Inhibitors of blood platelet aggregation. Effects of some 1,2-benzisothiazol-3-ones on platelet responsiveness to adenosine diphosphate and collagen.

A series of substituted 1,2-benzisothiazol-3-ones was synthesized, and the compounds were tested for ability to inhibit platelet aggregation induced by adenosine diphosphate and collagen in rats and guinea pigs ex vivo. Alkyl substituents at the 2-position bearing a basic group were necessary for ex vivo activity. Several of the compounds were potent inhibitors of adenosine diphosphate induced first-phase aggregation, but adverse toxicological findings terminated their further development. Preliminary studies suggested that inhibition of aggregation was not attributable to inhibition of prostanoid synthesis or to raised levels of cyclic 3',5'-adenosine monophosphate.

Innervation of the gallbladder: structure, neurochemical coding, and physiological properties of guinea pig gallbladder ganglia.

The muscle and epithelial tissues of the gallbladder are regulated by a ganglionated plexus that lies within the wall of the organ. Although these ganglia are derived from the same set of precursor neural crest cells that colonize the gut, they exhibit structural, neurochemical and physiological characteristics that are distinct from the myenteric and submucous plexuses of the enteric nervous system. Structurally, the ganglionated plexus of the guinea pig gallbladder is comprised of small clusters of neurons that are located in the outer wall of the organ, between the serosa and underlying smooth muscle. The ganglia are encapsulated by a shell of fibroblasts and a basal lamina, and are devoid of collagen. Gallbladder neurons are rather simple in structure, consisting of a soma, a few short dendritic processes and one or two long axons. Results reported here indicate that all gallbladder neurons are probably cholinergic since they all express immunoreactivity for choline acetyltransferase. The majority of these neurons also express substance P, neuropeptide Y, and somatostatin, and a small remaining population of neurons express vasoactive intestinal peptide (VIP) immunoreactivity and NADPH-diaphorase enzymatic activity. We report here that NADPH-diaphorase activity, nitric oxide synthase immunoreactivity, and VIP immunoreactivity are expressed by the same neurons in the gallbladder. Physiological studies indicate that the ganglia of the gallbladder are the site of action of the following neurohumoral inputs: 1) all neurons receive nicotinic input from vagal preganglionic fibers; 2) norepinephrine released from sympathetic postganglionic fibers acts presynaptically on vagal terminals within gallbladder ganglia to decrease the release of acetylcholine from vagal terminals; 3) substance P and calcitonin gene-related peptide, which are co-expressed in sensory fibers, cause prolonged depolarizations of gallbladder neurons that resemble slow EPSPs; and 4) cholecystokinin (CCK) acts presynaptically within gallbladder ganglia to increase the release of acetylcholine from vagal terminals. Results reported here indicate that hormonal CCK can readily access gallbladder ganglia, since there is no evidence for a blood-ganglionic barrier in the gallbladder. Taken together, these results indicate that gallbladder ganglia are not simple relay stations, but rather sites of complex modulatory interactions that ultimately influence the functions of muscle and epithelial cells in the organ.

Silver sulfadiazine induced Clostridium difficile toxic megacolon in a burn patient: case report.

A 53 yr old diabetic male presented with a 34% total body surface area (TBSA) deep partial- and full-thickness burns. On post burn days 4 and 9, all of his burns were excised and grafted. Although he had only been treated with topical antibiotics, he developed Clostridium difficile colitis after his second surgery that progressed to Toxic Megacolon and perforation. The incidence and treatment of Toxic Megacolon secondary to C. difficile is reviewed. Early diagnosis and treatment with colonoscopic decompression may obviate the need for surgery.

Xenogeneic acellular dermal matrix as a dermal substitute in rats.

Acellular dermal matrix (ADM) has been used as a dermal substitute for the treatment of deep burns, but the availability of cadaver skin for the production of ADM is limited. The usefulness of porcine ADM as a xenogeneic dermal substitute in rats was studied. With the use of Dispase II (Boehringer Mannheim, Indianapolis, Ind) and Triton X-100 (US Biochemicals, Cleveland, Ohio), xenogeneic ADM was prepared from commercially available, cryopreserved porcine skin, and allogeneic ADM from the rats was also prepared. Four full-thickness injuries 225 mm2 in size were created on the dorsum of each rat. One of these wounds was treated with xenogeneic ADM and 1 was treated with allogeneic ADM, and immediately a 0.005-in thick split-thickness skin graft was placed over the ADM. The other 2 wounds were covered with 0.005- or 0.017-in thick split-thickness skin grafts alone. The wounds were evaluated macro- and microscopically 10, 14, 20, and 30 days after grafting. At 30 days after grafting, contraction of the wounds that contained xenogeneic ADM was significantly greater than that of the wounds that contained allogeneic ADM. Graft take was poor in the wounds that contained xenogeneic ADM at 14 days after surgery and moderately good in those that contained allogeneic ADM. The use of thick autografts resulted in the best wound healing, whereas the use of thin autografts resulted in considerable wound contraction. Allogeneic ADM diminished this contraction, but wound healing was significantly worsened when xenogeneic ADM was used.

PGE2 hyperpolarizes gallbladder neurons and inhibits synaptic potentials in gallbladder ganglia.

Gallbladder prostaglandin E2 (PGE2) levels are significantly elevated in pathophysiological conditions, resulting in changes in gallbladder motility or secretion that may involve actions of the prostanoid in intramural ganglia. This study was undertaken to examine the effects of PGE2 on neurons of the intramural ganglia of the guinea pig gallbladder. Application of PGE2 by microejection or superfusion elicited a complex triphasic change in the resting membrane potential (RMP). For example, application of PGE2 by microejection (100 microM) resulted in a brief hyperpolarization (mean duration 11.1 +/- 1.3 s), followed by a mid-phase repolarization toward or above RMP (mean duration 50.7 +/- 8.1 s), and finally a long-lasting hyperpolarization (mean duration 157.3 +/- 36.7 s). Associated with these PGE2-evoked alterations in RMP were changes in input resistance measured via injection of hyperpolarizing current pulses. An examination of the action potential afterhyperpolarization (AHP) during the PGE2-evoked response revealed an attenuation of both the amplitude and duration of the AHP. However, only a slight increase in excitability of gallbladder neurons in the presence of PGE2 was evident in response to depolarizing current pulses, and PGE2 did not cause the cells to fire spontaneous action potentials. Application of PGE2 reduced the amplitudes of both fast and slow excitatory synaptic potentials. These results suggest that increased prostaglandin production may decrease ganglionic output and therefore contribute to gallbladder stasis.

Actions of calcitonin gene-related peptide in guinea pig gallbladder ganglia.

The actions of calcitonin gene-related peptide (CGRP) have been determined from intracellular recordings obtained from gallbladder neurons in intact whole mount preparations. In most cells, pressure microejection of CGRP elicited a slow, monophasic depolarization, 4 mV in amplitude, that was associated with a decrease in input resistance and increased excitability. The CGRP-induced depolarization was attenuated in a low-Na+ solution and had a reversal potential of -8 mV. In 10% of the cells, microejection of CGRP elicited a biphasic response that was composed of a rapid transient depolarization followed by a slow depolarization that was similar to the monophasic response. Addition of CGRP (1-10 nM) to the bathing solution elicited a monophasic depolarization and desensitized the cells to applications of CGRP by microejection. Forskolin, applied either by microejection or bath application, also depolarized gallbladder neurons and produced cross-desensitization to CGRP. Responses to substance P were not enhanced by CGRP, and CGRP did not affect fast synaptic responses. It is concluded that CGRP may contribute to a local axon reflex response in gallbladder ganglia.

Neural control of the gallbladder: an intracellular study of human gallbladder neurons.

BACKGROUND/AIMS: Gallbladder neurons are important governors of gallbladder function. In animal models, gallbladder ganglia can be regulated both by neural and hormonal inputs. The purpose of this study was to demonstrate the feasibility of obtaining recordings from human gallbladder neurons. METHODS: Human gallbladders (n = 33) were bathed in oxygenated Krebs solution (37 degrees C) containing the vital fluorescent stain 4-Di-2-ASP to localize the ganglia. Cells were characterized using conventional intracellular recording techniques. RESULTS: The mean resting membrane potential of human gallbladder neurons was -51.2 +/- 1.8 mV (n = 11). Depolarizing current pulses elicited only 1-4 spikes regardless of the amplitude or duration of the stimulus. Afterspike hyperpolarizations had a mean duration of 144.5 +/- 19.2 ms (n = 10). Anodal break excitation was not recorded with hyperpolarizing current pulses. Fiber tract stimulation elicited fast excitatory postsynaptic potentials in all neurons tested. CONCLUSION: Intracellular recordings of human gallbladder neurons utilizing 4-Di-2-ASP are thus feasible, but are very problematic due to the density of connective tissue overlying the ganglia. As human and guinea pig gallbladder neurons have similar basic electrical properties, the guinea pig may be an appropriate model for further electrophysiological studies into gallbladder disease.

Actions of histamine on muscle and ganglia of the guinea pig gallbladder.

Histamine is an inflammatory mediator present in mast cells, which are abundant in the wall of the gallbladder. We examined the electrical properties of gallbladder smooth muscle and nerve associated with histamine-induced changes in gallbladder tone. Recordings were made from gallbladder smooth muscle and neurons, and responses to histamine and receptor subtype-specific compounds were tested. Histamine application to intact smooth muscle produced a concentration-dependent membrane depolarization and increased excitability. In the presence of the H(2) antagonist ranitidine, the response to histamine was potentiated. Activation of H(2) receptors caused membrane hyperpolarization and elimination of spontaneous action potentials. The H(2) response was attenuated by the ATP-sensitive K(+) (K(ATP)) channel blocker glibenclamide in intact and isolated smooth muscle. Histamine had no effect on the resting membrane potential or excitability of gallbladder neurons. Furthermore, neither histamine nor the H(3) agonist R-alpha-methylhistamine altered the amplitude of the fast excitatory postsynaptic potential in gallbladder ganglia. The mast cell degranulator compound 48/80 caused a smooth muscle depolarization that was inhibited by the H(1) antagonist mepyramine, indicating that histamine released from mast cells can activate gallbladder smooth muscle. In conclusion, histamine released from mast cells can act on gallbladder smooth muscle, but not in ganglia. The depolarization and associated contraction of gallbladder smooth muscle represent the net effect of activation of both H(1) (excitatory) and H(2) (inhibitory) receptors, with the H(2) receptor-mediated response involving the activation of K(ATP) channels.

Control of exocrine secretion in the guinea-pig pancreas by histamine H3 receptors.

The aim of this study was to investigate the possible involvement of the histamine H3 receptor in control of exocrine pancreatic secretion from the guinea-pig. In in vitro experiments, the H3 receptor agonist (R)-alpha-methylhistamine (0.01-10 microM) elicited a concentration-dependent decrease in the release of alpha-amylase. (R)-alpha-Methylhistamine concentrations above 10 microM evoked a concentration-dependent increase in alpha-amylase secretion. Application of mepyramine (1 microM) partially blocked this increase. The H3 receptor antagonist thioperanide (1 microM) blocked the effects of (R)-alpha-methylhistamine below 10 microM. Histamine and (R)-alpha-methylhistamine attenuated both protein release elicited during electrical-field stimulation and the release of tritiated choline, and these effects were reversed by thioperamide. In an in vivo study, (R)-alpha-methylhistamine increased juice secretion and total protein content of the juice by 40%. Histamine H1 and H2 receptor antagonists blocked this increase and uncovered an attenuation of the secretory parameters (juice flow 28%, total protein content 44%). This attenuation was blocked by thioperamide. These observations suggest that stimulation of the histamine H3 receptor in the pancreas results in a decreased fluid and enzyme release by inhibition of acetylcholine release from intrinsic pancreatic nerves.

Cholesterol inhibits spontaneous action potentials and calcium currents in guinea pig gallbladder smooth muscle.

Elevated cholesterol decreases agonist-induced contractility and enhances stone formation in the gallbladder. The current study was conducted to determine if and how the electrical properties and ionic conductances of gallbladder smooth muscle are altered by elevated cholesterol. Cholesterol was delivered as a complex with cyclodextrin, and effects were evaluated with intracellular recordings from intact gallbladder and whole cell patch-clamp recordings from isolated cells. Cholesterol significantly attenuated the spontaneous action potentials of intact tissue. Furthermore, calcium-dependent action potentials and calcium currents were reduced in the intact tissue and in isolated cells, respectively. However, neither membrane potential hyperpolarizations induced by the ATP-sensitive potassium channel opener, pinacidil, nor voltage-activated outward potassium currents were affected by cholesterol. Hyperpolarizations elicited by calcitonin gene-related peptide were reduced by cholesterol enrichment, indicating potential changes in receptor ligand binding and/or second messenger interactions. These data indicate that excess cholesterol can contribute to gallbladder stasis by affecting calcium channel activity, whereas potassium channels remained unaffected. In addition, cholesterol enrichment may also modulate receptor ligand behavior and/or second messenger interactions.

Use of porcine acellular dermal matrix as a dermal substitute in rats.

OBJECTIVE: To examine porcine acellular dermal matrix (ADM) as a xenogenic dermal substitute in a rat model. SUMMARY BACKGROUND DATA: Acellular dermal matrix has been used in the treatment of full-thickness skin injuries as an allogenic dermal substitute providing a stable wound base in human and animal studies. METHODS: Xenogenic and allogenic ADMs were produced by treating porcine or rat skin with Dispase and Triton X-100. Full-thickness skin defects (225 mm2) were created on the dorsum of rats (n = 29), porcine or rat ADMs were implanted in them, and these were overlain with ultrathin split-thickness skin grafts (STSGs). In two adjacent wounds, 0.005- or 0.017-inch-thick autografts were implanted. In other experiments, the antimicrobial agent used during ADM processing (azide or a mixture of antibiotics) and the orientation of the implanted ADM (papillary or reticular side of ADM facing the STSG) were studied. Grafts were evaluated grossly and histologically for 30 days after surgery. RESULTS: Significant wound contraction was seen at 14, 20, and 30 days after surgery in wounds receiving xenogenic ADM, allogenic ADM, and thin STSGs. Contraction of wounds containing xenogenic ADM was significantly greater than that of wounds containing allogenic ADM at 30 days after surgery. Graft take was poor in wounds containing xenogenic ADM and moderately good in those containing allogenic ADM. Wound healing was not significantly affected by the antimicrobial agent used during ADM preparation or by the ADM orientation. CONCLUSION: Dispase-Triton-treated allogenic ADM was useful as a dermal substitute in full-thickness skin defects, but healing with xenogenic ADM was poor.

The source and action of histamine in the isolated guinea-pig gallbladder.

We have investigated the effects of histamine on motility of the gallbladder and characterized the receptor types involved. Histamine and the histamine H1-receptor agonist, 2-thiazolylethylamine (2-TEA) contracted the isolated guinea-pig gallbladder strip in a dose dependent manner. The contractile response to histamine was shifted to the right by the H1-receptor antagonist, mepyramine. In pre-contracted gallbladder strips, the H2-receptor agonist dimaprit reduced the tension generated in a dose dependent fashion. The histamine H2-receptor antagonist, ranitidine shifted the histamine concentration effect curve to the left and attenuated the dose dependent relaxations elicited at high concentrations. The histamine H3-receptor agonist, (R)-alpha-methylhistamine (RMHA) elicited dose dependent contraction of the tissue which was significantly inhibited in the presence of mepyramine. The effects of electrical field stimulation (EFS) on the strips were not significantly altered by the presence of RMHA (10(-10) - 10(-7) M) indicating little pre-synaptic H3 activity in this tissue. Histamine immunoreactivity (IR) was detected in gallbladder whole mount preparations of the mucosa and the muscularis/serosa. The histamine IR appeared cell bound in cells of varying morphological characteristics but no IR was detected in nerve fibres or cell bodies (ganglia). Alcian blue staining was consistent with the distribution of histamine IR cells as mast cells. The results indicate that histamine is distributed in the guinea-pig gallbladder and it can regulate contractile activity via activation of H1 and H2 but not H3 receptors.

Inhibition of herpes proteases and antiviral activity of 2-substituted thieno[2,3-d]oxazinones.

Cinnamyl derivatives of thieno[2,3-d]oxazinones are mechanism-based inhibitors of the HSV-2, VZV and CMV herpes proteases which demonstrate nanomolar potency. Compounds 5 and 28 inhibit protease processing in HSV-2 infected cells with a selectivity index of at least 30.

Inhibition of human cytomegalovirus protease by enedione derivatives of thieno[2,3-d]oxazinones through a novel dual acylation/alkylation mechanism.

Enedione derivatives of thieno[2,3-d]oxazinones are nanomolar inhibitors of CMV protease which act through a novel dual acylation of the catalytic serine and alkylation of the protease cysteine 161 via a Michael addition to the enedione moiety of the inhibitor.