, tyrphostin (40 microM) also blocked EGF-URO triggered phosphorylation of substrates detected on Western blots using monoclonal antiphosphotyrosine antibodies.(ABSTRACT TRUNCATED AT 250 WORDS)     

Neutral endopeptidase modulates endothelin-1-induced airway smooth muscle contraction in guinea-pig trachea.

This study was designed to evaluate the role of neutral endopeptidase (NEP) in modulating the airway smooth muscle contraction induced by endothelin-1 in isolated segments of guinea-pig trachea. Endothelin-1 (10(-9)-10(-6) M) produced a concentration-dependent contraction that reached a maximum by 30 min. The NEP inhibitor leucine-thiorphan (10(-5) M) significantly increased the contractile response to endothelin-1. The addition of leucine-thiorphan to tracheal segments precontracted by 10(-9) and 10(-8) M endothelin-1 increased isometric tension by 181 +/- 65% (mean +/- 1 S.E.M.; P less than 0.05) and by 138 +/- 49% (P less than 0.05), respectively. In contrast, the kininase II inhibitor captopril and the peptidase inhibitors leupeptin and bestatin had no effect. Preincubation of endothelin-1 with 1 microgram recombinant human NEP decreased the contractile activity of endothelin-1 by 72 +/- 9%, whereas no effect was observed using heat-inactivated NEP. We conclude that NEP modulates endothelin-induced contraction of airway smooth muscle in the guinea-pig trachea.     

Role of M2 muscarinic receptors in airway smooth muscle contraction

Airway smooth muscle expresses both M2 and M3 muscarinic receptors with the majority of the receptors of the M2 subtype. Activation of M3 receptors, which couple to Gq, initiates contraction of airway smooth muscle while activation of M2 receptors, which couple to Gi, inhibits beta-adrenergic mediated relaxation. Increased sensitivity to intracellular Ca2+ is an important mechanism for agonist-induced contraction of airway smooth muscle but the signal transduction pathways involved are uncertain. We studied Ca2+ sensitization by acetylcholine (ACh) and endothelin-1 (ET-1) in porcine tracheal smooth muscle by measuring contractions at constant [Ca2+] in strips permeabilized with Staphylococcal alpha-toxin. Both ACh and ET-1 contracted airway smooth muscle at constant [Ca2+]. Pretreatment with pertussis toxin for 18-20 hours reduced ACh contractions, but had no effect on those of ET-1 or GTPgammaS. We conclude that the M2 muscarinic receptor contributes to airway smooth muscle contraction at constant [Ca2+] via the heterotrimeric G-protein Gi.     

Thyroid status and response to endothelin-1 in rat arterial vessels

We have previously reported that changes in thyroid status are associated with significant alterations in skeletal muscle blood flow during exercise and that changes in endothelium-dependent vasodilation may contribute to these blood flow abnormalities. The purpose of this study was to test the hypothesis that altered endothelium-dependent vasoconstriction is also associated with changes in thyroid status. To test this hypothesis, rats were rendered hypothyroid with propylthiouracil (Hypo, n = 14) or hyperthyroid with triiodothyronine (Hyper, n = 14) over approximately 3 mo. Treatment efficacy was confirmed by altered (P < 0.05) citrate synthase activity in several hindlimb skeletal muscles from Hypo and Hyper, compared with that in muscles from euthyroid rats (Eut, n = 12). Vascular rings were prepared from abdominal aortae, and responses to several vasoactive agents were determined in vitro. As found previously, maximal acetylcholine-induced vasorelaxation was modulated by thyroid status (Eut, 47 +/- 9; Hypo, 28 +/- 6; Hyper, 68 +/- 5%; P < 0.05). Contractile responses of vascular rings with intact endothelium to the endothelium-derived constrictor endothelin-1 (ET-1), however, were similar among groups across a range of ET-1 concentrations. In addition, maximal responses [Eut, 3.75 +/- 0.47; Hypo, 2.72 +/- 0.25; Hyper, 3.22 +/- 0.42 g; not significant (NS)] and sensitivities (Eut, 8.12 +/- 0.09; Hypo, 8.10 +/- 0.06; Hyper, 8.28 +/- 0.09 -log M; NS) to ET-1 were similar among groups. If these findings from the conduit-type abdominal aorta extend into resistance vasculature, it appears that changes in endothelium-dependent vasoconstriction do not contribute to skeletal muscle blood flow abnormalities associated with thyroid disease states.     

姜黄素对小鼠离体十二指肠平滑肌舒缩活动的影响

目的:本研究采用小鼠离体十二指肠平滑肌观察姜黄素对胃肠道蠕动的影响,探讨其作用机制。方法:取小鼠离体十二指肠平滑肌条,放入37℃Krebs液浴槽中,通入95%氧气和5%二氧化碳混合气体,分组进行下列实验:对照组和分别加入10-40 M姜黄素组,测量记录十二指肠平滑肌的自主收缩变化;另取一组平滑肌条,分对照组、乙酰胆碱组、乙酰胆碱+姜黄素组、阿托品组、阿托品+姜黄素组,采用张力换能器连接多通道生理信号采集处理系统,测量比较十二指肠平滑肌舒缩的变化。结果:小鼠十二指肠平滑肌加入姜黄素孵育后,其自主收缩幅度有明显下降(P0.01),而且降低的幅度与姜黄素剂量相关;给与乙酰胆碱引起十二指肠收缩后,再加姜黄素孵育,十二指肠平滑肌的收缩幅度明显的下降(P0.01);给予阿托品引起小鼠平滑肌舒张后,再给予姜黄素孵育,平滑肌收缩幅度进一步降低。结论:姜黄素对小鼠离体十二指肠平滑肌具有直接舒张作用。     

Mechanical properties of human bronchial smooth muscle in vitro.

The in vitro mechanical properties of smooth muscle strips from 10 human main stem bronchi obtained immediately after pneumonectomy were evaluated. Maximal active isometric and isotonic responses were obtained at varying lengths by use of electrical field stimulation (EFS). At the length (Lmax) producing maximal force (Pmax), resting tension was very high (60.0 +/- 8.8% Pmax). Maximal fractional muscle shortening was 25.0 +/- 9.0% at a length of 75% Lmax, whereas less shortening occurred at Lmax (12.2 +/- 2.7%). The addition of increasing elastic loads produced an exponential decrease in the shortening and velocity of shortening but increased tension generation of muscle strips stimulated by EFS. Morphometric analysis revealed that muscle accounted for 8.7 +/- 1.5% of the total cross-sectional tissue area. Evaluation of two human tracheal smooth muscle preparations revealed mechanics similar to the bronchial preparations. Passive tension at Lmax was 10-fold greater and maximal active shortening was threefold less than that previously demonstrated for porcine trachealis by us of the same apparatus. We attribute the limited shortening of human bronchial and tracheal smooth muscle to the larger load presumably provided by a connective tissue parallel elastic component within the evaluated tissues, which must be overcome for shortening to occur. We suggest that a decrease in airway wall elastance could increase smooth muscle shortening, leading to excessive responses to contractile agonists, as seen in airway hyperresponsiveness.