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Biomedical subjects

S Hynie

Publications and source records attributed to S Hynie.

At least 55 records · Page 3Linked to original sources
PubMed1991

[The effect of alpha adrenergic agents on lipolysis in rat adipose tissue; the effect of nonselective alpha adrenomimetics and alpha adrenolytics in an experiment in vitro].

It is now generally accepted, that in most of the animal species the adrenergic control of lipolysis from adipose tissue is mediated by adrenergic beta 1 and alpha 2 receptors. Therefore, the problem we deal with in this article is concerned with the role of alpha adrenergic receptors in lipolysis in the rat adipose tissue because only in this species the function of alpha adrenergic receptors in lipolysis is still not clear. In in vitro experiments with epididymal adipose tissue of adult rats (where we followed up the release of free fatty acids into the albumin medium) we found: 1) Alpha adrenergic blocking agents phentolamine and phenoxybenzamine had no influence on the lipid mobilizing effect of adrenergic agonists. This effect was absent also when drugs with the strong alpha sympathomimetic effects, e.g. norepinephrine and noroxedrine, were used. 2) On the other hand, alpha adrenergic agonist phenylephrine was able to antagonize in rat adipose tissue the lipid mobilizing effect of beta adrenergic agonist isoproterenol. 3) From our experiments it can be concluded, that phenylephrine acts as a competitive dualist on beta adrenergic receptors, it reduces the effect of full agonist (e.g. isoproterenol) to the level of its own maximum lipolytic effect. No participation of alpha adrenergic receptors in described effects of phenylephrine were detected, because neither the lipolytic, nor the lipolysis blocking effects of phenylephrine were influenced by alpha adrenergic blocking agents. Our studies using alpha adrenergic agonist phenylephrine or nonselective alpha adrenergic blocking agents did not indicate the presence of any alpha adrenergically controlled lipolysis in the rat adipose tissue. However, the role of antilipolytic alpha 2 adrenoceptors in rat adipose tissue cannot be completely excluded, some of these receptors were found on the membranes of rat adipocytes. Our future study deals with this problem.

Adipose Tissue↗
PubMed1990

Inhibitory effects of clonidine and dopamine on adenylate cyclase of rabbit ciliary processes.

The inhibitory effects of the alpha 2-adrenergic agonist clonidine and that of dopamine were studied on the adenylate cyclase activity in homogenates of ciliary processes. Clonidine inhibited in a dose-dependent manner basal adenylate cyclase activity as well as that stimulated by isoproterenol or forskolin. However, the adenylate cyclase activity stimulated by isoproterenol was sensitive to at least one order lower inhibitory concentrations of clonidine than basal or forskolin-stimulated adenylate cyclase. Dopamine inhibited adenylate cyclase stimulated by isoproterenol considerably less potently than clonidine. The slope of the dopamine dose-response curve was, however, similar to that of the dose-response curve of clonidine. The inhibitory effects of clonidine and dopamine were antagonized by an alpha 2-adrenergic antagonist, yohimbine, in a manner suggesting a competitive nature of this interaction. On the contrary, the inhibitory effects of neither clonidine nor dopamine were prevented by an alpha 1-adrenergic antagonist, prazosin. In addition, the effect of dopamine was not antagonized by the D2-antagonist, tiapride. Taken together, these results strongly indicate that both clonidine and dopamine exert their inhibitory effects by the stimulation of alpha 2-adrenergic receptors. Accordingly, they provide experimental evidence that both basal and drug-stimulated adenylate cyclase activity of ciliary processes can be inhibited via stimulation of alpha 2-adrenergic receptors. The substantially higher sensitivity of isoproterenol-stimulated than basal or forskolin stimulated adenylate cyclase to alpha 2-adrenergic inhibition seems to be a unique feature of this enzyme of ciliary processes. It is suggested that this may reflect an involvement of alpha 2-adrenergic receptors in the physiological feedback mechanism preventing the over-stimulation of adenylate cyclase of ciliary processes during excessive adrenergic drive.

Adenylyl Cyclase Inhibitors↗
PubMed1990

Inhibitory effects of neuropeptide Y on adenylate cyclase of rabbit ciliary processes.

The inhibitory effect of neuropeptide Y (NPY) was studied on the adenylate cyclase (AC) activity in homogenates of rabbit ciliary processes and compared with that of the alpha 2-adrenergic agonist clonidine (CLN). NPY inhibited basal AC activity as well as AC activity stimulated by isoproterenol (ISO), vasoactive intestinal polypeptide (VIP) or forskolin (FSK). The extent of this inhibition corresponded well to the inhibition elicited by CLN. The inhibitory effects of NPY and CLN appeared to be nonadditive. AC activity stimulated by ISO was considerably more sensitive to the effects of either NPY or CLN than basal, VIP- or FSK-stimulated AC activity. It was inferred that NPY inhibitory effects were mediated by the activation of NPY receptors coupled negatively to the catalytic unit of AC via the inhibitory Gi protein. Moreover, involvement of NPY in physiological modulation of AC activity in ciliary processes and in the regulation of aqueous humor formation and intraocular pressure is suggested.

Adenylyl Cyclase Inhibitors↗
PubMed1990

[2 different populations of adrenergic alpha receptors in the splenic capsule in rats].

Using the contraction of the smooth muscle of rat spleen capsula, studies of the character of the alpha-adrenergic receptors involved in this reaction where performed in vitro. By computer analysis, the flat dose-response curve of noradrenaline shows the presence of two different subpopulations of alpha-receptors, each being responsible for approximately 50% of the maximal overall contraction. The two subpopulations differ roughly one hundred times by their apparent affinity for noradrenaline (pD2 cca 8 and pD2 cca 6). Solely the high-affinity component is competitively antagonized by the alpha 1-blocker prazosin, needs necessarily extracellular Ca2+ for evoking the contraction and is desensitized by previous contact with a high concentration of noradrenaline. Neither of the two components is influenced in its action by calcium-channel blockers nifedipine and verapamil. The needed exogenous calcium thus enters the cell by different routes than by those affected by the mentioned blockers.

Animals↗
PubMed1990

[Closer characterization of alpha-receptor subpopulations in the smooth muscle of the splenic capsule in rats].

Two different subpopulations of adrenergic alpha-receptors -- "high-affinity" (pD2 less than 8) and "low-affinity" (pD2 less than 6) ones -- are involved in alpha-adrenergic contractions of the rat spleen muscle evoked by noradrenaline in vitro. Only the "high-affinity" subpopulation is agonistically influenced by the alpha 1-mimetic phenylephrine (pD2 cca 6, pKA cca 4.8), antagonistically influenced by prazosin (pA2 cca 9); it has a substantial receptor reserve for noradrenaline and a somewhat lower reserve for phenylephrine, it can be desensitized by these mimetics and it requires the presence of exogenous Ca2+ in the medium for evoking the contraction. -- Only the "low-affinity" subpopulation is agonistically influenced by the alpha 2-mimetic UK-14304. Both subpopulations are activated by noradrenaline and competitively blocked by yohimbine. The effect of neither subpopulation is influenced by nifedipine. According to the new classification (11) the "high-affinity" receptors can be described as alpha 1A, the "low-affinity" ones as alpha 2A. Contrarily to current data, the peculiar feature of this second subpopulation is a low affinity for yohimbine (pA2 less than 7) and a certain extent of blockability by phenoxybenzamine.

Animals↗
PubMed1989

[Membrane receptors and G regulatory proteins].

The article summarizes new findings concerning membranous receptor-effector complexes that are stimulated by various extracellular signals like hormones, neurotransmitters, growth factors, etc. Central role in this transmembranous signalling process play so-called G regulatory proteins (they bind GTP), that ensure the activation-deactivation processes between receptor and effector (enzymes or ion channels). The examples of intracellular signals ("second messengers") are cyclic AMP, inositol-trisphosphate, diacylglycerol or the accumulated ions (e. g. Ca2+). G regulatory proteins are composed of three subunits: receptor activation leads to their dissociation and the released alpha subunit with bound GTP activates the appropriate effector. Its inactivation occurs after GTP degradation by the intrinsic GTPase activity of alpha subunit which then associates with beta gamma subunits. New findings concerning the regulatory role of G proteins enable the explanation of mutual relations between various membranous receptor-effector complexes and further they also serve as basis for the explanation of some clinical disorders that are called "receptor diseases".

Animals↗
PubMed1989

Profile of phosphatidylinositol metabolism stimulated by carbachol and glutamate in primary cultures of rat cerebellar neurons.

The formation of inositol phosphates, after stimulation of primary cultures of cerebellar neurons of the neonatal rat, in the presence of lithium chloride, by glutamate, carbachol, norepinephrine, histamine and Mg2+-free conditions, was measured by anion exchange high-pressure liquid chromatography (HPLC) with on-line radioactivity detection. All of the above agents caused a persistent, dose-dependent and calcium-sensitive preferential accumulation of inositol-4-phosphate, while the levels of inositol-1-phosphate were virtually unaffected. Agonist stimulation produced also a transient increase of a second peak which co-eluted with the standard for inositol 1,4-bisphosphate. However, no significant accumulation of inositol-1,4,5-trisphosphate and inositol-1,3,4,5-tetrakisphosphate was detected, possibly due to the fast kinetics of the metabolism of inositol phosphate. The results indicate that receptor-stimulated metabolism of inositol phosphate, in cultures of cerebellar granule cells, is due to a preferential hydrolysis of polyphosphoinositides and leads to the formation of inositol-4-phosphate through several calcium- and lithium-sensitive enzymatic steps.

Animals↗
PubMed1987

Pertussis toxin inhibits negative inotropic and negative chronotropic muscarinic cholinergic effects on the heart.

We injected rats with pertussis toxin, known to cause ADP ribosylation of the Gi regulatory protein of the adenylate cyclase complex and of another closely related GTP binding protein in the heart, and after 7 days we examined several effects of muscarinic activation on the heart. The negative chronotropic effect of carbamoylcholine on spontaneously beating perfused hearts was conspicuously diminished. While 10(-5) mol/l carbamoylcholine invariably produced heart arrest in control rats, the heart rate did not decrease by more than 20% in the toxin-treated rats even when the concentration of carbamoylcholine was raised to 10(-2) mol/l. The negative inotropic effect of carbamoylcholine examined on electrically paced ventricles perfused with isoproterenol was reduced, while the maximum positive inotropic effect of isoproterenol was substantially increased after toxin treatment. The inhibitory action of carbamoylcholine on the isoproterenol-stimulated accumulation of cyclic AMP in the heart auricles was attenuated. The weakening by pertussis toxin of the negative inotropic effect of carbamoylcholine is probably mainly due to the ADP ribosylation of the Gi regulatory protein and the subsequent loss of influence of muscarinic receptors on adenylate cyclase. The blockade of the negative chronotropic action of carbamoylcholine by pertussis toxin strongly indicates, together with other recently published evidence, that the Gi or another closely related GTP binding protein in the cardiac pacemaker cells is involved in the coupling of muscarinic receptors to the K+ channels.

Adenylate Cyclase Toxin↗
PubMed1987

The action of pertussis toxin on heart adenylate cyclase and lipolysis in the parametrial adipose tissue of the rat.

Pertussis toxin is now used as an experimental tool for the study of receptor-mediated inhibitory systems. Based on our previous work, where we demonstrated in rats pretreated with pertussis toxin the blockade of negative chronotropic and reduction of negative inotropic effects of carbamoylcholine, we examined the effects of cholinergic agents on the rat heart adenylate cyclase activity. Pertussis toxin pretreatment reduced the inhibitory effects of cholinergic agents on adenylate cyclase activity only very slightly. This contrasts to the strong antagonistic effect on the phenylisopropyladenosine-induced inhibition of adrenergic lipolysis, including that increased lipolysis after 48 hours starvation. These data suggest that the strong inhibition of negative chronotropic effect of muscarinic drugs by pertussis toxin may be related to the recently described No protein rather then Ni protein from the adenylate cyclase complex.

Adenylate Cyclase Toxin↗
PubMed1986

Graphical orientation procedure for the estimation of Kd and Bmax values of ligand binding to two receptor subpopulations.

Within a few minutes, the procedure described here provides to the investigator, performing binding studies, information about Kd and Bmax values of two possibly present receptor subpopulations. The procedure is based on the comparison of the experimental curve with values of ligand binding to only one receptor population at 4 defined levels of radioligand binding. The binding parameters are derived from comparison of 4 horizontal deviations at these levels with tabulated deviations. Kd and Bmax values can be further confirmed by comparison of the experimental data with the simulated binding curve obtained by entering the binding parameters found in the formula for ligand binding to two receptor subpopulations. The practical use of this procedure was demonstrated both for simulated and for experimental data; it was confirmed by comparison with binding parameters obtained by computer programs used for the evaluation of receptor heterogeneity.

Kinetics↗
PubMed1986

A simple and rapid orientation procedure for the estimation of affinities (1/Kd) and maximum binding capacities (Bmax) of ligand binding to two receptor subpopulations.

This paper describes a simple and rapid procedure for the estimation of specific parameters (dissociation constants, Kd and maximum binding capacities, Bmax) of ligand binding to two receptor subpopulations. This procedure provides, in a few minutes, the investigator, performing the actual binding studies, the necessary information about receptor heterogeneity, enabling the investigator to plan further experiments. The procedure is based on the graphical comparison of experimental binding data (ligand binding to one or two receptor subpopulations) with the theoretical values of ligand binding to one receptor population at four levels). The values of Kd and Bmax for high- and low-affinity receptors are derived from 4 horizontal deviations of experimental data from a theoretical data plot at these levels by their comparison with tabulated deviations. The correctness of the estimated parameters can be confirmed by the comparison of experimental data with those simulated on the basis of applying the values of Kd and Bmax found in the formula for ligand binding to two receptor subpopulations. The practical applicability of this procedure was demonstrated both on simulated and experimental data, and confirmed by the well known computer programs for evaluating receptor heterogeneity, namely "LIGAND" and "Affinity spectra".

Kinetics↗
PubMed1985

Inhibitory effects of pentacaine and some related local anaesthetics on rat hepatic adenylate cyclase.

In the present study effects of a new local anaesthetics, pentacaine (trans-2-pyrolidinocyclohexylester of 3-pentyloxyphenylcarbamic acid), and of some chemically related compounds on rat hepatic adenylate cyclase activity were studied under various experimental conditions. As compared with tetracaine, the local anaesthetics tested showed stronger inhibitory effects, regardless of the type of stimulating agents used to activate adenylate cyclase. The most potent effect was observed with pentacaine. Its inhibitory effects on glucagon, guanylylimidodiphosphate (Gpp/NH/p), sodium fluoride or forskolin stimulated activity suggest that it may directly act on the catalytic unit of adenylate cyclase. The same conclusion can be drawn based on its inhibitory effects on adenylate cyclase, regardless ATP concentrations used as the enzyme substrate, and on octylpyranoside solubilized enzyme activated by preincubation of the enzyme preparation with Gpp/NH/p. Structure-activity studies have suggested that the pentacaine molecule as a whole and none of its parts alone or its analogs are responsible for the inhibitory effect. However, the inhibitory effects of these compounds on the rat adenylate cyclase activity do not correlate with their local anaesthetic properties. The possibility of using adenylate cyclase inhibitors to decrease cyclic AMP production under pathological conditions, like in cholera, known to be due to a high adenylate cyclase activity, is discussed.

Adenylyl Cyclase Inhibitors↗