Search PubMed⌕ Search

Biomedical subjects

H R Besch

Publications and source records attributed to H R Besch.

At least 37 records · Page 2Linked to original sources
PubMed1982

Effects of streptozotocin diabetes on the noradrenergic innervation of the rat heart: a longitudinal histofluorescence and neurochemical study.

The effects of the age of induction and total duration of streptozotocin diabetes on the sympathetic noradrenergic innervation of the rat heart was examined with glyoxylic acid induced histofluorescence to demonstrate the distribution of noradrenergic fibers within the heart, and with high performance liquid chromatography with electrochemical detection to measure tissue levels of the neurotransmitter norepinephrine. Diabetes was induced in male Sprague-Dawley rats at 1, 2, and 4 months of age. Within each of these groups, diabetic rats survived for periods of 1, 2, and 4 months. Additional groups of diabetic rats survived to a chronological age of 8 months. Norepinephrine levels in the hearts of diabetic rats were increased over those of control rats in all groups at 1 month duration of diabetes. Ventricles were generally affected to a greater extent than atria. At 2 months duration of diabetes, ventricular levels remained elevated while atrial norepinephrine levels were at or below control levels. At 4 months duration of diabetes, and in all groups at 8 months of age, the norepinephrine levels were at or below control levels, except in the ventricles of rats induced at 4 months of age, which remained elevated. Histofluorescence studies demonstrated the presence of axon bundles and varicose noradrenergic profiles in the diabetic rat hearts, distributed in a pattern similar to that seen in controls. However, at 1 month duration of diabetes in all groups, the density of noradrenergic varicosities in diabetic rat hearts appeared increased with abundant branched profiles. These results are surprising, since studies on genetic models of diabetes have suggested decreased norepinephrine levels in the heart. The present study suggests that during the early phases of streptozotocin induced diabetes, noradrenergic nerves are still intact and may be susceptible to pharmacologic manipulation. The later fall of norepinephrine levels back to or below control levels may indicate actual neuronal damage, suggesting that early intervention may be necessary to protect these nerves from degeneration. This issue is potentially important in view of the reported toxic effects of high NE levels on the heart, and the high incidence of death from myocardial infarct in diabetic humans with autonomic neuropathy.

Animals↗
PubMed1981

Characterization of [3H](+/-)carazolol binding to beta-adrenergic receptors. Application to study of beta-adrenergic receptor subtypes in canine ventricular myocardium and lung.

[3H](+/-)Carazolol, a newly available beta-adrenergic receptor antagonist, can be used to characterize beta-adrenergic receptor subtypes present in membrane vesicles derived from canine ventricular myocardium and canine lung. [3H](+/-)Carazolol binding is saturable, of high affinity, and is displaceable by beta-adrenergic agents in accordance with their known pharmacological potencies. The interaction of carazolol with beta-adrenergic receptors is stereospecific; the (-) stereoisomer demonstrates greater potency than the (+) stereoisomer. Kinetic analysis of [3H](+/-)carazolol interaction with beta-adrenergic receptors suggests that presence of two phases of interaction, consistent with initial rapidly reversible "low" affinity association of ligand with receptor, followed by isomerization to form a high affinity, slowly reversible complex. Through use of a [3H](+/-)carazolol binding assay based on the high affinity complex, pharmacological specificities of beta-adrenergic receptor populations of canine myocardium and lung were quantified. Analysis using computer-assisted techniques suggests a beta 1/beta 2 receptor ratio of approximately 85%/15% for canine myocardium and 5%/95% for canine lung. In the absence of added guanine nucleotides, comparison of potencies of beta-adrenergic agonists in the two membrane systems suggests significant beta 2 selectivity of l-isoproterenol and l-epinephrine, and non-selectivity of norepinephrine. In the presence of saturating levels of guanine nucleotides, comparison of agonist potencies confirms the non-selectivity of l-isoproterenol and l-epinephrine, and beta 1 selectivity of norepinephrine. These results demonstrate that the state of guanine nucleotide regulation of receptors should be defined when examining agonist selectivities for beta-adrenergic receptor subtypes in vitro.

Adrenergic beta-Antagonists↗
PubMed1980

Unmasking effect of alamethicin on the (Na+,K+)-ATPase, beta-adrenergic receptor-coupled adenylate cyclase, and cAMP-dependent protein kinase activities of cardiac sarcolemmal vesicles.

A mechanism for the activating effect of alamethicin on membrane enzymes was investigated, using a purified preparation of cardiac sarcolemmal vesicles. (Na+,K+)-ATPase, beta-adrenergic receptor-coupled adenylate cyclase, and cAMP-dependent protein kinase activities were measured. alamethicin increased ouabain-sensitive (Na+,K+)-ATPase activity of sarcolemmal vesicles 5- to 7-fold and adenylate cyclase activity 2.5- to 4-fold. Adenylate cyclase retained its sensitivity to the beta-adrenergic agonist isoproterenol after membranes were treated with alamethicin. Alamethicin caused a 4- to 6-fold increase in the number of detectable (Na+,K+)-ATPase enzymic sites, but no increase ws noted for the number of muscarinic-cholinergic receptor-binding sites. Phosphorylation of endogenous proteins of sarcolemmal vesicles by an intrinsic cAMP-dependent protein kinase activity was stimulated 5- to 7-fold by alamethicin. The regulatory subunit of the membrane-bound cAMP-dependent protein kinase was labeled with the photoaffinity probe 8-azido-adenosine 3':5'[32P]monophosphate (8-N3-[32P]cAMP), and it migrated with an apparent molecular weight of 55,000 in sodium dodecyl sulfate polyacrylamide gels. Alamethicin stimulated autophosphorylation of the regulatory subunit by [gamma-32P]ATP 6-fold and incorporation of of 8-N3-[32P]cAMP into the subunit 2.6-fold. The results suggest that alamethicin disrupts membrane barriers of sarcolemmal vesicles, which are mostly right side out, giving substrates and activators access to enzymic sites in the interior of the vesicles, while preserving functional coupling of enzymes to their effectors.

Adenylyl Cyclases↗
PubMed1979

Separation of vesicles of cardiac sarcolemma from vesicles of cardiac sarcoplasmic reticulum. Comparative biochemical analysis of component activities.

Sarcolemmal and sarcoplasmic reticulum membrane vesicle fractions were isolated from cardiac microsomes. Separation of sarcolemmal and sarcoplasmic reticulum membrane markers was documented by a combination of correlative assay and centrifugation techniques. To facilitate the separation, the crude microsomes were incubated in the presence of ATP, Ca2+, and oxalate to increase the density of the sarcoplasmic reticulum vesicles. After sucrose gradient centrifugation, the densest subfraction (sarcoplasmic reticulum) contained the highest (K+,Ca2+)-ATPase activity and virtually no (Na2+,K+)-ATPase activity, even when latent (Na+,K+)-ATPase activity was unmasked. In addition, the sarcoplasmic reticulum fraction contained no significant sialic acid, beta receptor binding activity, or adenylate cyclase activity. Sarcolemmal membrane fractions were of low buoyant density. Preparations most enriched in sarcolemmal vesicles contained the highest level of all the other parameters and only about 10% of the (K+,Ca2+)-ATPase activity of the sarcoplasmic reticulum fraction. The results suggest that (Na+,K+)-ATPase, sialic acid, beta-adrenergic receptors, and adenylate cyclase can be entirely accounted for by the sarcolemmal content of cardiac microsomes. Gel electrophoresis of the sarcolemmal and sarcoplasmic reticulum membrane fractions showed distinct bands. Membrane proteins exclusive to each of the fractions were also demonstrated by phosphorylation. Cyclic AMP stimulated phosphorylation by [gamma-32P]ATP of two proteins of apparent Mr = 20,000 and 7,000 that were concentrated in sarcoplasmic reticulum, but the stimulation was markedly dependent on the presence of added soluble cyclic AMP-dependent protein kinase. Cyclic AMP also stimulated phosphorylation of membrane proteins in sarcolemma, but this phosphorylation was mediated by an endogenous protein kinase activity. The apparent molecular weights of these phosphorylated proteins were 165,000, 90,000, 56,000, 24,000, and 11,000. The results suggest that sarcolemma may contain an integral enzyme complex, not present in sarcoplasmic reticulum, that contains beta-adrenergic receptors, adenylate cyclase, cyclic AMP-dependent protein kinase, and several substrates of the protein kinase.

Animals↗
PubMed1979

Adrenergaically mediated ventricular fibrillation in probucol-treated dogs: roles of alpha and beta adrenergic receptors.

A high incidence of sudden death due to ventricular fibrillation (VF) has been observed in dogs under chronic treatment with probucol, a new hypocholesterolemic agent. The present study describes the cardiac electrophysiologic properties of probucol-treated dogs and characterizes the electrophysiological response of these animals to manipulation of the autonomic nervous system. There was no significant difference in the spontaneous sinus cycle length, the QT interval, refractory period of the atrium, ventricle or A-V junction between normal and probucol-treated dogs. Epinephrine produced VF with few and sometimes no preceding premature ventricular extrasystoles. Electrical stimulation of the stellate ganglion induced VF in 16/19 dogs whereas stimulation of the right stellate ganglion induced VF in 1/19 dogs. Phenylephrine induced VF in 0/19 dogs, isoproterenol in 5/19 dogs, but phenylephrine + isoproterenol induced VF in 9/11 dogs in which isoproterenol did not produce VF. alpha (phentolamine) or beta (propranolol) blockade prevented initiation of VF by epinephrine, phenylephrine + is isoproterenol, and left stellate stimulation but alpha blockade did not prevent induction of VF by isoproterenol when isoproterenol alone produced VF. In this nonischemic model, we conclude that left stellate stimulation is a far more potent initiator of VF than right stellate stimulation and that induction of VF appears to require both alpha and beta adrenergic receptor stimulation.

Angiotensin II↗
PubMed1979

Acetylcholine antagonism of the electrophysiological effects of isoproterenol on canine cardiac Purkinje fibers.

The purpose of these experiments was to determine whether or not acetylcholine modulated the electrophysiological effects of isoproterenol on canine cardiac Purkinje fibers. Conventional microelectrode techniques were used. Predictably, isoproterenol produced shortening of action potential duration; acetylcholine significantly blunted this effect of isoproterenol. Isoproterenol restored excitability to fibers exposed to 22 mM potassium solutions, and acetylcholine abolished this isoproterenol-restored excitability. Both of these antagonistic effects of acetylcholine were blocked by atropine. Acetylcholine alone did not affect action potential duration in polarized fibers or excitability in potassium-depolarized fibers. Furthermore, acetylcholine had no effect on the decrease in action potential duration induced by premature electrical stimulation or by acetylstrophanthidin administration, or on excitability of fibers exposed to a zero sodium, high calcium superfusant. These data demonstrate a direct cellular basis for cholinergic antagonism of the electrophysiological effects of beta-adrenergic stimulation of canine cardiac specialized intraventricular conducting tissue.

Acetylcholine↗
PubMed1979

Calcium handling by cardiac sarcoplasmic reticulum.

Over the past ten years knowledge of the biochemistry of cardiac sarcoplasmic reticulum vesicles has been considerably extended. In almost all respects the Ca2+ pump of cardiac sarcoplasmic reticulum shows striking similarities to the Ca2+ pump of skeletal muscle sarcoplasmic reticulum. On the other hand, Ca2+ release mechanisms seem to be more complex in cardiac than in skeletal sarcoplasmic reticulum. Future research undoubtedly will involve characterizing the function of the many additional proteins present in cardiac sarcoplasmic reticulum, and determining possible roles for these proteins in regulating Ca2+ uptake and Ca2+ release by these membranes.

Animals↗
PubMed1979

Ryanodine: its alterations of cat papillary muscle contractile state and responsiveness to inotropic interventions and a suggested mechanism of action.

Cat right ventricular papillary muscles responded biphasically to cumulative additions of ryanodine. A progressive and pronounced negative inotropic effect was observed with low to intermediate ryanodine concentrations (5 nM-1 muM) while a rebound or reversal of these initial changes back toward pre-drug values was obtained as the ryanodine concentration was further increased to 100 muM. Active force development (DF), the rate of force development (dF/dt), as well as the rate of relaxation all exhibited these bidirectional changes. In contrast, time to peak force underwent only a progressive prolongation over the entire concentration range tested. This response pattern was observed with both normal and K+-depolarized (isoproterenol- or dibutyryl cAMP-restored) preparations. The response to a single addition of 100 muM ryanodine, in the presence of 2.5 mM Ca++ mimicked both the qualitative and quantitative aspects of the cumulative concentration response curve. In the presence of 5.0 mM Ca++ the high concentration of ryanodine no longer caused depression but instead caused only a slowly developing, monophasic increase in DF. Ryanodine also changed the response of ventricular muscle to other inotropic interventions. Ryanodine (1 muM; 2.5 mM Ca++) abolished the normal increase in dF/dt following either paired electrical stimulation (PES) or 50 mOsM mannitol, but not that in response to a doubling of the stimulation rate (0.2--0.4 Hz). After ryanodine exposure, the potentiation of developed force by PES was shifted from the first (regular) to the second (premature) contraction, producing a summation-like waveform. Prior addition of the calcium channel antagonist D600 (1 muM) did not alter ryanodine-induced changes in PES. Caffeine (1 mM) produced alterations in the responses to PES and hyperosmolarity which were similar to those observed with ryanodine. In the presence of high concentrations of both ryanodine (100 muM) and calcium (5 mM) both the transient and steady-state responses to a doubling of the stimulation rate (0.2--0.4 Hz) were markedly depressed, whereas the decrease in DF or dF/dt normally accompanying a reduction in the rate of stimulation was attenuated. The data obtained in the present study are consistent with a functional inhibition of sarcoplasmic reticular calcium release by ryanodine.

Alkaloids↗
PubMed1978

Muscarinic cholinergic receptor modulation of beta-adrenergic receptor affinity for catecholamines.

The effects of the muscarinic cholinergic agonist methacholine on affinity of beta-adrenergic receptors for isoproterenol and on isoproterenol-induced stimulation of adenylate cyclase activity were assessed in canine myocardium. GTP and guanyl-5'-yl imidoiphosphate both decreased the affinity of beta-adrenergic receptors for isoproterenol without altering the affinity of these receptors for propranolol. Methacholine (10 nM to 10 micronM) antagonized the guanine nucleotide-induced reduction in beta-adrenergic receptor affinity for isoproterenol. This effect of methacholine was reversed by atropine. The choline ester had no effect on the affinity of beta-adrenergic receptors for isoproterenol in the absence of guanine nucleotides. Likewise, methacholine had no effect on the affinity of beta-adrenergic receptors for propranolol, either in the presence or absence of guanine nucleotides. Methacholine also attenuated GTP-induced activation of adenylate cyclase or isoproterenol-induced activation of the enzyme in the presence of GTP. The effects of methacholine on myocardial adenylate cyclase activity were apparent only in the presence of GTP. These effects were also reversed by atropine. The choline ester had no effect on adenylate cyclase activity in the presence of guanyl-5'-yl imidodiphosphate or NaF. The results of the present study suggest that muscarinic cholinergic agonists can regulate both beta-adrenergic receptors and adenylate cyclase by modulating the effects of GTP.

Adenylyl Cyclases↗
PubMed1978

Effect of l-dopa on sympathetic nerve activity and blood pressure in the spontaneously hypertensive rat.

We examined the effect of L-Dopa, after peripheral L-amino acid decarboxylase inhibition, on sympathetic nerve activity (SNA) and blood pressure in spontaneously hypertensive rats (SHR) and in normotensive control rats. L-Dopa reduced SNA in both groups of animals. The SHRs were significantly more sensitive to the depressor effect of L-dopa than were the control animals, the threshold dose for reduction of SNA being 3 mg/kg in the SHR and 15 mg/kg in control rats. Similarly, the magnitude of inhibition of SNA was substantially greater in the SHR than in normotensive rats. The reduction in SNA in the SHR accompanied by a parallel fall in blood pressure. In contrast, blood pressure in control rats did not change significantly, even though SNA was diminished. Studies of the penetration of L-dopa into the cerebral parenchyma revealed that equivalent amounts of the amino acid entered the brains of the two groups of rats. These results suggest that the SHRs are more sensitive to the SNA-inhibiting effects of L-dopa than are normotensive rats. In addition, they confirm our previous suggestion that excessive SNA plays a causative role in the hypertension of the SHR.

Animals↗