Cotransmission from sympathetic vasoconstrictor neurons to small cutaneous arteries in vivo.
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This study has characterized constrictions of small cutaneous arteries in the guinea pig ear in response to electrical stimulation of the cervical sympathetic nerve (SNS) in vivo. Video microscopy and on-line image analysis were used to examine diameter changes of ear arteries (80-140 micrometers resting diameter) in anesthetized guinea pigs. Trains of 50-300 impulses, but not single pulses or short trains, produced frequency-dependent (2-20 Hz) constrictions. The purinoceptor antagonist suramin (30 microM) greatly reduced constrictions produced by exogenous ATP but did not affect constrictions produced by SNS at 10 Hz or exogenous norepinephrine. The alpha(2)-adrenoceptor antagonist yohimbine (1 microM) enhanced the peak amplitude of sympathetic constrictions at lower stimulation frequencies (1-5 Hz). The amplitude of constrictions to SNS at 10 Hz was reduced, and the latency of constrictions was increased by the alpha(1)-adrenoceptor antagonist prazosin (1 microM). Constrictions to SNS at 10 Hz remaining after prazosin treatment were reduced in amplitude by dihydroergotamine (2 microM) and were attenuated further by the neuropeptide Y Y(1)-receptor antagonist 1229U91 (0.3 microM). Thus norepinephrine and neuropeptide Y act as cotransmitters to mediate sympathetic constriction of small ear arteries at higher stimulation frequencies (10 Hz), but ATP does not seem to contribute directly to these constrictions. (+info)
Enhanced ET(A)-receptor-mediated inhibition of K(v) channels in hypoxic hypertensive rat pulmonary artery myocytes.
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Endothelin (ET)-1 has been implicated as a critical mediator in the pathogenesis of hypoxic pulmonary hypertension. We questioned whether, during exposure to chronic hypobaric hypoxia, rat pulmonary artery smooth muscle cells (PASMC) became sensitized to ET-1. Two effects of ET-1, inhibition of voltage-gated K(+) (K(v)) channels and release of intracellular Ca(2+), were studied using whole cell patch clamp and single cell indo 1 fluorescence, respectively. In both normotensive and chronically hypoxic-hypertensive PASMC, ET-1 caused concentration-dependent inhibition of voltage-gated K(+) current [I(K(v))], with maximum inhibition of 12-18% seen at a concentration of 0.1-1 nM. Although the chronically hypoxic-hypertensive PASMC was no more susceptible to ET-1-mediated I(K(v)) inhibition, a switch in coupling between ET-1 and I(K(v)) from ET(B) to ET(A) receptors occurred. This switch in receptor coupling, combined with reduced I(K(v)) density and increased ET-1 production in the hypoxic rat lung, may help explain the ability of ET(A)-receptor blockers to attenuate the development of hypoxic pulmonary hypertension in vivo. (+info)
Relevance of aromatic residues in transmembrane segments V to VII for binding of peptide and nonpeptide antagonists to the human tachykinin NK(2) receptor.
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We used membranes from Chinese hamster ovary cells stably transfected with the human tachykinin NK(2) receptor, either wild-type or mutated, at four aromatic residues (His(198), Tyr(266), Phe(270), Tyr(289)) located in transmembrane segments V to VII, to assess the role of these residues in the binding of natural tachykinins and peptide and nonpeptide antagonists. Three radioligands, the agonist [(125)I]neurokinin A (NKA), the peptide antagonist [(3)H]MEN 11420, and the nonpeptide antagonist [(3)H]SR 48968 bound to the wild-type receptor with high affinity (K(d) = 2.4 nM, 0.3 nM, and 4.0 nM, respectively). Four of the six mutant receptors tested retained high affinity for at least one of the radioligands. H(198)A mutation abrogated the binding of NKA but not that of MEN 11420 or SR 48968 (K(d) = 4.8 and 11.5 nM, respectively); Y(266)F mutation abrogated the binding of MEN 11420 but not that of NKA or SR 48968 (K(d) = 2.8 nM and 1.2 nM, respectively); F(270)A mutation abrogated the binding of both NKA and MEN 11420 but not that of SR 48968 (K(d) = 1.6 nM); Y(289)F mutation abrogated the binding of SR 48968 but not that of NKA and MEN 11420 (K(d) = 2.0 and 2.9 nM, respectively). Y(266)A and Y(289)A mutations abrogated the binding of all radioligands. Among the unlabeled antagonists, the affinity of the nonpeptide GR 159897, at variance with SR 48968, resulted heavily compromised by H(198)A and Y(266)F mutations; the peptide antagonists R396 and MEN 10376 essentially followed the binding profile of NKA, but R396 showed markedly increased affinity for the Y(289)F mutant receptor. Taken together, these results indicate that different, partially overlapping sets of sites may be involved in the binding of agonists and diverse antagonists to the human tachykinin NK(2) receptor. (+info)
An open, phase III study of lanreotide (Somatuline PR) in the treatment of acromegaly.
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Acromegaly is a disorder caused by excessive secretion of human growth hormone (GH). Somatostatin and its analogue-prolonged release formulation, lanreotide (Somatuline PR), inhibit the secretion of growth hormone. The aim of this open Phase III study was to investigate the clinical efficacy of lanreotide in the treatment of six acromegalic patients with a mean age of 44 +/- 13 yr including two patients with diabetes mellitus. All the patients previously received transsphenoidal or transcranial hypophysectomy. Lanreotide was given intramuscularly every 2 weeks at a fixed dose of 30 mg for 12 weeks. Serum GH and insulin-like growth factor-I (IGF-I) levels were evaluated before, 2, 6 and 12 weeks after treatment. After 12 weeks of treatment, mean (+/- SEM) GH levels decreased from 24.8 +/- 12.5 to 6.9 +/- 3.3 ng/ml and mean serum IGF-I levels decreased from 689 +/- 282 to 430 +/- 216 ng/ml. Abdominal ultrasonographic examinations showed no gallbladder stone or bile sand formation before or after the treatment. Three of the patients who did not receive octreotide presented with manifestations of mild gastrointestinal adverse effect such as mild abdominal pain and diarrhea. In conclusion, lanreotide is effective in the treatment of active postoperative acromegaly. (+info)
Effect of nodularin on the expression of glutathione S-transferase placental form and proliferating cell nuclear antigen in N-nitrosodiethylamine initiated hepatocarcinogenesis in the male Fischer 344 rat.
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The tumor-promoting effect of nodularin during carcinogenesis was investigated. Male Fischer 344 rats were injected with nodularin for 10 weeks from week 3 after N-nitrosodiethylamine initiation without partial hepatectomy. Rats were further maintained for 10 weeks after the cessation of nodularin and were periodically killed. In contrast to the minimal foci in the DEN and nodularin alone groups, treatment with DEN and nodularin produced four kinds of nodules with eosinophilic, clear, mixed and basophilic cells. After the cessation of nodularin, the maximally increased number, but not the area, of glutathione S-transferase placental form-positive [GST-P(+)] nodules at week 12 decreased significantly and the appearance of two types of hyperplastic nodules was noted by GST-P immunostaining; homogeneously stained dense nodules (DN) and heterogeneously stained pale nodules (PN), which appeared only after the cessation of nodularin. DN were well circumscribed by enzyme-altered cells, as opposed to poorly in PN. Moreover, normal-appearing hepatocytes replaced the enzyme-altered cells in PN. In contrast to the higher PCNA index in GST-P(+) DN, the background level returned to that of the control at week 15. PCNA indices in DN were significantly higher than in PN, which were still higher than the control, indicating that nodularin affected the PCNA index differentially in the altered and unaltered hepatocytes. However, nodularin without DEN initiation significantly increased the PCNA index through initial cell death and subsequent hepatocyte proliferation. These results suggest that: (i) nodularin has a promoting effect by inducing hepatocyte proliferation in both enzyme-altered hyperplastic nodules and the surrounding parenchyma; (ii) proliferation is transient in background cells but not in enzyme-altered hepatocytes; (iii) GST-P(+) DN can be regarded as progressive and GST-P(+) PN as regressive, revealed by both immunohistochemistry and PCNA index. (+info)
Importance of the beta12-beta13 loop in protein phosphatase-1 catalytic subunit for inhibition by toxins and mammalian protein inhibitors.
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Type-1 protein serine/threonine phosphatases (PP1) are uniquely inhibited by the mammalian proteins, inhibitor-1 (I-1), inhibitor-2 (I-2), and nuclear inhibitor of PP1 (NIPP-1). In addition, several natural compounds inhibit both PP1 and the type-2 phosphatase, PP2A. Deletion of C-terminal sequences that included the beta12-beta13 loop attenuated the inhibition of the resulting PP1alpha catalytic core by I-1, I-2, NIPP-1, and several toxins, including tautomycin, microcystin-LR, calyculin A, and okadaic acid. Substitution of C-terminal sequences from the PP2A catalytic subunit produced a chimeric enzyme, CRHM2, that was inhibited by toxins with dose-response characteristics of PP1 and not PP2A. However, CRHM2 was insensitive to the PP1-specific inhibitors, I-1, I-2, and NIPP-1. The anticancer compound, fostriecin, differed from other phosphatase inhibitors in that it inhibited wild-type PP1alpha, the PP1alpha catalytic core, and CRHM2 with identical IC(50). Binding of wild-type and mutant phosphatases to immobilized microcystin-LR, NIPP-1, and I-2 established that the beta12-beta13 loop was essential for the association of PP1 with toxins and the protein inhibitors. These studies point to the importance of the beta12-beta13 loop structure and conformation for the control of PP1 functions by toxins and endogenous proteins. (+info)
In vitro activities of polycationic peptides alone and in combination with clinically used antimicrobial agents against Rhodococcus equi.
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The in vitro activities of magainin II, nisin, and ranalexin alone and in combination with other antimicrobial agents against six clinical isolates of Rhodococcus equi were investigated by MIC and time-kill studies. All isolates were more susceptible to nisin. A positive interaction was observed when the peptides were combined with ampicillin, ceftriaxone, rifabutin, rifampin, azithromycin, clarithromycin, and vancomycin. (+info)
Ionophoretic properties and mitochondrial effects of cereulide: the emetic toxin of B. cereus.
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The emetic toxin of Bacillus cereus, found to cause immobilization of spermatozoa and swelling of their mitochondria, was purified and its structure found to be identical to the earlier known toxin cereulide. It increased the conductance in black-lipid membranes in KCl solutions in an ionophore-like manner. It formed adducts with K+, Na+, and NH4+ but the conductance was highly selective for K+ in relation to Na+ and H+ (three orders of magnitude). The increase in the kinetics of conductance indicated a stoichiometric ratio between the cereulide and K+. Its ionophoretic properties are thus similar to those of valinomycin. In addition, its effects on rat liver mitochondria were similar: it stimulated swelling and respiration in respiring mitochondria in the presence but not in the absence of K+, it reduced the transmembrane potential under these conditions. In nonrespiring mitochondria, swelling was seen in KNO3- but not in NaNO3-containing media, less in acetate. In NaNO3 media addition of the cereulide caused a transient diffusion potential which was reduced by adding K+. It is concluded that the toxic effects of cereulide are due to it being a K+ ionophore. (+info)