Adrenomedullin-induced dilation of human placental arteries is modulated by an endothelium-derived constricting factor

Adrenomedullin is synthesized and secreted by fetoplacental tissues. Given that the placenta lacks autonomic innervation, we proposed that adrenomedullin acts locally to control blood flow in the placental vasculature through a balance of dilatory and constrictive pathways. Placental stem villous arteries (200 microm) from normotensive human pregnancies were dissected and mounted on a wire myograph. The vessels were preconstricted with the thromboxane A(2) mimetic U46619 (EC(80) concentration), and exposed to cumulative concentrations of adrenomedullin (1 x 10(-9) to 3 x 10(-7) mol/L). Adrenomedullin caused concentration-dependent vasorelaxation which, in endothelium-intact vessels, was attenuated in the presence of the nitric oxide synthase inhibitor L-NMMA. This suggested that the vasodilation was mediated, at least in part, through nitric oxide. However, removal of the endothelium did not similarly alter the response. Nor did L-NMMA have any effect in endothelium-denuded vessels. We hypothesized that adrenomedullin must induce release of both endothelium-derived relaxing (nitric oxide) and constricting factors. When we blocked the two major pathways through which adrenomedullin is known to induce vasodilation, by incubating the vessels with L-NMMA (nitric oxide synthase inhibitor) and Rp-cAMPS (cAMP-dependent protein kinase inhibitor), adrenomedullin induced concentration-dependent vasoconstriction. This was not mediated through endothelin, since addition of the non-specific endothelin receptor antagonist PD142893 failed to alter the response to adrenomedullin. We conclude that, in addition to increasing endothelial nitric oxide biosynthesis in placental stem villous arteries, adrenomedullin induces release of an endothelium-derived constricting factor.     

Involvement of nitric oxide in endothelium-dependent arterial relaxation by leptin

Leptin is a polypeptide, mainly produced in white adipose tissue, and increases sympathetic nerve activity. A few studies investigated leptin's effect on peripheral vessels. We examined the vasorelaxant effects of human leptin on rat arteries. Arterial rings were precontracted with 1 x 10(-6) mol/l of phenylephrine, and leptin was superfused. Leptin relaxed phenylephrine-precontracted arterial rings in a dose-dependent manner. ED50 was calculated to 8.4 microg/ml. Removal of endothelium abolished the effects of leptin. Indomethacin (1 x 10(-5) mol/l) did not affect the vasorelaxation by leptin, whereas 1 x 10(-4) mol/l of N(omega)-nitro-L-arginine methyl ester (L-NAME) completely suppressed it. The inhibition was antagonized by 1 x 10(-4) mol/l of L-arginine. Leptin normally relaxed arterial rings during superfusion of K channel blockers, including 3 x 10(-5) mol/l of glibenclamide, 1 x 10(-6) of mol/l apamin, and 5 x 10(-7) mol/l of charybdotoxin. Low Cl(-) solution (8. 3 mmol/l) inhibited leptin-induced relaxation, but endothelium-independent vasodilatation by nitroprusside was not impaired at low Cl(-) solution. These results suggest that arterial relaxation by leptin is mediated by nitric oxide released from endothelium, and Cl(-) plays an important role in leptin-induced nitric oxide release.     

Guanylyl cyclase mediates ANP-induced vasoconstriction of murine splenic vessels

We have previously shown that ANP causes differential constriction of the splenic vasculature of the rat (veins greater than arteries), which may be inhibited by blocking the production of cGMP with A7195. In this paper, we report experiments done on vessels derived from guanylyl cyclase (GC)-A knockout mice. Small splenic arteries ( approximately 150-microm diameter) and veins ( approximately 250-microm diameter) were dissected from male GC-A-deficient 129sv mice or age-matched wild-type controls and mounted in a wire myograph. In the wild-type mice, ANP exhibited higher potency in the veins than in the arteries (EC(50) values wild-type mice: artery, 8 +/- 3 x 10(-9) M, n = 5 vs. vein, 6 +/- 4 x 10(-10) M, n = 5; P < 0.05). The concentration-response curve for ANP-induced vasoconstriction was also shifted leftward in denuded compared with intact arteries (EC(50) values: denuded artery: 5 +/- 3 x 10(-10) M, n = 5 vs. intact artery, 8 +/- 3 x 10(-9) M, n = 5; P < 0.05), i.e., the denuded vessels were more reactive. By contrast, ANP caused no significant change in tension from baseline in intact splenic arteries, intact splenic veins, or denuded splenic arteries derived from the GC-A-deficient mice, although these vessels did show normal concentration-dependent increases in tension to phenylephrine. We conclude that ANP causes vasoconstriction in the splenic vasculature by an endothelium-independent mechanism, mediated via guanylyl cyclase.     

Elucidation of the temporal relationship between endothelial-derived NO and EDHF in mesenteric vessels

Although the endothelium co-generates both nitric oxide (NO) and endothelium-derived hyperpolarizing factor (EDHF), the relative contribution from each vasodilator is not clear. In studies where the endothelium is stimulated acutely, EDHF responses predominate in small arteries. However, the temporal relationship between endothelial-derived NO and EDHF over more prolonged periods is unclear but of major physiological importance. Here we have used a classical pharmacological approach to show that EDHF is released transiently compared with NO. Acetylcholine (3 x 10(-6) mol/l) dilated second- and/or third-order mesenteric arteries for prolonged periods of up to 1 h, an effect that was reversed fully and immediately by the subsequent addition of L-NAME (10(-3) mol/l) but not TRAM-34 (10(-6) mol/l) plus apamin (5 x 10(-7) mol/l). When vessels were pretreated with L-NAME, acetylcholine induced relatively transient dilator responses (declining over approximately 5 min), and vessels were sensitive to TRAM-34 plus apamin. When measured in parallel, the dilator effects of acetylcholine outlasted the smooth muscle hyperpolarization. However, in the presence of L-NAME, vasodilatation and hyperpolarization followed an identical time course. In vessels from NOSIII(-/-) mice, acetylcholine induced small but detectable dilator responses that were transient in duration and blocked by TRAM-34 plus apamin. EDHF responses in these mouse arteries were inhibited by an intracellular calcium blocker, TMB-8, and the phospholipase A(2) inhibitor AACOCF(3), suggesting a role for lipid metabolites. These data show for the first time that EDHF is released transiently, whereas endothelial-derived NO is released in a sustained manner.     

Disruption of endothelial caveolae is associated with impairment of both NO- as well as EDHF in acetylcholine-induced relaxation depending on their relative contribution in different vascular beds

Caveolae represent an important structural element involved in endothelial signal-transduction. The present study was designed to investigate the role of caveolae in endothelium-dependent relaxation of different vascular beds. Caveolae were disrupted by cholesterol depletion with filipin (4x10(-6) g L(-1)) or methyl-beta-cyclodextrin (MCD; 1x10(-3) mol L(-1)) and the effect on endothelium-dependent relaxation was studied in rat aorta, small renal arteries and mesenteric arteries in the absence and presence of L-NMMA. The contribution of NO and EDHF, respectively, to total relaxation in response to acetylcholine (ACh) gradually changed from aorta (71.2+/-6.1% and 28.8+/-6.1%), to renal arteries (48.6+/-6.4% and 51.4+/-6.4%) and to mesenteric arteries (9.1+/-4.0% and 90.9+/-4.1%). Electron microscopy confirmed filipin to decrease the number of endothelial caveolae in all vessels studied. Incubation with filipin inhibited endothelium-dependent relaxation induced by cumulative doses of ACh (3x10(-9)-10(-4) mol L(-1)) in all three vascular beds. In aorta, treatment with either filipin or MCD only inhibited the NO component, whereas in renal artery both NO and EDHF formation were affected. In contrast, in mesenteric arteries, filipin treatment only reduced EDHF formation. Disruption of endothelial caveolae is associated with the impairment of both NO and EDHF in acetylcholine-induced relaxation.     

Direct and prolonged effect of thyroliberin in ultra small doses on contractility of the white rat mesentery lymphatic vessels

The prolonged effect of thyroliberin in ULD after single intramuscular injection on contractility of lymphatic vessels directly was investigated. The controlled group of animals received injection of 0.2 ml of physiological solution. The experimental group was injected by 0.2 ml of thyroliberin in concentrations of 10(-10) or 10(-16) mol/l (1 x 10(-4) and 1 x 10(-10) micrograms/kg of the body weight respectively). During the experiment the animals were grouped in the following way: 1) directly after the injection; 2) 3 hours later; 3) on the 1st day and then every day during 2 weeks. Lymphatic vessels reactivity of the experimental animals as well as controlled was studied by application of thyroliberin and noradrenalin (in concentrations of 1 x 10(-16) and 1 x 10(-6) mol/l respectively) directly on mesentery lymphatic vessels. The lymphatic vessels reaction in control group of animals on the noradrenalin and thyroliberin was the same during the period of observation. Thyroliberin stimulated contractility at concentration of 1 x 10(-16) mol/l. The reaction of experimental group was dramatically decreased to 10(-4) mol/l on the 1st and the 3rd day (in the case i.m. injected concentration 1 x 10(-10) mol/l) and to 10(-10) mol/l (in the case of i.m. injected concentration 10(-16) mol/l). The lymphatic vessels reactivity to exogenous thyroliberin gradually established at the 6-7th days till 12th day from the moment of thyroliberin injection. The mechanisms of the action of thyroliberin in ULD are discussed.     

B(1) and B(2) bradykinin receptors on adventitial fibroblasts of cerebral arteries are coupled to recombinant eNOS

Our previous ex vivo and in vivo studies reported that expression of the recombinant endothelial nitric oxide (NO) synthase (eNOS) gene in adventitial fibroblasts recovers NO production in arteries without endothelium in response to bradykinin. The present study was designed to characterize subtypes of bradykinin receptors on adventitial fibroblasts coupled to the activation of recombinant eNOS. Endothelium-denuded segments of canine basilar arteries were transduced with beta-galactosidase (beta-Gal) gene or eNOS gene ex vivo, using a replication-defective adenoviral vector (10(10) plaque-forming units/ml) for 30 min at 37 degrees C. Twenty-four hours later, isometric force recording or cGMP measurement was carried out. B(1) bradykinin receptor agonist (des-Arg(9)-bradykinin, 10(-10)-10(-8) mol/l) did not significantly affect vascular tone in control or beta-Gal gene-transduced canine basilar arteries without endothelium. In contrast, this agonist caused concentration-dependent relaxations in recombinant eNOS gene-transduced arteries without endothelium. Relaxations to B(1) receptor agonist in the eNOS arteries were abolished by B(1) receptor antagonist (des-Arg(9)-[Leu(8)]bradykinin, 6 x 10(-9) mol/l) but not by B(2) receptor antagonist (Hoe-140, 5 x 10(-8) mol/l). Bradykinin did not significantly alter vascular tone in control or beta-gal arteries without endothelium, whereas this peptide (10(-11)-10(-8) mol/l) induced concentration-dependent relaxations, as well as an increase in cGMP formation in endothelium-denuded eNOS-transduced arteries. Stimulatory effects of bradykinin were prevented in the presence of a B(2) receptor antagonist but not in the presence of a B(1) receptor antagonist. B(1) and B(2) receptor antagonists had no effect on relaxations to substance P, confirming the selectivity of the compounds. Our results suggest that B(1) and B(2) bradykinin receptors are coupled to activation of recombinant eNOS expressed in adventitial fibroblasts.     

Modulatory effect of diclofenac on antispasmodic effect of pitofenone in cholinergic spasm

Biliary, ureteric and intestinal colic are extremely common clinical conditions associated with smooth muscle spasm. In the present study, antispasmodic activity was carried out against acetylcholine (10-640 ng/ml)-induced contractions on guinea pig ileum. Acetylcholine (10-640 ng/ml) induced concentration-dependent contraction of smooth muscle. Diclofenac, in varying concentration (9.4 x 10(-5) mol/l and 14.1 x 10(-5) mol/l) shifted the concentration response curve of acetylcholine to the right without suppressing the maximal response. However, in higher concentration diclofenac (18.9 x 10(-5) mol/l) blocked the response in an unsurmountable fashion. Further, analgin (11.09 x 10(-5), 16.63 x 10(-5) and 22.18 x 10(-5) mol/l) in equimolar concentrations did not alter the concentration response curve of acetylcholine, but in higher concentration analgin (44.36 x 10(-5) mol/l) also blocked the response in an unsurmountable fashion. Pitofenone (2.5 x 10(-6) mol/l) also, shifted the concentration response curve of acetylcholine to right in a parallel fashion with no change in maximal response. The present study confirms the potent antispasmodic activity of diclofenac-pitofenone combination in comparison to analgin-pitofenone in molar equivalent concentration (in comparison to diclofenac) against acetylcholine-induced contractions of guinea pig ileum.     

Alterations in relaxation to lactate and H(2)O(2) in human placental vessels from gestational diabetic pregnancies

We determined whether alterations in the mechanism of relaxation to H(2)O(2) potentially contribute to the enhanced prostaglandin-mediated contractile response to H(2)O(2) and posthypoxic reoxygenation seen in human placental vessels of pregnancies with gestational diabetes mellitus (GDM). Isolated placental arteries and veins from GDM and uncomplicated full-term pregnancies were precontracted with prostaglandin F(2alpha) (PO(2) 35-38 Torr) and then exposed to lactate (1-10 mM), arachidonic acid (0.01-10 microM), nitroglycerin (1 nM-1 microM), forskolin (0.01-10 microM), or H(2)O(2) (1 microM-1 mM + 10 microM indomethacin). The rates of tissue H(2)O(2) metabolism by catalase and nitrite production were measured. The relaxation to lactate was reduced in GDM placental arteries and veins by 54-85 and 66-80%, and the relaxation to H(2)O(2) was inhibited by 80-94% in GDM placental veins compared with vessels from uncomplicated full-term pregnancies. H(2)O(2) caused only minimal relaxation of placental arteries. Responses to other relaxing agents were not altered in the GDM placental vessels. Diabetic vessels showed rates of nitrite production that were increased by 113-195% and rates of H(2)O(2) metabolism by catalase that were decreased by 44-61%. The loss of relaxation to H(2)O(2) and lactate (mediated via H(2)O(2)), perhaps as a result of the inhibition of catalase by nitric oxide, may explain the previously reported enhancement of prostaglandin-mediated contractile responses to H(2)O(2) and posthypoxic reoxygenation seen in GDM placental vessels.     

Real-time investigation of the interaction between primaquine phosphate and bovine serum albumin (BSA) by piezoelectric quartz crystal impedance analysis

Real-time investigation of the interaction between primaquine phosphate and bovine serum albumin by the piezoelectric quartz crystal impedance (PQCI) analysis was carried out for the first time. Three kinds of electrodes were investigated. Compared with bare gold (Au) electrode, the gold electrode self-assembled of nanogold colloids exhibits maintained biocompatibility, increased capacity and more bioactivity. Additionally, on the basis of the multi-dimensional information provided by the PQCI analysis, the real-time interaction information and the kinetics of the binding process was investigated and a response model was deduced. At 37 degrees C, the binding rate (k1), dissociation rate (k(-1)) and equilibrium constants (Ka) were 4.19x10(2) (mol l(-1))(-1) s(-1), 1.01x10(-3) s(-1) and 4.15x10(5) (mol l(-1))(-1) for the electrode modified by nanogold particles; 3.83x10(2) (mol l(-1))(-1) s(-1), 9.70x10(-4) s(-1) and 3.95x10(5) (mol l(-1))(-1) for the bare gold electrode, respectively.     

Neuropeptide modulation of lymphatic smooth muscle tone in the canine forelimb

Neurokinin A and B are putative inflammatory mediators. We assessed their ability to alter prenodal lymphatic resistance. Intralymphatic neurokinin A (3.0 x 10(-6), 3.0 x 10(-5) and 3.0 x 10(-4) mol l(-1)) significantly constricted lymphatics at the two highest doses. Preliminary experiments suggested that neurokinin B might dilate lymphatics. To test this, lymphatic pressure was increased by norepinephrine (3.1 x 10(-6) mol l(-1)). Neurokinin B (2.7 x 10(-4) mol l(-1)) was then infused intralymphatically during norepinephrine infusion. Norepinephrine increased perfusion pressure from 5.6 +/- 0.6 mmHg to 12.1 +/- 1.4 mmHg. Subsequent infusion of neurokinin B significantly decreased lymphatic perfusion pressure from 11.9 +/- 1.3 mmHg to 9.9 +/- 1.1 mmHg. These data indicate that neurokinin A and B can alter lymphatic resistance and are consistent with the hypothesis that lymph vessel function may be subject to modulation by neurokinins.     

ETB receptor dependent alteration in aortic responses to ET-1 in the cardiomyopathic hamster

The aim of this study was to verify whether an alteration in the aortic endothelin-1 (ET-1) response takes place in UM-X7.1 cardiomyopathic hamsters. Our results showed that ET-1 (10(-12) - 10(-5) mol/L) induces dose-dependent sustained increases in tension in the intact and endothelium denuded aortas from both normal and cardiomyopathic hamsters. The EC50 values of ET-1 of both intact and endothelium denuded aortas of normal hamsters were similar (2.2 x 10(-9) mol/L and 1.8 x 10(-9) mol/L, respectively). However, in cardiomyopathic hamsters, the EC50 of ET-1 in intact aortas was higher (1.5 x 10(-8) mol/L) than that of the endothelium denuded preparations (2.7 x 10(-9) mol/L). The EC50 of ET-1 in normal and cardiomyopathic hamster denuded aortas were similar. However, the EC50 of ET-1 in intact aortas of cardiomyopathic hamster was higher (1.5 x 10(-8) mol/L) than that of normal hamsters (2.2 x 10(-9) mol/L). Pre-treatment with the ETA receptor antagonist ABT-627 (10(-5)mol/L) of intact and endothelium denuded aortas from both normal and cardiomyopathic hamsters significantly prevented ET-1 (10(-7) mol/L) from inducing an increase in tension. Pre-treatment with the ETB receptor antagonist A-192621 (10(-5) mol/L) had no effect on the ET-1-induced increase in tension in endothelium denuded aortas of both normal and cardiomyopathic hamsters, as well as in intact preparations of normal animals. However, blockade of the ETB receptors in intact aortas of cardiomyopathic hamsters significantly (p < 0.001) potentiated the ET-1-induced increase in tension. In summary, an attenuation of the contraction response to ET-1 was found in UM-X7.1 cardiomyopathic hamsters when compared with normal age-matched hamsters. This alteration of the ET-1 effect in the aortas of cardiomyopathic hamsters seems to be dependent on the presence of the endothelium and could be due, in part, to an increase in the contribution of endothelial ETB receptors to relaxation, which in turn acts as a physiological depressor of ET-1 vasoconstriction. Our results suggest that an increase in the endothelium ETB receptor density may play a role in the development of hypotension in UM-X7.1 cardiomyopathic hamsters.     

The immune response to GHRH, relationship to conformation

Antibodies to GHRH1-44, GHRH1-29, and proinsulin were induced in guinea pigs. GHRH1-44 forms 7 S and 10 S complexes with antibodies. It is a divalent antigen. The sequence 30-44 bound 85% of the antibodies to GHRH1-44 with high affinity (3.8 +/- 0.9 x 10(9) l/mol). The fragment 1-29 bound with low affinity (0.6 +/- 0.3 x 10(9) l/mol) 15% of the antibodies (2p less than 0.001). Antibodies to GHRH1-29 had low affinity towards the native hormone (0.4 +/- 0.2 x 10(9) l/mol) and the region 1-29 (0.3 +/- 0.2 x 10(9) l/mol). Antibodies to proinsulin bound linear C-peptide with lower affinity (0.3 +/- 0.2 x 10(9) l/mol) than the C-peptide loop in proinsulin (3.4 +/- 0.9 x 10(9) l/mol). It is concluded that the conformation of the epitopes on the sequence 1-29, recognized during the immune response, i.e. on the cell membrane, is different from the conformation of GHRH1-29 or GHRH1-44 in aqueous solution.     

Liquid chromatography with amperometric detection using functionalized multi-wall carbon nanotube modified electrode for the determination of monoamine neurotransmitters and their metabolites

The fabrication and application of a novel electrochemical detection (ED) method with the functionalized multi-wall carbon nanotubes (MWNTs) chemically modified electrode (CME) for liquid chromatography (LC) were described. The electrochemical behaviors of dopamine (DA) and other monoamine neurotransmitters at the CME were investigated by cyclic voltammetry (CV) and differential pulse voltammetry (DPV). The results indicated that the CME exhibited efficient electrocatalytic effects on the current responses of monoamine neurotransmitters and their metabolites with high sensitivity, high stability and long-life activity. In LC-ED, DA, norepinephrine (NE), 3-methoxy-4-hydroxyphenylglycol (MHPG), 3,4-dihydroxyphenylacetic acid (DOPAC), 5-hydroxytryptamine (5-HT), 5-hydroxyindoleacetic acid (5-HIAA) and homovanillic acid (HVA) had good and stable current responses at the CME. The linear ranges of seven analytes were over four orders of magnitude and the detection limits were 2.5 x 10(-10) mol/l for DA, 2.5 x 10(-10) mol/l for NE, 5.0 x 10(-10) mol/l for MHPG, 3.0 x 10(-10) mol/l for DOPAC, 3.5 x 10(-10) mol/l for 5-HT, 6.0 x 10(-10) mol/l for 5-HIAA, 1.25 x 10(-9) mol/l for HVA. The application of this method coupled with microdialysis sampling for the determination of monoamine neurotransmitters and their metabolites in Parkinsonian patients' cerebrospinal fluid was satisfactory.     

Effect of indomethacin and deendothelisation on vascular responses in the renal artery

Vasodilator prostaglandins (PGE2, PGI2) play an important role in the regulation of renal blood flow. Hence, inhibition of their production with nonsteroidal anti-inflammatory drugs increases renal vascular resistance and exerts adverse renal effects. It has been reported that besides endothelium-derived prostaglandin products, nitric oxide (NO) may be mainly involved in regulation of renal functions. The aim of our study was to evaluate the effect of cyclooxygenase inhibition with indomethacin and endothelium removal on vascular responses of the renal artery as a model vessel. Isolated segments of rabbit renal arteries were perfused at constant flow. Indomethacin administration (10(-5) mol x l(-1)) significantly increased the responses to single doses (0.1, 1, 10 microg) of noradrenaline (NA) as compared with the controls. In indomethacin-pretreated vessels, subsequent deendothelisation by air bubbles enhanced the constrictor responses to NA. In reversed order, when deendothelisation was followed by indomethacin administration, the responses to NA were similar in character. A comparison of renal artery responses to NA in both experimental situations did not reveal any significant differences. It can be supposed that endothelial and non-endothelial factors may be involved in local regulation of renal vascular tone.     

Effect of sensory neuropeptides on canine bronchial and pulmonary vessels in vitro

Sensory neuropeptides may be important in the noncholinergic component of parasympathetic vasodilation in the tracheobronchial circulation. We studied the effects of substance P (SP), neurokinin A (NKA), neurokinin B (NKB) and calcitonin gene-related peptide (CGRP) on the isolated canine bronchial artery and used pulmonary artery and vein of similar size for comparison. CGRP (10pM-300nM) was a potent relaxant of the bronchial and pulmonary arteries, and the pulmonary vein with equal potency in all vessels. SP in low concentrations (10pM-100nM) caused vasodilation of the precontracted bronchial artery and in high concentration (10-100 microM) contracted the vessel from resting tone. SP also relaxed the pulmonary artery and vein. NKA and NKB caused relaxation in all three vessels. All of the vascular effects of the sensory neuropeptides were concentration-dependent. The order of potency of the neuropeptides in the bronchial and pulmonary artery was SP greater than NKA greater than CGRP greater than NKB. In the pulmonary vein NKB caused a much larger relaxation than SP and NKA but it was less potent than either NKA or CGRP. Capsaicin (1 microM) caused a large contraction of the bronchial artery, similar in magnitude to the contraction caused by high dose of SP. Neuropeptide Y was also studied and found to cause no consistent constriction of any of the vessels studied. In conclusion, CGRP is a universal dilator of the bronchial and pulmonary blood vessels. SP and NKA exert their main effect on arterial vasomotor tone, whereas NKB is the only tachykinin producing marked dilation of the pulmonary vein.     

The actions of prostaglandins and cyclo-oxygenase inhibition on the resistance vessels supplying the human fetal placenta

The resistance arteries supplying individual exchange villi of the full-term human fetal placenta were examined for their reactivity to various prostaglandins (PG's) as well as for their ability to synthesize biologically active PG's. PGA1, PGF2 alpha, PGE2 and PGE1 produced dose-dependent contractions between 10(-7) and 10(-5)M. The order of potency observed was PGA1 approximately PGF2 alpha greater than PGE2 greater than PGE1. TXB2 was without activity in this preparation. Prostacyclin (PGI2) produced a dose-dependent relaxation of pre-contracted strips between 10(-8)M and 10(-5)M. Arachidonic acid (A.A.) produced stable dose-dependent contractions (10(-5) M to 10(-3)M) which were totally abolished by pretreatment with 10(-7)M meclofenamate (MF). At no concentration of A.A. was any evidence of vascular relaxation observed. Larger concentrations of MF (greater than 10(-6)M) resulted in a non-specific depression of the placental vascular smooth muscle. Meclofenamate (10(-7)M) pretreatment of strips subjected to dose-response studies using PGF2 alpha, PGE2, bradykinin (B K) and angiotensin II (AII) revealed a significant reduction in tension developed to both BK and AII. This finding suggests that the vasoactive peptides BK and AII stimulate the synthesis of vasoconstricting PG's in the fetal placental resistance arteries which relax in response to PGI2 and contract in response to the other PG's tested.     

Length-tension relationships of small arteries, veins, and lymphatics from the rat mesenteric microcirculation

The passive and active length-tension relationships of isolated rat mesenteric lymphatics ( approximately 150 microm ID), and adjacent small arteries ( approximately 240 microm) and veins ( approximately 275 microm) were compared under isometric conditions using a wire myograph. About 60% of the lymphatic vessels developed spontaneous contractions in physiological saline solution at nominal preload. To maximally activate smooth muscle, 145 mM K(+) + 5 x 10(-5) M norepinephrine was used for arteries, and 145 mM K(+) + 1 x 10(-6) M substance P was used for lymphatics and veins. In response, arteries exhibited monotonic force development to a plateau level, whereas lymphatics and veins showed biphasic force development, consisting of a transient force peak followed by partial relaxation to a plateau over approximately 5 min. The passive and the active length-tension curves were similar in shape among all three vessels. However, the maximal active tension of arteries (3.4 +/- 0.42 mN/mm) was significantly greater than peak active tension (0.59 +/- 0.04 mN/mm) or plateau tension (0.20 +/- 0.04 mN/mm) in small veins and greater than peak active tension (0.34 +/- 0.02 mN/mm) or plateau tension (0.21 +/- 0.02 mN/mm) in lymphatics. Maximal active medial wall stress was similar between lymphatics and veins but was approximately fivefold higher in small arteries. For lymphatics, the pressure calculated from the optimal preload was significantly higher than that found previously in isobaric studies of isolated lymphatics, suggesting the capacity to operate at higher than normal pressures for increased responsiveness. Our results represent the first mechanical comparisons of arterial, venous, and lymphatic vessels in the same vasculature.     

Neuropeptide Y inhibits relaxations of the guinea pig uterine artery produced by VIP

Interactions between neuropeptides contained in autonomic vasodilator neurons supplying the guinea pig uterine artery were investigated in isolated segments of the artery precontracted with prostaglandin F2 alpha. Neither somatostatin-14 (10(-6) mol.l-1) nor dynorphin A(1-17) (10(-6) mol.l-1) had direct effects on vascular tone, and did not affect relaxations produced by guinea pig vasoactive intestinal peptide (gpVIP). Both the porcine and the guinea pig forms of neuropeptide Y (NPY; 10(-7)-10(-5) mol.l-1) caused transient contraction of the precontracted arteries. NPY also inhibited relaxations of the artery produced by gpVIP, an action which was not directly related to the NPY contractions. NPY caused both a concentration-dependent rightward shift in the gpVIP concentration-response curve, and a reduction in size of the maximum relaxation to gpVIP. NPY (10(-6) mol.l-1) also produced a rightward shift in the concentration-response curves for the vasodilators forskolin and glyceryl trinitrate, but did not reduce the maximum relaxations to these compounds. Thus NPY, which is colocalized with VIP in vasodilator neurons supplying the uterine artery, can greatly reduce the vasodilator potency of VIP.     

Influence of maturation on constrictive response to stimulation of C-fiber afferents in isolated guinea pig airways

We investigated whether the airway constrictive response to stimulation of bronchopulmonary C-fiber afferents is altered during the maturation process. Isometric tension was measured in airway rings isolated from three tracheobronchial locations (intrathoracic trachea and main and hilar bronchi) and compared in mature [M, 407 +/- 10 (SE) g body wt, n = 36] and immature (IM, 161 +/- 5 g body wt, n = 35) guinea pigs. Our results showed no difference in the ACh (10(-5) M)- or KCl (40 mM)-induced contraction between M and IM groups, regardless of the airway location. In sharp contrast, the concentration-response curves of 10(-8)-10(-6) M capsaicin were distinctly lower in IM hilar bronchi; for example, response to the same concentration of capsaicin (10(-6) M) was 89.2 +/- 15.3% of the response to 10(-5) M ACh in IM and 284.7 +/- 43.2% in M animals. Similar, but smaller, differences in the bronchoconstrictive response to capsaicin between IM and M groups were also observed in the trachea and main bronchus. Electrical field stimulation induced airway constriction in all three locations in M and IM groups. However, after administration of 10(-6) M atropine and 10(-6) M propranolol, electrical field stimulation-induced contraction was significantly smaller in the hilar bronchus of IM than M animals, and this difference was not prevented by pretreatment with 5 x 10(-5) M indomethacin. Although radioimmunoassay showed no difference in the tissue content of substance P between M and IM airways, the constrictive responses to exogenous substance P and neurokinin A were markedly greater in M airways at all three locations. In conclusion, the constriction of isolated airways evoked by C-fiber stimulation was significantly weaker in the IM guinea pigs, probably because of a less potent effect of tachykinins on the airway smooth muscle.