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F Urthaler

Publications and source records attributed to F Urthaler.

At least 19 recordsLinked to original sources
PubMed2004

Activation of leptin expression by an inhibitor of carnitine palmitoyltransferase-1.

Leptin may regulate peripheral fatty acid oxidation and invoke a feedback mechanism that affects leptin expression in adipocytes. The objective of this study, therefore, was to determine whether inhibiting systemic fatty acid oxidation at the level of carnitine palmitoyltransferase-1 (CPT1) affects leptin expression. To accomplish this objective, fed or overnight fasted rats were treated with 2-tetradecylglycidic acid (TDGA), a specific, irreversible CPT1 inhibitor, and acute changes in rat epididymal leptin expression and serum leptin content were measured using Northern, RT-PCR, and radioimmunoassay analyses. Overnight fasting decreased both epididymal leptin mRNA content and serum leptin. Treating overnight fasted rats with TDGA increased both their epididymal leptin mRNA and their serum leptin significantly in a time- and concentration-dependent manner. TDGA affected neither epididymal leptin mRNA nor serum leptin in fed rats where systemic fatty acid oxidation is low. These results support the conclusion that CPT1-linked fatty acid oxidation is a key modulator of leptin expression in fasting rats.

Animals↗
PubMed1999

2-Tetradecylglycidic acid, an inhibitor of carnitine palmitoyltransferase-1, induces myocardial hypertrophy via the AT1 receptor.

Activation of the antiogensin II, type 1 (AT1) receptor mediates the myocardial response to numerous hypertrophic stimuli. This study tested the hypothesis that 2-tetradecylglycidic acid (TDGA), an oxirane carboxylate inhibitor of mitochondrial carnitine plamitoyltransferase-1, induces myocardial hypertrophy via the AT1 receptor system. Male Sprague-Dawley rats treated with 10 mg TDGA/kg/day for 7 days had a heart wet weight:body weight ratio of 3. 58+/-0.16 mg/g compared with a ratio of 2.79+/-0.07 for rats treated with vehicle (P<0.05). The plasma level of antiogensin II was 117. 75+/-17.39 pg/ml in rats treated with 10 mg TDGA/kg/day compared with 54.0+/-11.38 pg/ml for rats treated with vehicle (P<0.05). The plasma level of angiotensin I in these two groups of rats was not different statistically. Rats treated with TDGA and given drinking water containing 1 mg losartan/ml had a heart wet weight:body weight ratio of 2.84+/-0.05 mg/g. This value was not statistically different from the value measured in rats given drinking water containing 1 mg losartan/ml and treated with vehicle alone. No significant difference in the heart wet weight:dry weight ratio occurred among these groups of rats. Finally, treating rats with TDGA or giving rats drinking water that contained 1 mg losartan/ml altered neither their heart rate nor their mean arterial blood pressure when compared with untreated rats. This data, therefore, suggests that oxirane carboxylates induce myocardial hypertrophy by activating the AT1 receptor independent of changes in systemic hemodynamics.

Animals↗
PubMed1999

Peroxynitrite irreversibly decreases diastolic and systolic function in cardiac muscle.

Much of the damaging action of nitric oxide in heart may be due to its diffusion-limited reaction with superoxide to form peroxynitrite. Direct infusion of peroxynitrite into isolated perfused hearts fails to model the effects of in situ formation because the bulk of peroxynitrite decomposes before reaching the myocytes. To examine the direct effects of peroxynitrite on the contractile apparatus of the heart, we exposed intact and skinned rat papillary muscles to a steady state concentration of 4-microM peroxynitrite for 5 min, followed by a 30-min recovery period to monitor irreversible effects. In intact muscles developed force fell immediately to 26% of initial force, recovering to 43% by 30 min. Resting tension increased by 600% immediately, and was still elevated 500% by 30 min. Nitrotyrosine immunochemistry showed that peroxynitrite can induce tyrosine nitration at low concentrations and is capable of penetrating 200-380 microm into the papillary muscle after a 5-min infusion. Decomposed peroxynitrite had no effect on either intact or skinned muscle developed force or resting tension. Our results show that peroxynitrite directly damages both developed force and resting tension of isolated heart muscle, which can be extrapolated to systolic and diastolic injury in intact hearts.

Animals↗
PubMed1997

MDL-28170, a membrane-permeant calpain inhibitor, attenuates stunning and PKC epsilon proteolysis in reperfused ferret hearts.

OBJECTIVES: This paper tests the hypothesis that calpains are activated in the ischemic (I)/reperfused (R) heart and contribute to myocardial stunning. METHODS: Isolated ferret hearts were Langendorff perfused isovolumically, and subjected to 20 min of global I followed by 30 min of R in the presence or absence of 0.2 microM MDL-28170, a membrane-permeant calpain inhibitor. Right trabeculae then were isolated from these hearts, skinned chemically, and pCa(2+)-force curves obtained. Samples of left ventricle were extracted subjected to SDS-PAGE, and Western analyzed for PKC epsilon and PKM epsilon. RESULTS: Perfused ferret hearts exhibit a 43% decline in left ventricular developed pressure during R. Pre-treatment of hearts with MDL-28170 prior to I significantly improves function during R. Trabecular myofilaments from normal hearts have a KD for Ca2+ of 6.27 +/- 0.06; I/R decreased the KD to 6.09 +/- 0.04; trabeculae from I/R hearts pre-treated with MDL-28170 have a KD of 6.28 +/- 0.04. Western analysis shows ferret hearts to contain a single approximately equal to 96 kDa species of PKC epsilon. I/R hearts contain the native PKC epsilon and a approximately equal to 25 kDa smaller species of PKC epsilon which corresponds to PKM epsilon, the calpain proteolyzed form of PKC epsilon. Pre-treatment of I/R hearts with MDL-28170 markedly diminishes PKM epsilon in reperfused hearts. CONCLUSIONS: Mechanical stunning during R is sensitive to MDL-28170. Depressed mechanical function is reflected in a hyposensitization of trabecular myofilaments to Ca2+. Western analysis shows that PKM epsilon is present in R hearts.

Animals↗
PubMed1994

Estimates of beat to beat handling of activator calcium using measurements of [Ca2+]i in aequorin loaded ferret cardiac muscle.

OBJECTIVE: The aims were (1) to measure simultaneously and on a beat to beat basis intracellular calcium concentration ([Ca2+]i) transients and force transients in isolated ferret cardiac trabeculae; (2) to obtain and compare independent estimates of the recirculating fraction of Ca2+ using the [Ca2+]i data and the force data (recirculating fraction is the fraction of activator Ca2+ taken up by the sarcoplasmic reticulum in each beat and, in the steady state twitch, the fraction of activator Ca2+ released by the sarcoplasmic reticulum); and (3) to estimate the amount of Ca2+ that returns to the sarcoplasmic reticulum and the amount that, during steady state contractions, enters the cytosol, presumably from the extracellular compartment, with each beat. METHODS: Eight trabeculae were mounted in the myograph. The servo-controlled muscle length was 98% of the length at which developed force was maximal. A modified technique was used for chemical loading of aequorin, and a new method for computer controlled low level photon counting, storage, calibration, and analysis. [Ca2+]i transients and force transients were simultaneously recorded during potentiated beats, together with their respective decays toward control steady state [Ca2+]i transients and force transients. A modified test of postextrasystolic potentiation achieved with a brief train of rapid pacing followed by a pause was used to evoke the potentiated beats. RESULTS: At 2.0 mM extracellular Ca2+ ([Ca2+]o), resting [Ca2+]i was 283(SD 77) nM. The resting tension was 1.6(0.3) g.mm-2. The steady state [Ca2+]i transient and the peak potentiated [Ca2+]i transient averaged 992(165) and 1290(154) nM respectively. The corresponding tensions were 4.0(1.9) and 8.7(3.1) g.mm-2 respectively. The recirculating fraction of Ca2+ calculated from the dissipation of the potentiated [Ca2+]i transient averaged 45(4)%. This recirculating fraction was indistinguishable from the one calculated with another method from the decay of the force potentiation. CONCLUSIONS: This is the first study to estimate the recirculating fraction of activator Ca2+ using measurements of [Ca2+]i. The results indicate that over a wide range of [Ca2+]i and tensions the Ca(2+)-force relationship is well approximated by a straight line. At 2.0 mM [Ca2+]o it appears that some 450 nM of Ca2+ recirculates and that a similar amount per steady state beat enters the cytosol, probably from the extracellular compartment.

Aequorin↗
PubMed1993

A stable model of left ventricular dysfunction in an intact animal assessed with high fidelity pressure and cinemagnetic resonance imaging.

OBJECTIVE: Numerous models of acute and chronic left ventricular dysfunction have been used over the years. However, few can produce a rapid onset of global systolic and diastolic dysfunction that is stable and potentially reversible. The aim of this study was to develop such a model. METHODS: A model of left ventricular dysfunction was produced in six intact dogs using 1% halothane anaesthesia and pharmacological autonomic blockade with atropine (0.1 mg.kg-1) and propranolol (2 mg.kg-1). Left ventricular function was assessed by combined high fidelity pressure and cinemagnetic resonance imaging (cine-MR) during increases in afterload using infusions of angiotensin. RESULTS: Left ventricular systolic dysfunction was characterised by a diminished resting ejection fraction of 45(SD 4)% and a depressed +dP/dtmax of 1537(100) mm Hg.s-1. Diastolic dysfunction was manifested by an increased left ventricular end diastolic pressure of 16(2) mm Hg, a decreased -dP/dtmax of -1705(369) mm Hg.s-1, and a prolonged time constant of left ventricular relaxation of 42(9) ms. As left ventricular systolic pressure steadily rose with angiotensin infusion from 87(7) to 124(13) to 152(10) mm Hg (p < 0.001), left ventricular ejection fraction decreased markedly from 45(4) to 35(4) to 27(4)% (p < 0.001). Left ventricular +dP/dtmax did not change [1537(100) to 1500(110) to 1498(84) mm Hg.s-1] in spite of a significant increase in left ventricular end diastolic pressure from 16(2) to 21(5) to 29(7) mm Hg (p < 0.001) and left ventricular end diastolic volume from 59(12) to 71(14) to 78(17) ml (p < 0.001). Individual slopes of the end systolic pressure-volume relationship were also low, ranging between 2.1 and 4.4 mm Hg.s-1 (r = 0.99 to 1.00), typical of impaired contractility. CONCLUSIONS: Halothane anaesthesia in dogs pretreated with large amounts of propranolol and appropriate muscarinic cholinergic blockade produces a moderate decrease in baseline systolic and diastolic function in our intact dog model. However, left ventricular systolic function showed limited contractile reserve when challenged by physiological increases in systemic arterial pressure. Impaired systolic and diastolic function may, at least in part, be related to diminished activator calcium produced by halothane in addition to the well known negative inotropic action of beta adrenergic blockade.

Anesthesia↗
PubMed1993

Beat-to-beat measurements of [Ca2+]i and force in ferret cardiac muscle after chemical loading of aequorin.

This communication reports the development of a modified procedure for chemical loading of aequorin in small multicellular cardiac preparations, with special emphasis directed toward the implementation of a new method for computer-controlled low-photon counting and digital processing and analysis of the data to obtain intracellular Ca2+ concentration ([Ca2+]i). In eight ferret right ventricular trabeculae, we measured the mechanical performance and found that, at 1.25 mM extracellular Ca2+ concentration ([Ca2+]o), resting tension, developed tension, and time to peak tension were unchanged by the loading procedure. Estimated resting and peak systolic [Ca2+]i were 299 +/- 65 and 766 +/- 131 nM, respectively. Thirty minutes after raising the [Ca2+]o to 5 mM, there was a robust increase in mechanical performance, with peak systolic [Ca2+]i averaging 1,218 +/- 222 nM. The diastolic [Ca2+]i remained unchanged. In four other trabeculae, exposure to a low-Na(+)-containing superfusate demonstrated a remarkable beat-to-beat correspondence of increases in diastolic [Ca2+]i and resting tensions. The same beat-to-beat concordance was also observed between the rapidly changing amplitudes of peak [Ca2+]i and developed tension. In additional experiments, simultaneous recordings of [Ca2+]i and force transients were obtained during rapid pace pause maneuvers. These studies showed distinct and quantifiable fluctuations of [Ca2+]i in a 1:1 relation to the mechanical record to a frequency of at approximately 300 beats/min. These results demonstrate that beat-to-beat measurements of [Ca2+]i and tension transients can be obtained with good resolution in multicellular cardiac preparations.

Aequorin↗
PubMed1992

Quantitative effects of sympathetic and vagal nerve stimulations on sinus and AV junctional rhythms.

Responses of the sinus node and atrioventricular (AV) junctional pacemakers to autonomic denervation and to individual stimulations of the right and left stellate and both vagi were studied in 33 anesthetized dogs. Autonomic denervation depressed sinus node automaticity by only 18% from control, whilst AV junctional automaticity was reduced by 48.5% from control. Sympathetic and parasympathetic stimulation frequency-response curves (0.25, 0.5, 1, 2, 4, 8, 16 and 32 Hz) were obtained. In the sinus node the chronotropic responses to sympathetic stimulations reflect a bilaterally asymmetrical innervation with a right sided preponderance. In contrast, sinus slowing in response to either right or left vagal stimulations were indistinguishable when lower frequencies of stimulation were used. At 4 Hz and higher frequencies there is a right vagal preponderance. The AV junctional chronotropic responses suggest that this major subsidiary pacemaker receives a bilaterally symmetrical autonomic innervation. The chronotropic responses to individual nerve stimulations expressed as percent changes in sinus rate and AV junctional rate from their respective controls after autonomic denervation show that the AV junction is far more responsive than the sinus node to both sympathetic and parasympathetic stimulations. To allow for more meaningful comparisons the data were normalized using the respective maximum increase and maximum decrease of sinus node and AV junctional rates to left and right sympathetic and parasympathetic stimulations as the 100% reference. These normalized curves show that 50% of the maximal chronotropic responses were always achieved at a lower stimulus frequency in the AV junction than in the sinus node; shift of the AV junctional response curves to the left of the sinus node response curves by a 0.2 (sympathetic) and 0.3 (parasympathetic) log units was observed. These studies further showed that sympathetic activity in the AV junction is an absolute prerequisite to maintain regular AV junctional rhythms especially during the bradycardic episodes evoked in the study of vagal stimulus frequency-response curves.

Animals↗
PubMed1991

Influence of ionic modification on electrical activity of Purkinje fibers obtained from dogs with 1-day-old myocardial infarction.

A stable sustained rhythmic activity (SRA) occurred in 62 of 192 specimens isolated from the infarcted subendocardium of 48 dogs 24 h after a left descending coronary artery occlusion. Changes in [Na+]o and/or [Ca2+]o of the superfusate allowed us to distinguish two types of responses, suggestive of two different mechanisms for SRA. In type 1 responses at constant [Na+]o, the rate of SRA decreased when [Ca2+]o was increased and increased when [Ca2+]o was decreased. When [Ca2+]o was held constant, the rate of SRA was directly related to [Na+]o. In type 2 responses, at constant [Na+]o, the rate of SRA was directly proportional to [Ca2+]o. In contrast, at constant [Ca2+]o, SRA was inversely proportional to [Na+]o. When a constant [Ca2+]o/[Na+]o3 ratio was maintained, the type 2 response became indistinguishable from the type 1 response. The combination of lower temperature (36 degrees C) and high initial [Ca2+]o (2.7 mM) favored the type 2 response (28 of 32 preparations). In contrast, 25 of 30 preparations studied at 39 degrees C and 1.35 mM [Ca2+]o showed the type 1 response. These results suggest that SRA in the 24-h infarct model can be due to both abnormal automaticity (type 1) or triggered activity (type 2) and that changes in temperature and ionic milieu will largely determine which of the two mechanisms is responsible for SRA.

Animals↗
PubMed1990

Excitation-contraction coupling model to estimate the recirculating fraction of activator calcium in intact cardiac muscle.

Potentiated contractions were evoked with rapid pace pause maneuver in 14 length-clamped ferret papillary muscles paced 12 times/min at 25 degrees C. At 1.25 mM [Ca2+]o the average steady-state force was 2.94 +/- 1.08 g/mm2 and the potentiated contraction averaged 10.96 +/- 1.61 g/mm2. At 5.0 mM [Ca2+]o the steady-state force increased to 6.18 +/- 1.23 g/mm2 and the potentiated contraction averaged 12.08 +/- 1.15 g/mm2. Under the conditions of these experiments the potentiated contraction obtained at 5.0 mM [Ca2+]o is equal to the maximum twitch tension (Fmax) these muscles can generate. We have previously shown that Fmax is an equivalent of maximal calcium activated force. Since there is a beat to beat nearly exponential decay of the evoked potentiation, the fraction (= fraction x) of the potentiation that is not dissipated with each beat is nearly constant. Using an excitation-contraction coupling model we have previously found that x reflects a measure of the recirculating fraction of activator calcium. Because the tension-calcium relationship is better characterized by a sigmoidal curve, we have now incorporated the Hill equation in the model. To account for the inverse relationship between [Ca2+]i and the magnitude of the slow inward current, a term for negative feedback (h) was also included. We have determined the quantity (x-h) because x and h could not be determined separately. The quantity (x-h) was denoted as x'. The average values of x' at 1.25 and 5.0 mM [Ca2+]o were significantly different (p less than 0.0001), approximately 20% at the lower [Ca2+]o and about 50% at the higher [Ca2+]o.(ABSTRACT TRUNCATED AT 250 WORDS)

Acetylcholine↗
PubMed1989

Effects of ryanodine on contractile performance of intact length-clamped papillary muscle.

Extent, time course, and underlying mechanisms of the negative inotropic effect of ryanodine were examined in 22 length-clamped ferret right ventricular papillary muscles paced 12/min at 25 degrees C. After 60 minutes of exposure to 5 microM ryanodine a new steady state was attained with developed forces averaging 10-15% of maximum twitch force. Ryanodine does not pharmacologically excise the sarcoplasmic reticulum (SR) in this preparation. Ryanodine does not appreciably inhibit the ability of the SR to take up Ca2+ as evidenced by the potentiated beats obtained after a short pause that are nearly as large after ryanodine as before. On comparing equipotent beats before and after ryanodine, we found that ryanodine actually increases the rate at which Ca2+ is released during the twitch if the SR Ca2+ stores are equal or similar. The evidence for this conclusion is a larger maximum rate of tension rise and briefer time to peak tension after ryanodine. Since ryanodine increases the time that SR Ca2+ release channels are open and decreases their conductivity, it must follow that the former effect predominates over the latter in our experiments. Ryanodine increases the leakiness of the SR during diastole probably by inhibiting closure of SR Ca2+ release channels. The evidence for this conclusion is as follows: the early peak of the restitution curves after ryanodine, the brevity of the time required for a rested state contraction after ryanodine, and the small amplitude of the steady-state contraction at a rate of 12/min. The SR leaks even in the absence of ryanodine, but if external Ca2+ is so high that Ca2+ loss from the cell is slowed or a Ca2+ leak into the cell through the sarcolemma cancels the SR leak, then the effects of the SR leak are minimized. The evidence for this conclusion is the time required for rested-state contraction to occur or the slope of the descending limb of restitution curve; however, in presence of ryanodine even high external Ca2+ cannot prevent rapid depletion of SR Ca2+ stores. Even though we have presented evidence for a mechanism whereby ryanodine increases the number of open SR Ca2+ release channels in both systole and diastole, we do not mean to imply that most of them stay open in diastole; the SR would leak too fast to accumulate any Ca2+ for the potentiated beat. Thus, probably most channels close after being open a certain length of time, even in the presence of ryanodine.

Alkaloids↗
PubMed1988

Maximal twitch tension in intact length-clamped ferret papillary muscles evoked by modified postextrasystolic potentiation.

A modified test of postextrasystolic potentiation achieved with a brief episode of rapid pacing followed by a 6-second pause (RPP maneuver) was used to evoke maximal force in isolated intact ferret right ventricular papillary muscles. Maximal RPP tensions were examined under length-clamped conditions and compared with the steady-state forces obtained when further increases in [Ca2+]o, did not further increase force and to the tensions recorded at the point of saturation of force when similarly length-clamped muscles were subjected to caffeine-induced tetanization. The results show that the calculated maximal twitch tension achieved with RPP is comparable to the 25-35 g/mm2 observed in intact single skeletal muscle fibers. The study also shows that the beat-to-beat decay of the potentiated contraction is exponential. While the amount of the constant fractional beat-to-beat decay is a function of [Ca2+]o, it is not influenced by length. During the decay of potentiation, the ratio of the potentiation of any beat divided by that of the previous beat is a constant, called (X). With certain assumptions, it is shown that (X) is a measure of the fraction of activator calcium taken up by the sarcoplasmic reticulum in each beat and, in the steady state, the fraction of activator calcium that comes from the sarcoplasmic reticulum. The (X) amounted to 33%, 50%, and 65% when [Ca2+]o was 1.25, 2.50, and 5.0 mM, respectively. Thus, at 1.25 mM [Ca2+]o, some two thirds of the total calcium required to activate the myofilaments comes from the extracellular compartment during excitation and only one third is contributed via release from the sarcoplasmic reticulum. In the region of optimal myofilament overlap, RPP force-length curves are remarkably shallow and almost indistinguishable from the sarcomere length-tension relation observed in skinned single cardiac cells. Tetanus plateau tensions are significantly smaller than RPP forces at any length, and the slope of the tetanus force-length curves is greater than that obtained with RPP. Thus, and by exclusion, we also suggest that caffeine may exert significant downstream inhibitory effects.

Algorithms↗
PubMed1987

[The appearance and development of ventricular rhythm disorders in the 1st 24 hours after the start of experimental myocardial infarct in dogs].

The emergence of ventricular tachycardia (VT), its temporal progress and response to high-frequency stimulation were studied in 10 dogs subjected to two-step occlusion of the left descending coronary artery (LDA). Within two hours after the LDA ligation under atrioventricular block all animals developed an atrioventricular nodal rhythm of 37 +/- 9 pulses per minute that could be suppressed by high-frequency ventricular stimulation, i.e. the so-called overdrive suppression (OS) phenomenon was occurring. Three or four hours after LDA ligation, atrioventricular block brought out VT in 8 dogs. The onset of VT was always abrupt, its episodes being short-lived at first and growing progressively longer with time. Once VT was established, its rate increased gradually to reach the peak that exceed the base line VT rate by 21 +/- 9% 2 or 3 hours later. As the VT rate increased, the OS phenomenon grew less pronounced and disappeared altogether as the VT peak was reached. The results suggest that the abrupt emergence of VT 3 or 4 hours after the onset of myocardial infarction can be a result of ectopic pacemaker activity of partially depolarized fibres that in some cases may be due to the effects of a trigger mechanism.

Animals↗
PubMed1986

Differential inotropic actions of ethmozine and ethacizin (diethylamine analog of ethmozine).

The direct inotropic actions of ethmozine and of its diethylamine analog, ethacizin, were studied in the presence of muscarinic and beta-adrenoreceptor blockade in 12 ferret right ventricular papillary muscles. In each muscle ethmozine caused a small but consistent and significant (p less than 0.05) increase in contractile performance, whereas ethacizin significantly (p less than 0.05) diminished contractility. Although both phenothiazines are fast channel blockers, it appears that the net positive inotropic action of ethmozine is due to its stimulatory effect on the slow inward current and that the negative inotropic action of ethacizin is largely due to its recently demonstrated decreases of the slow inward current.

Adrenergic beta-Antagonists↗
PubMed1986

Ventricular echo beats during ventricular pacing or junctional bradycardia: studies in the normal canine heart.

In 15 adult dogs ventricular echoes were elicited during sinus rhythm by incremental ventricular pacing and during atrioventricular (AV) junctional rhythm by depressing simultaneously AV junctional automaticity and retrograde AV nodal conduction. Concomitant slowing of AV junctional automaticity and conduction was achieved by selective intranodal administration of verapamil. In three dogs incremental pacing from either ventricle failed to retrogradely activate the atria, and in each case the site of block was found to be in the AV node. In two dogs with retrograde atrial capture there was little or no rate-dependency of retrograde ventriculoatrial (VA) conduction. During incremental ventricular pacing a single ventricular echo beat was observed in 10 of the 12 dogs that had atrial capture, and the atrium appears to be an essential link in the production of each ventricular echo. Ventricular echo occurred when the time allotted for retrograde VA conduction amounted to 70 +/- 4% of the duration of the ventricular pacing cycle length. During AV junctional rhythm, a single ventricular echo was elicited in half of the dogs and in each of those cases intranodal verapamil produced a profound depression of retrograde VA conduction. These experiments suggest that retrograde AV nodal longitudinal dissociation occurs in the slow current-dependent cells of the AV node.

Animals↗
PubMed1986

Differential interaction of adrenergic and cholinergic effects on AV junctional automaticity and AV conduction.

The effects of postsynaptic autonomic interactions on atrioventricular (AV) junctional automaticity and AV conduction were studied in six canine heart in situ using direct injections of norepinephrine (NE) and physostigmine (PSM) into the AV node artery. Injection of NE (0.05 microgram/ml, 2 ml) caused an AV junctional rhythm (AVJR) in every dog. After injection of PSM (10 micrograms/ml, 2 ml), the responses of AVJR to NE were virtually identical to those observed before cholinesterase inhibition (160 +/- 13 vs 162 +/- 12 bpm). In contrast, this moderate cholinesterase inhibition still had a readily demonstrable negative dromotropic effect. In any given dog, depressed AV conduction was characterized by one of two types (I and II) of retrograde atrial capture during AVJR. Before PSM in the AV junction, onset of atrial depolarization during AVJR preceded the onset of ventricular depolarization in both type I and type II responses. After PSM, atrial depolarization occurred later with respect to ventricular depolarization (i.e., during or mostly after ventricular activation) in type I, whereas in the type II responses atrial depolarizations began much earlier than before PSM, thus being completed long before the onset of ventricular activation. Because of such differential responsiveness of AV junctional automaticity and AV conduction and because of the two types of intranodal conduction observed after administration of PSM into the AV junction, we can postulate that under appropriate autonomic imbalance retrograde or antegrade AV block could readily develop in spite of preserved AV junctional automaticity.

Animals↗
PubMed1986

The direct negative inotropic effect of gossypol.

Gossypol, an effective male antifertility agent, had a minor but significant negative inotropic action in isolated ferret right ventricular papillary muscles at concentrations of 1-5 micrograms/ml. Reduction of peak developed force and maximum extent of shortening was readily demonstrable at three different resting control contractile states achieved through increases in extracellular calcium from 0.625 to 2.5 mM/l. Gossypol had no significant effect on maximum rate of tension rise nor on maximum velocity of shortening. These results suggest that gossypol reduces the total number of crossbridges without significantly influencing the rate of making and breaking crossbridges and that its negative inotropic action is probably mediated through interactions at the myocardial cell surface.

Animals↗