To study the effects of a novel calcium channel blocker, m-nisoldipine, on vascular calcium overload (VCO) at both tissue and cellular levels.VCO was induced in Wistar rats by treatment with colecalciferol (Col, 400,000 IU.kg-1, p.o.) and an aqueous mixture of ethanol and polyethyleneglycol-400 for 3 d. The tissue and subcellular calcium contents of aorta were determined by atomic absorption spectrometer and electron probe microanalysis, respectively.Chronic treatment with m-nisoldipine (m-Nis, 1-15 mg.kg-1, p.o., bid) only had mild inhibition on the elevation of total calcium in aorta, and the dose-response relationship of m-Nis displayed a bell shape, with inhibition ratio of 24% only for m-Nis 2.5 mg.kg-1. The effect of verapamil (12.5 mg.kg-1, p.o., bid) was a little better than that of m-Nis. The intracellular VCO in medial smooth muscle cells of aorta were remarkably inhibited by m-Nis (2.5 mg.kg-1), with inhibition ratios of 72% for cytoplasm and 76% for mitochondrion. The calcium accumulation in nucleus was reduced to a lesser degree than those in cytoplasm and mitochondrion.As for aorta in VCO rats, m-Nis mainly had conspicuous inhibition on intracellular VCO in medial smooth muscle cells, particularly in cytoplasm and mitochondrion, but with little effect on extracellular calcium deposition at tissue level.
Iv (-)-SPD lowered the blood pressure in anesthetized rat, the ED50 value was 5.1 +/- 2.5 mg.kg-1. In the experiments of rat and rabbit aortic strips, (-)-SPD 0.3-100.0 mumol.L-1 inhibited the contraction initiated by clonidine (alpha 2) and phenylephrine (alpha 1) and shifted the dose-response curve to the right parallely without change in maximum response. The inhibitory ratio of (-)-SPD acting on alpha 2/alpha 1 adrenergic receptors was about 7.2, and (-)-SPD thus was predominant inhibition on alpha 2 adrenergic receptors. In the experiment of aortic strips from reserpinized rabbits, the inhibition of (-)-SPD on contraction evoked by clonidine was diminished markedly. The results suggest that (-)-SPD stimulated mainly the alpha 2-adrenergic receptors of presynaptic nerve endings. Moreover (-)-SPD 1 mumol.L-1 inhibited the release of intracellular Ca2+ initiated by NE. (-)-SPD 3-30 mumol.L-1 blocked the voltage-dependent Ca2+ channel.
Dose-response relationships of epinephrine(EPI), noreepinephrine(NE), phenylephrine(PE) and isoproterenal(ISO),on isolated mice uteri at 4 hormonal states(estrogen primed, early pregnancy, late pregnancy and post-partum) were investigated. At estrogen primed and early pregnant states after propranolol(0.1 mM), the inhibitory effects of ISO were blocked whereas those of EPI, NE and PE reversed, leaving only the excitatory effect with pD2 values in the order of EPI>NE>PE>ISO. These results indicate the existence of alpha-adrenoceptor in mice uteri during these 2 states. No effects of these 4 sympathomimetic amines were observed in late pregnant and post-partum uteri after propranolol.In the presence of phentolamine(0.01 mM), these 4 amines only evoked inhibitory effects and the order of the pD2 values was ISO>EPI>NE>PE, indicating the existence of beta-adrenoceptor in the mice uteri during 4 hormonal states. The pD2 values of inhibitory effects of these 4 amines in early pregnant and post-partum mice uteri are greater than those in estrogen primed and late pregnant ones, suggesting that the number and/or the activity of beat-adrenoceptor is related to progesterone.Excitatory effects were elicited by EPI, NE and PE only during estrogen treatment and early pregnancy indicating that the presence of alpha-adrenoceptor may be related to estrogen.
The present study identified Arabidopsis miR394 and its target, an F-box (SKP1-Cullin/CDC53-F-box) gene At1g27340 (here referred to as LEAF CURLING RESPONSIVENESS, LCR), for regulation of leaf curling-related morphology. The loss-of-function lcr mutants exhibit pleiotropic defects with semi-dwarfism, altered leaf shape and a shorter stem. Overexpression of an miR394-resistant version of LCR under the 35S promoter (35S:m5LCR) and target mimicry MIM394 resulted in a curled-down leaf defect. Conversely, transgenic plants overexpressing 35S:MIR394a/b display a curled-up leaf phenotype. Detailed analyses show that there is a certain level of LCR that is optimal for leaf morphology, but lower or higher levels lead to abnormal leaf development, indicating that expression of miR394 in the leaf lamina is necessary for proper leaf morphology. Because the phytohormone auxin plays a crucial role in leaf morphogenesis and patterning, the DR5-GUS reporter gene was used to monitor the auxin response. We show that DR5 expression patterns in lcr and 35S::m5LCR plants were significantly different from those in the wild type. Also, overexpression of LCR in 35S::m5LCR plants drastically decreased the expression of the auxin-responsive genes IAA3, AXR3 and IAMT1, whereas increased expression of the genes was found in 35S::MIR394a plants. These results indicate that miR394 and its target LCR are involved in the regulation of leaf development.
The binding of radioligand to cell membrane prepared from mouse myometrium was used to identify the characteristics of beta-adrenoceptors. Uteri were taken from mature mice (Kunming Strain) weighing 40 +/- 5 g pretreated with estradiol benzoate 1 mg.kg-1.d-1 ip for 2 d. The binding of [3H]dihydroalprenolol ([3H]DHA) to uterine membrane was saturable, having a Bmax of 378 fmol/mg protein and a KD of 3.1 nmol.L-1. The slope of Hill plot (nH = 1.03) indicated the absence of cooperative interactions. IC50 and K1 values of l-norepinephrine (NE), dl-propranol (Pro), d-timolol (d-Tim), and l-Tim competed for the [3H]DHA binding sites were 171 +/- 10, 10.3 +/- 4.3, 6.5 +/- 2.1, 0.40 +/- 0.23 nmol.L-1 and 113 +/- 6, 6.3 +/- 2.8, 4.0 +/- 1.3, 0.25 +/- 0.14 nmol.L-1, respectively. These 4 agents competed for the [3H]DHA binding sites in an order of potency: l-Tim > d-Tim > Pro > NE. Atenolol (Ate) did not compete for [3H]DHA binding sites. The results suggested that these binding sites for [3H]DHA in mouse myometrium appeared to be beta 2-adrenoceptor.
The pA2 values of propranolol,practolol, pindolol,alprenolol,oxprenolol and atenolol were determined on isolated rabbit atrium and guinea-pig trachea preparations utilizing isoprenaline as a beta-receptor agonist. The cumulative dose-response curves of isoprenaline were shifted to the right by all the 6 drugs. When the dose ratios log(x-1) were plotted against negative log molar values of the given beta-blockers,the regression slopes, with the exception of practolol, approximated to the theoretical ones,comparable to the characteristics of competitive antagonism. In the isolated rabbit right atrium preparation, the pA2 values of propranolol,practolol, pindolol, alprenolol, oxprenolol and atenolol antagonizing the chronotropic action of isoprenaline were 8.67,7.22,8.79,8.22,8.28 and 7.48,respectively. In the isolated guinea-pig trachea preparation,the pA2 values of these drugs antagonizing the isoprenaline-induced relaxation were 8.76,6.33,9.14,8.33,8.44 and 5.49 respectively.The potencies of blockade by propranolol, pindolol, alprenolol and oxprenolol on beta1 and beta2 receptors were similar, suggesting no selectively. The [pA2(beta1)-pA2(beta2)] value of practolol was shown to be 0.89. Hence its blocking effect on cardiac beta receptors was 7.8 times that of trachea beta receptors, suggesting that it is a selective antagonist of cardiac beta1 receptors. By contrast, The [pA2(beta1)-pA2(beta2)] value of atenolol was 1.99, suggesting its beta-blocking action in the atrium being nearly 100 times that in the trachea.These results give substantial support to the classification of beta1 and beta2 receptors, and atenolol is proposed to be a more effective cardiac selective beta1 blocking drug.
Endothelin, a novel endothelium derived 21-residue vasoconstrictor peptide synthesized by Peninsula Laboratories, provoked a concentration-dependent contraction of porcine coronary arterial strips. EC50 value for endothelin was 14 +/- SD 4 nmol/L (n = 6), and significantly lower than the values for 5-hydroxytryptamine (5-HT, 0.28 +/- 0.07 mumol/L, n = 6) and 15-methyl-prostaglandin F2 alpha (15-methyl-PGF2 alpha, 4 +/- 3 mumol/L, n = 7). The maximal increase in tension caused by endothelin was 5.4 +/- 1.1 g, being much greater than that induced by 5-HT (3.7 +/- 0.8 g, P less than 0.05) and 15-methyl-PGF2 alpha (3.7 +/- 0.6 g, P less than 0.01). The changes in tension provoked by endothelin (2-20 nmol/L) were attenuated significantly after pretreated with tetrodotoxin (TTX, 30 mumol/L, P less than 0.05 or 0.01). The results suggest that endothelin is one of the most potent vasoconstrictive agents, and its action is partially related to voltage-sensitive Na+ channel in the cell membrane.
Cycleanine is an active principle from Stephania epigeae H. S. Lo. The potencies of the blocking effects of its derivative, cycleanine dimethobromide, were studied on the transmission of the impulses through isolated rabbit supracervical sympathetic ganglia and rat phrenic nerve-diaphragm preparations in comparison with those of d-tubocurarine. The relative potency of ganglionic blocking effect of this drug was found to be 28.5% of that of d-tubocurarine. As to the muscle relaxant effect, this value was only 2.3%. The EC50 values for the ganglion blocking and muscular relaxant actions of d-tubocurarine were found to be 15.3 microg/ml and 1.1 microg/ml, respectively; while those of cycleanine were 58 microg/ml and 46 microg/ml. The results show that the muscular relaxant action of cycleanine is much more weaker than d-tubocurarine. This is consistent with the clinical report that cycleanine might preferably be used in controlled hypotension during surgical operation rather than as a muscular relaxant.
The effects of ephedrine (Eph) were compared with those of tyramine (Tyr) and phenylephrine (Phe) in ring segments of guinea pig portal vein in vitro. Eph (3-1000 mumol/L), Tyr (10-1000 mumol/L) and Phe (1-1000 mumol/L) all produced concentration-dependent contractile responses, which were exceedingly depressed by alpha-adrenoceptor blocker phentolamine (31 mumol/L). Pretreatment with reserpine 1 mg/(kg.d) x 2 d markedly diminished the effect of Tyr, but greatly potentiated the effects of Eph and Phe. Both Eph (1-30 mumol/L) and Tyr (10-100 mumol/L), but not Phe, significantly increased the electrical field stimulation (duration 2 ms, 3 Hz, 10 s, 50 V, 10 min intervals) evoked contractions of the portal veins. beta-Adrenoceptor blocker propranolol (0.5 mumol/L) greatly inhibited this effect of Eph, without affecting that of Tyr. It is suggested that the effect of Tyr is mainly due to its release of endogenous norepinephrine (NE) from the nerve terminals; conversely, Eph mainly bcts on postsynaptic alpha-adrenoceptors directly with some NE-releasing action which may involve the activation of presynaptic beta-adrenoceptors.
In porcine coronary arterial strips, the antagonistic effects of nifedipine (Nif), nimodipine (Nim), nicardipine (Nic), felodipine (Fel), and verapamil (Ver) to CaCl2-evoked contraction in Ca(2+)-free, K(+)-depolarized solution were greater than that to 5-HT. The order of potency (pD2') was Nif (9.1) greater than Fel (8.4) greater than Nim (7.9) greater than Nic (7.8) greater than Ver (7.2) to CaCl2 and Nif (8.3) greater than Nim (7.5) greater than Fel (6.8) greater than Ver (5.6) greater than Nic (5.3) to 5-HT. Ver inhibited 2 components of 5-HT-evoked contraction in Ca(2+)-free solution, but Fel inhibited only extracellular Ca(2+)-dependent contraction, suggesting that their action modes are different.
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