Mediation of EDHF-induced reduction of smooth muscle [Ca(2+)](i) and arteriolar dilation by K(+) channels, 5,6-EET, and gap junctions

OBJECTIVE

To characterize the role of K(+) channels, the cytochrome P-450 (CYP) metabolite 5,6-EET, and gap junctions in modulation of arteriolar myogenic tone by a non-nitric oxide nonprostaglandin mediator, termed "endothelium-dependent hyperpolarizing factor" (EDHF), released to acetylcholine (ACh) in skeletal muscle arterioles.

METHODS

In isolated rat gracilis arterioles, simultaneous changes in smooth muscle (aSM) [Ca(2+)](i) (assessed by changes in fura-2 ratiometric signal, R(Ca)) and diameter were measured in response to ACh in the presence of indomethacin and L-NAME.

RESULTS

ACh, the K(ATP) channel opener pinacidil, and the Ca(2+) channel inhibitor verapamil elicited comparable decreases in aSM [Ca(2+)](i) (max.: -32 +/- 3%, 29 +/- 3%, and -30 +/- 3%, respectively) and arteriolar dilations (max.: 90 +/- 4%, 96 +/- 2%, and 95 +/- 2%, respectively). ACh-induced responses were inhibited by KCl-depolarization, K(Ca) channel blockers (TEA, charybdotoxin), or gap junction inhibitors (18alpha-glycyrrhetinic acid, hyperosmolar sucrose). The K(ATP) channel inhibitor glibenclamide, the K(IR) channel inhibitor barium chloride, or the CYP inhibitor 17-octadecynoic acid (ODYA) were without effect. The putative EDHF analogue 5,6-EET elicited constrictions in the presence of the endothelium that could be prevented by indomethacin or a TxA(2) receptor antagonist, whereas in the absence of the endothelium, EDHF elicited only small, charybdotoxin-insensitive decreases in aSM R(Ca) and dilations (max.: -8 +/- 2% and 27 +/- 4%, respectively).

CONCLUSIONS

In skeletal muscle arterioles, EDHF 1) substantially and rapidly reduces myogenic tone by decreasing aSM [Ca(2+)](i) via opening K(Ca) channels, 2) it is unlikely to be 5,6-EET or other CYP metabolites, but 3) requires functional gap junctions.

[Methicillin-resistant Staphylococcus aureus (MRSA). Current status and significance of preventing infection in technical orthopedics]

Many patients of the Clinic for Technical Orthopedics and Rehabilitation of the Munster University are facing several risk factors at the same time, which have to be considered for infection registration and therapy accordingly. The interaction of the known late consequences of diabetes mellitus creates the prerequisites which give way for infections of the soft parts and bones. Very often, patients are only being transferred to special university clinics after long-lasting pre-treatments as day-patients or inpatients. The integrity of patients physiological barriers is often broken through by the already existing morphological damages, and the function of the immune systems defence possibly is affected by already existing basic diseases. Parallel to the increasing importance of Staphylococcus aureus (S. aureus) being the pathogen for nosocomial infections, the resistance situation towards a lot of antibiotics has significantly and increasingly deteriorated. The methicillin resistance of S. aureus, i.e. the resistance of the pathogen towards so-called staphylococcus-effective penicillinase-resistant penicillins (isoxazolylpenicillins), is presently creating the especially for the clinical practice problematic resistance mechanisms. The methicillin (oxacillin)-resistant S. aureus (MRSA, ORSA) stems usually present the phenomenon of multiresistance, i.e. the resistance towards substances of several classes of antibiotics, and, therefore, are not only resistant to all beta-lactamantibiotics (penicillins, cephalosporins, carbapenems). Thus, MRSA infections become a significant risk factor for the respective patients. In many cases there are only a very few options left for an antibiotic therapy. The increasing and often unquestioned use of "reserve substances" is leading to a selection of pathogens creating resistances to the corresponding substances. This results in a resistance spiral which makes an antibiotic therapy more and more difficult.

Selected contribution: NO released to flow reduces myogenic tone of skeletal muscle arterioles by decreasing smooth muscle Ca(2+) sensitivity

To clarify the contribution of intracellular Ca(2+) concentration ([Ca(2+)](i))-dependent and -independent signaling mechanisms in arteriolar smooth muscle (aSM) to modulation of arteriolar myogenic tone by nitric oxide (NO), released in response to increases in intraluminal flow from the endothelium, changes in aSM [Ca(2+)](i) and diameter of isolated rat gracilis muscle arterioles (pretreated with indomethacin) were studied by fluorescent videomicroscopy. At an intraluminal pressure of 80 mmHg, [Ca(2+)](i) significantly increased and myogenic tone developed in response to elevations of extracellular Ca(2+) concentration. The Ca(2+) channel inhibitor nimodipine substantially decreased [Ca(2+)](i) and completely inhibited myogenic tone. Dilations to intraluminal flow (that were inhibited by N(omega)-nitro-L-arginine methyl ester) or dilations to the NO donor S-nitroso-N-acetyl-DL-penicillamine (that were inhibited by the guanylate cyclase inhibitor 1H-[1,2,4]oxadiazolo[4,3-a]quinoxalin-1-one) were not accompanied by substantial decreases in aSM [Ca(2+)](i). 8-Bromoguanosine cGMP and the cGMP-specific phosphodiesterase inhibitor zaprinast significantly dilated arterioles yet elicited only minimal decreases in [Ca(2+)](i). Thus flow-induced endothelial release of NO elicits relaxation of arteriolar smooth muscle by a cGMP-dependent decrease of the Ca(2+) sensitivity of the contractile apparatus without substantial changes in the pressure-induced level of [Ca(2+)](i).

EDHF mediates flow-induced dilation in skeletal muscle arterioles of female eNOS-KO mice

Vasodilation to increases in flow was studied in isolated gracilis muscle arterioles of female endothelial nitric oxide synthase (eNOS)-knockout (KO) and female wild-type (WT) mice. Dilation to flow (0-10 microl/min) was similar in the two groups, yet calculated wall shear stress was significantly greater in arterioles of eNOS-KO than in arterioles of WT mice. Indomethacin, which inhibited flow-induced dilation in vessels of WT mice by approximately 40%, did not affect the responses of eNOS-KO mice, whereas miconazole and 6-(2-proparglyoxyphenyl)hexanoic acid (PPOH) abolished the responses. Basal release of epoxyeicosatrienonic acids from arterioles was inhibited by PPOH. Iberiotoxin eliminated flow-induced dilation in arterioles of eNOS-KO mice but had no effect on arterioles of WT mice. In WT mice, neither N(omega)-nitro-L-arginine methyl ester nor miconazole alone affected flow-induced dilation. Combination of both inhibitors inhibited the responses by approximately 50%. 1H-[1,2,4]oxadiazolo[4,3-a]quinoxalin-1-one (ODQ) alone inhibited flow-induced dilation by approximately 49%. ODQ + indomethacin eliminated the responses. Thus, in arterioles of female WT mice, nitric oxide and prostaglandins mediate flow-induced dilation. When eNOS is inhibited, endothelium-derived hyperpolarizing factor substitutes for nitric oxide. In female eNOS-KO mice, metabolites of cytochrome P-450, via activation of large-conductance Ca2+-activated K+ channels of smooth muscle, mediate entirely the arteriolar dilation to flow.

Gender-specific compensation for the lack of NO in the mediation of flow-induced arteriolar dilation

Flow-induced dilation of gracilis muscle arterioles was examined in both genders of control rats and rats chronically treated with N ω-nitro-l-arginine methyl ester (l-NAME). After l-NAME treatment (4 wk), systolic blood pressure was significantly increased compared with control, whereas the plasma concentration of nitrate/nitrite was significantly reduced. Isolated and pressurized arterioles dilated significantly in response to increases in flow (0–25 μl/min). Flow-induced dilation was comparable in arterioles of control andl-NAME-treated rats but was significantly greater in female than in male rats. l-NAME + indomethacin, which abolished flow-induced dilation in arterioles of male control rats, inhibited the dilation by only ∼75% in female control rats. The residual portion of the response was eliminated by additional administration of miconazole, an inhibitor of cytochrome P-450. Indomethacin did not affect the dilation in femalel-NAME-treated rats but completely inhibited the response in male l-NAME-treated rats. The indomethacin-insensitive, flow-induced dilation in female l-NAME-treated arterioles was abolished by miconazole, 6-(2-proparglyoxyphenyl)hexanoic acid, or charybdotoxin. Thus an augmented release of endothelial prostaglandins accounts for the preserved flow-induced dilation in arterioles of male rats, whereas a metabolite of cytochrome P-450 is responsible for the maintenance of flow-induced dilation in female rats, suggesting important differences in the adaptation of the endothelium of arterioles from male and female rats to the lack of nitric oxide (NO) synthesis.

Homocysteine reduces smooth muscle [Ca2+]i and constrictor responses of isolated arterioles

Chronic elevation of plasma homocysteine concentration has been shown to be associated with impaired vascular function. The acute direct effect of homocysteine on the tone and vasoactive responses of arterioles and the possible underlying mechanisms, however, have not yet been elucidated. Thus arterioles were isolated from gracilis muscle of rats (d: approximately 130 microm) and their diameter was measured by videomicroscopy. Homocysteine (10(-6)-10(-4) M) elicited dose-dependent dilation of arterioles (maximum: 44+/-6% at 10(-4) M). The dilation was not affected by the presence of the nitric oxide synthase inhibitor Nomega-nitro-L-arginine methyl ester or by removal of the endothelium, or the free radical scavenger catalase and superoxide dismutase, or the K+ channel inhibitors glibenclamide, 4-aminopyridine, or tetraethyl ammonium. Incubation of vessels with homocysteine (10(-4) M, 20 min) did not affect dilations to acetylcholine or sodium nitroprusside, whereas it significantly decreased constrictions to norepinephrine (at 10(-6) M; control: 57+/-7%, homocysteine: 21+/-5%) and to the thromboxane A2 analogue U46619 (at 10(-8) M: control: 44+/-3%, homocysteine: 20+/-4%). Homocysteine (10(-4) M), similar to the voltage-operated Ca2+ channel inhibitor nitrendipine (10(-8) M), significantly decreased the arteriolar smooth muscle [Ca2+]i as assessed by changes in the fura-2 ratiometric signal (R(Ca), -6+/-1% and -24+/-3%, respectively). These data suggest that in isolated arterioles homocysteine decreases pressure-induced tone and responses to vasoconstrictor agents, likely by altering Ca2+ signaling of arteriolar smooth muscle.

Endothelial microtubule disruption blocks flow-dependent dilation of arterioles

The cytoskeleton is believed to have an important role in the structural and functional integrity of endothelial cells. The role of the endothelial cytoskeleton, specifically microtubules, in the mediation of flow-induced dilation of arterioles has not yet been studied. Thus the aim of our study was to investigate the role of microtubules in the endothelial mechanotransduction of flow-induced dilation of isolated gracilis arterioles of the rat. The active diameter of arterioles at a constant perfusion pressure (80 mmHg) was approximately 63 microm, whereas their passive diameter (Ca(2+)-free solution) was approximately 119 microm. At a constant pressure, increases in flow of the perfusate solution (from 0 to 10 and from 10 to 20 microl/min) elicited increases in diameter up to approximately 95 microm (approximately a 53% increase). Intraluminal administration of nocodazole at concentrations of 5 x 10(-9) and 5 x 10(-8) M had no discernible effects on the structure of endothelial microtubules or on flow-induced dilation, whereas it disassembled microtubules and eliminated flow-induced dilation at a concentration of 5 x 10(-7) M. At this higher concentration, however, the basal diameter and dilations to acetylcholine (10(-8) M), sodium nitroprusside (10(-7) M), arachidonic acid (5 x 10(-6) M), and prostaglandin E2 (10(-8) M) were unaffected. Colchicine (5 x 10(-7) M) also disassembled microtubules and eliminated flow-induced dilation. We concluded that, in isolated arterioles, the integrity of the endothelial cytoskeleton is essential for the transduction of the shear stress signal that results in the release of endothelial factors evoking dilation.

Reestablishment of foot-stability with external fixation in cases of neurogenic osteoarthropathy

The localization of neurogenic osteopathy in the hindfoot often results in deformities which cannot be corrected by conservative methods. Indications for operation are recurring ulcers, deep infection, and reduced stability with progressive deformity. The aim of this study was to ascertain whether external fixation enables reestablishment of foot stability even when the osteoarthropathic processes have not entirely ceased. A bilaterally mounted Hoffman 2 fixator was used for open repositioning and restabilization on 14 patients with osteoarthropathy of the hindfoot: 12 had diabetes mellitus and 13 had florid processes. Revision with axial correction was necessary in 2 patients. One underwent amputation according to Syme and received a prosthesis. Thirteen were completely remobilized: ten were fitted with an orthosis and three with a rigid orthopedic shoe. Complicated deformities of the hindfoot from neurogenic arthropathy can be satisfactorily restabilized in the edematous and demineralizing stages by surgery and the application of external fixation.

Holt-Oram syndrome. Three case reports and their physiotherapeutic, ergotherapeutic, and technical orthopedic treatment

The combination of organ and skeletal malformation as well as the fact that Holt-Oram syndrome appears in many forms with related functional disturbances and makes it mandatory that the therapy for these patients be determined on an individual basis. Supportive statomotoric therapy of young patients plays a particularly central role, as do development-synchronized treatment aids. Physiotherapy, ergotherapy, and technical orthopedic support oriented toward functionality are all part of the therapeutic concept.

Regular exercise enhances blood pressure lowering effect of acetylcholine by increased contribution of nitric oxide

This study is aimed to test the hypothesis, that short-term daily bouts of exercise alter the endothelial regulation of peripheral vascular resistance by nitric oxide. Rats ran on a treadmill once a day, 5 days a week, for an average of three weeks with gradually increasing intensity (EX), while a control group remained sedentary (SED). Dose dependent reductions in mean arterial blood pressure (resting MABP; SED: 120.0 +/- 3.4 and EX: 127.8 +/- 4.0 mm Hg) of pentobarbital anesthetized rats to intravenous endothelium independent dilator sodium nitropmsside (SNP; 0.6-3.0 microg/kg) were not different in EX and SED animals. In contrast, dose dependent reductions in MABP to endothelium dependent dilator acetylcholine (ACh) were significantly enhanced in EX compared to those in SED rats (at 0.5 and 1.0 microg/kg ACh: 60.3 +/- 2.4 and 66.5 +/- 1.8 vs 52.8 +/- 2.0 and 59.8 +/- 1.7 mmHg, respectively, p<0.01). There was no significant difference in the heart rate (HR) response to ACh and SNP in the two groups of rats. Intravenous administration of 20 mg/kg Nomega-nitro-L-arginine (L-NNA, a nitric oxide synthase inhibitor) elicited a similar increase (approximately 30%) in the MABP in the two groups and eliminated the difference between ACh-induced blood pressure lowering responses in EX and SED rats (at 0.5 and 1.0 microg/kg ACh: 44.6 +/- 4.7 and 56.3 +/- 4.4 vs 50.9 +/- 4.5 and 59.4 +/- 3.6 mm Hg, respectively). Thus, we suggest that the enhanced acetylcholine-induced decrease in systemic blood pressure following regular daily exercise is primarily due to the augmented synthesis of nitric oxide in the endothelium of peripheral vasculature. This change in the function of endothelium could be important in the adaptation of circulation to exercise training.

[Syme amputation in heel defects]

The main advantage of Syme's amputation is the end-bearing stump. A defective heel pad often leads to below-knee amputation. The question of interest is whether an atypical cutaneous flap also provides a covering for the stump adaptable to weight-bearing. Thirteen patients with heel pad ulcers or tumors who could not be attended to with a classic Syme's amputation were operated on in a modified fashion. Skin from the dorsum of the foot or a medial flap was used for covering the stump. Two patients underwent transtibial amputation. The remaining 11 patients received a covering for the end of the stump composed of tissue thick and bulky enough for weight-bearing in a prosthesis typical for a Syme stump. The results show that a transtibial amputation can be prevented by atypical soft-tissue coverage of a Syme stump with satisfactory results regarding function and cosmetics.

[Incidence and detection of nosocomial infections in technical orthopedics]

The significance of nosocomial infections is increasing. The reasons for this are a higher concentration of problematic patients in hospitals due to the increasing number of outpatient surgeries, the increase of invasive therapeutic and diagnostic procedures, the growing share of immunodeficient patients as well as the increase in antibiotic-resistant and multiresistant pathogenic organisms. Basic changes in the medical system call for a systematic discussion about directed quality management. Surveillance, i.e., the systematic registration and evaluation of occurred diseases as well as the feedback to the personnel in charge is very important in this context, particularly when complemented by comprehensive hygienic measures. The growing significance of hospital infections increasingly triggered by multiresistant pathogenic organisms emphasizes the importance of general prevention. Each hospital has to determine which surveillance methods for the registration of nosocomial infections and multiresistant pathogenic organisms are the most appropriate under their respective conditions. To get a first idea of possible problem areas, prevalence studies are very suitable for the start before moving on to well-directed incidence studies in certain wards and for certain kinds of infection.

Endothelial K(ca) channels mediate flow-dependent dilation of arterioles of skeletal muscle and mesentery

The role of Ca(2+)-activated potassium channels (K(Ca)) in flow-initiated intracellular events in microvessels is not known. We hypothesized that K(Ca) channels in the arteriolar endothelium are responsible for the mechanotransduction of flow/shear stress-induced arteriolar dilation in skeletal muscle and mesentery of rats. The active diameter of arterioles isolated from gracilis (80 mm Hg) and cremaster (60 mm Hg) muscles and mesentery (80 mm Hg) at a constant intraluminal pressure was 53 +/- 3, 77 +/- 5, and 72 +/- 6 microm, respectively. Their passive diameter (in Ca(2+)-free solution) was 113 +/- 3, 152 +/- 12, and 121 +/- 7 microm, respectively. At a constant intraluminal pressure stepwise increases in perfusate flow (25, 40, and 14 microL/min in 5, 10, and 2 microL/min steps) elicited a gradual increase in diameter of all three groups of arterioles up to 93 +/- 5, 137 +/- 11, and 102 +/- 7 microm, respectively. Flow-induced dilations of arterioles were eliminated by intraluminal administration of iberiotoxin (ibTX 10(-9) M), an inhibitor of high conductance K(Ca) channels (BK(Ca)). In contrast, arteriolar dilations to acetylcholine and sodium nitroprusside were not altered by this agent, indicating that BK(Ca) channels are not involved in the receptor-mediated endothelial synthesis of nitric oxide (NO) and that the inhibitor did not affect the action of NO on smooth muscle. Abluminal application of ibTX (10(-8) M) did not affect flow-dependent dilation. We conclude that in arterioles of several tissues activation of endothelial BK(Ca) channels is an obligatory step in the transduction of the signal initiated by changes in intraluminal flow/shear stress, leading to the release of endothelial factors evoking dilation.

Import of peroxisomal matrix and membrane proteins

This review summarizes the progress made in our understanding of peroxisome biogenesis in the last few years, during which the functional roles of many of the 23 peroxins (proteins involved in peroxisomal protein import and peroxisome biogenesis) have become clearer. Previous reviews in the field have focussed on the metabolic functions of peroxisomes, aspects of import/biogenesis the role of peroxins in human disease, and involvement of the endoplasmic reticulum in peroxisome membrane biogenesis as well as the degradation of this organelle. This review refers to some of the earlier work for the sake of introduction and continuity but deals primarily with the more recent progress. The principal areas of progress are the identification of new peroxins, definition of protein-protein interactions among peroxins leading to the recognition of complexes involved in peroxisomal protein import, insight into the biogenesis of peroxisomal membrane proteins, and, of most importance, the elucidation of the role of many conserved peroxins in human disease. Given the rapid progress in the field, this review also highlights some of the unanswered questions that remain to be tackled.

Flow-induced constriction in arterioles of hyperhomocysteinemic rats is due to impaired nitric oxide and enhanced thromboxane A(2) mediation

Hyperhomocysteinemia (HHcy) is thought to promote arteriosclerosis and peripheral arterial disease, in part by impairing the function of endothelium. Because flow-induced dilation is mediated by the endothelium, we hypothesized that HHcy alters this response by interfering with the synthesis/action of NO and prostaglandins. Thus, changes in the diameter of isolated, pressurized (at 80 mm Hg) gracilis skeletal muscle arterioles (diameter approximately 170 microm) from control and methionine diet-induced HHcy rats were investigated with videomicroscopy. Increases in intraluminal flow (from 0 to 25 microL/min) resulted in dilations of control arterioles (maximum, 34+/-4 microm). In contrast, increases in flow elicited constrictions of HHcy arterioles (-36+/-3 microm). In control arterioles, the NO synthase inhibitor N:(omega)-nitro-L-arginine-methyl ester significantly attenuated (approximately 50%) dilation, whereas the additional administration of indomethacin, an inhibitor of cyclooxygenase, eliminated flow-induced dilation. In the arterioles of HHcy rats, flow-induced constriction was not affected by N:(omega)-nitro-L-arginine-methyl ester, whereas it was abolished by indomethacin or the prostaglandin H(2)/thromboxane A(2) (TXA(2)) receptor antagonist SQ 29,548 or the TXA(2) synthase inhibitor CGS 13,080. Thus, in HHcy, increases in intraluminal flow elicit constrictions of skeletal muscle arterioles due to the impaired NO and enhanced TXA(2) mediation of the response, alterations that likely contribute to the development of peripheral arterial disease.

Release of muscle proteins after downhill running in male and female subjects

The release of muscle proteins after downhill running, which mainly includes eccentric muscle action, was compared in females (F; n=9) and males (M; n=9). They performed 20 min of downhill treadmill running with 16% decline with a target heart rate of 70% of the individual VO2peak, which was determined two weeks before. Blood samples were drawn before, 6 and 24 h after exercise to measure plasma levels of skeletal troponin I (sTnI), myosin heavy chain fragments (MHC), creatine kinase (CK), and myoglobin (Mb). Baseline levels before exercise were significantly higher in males compared to females for the cytoplasmic proteins CK and Mb, but the difference for MHC and sTnI was not significant. Both groups displayed marked and significant early (6 h) increases (P<0.05) for sTnI (median: F: 8.2 microg/L; M: 22.0 microg/L), Mb (median: F: 86.8 microg/L; M: 407 microg/L), and CK (median: F: 162 U/L; M: 339 U/L). A significant (P<0.05) but delayed (24 h) increase was found for MHC (median: F: 482 microU/L; M: 651 microU/L). The absolute values for all four parameters were significantly (P<0.05) higher in males compared to females; however, no difference was found for the relative increases and the time course of all parameters between females and males. We conclude 1) that there were no significant differences in the basal concentrations of predominantly bound proteins, and 2) that there were no differences in the relative muscle protein release between females and males before and after one bout of high-intensive eccentric exercise. The higher plasma concentrations of all measured muscle proteins in males are probably caused by the higher muscle mass compared to females.

Nitric oxide-mediated arteriolar dilation after endothelial deformation

Previously, we frequently observed dilation of arterioles after agonist-induced constrictions. We hypothesized that deformation of the endothelium during decreases in diameter of isolated arterioles elicits the release of nitric oxide (NO). In isolated arterioles of rat mesentery, phenylephrine (PE, 10(-7) M)-, U-46619 (10(-7) M)-, and KCl (50 mM)-induced constrictions were followed by potent dilations. Inhibition of NO synthase with N(omega)-nitro-L-arginine (L-NNA, 2 x 10(-4) M) or removal of the endothelium significantly enhanced constriction and reduced the postconstriction dilation. In the presence of 80 mmHg of intraluminal pressure, an increase in extraluminal pressure (P(e)) to 75 mmHg for 20 s and 1 and 2 min decreased vessel diameter. After release of P(e), arterioles dilated as a function of the duration of diameter reduction by P(e). Removal of the endothelium or administration of L-NNA significantly diminished the post-P(e) dilations. In cultured mesenteric arteriolar endothelial cells (EC), PE, U-46619, or KCl did not increase, whereas ACh did increase, the production of NO, as measured by a fluorometric assay for nitrite. Furthermore, when EC, cultured on a stretched silicone membrane, were subjected to deformation by shortening the membrane to 50% of its original length, NO release increased significantly. Based on all of the above, we propose that deformation of EC per se elicits release of NO, a mechanism that modulates arteriolar constriction.

Hyperosmolality dilates rat skeletal muscle arterioles: role of endothelial K(ATP) channels and daily exercise

The purpose of this study was to investigate the mechanism underlying arteriolar responses to hyperosmolality and to determine the effects of daily exercise on this response. Dilator responses were measured in isolated, cannulated, and pressurized skeletal muscle arterioles. Osmolality was increased from approximately 290 to 330 mosmol/kgH(2)O by adding glucose, sucrose, or mannitol to the superfusion solution. All three compounds elicited similar changes in vessel diameter, suggesting that this response was due to changes in osmolality. Responses to glucose were abolished by endothelium removal but were not altered in endothelium-intact vessels by superfusion with the nitric oxide synthase inhibitor N(omega)-nitro-L-arginine or the cyclooxygenase inhibitor indomethacin. In endothelium-intact arterioles, responses to glucose superfusion with the ATP-sensitive potassium (K(ATP)) channel inhibitor glibenclamide; however, intraluminal perfusion with glibenclamide nearly abolished the responses to glucose and mannitol. Intraluminal administration of glucose elicited a significantly greater dilation than extraluminal glucose. The response to intraluminal glucose was also inhibited by intraluminal glibenclamide. Four weeks of daily exercise did not significantly alter the responses to hyperosmolality in gracilis or soleus muscle arterioles. These data demonstrate that physiological increases in intraluminal osmolality dilate rat skeletal muscle arterioles via activation of endothelial K(ATP) channels; however, this endothelium-dependent response is not augmented by daily exercise.

Endothelin and prostaglandin H(2)/thromboxane A(2) enhance myogenic constriction in hypertension by increasing Ca(2+) sensitivity of arteriolar smooth muscle

The myogenic response of skeletal muscle arterioles is enhanced in hypertension because of the release of endothelin (ET) and prostaglandin H(2) (PGH(2))/thromboxane A(2) (TxA(2)) from the endothelium. We hypothesized that ET and PGH(2)/TxA(2) modulate Ca(2+) signaling in arteriolar smooth muscle and thereby enhance myogenic constriction. Thus, simultaneous changes in intracellular Ca(2+) concentration in smooth muscle ([Ca(2+)](i)), measured by fura 2 microfluorometry (expressed as Ca(2+) fluorescence ratio [R(Ca)]), and diameter were obtained as a function of intraluminal pressure (P(i)) in isolated cannulated gracilis muscle arterioles (diameter approximately 120 micrometer) of normotensive Wistar rats (WR) and spontaneously hypertensive rats (SHR). In the absence of extracellular Ca(2+), increases in P(i) from 20 to 160 mm Hg increased the passive diameter of arterioles without changes in R(Ca). In the presence of extracellular Ca(2+) and endothelium, increases in P(i) elicited similar increases in R(Ca) (30+/-7% for control and 33+/-8% for SHR at 160 mm Hg) but a significantly (P<0.05) greater constriction of SHR arterioles compared with WR arterioles (at 160 mm Hg, 55+/-4% versus 38+/-2%, respectively, of passive diameter). In the absence of the endothelium, P(i)-induced changes in the R(Ca) and diameter of SHR and WR arterioles did not differ significantly. Also, a step increase in P(i) (from 80 to 140 mm Hg) elicited a similar increase in R(Ca) but greater constrictions in SHR versus WR arterioles. In the presence of the TxA(2) receptor inhibitor SQ29,548 and the ET(A) receptor inhibitor BQ123, there was no difference between responses of SHR and WR arterioles. In WR arterioles, increasing concentrations of KCl elicited a significant increase in R(Ca) (38+/-7% at 80 mmol/L) and completely constricted the arterioles. In contrast, constrictions to ET (52+/-7% at 3x10(-12) mol/L) and the TxA(2) agonist U46619 (40+/-8% at 3x10(-9) mol/L) were not accompanied by increases in R(Ca) at submaximal concentrations. Collectively, these findings suggest that in hypertension, endothelium-derived ET and PGH(2)/TxA(2) increase the Ca(2+) sensitivity of the contractile apparatus of arteriolar smooth muscle; thus, the similar increases in [Ca(2+)](i) in response to the elevation of intraluminal pressure elicit greater myogenic constriction.

First ovulation and ketone body status in the early postpartum period of dairy cows

The effect of ketone body status on occurrence of first ovulation during early lactation was assessed in 84 multiparous dairy cows under field conditions. Animals were equally distributed across 8 farms and were controlled by the same herd fertility monitoring program. Cows were visited twice antepartum and 6 times postpartum at weekly intervals between 5:30 and 8:30 AM. On these occasions, body condition scores and milk yields were measured, blood and milk samples were taken, cows were gynecologically examined, and parameters of reproduction were determined. The onset of first ovulation was specified by milk progesterone determination and rectal palpation. Cows starting postpartum ovarian cyclicity within or after 30 d were classified as early and late responders (ER and LR, respectively). Resumption of the estrous cycle within 30 d postpartum is considered optimal under practical conditions, and classification based on this threshold value resulted in groups of equal size and equal distribution of ER + LR cows within farms. Ketone bodies measured were beta-hydroxybutyrate in serum and acetoacetate and acetone in serum and milk. Blood serum and milk ketone body concentrations during the first 6 wk of lactation were higher in LR than in ER, whereas plasma glucose and nonesterified fatty acid and milk fat, protein and urea concentrations did not differ between groups. Maximal concentrations of ketone bodies from parturition to first ovulation were better predictors of the onset of the estrous cycle than mean or minimal concentrations over the same period. Milk acetone and serum beta-hydroxybutyrate concentrations provided the most reliable information with regard to resumption of ovarian activity of all ketone bodies.

Renal oncocytoma with prominent intracytoplasmic vacuoles of mitochondrial origin

AIMS

We observed two oncocytomas with prominent intracytoplasmatic vacuoles. To investigate if this previously undescribed finding is a diagnostic feature and compatible with the diagnosis of oncocytoma, we characterized these vacuoles by electron microscopy and immunohistochemistry.

METHODS AND RESULTS

The tumours were analysed by transmission electron microscopy. Immunohistochemistry was performed with antimitochondrial antibody, anti-Golgi-zone antibody, anti-lysozyme antibody and anti-human-trans-Golgi-network antibody. By electron microscopy, the vacuoles were found to be double-membrane-bounded, and some contained fragmented christae. Immunohistochemistry showed a positive reaction of the vacuoles with anti-mitochondrial antibody. Staining with anti-Golgi-zone antibody, anti-lysozyme antibody and anti-human-trans-Golgi-network antibody was negative.

CONCLUSION

Both tumours are benign oncocytomas. The phenomena of cells with prominent intracytoplasmatic vacuoles is not inconsistent with the diagnosis of oncocytoma. The vacuoles are of mitochondrial origin and may develop, by balloon degeneration, as a mechanism of mitochondrial involution and elimination.

Concentration of cardiac troponin I in a horse with a ruptured aortic regurgitation jet lesion and ventricular tachycardia

An 18-year-old Thoroughbred gelding was evaluated because of sudden onset of ventricular tachycardia and signs of colic. Three years earlier, a diastolic decrescendo murmur, consistent with aortic regurgitation, had been detected, but the horse continued to perform well and compete successfully. Cardiac ultrasonographic examination revealed a defect in the interventricular septum below the aortic root, and serum concentrations of cardiac troponin I (cTnI) were higher than those measured in clinically normal horses. Repeated development of tachyarrhythmia during hospitalization prompted a decision to euthanatize the horse. A ruptured endocardial jet lesion below the aortic valve with formation of a cleft into the interventricular septum was found on necropsy. This report of increased serum cTnI concentrations in a horse with myocardial disease and our other findings suggest that assessment of cardiac troponin concentrations may be a useful tool in the evaluation of horses with suspected myocardial disease.

Serotonin reuptake inhibitor fluoxetine decreases arteriolar myogenic tone by reducing smooth muscle [Ca2+]i

Previous studies showed that the serotonin reuptake inhibitor (SSRI) antidepressant fluoxetine (Prozac) dilates skeletal muscle and cerebral arterioles independent of the endothelium. We hypothesized that fluoxetine affects the contractile activity of arteriolar smooth muscle by interfering with Ca2+ signaling pathways. The effects of fluoxetine on pressure-induced tone of isolated rat skeletal muscle arterioles (approximately 110 microm) were investigated by videomicroscopy. Changes in smooth muscle [Ca2+]i were measured simultaneously by the fura-2 ratiometric method. Elevation of intraluminal pressure (from 20 to 120 mm Hg) increased (by approximately 20%) the smooth muscle calcium fluorescence ratio (R(Ca)) and resulted in a significant myogenic constriction (approximately 40%). Fluoxetine and nifedipine significantly decreased R(Ca) (by approximately 30%) and abolished pressure-induced arteriolar tone (EC50, 3.1 x 10(-6) and 6.0 x 10(-9) M, respectively). Constrictions to the L-type Ca2+ channel opener Bay K 8644 also were inhibited and abolished by increasing doses of fluoxetine (3 x 10(-6) and 10(-5) M, respectively). In the presence of 10(-5) M fluoxetine, a concentration that elicited submaximal (approximately 80%) dilation, elevation of extracellular Ca2+ concentration (from 2.5 to 15 mM) normalized R(Ca) and restored arteriolar myogenic tone. Thus, fluoxetine reduces [Ca2+]i and tone of arteriolar smooth muscle, likely by interfering with Ca2+ entry. We speculate that the "calcium antagonist" effect of fluoxetine may be an additional element in the therapeutic actions of this drug.