Inhibitory effects of okadaic acid on rat uterine contractile responses to different spasmogens

Summary— In the present study, we examined the effects of okadaic acid, a selective inhibitor of type 1 and 2A protein phosphatases, on the mechanical responses evoked by oxytocin, K⁺- and Na+-modified solutions and ouabain in estrogen-primed rat myometrium. Oxytocin elicited a rapid, phasic contraction followed by rhythmic oscillations. The phasic response was partially resistant to the absence of external Ca²⁺. Okadaic acid (1 μM) and the L-type calcium channel blocker nifedipine (1 μM) abolished the oscillatory component and reduced the initial, phasic response to about 80% of the control response. High K⁺ (60 mM) solution, ouabain (1 mM), K⁺-free medium and low Na⁺ (25 mM) solution induced extracellular Ca²⁺-dependent biphasic responses composed by an early rapid (KCl, ouabain and K⁺-free solution) or slower developed (25 mM Na⁺ solution) phasic contraction followed by a sustained increase in tension. Okadaic acid and nifedipine, alone or in combination, abolished or decreased similarly the contractile response evoked by these stimulants. The okadaic acid- and nifedipine-insensitive responses to ouabain, K⁺-free and low Na⁺ solution were enhanced by increasing the extracellular concentration of Ca²⁺ in the medium and were inhibited in a dose-dependent manner by amiloride (0.05–0.5 mM). These data suggest that, in estrogen-primed rat uterus, dephosphorylating mechanisms by OA-sensitive protein phosphatases play an important role in regulating myometrial contractions elicited by Ca²⁺ entry through voltage-sensitive Ca²⁺ channels.     

Levcromakalim decreases vascular tone, cytoplasmic Ca2+ and Ca2+ sensitivity in canine basilar artery

Summary— The involvement of large conductance Ca²⁺-activated K⁺ channels (BK) and ATP-sensitive K⁺ (K_ATP) channels in the regulation of canine basilar arterial tone was estimated in the presence of the agonist and blockers of these channels, by simultaneously measuring the changes in intracellular Ca²⁺ concentration ([Ca²⁺]_i) with the fura-2 microfluorimetric method. In the resting condition, levcromakalim reduced [Ca²⁺]_i and vascular tone. Levcromakalim suppressed the serotonin-induced increases in [Ca²⁺]_i and force of contraction, the maximum effects of which were much greater than those of nicardipine. The inhibitory effects of levcromakalim were blocked by glibenclamide but not by tetraethylammonium (TEA) or iberiotoxin (IbTX). In the presence of levcromakalim, the curve relating [Ca²⁺]_i with force in the presence of serotonin at different extracellular Ca²⁺ concentration ([Ca²⁺]_o) was shifted down- and right-ward compared with that in the absence of levcromakalim, suggesting that levcromakalim may reduce the Ca²⁺-sensitivity of the contractile proteins. Thus, levcromakalim may be a good candidate to suppress delayed cerebral vasospasm after subarachnoid hemorrhage.     

Local and systemic effects of Na+/K+ ATPase inhibition

The positive inotropic and electrophysiological effects of cardiac glycosides on cardiac muscle are mediated through inhibition of Na⁺/K⁺ ATPase by binding to a specific extracytoplasmic site of the a-subunit of this enzyme. The inhibition of Na⁺/K⁺ ATPase affects ionic flux and produces direct local effects on cardiac contractility, electrical excitability and conduction, but also profound systemic effects mainly as a result of haemodynamic changes. These effects are responsible for beneficial therapeutic as well as toxic effects.
Inhibition of Na⁺/K⁺ ATPase results in potentiation of K⁺ loss from cells and Na⁺ entry into cells, so consequently affects action potential generation and propagation. This also underlines the potentiation of certain effects of cardiac glycosides by hypokalemia and hypomagnesaemia, and the effects of changes in calcium homeostasis on the cardiac glycoside pharmacodynamics. Furthermore, inhibition of Na⁺/Ca⁺⁺ exchange enhances Ca⁺⁺ mobilization and promotes contractility. These effects (locally and systemically) differ greatly, depending on the haemodynamic status and myocardial oxygen supply.
Cardiac glycosides have less affinity for Na⁺/K⁺ ATPases at other sites (e.g. skeletal muscle), but some extracardiac effects (vascular effects, effects on colour vision, CNS and autonomic effects, renal effects) may be related to Na⁺/K⁺ ATPase inhibition.     

Effect of colchiceine and ursodeoxycholic acid on hepatocyte and erythrocyte membranes and liver histology in experimentally induced carbon tetrachloride cirrhosis in rats

Colchiceine and ursodeoxycholic acid (UDCA) are drugs currently in use as therapy for different types of liver damage. We evaluated their ability to reverse the damage induced by carbon tetrachloride (CCl₄) in rats. Six groups were analysed: (1) CCl₄ (0.4 g kg⁻¹, i.p., three times a week) for 13 weeks; (2) CCl₄ for 8 weeks followed by colchiceine (60 μg kg⁻¹) + CCl₄ for 5 weeks; (3) CCl₄ for 8 weeks and thereafter UDCA (25 mg kg⁻¹) + CCl₄ for 5 weeks. Groups 4, 5 and 6 were appropriate controls of colchiceine, UDCA and vehicles respectively. Na⁺,K⁺- and Ca²⁺-ATPase activities and the cholesterol–phospholipid (CH/PL) ratio from erythrocyte and hepatocyte membranes were quantified. Membrane enzymatic activities and CH/PL ratios were affected more in group 1 than groups 2 and 3. We concluded that colchiceine and UDCA were effective drugs in this model of liver damage.     

Effects of K+ channel inhibitors and antagonists on NS-004 evoked relaxations in guinea-pig isolated trachea

Summary— The smooth muscle relaxant responses to NS-004, an activator of charybdotoxin-sensitive, large conductance Ca²⁺-dependent K⁺ channels (BKCa) were studied on the basal spontaneous tone in guinea-pig trachea in vitro. The sensitivity of these responses to a range of K⁺ channel inhibitors and antagonists were also evaluated. NS-004 (0.1–30 μM) evoked concentration-related relaxations (pIC₅₀ 5.48 ± 0.13) on the spontaneous tone in guinea-pig tracheal rings, suspended in Krebs bicarbonate solution, with a maximum response not different to that to aminophylline (1 μM). Charybdotoxin (0.03 and 0.1 μM) or iberiotoxin (0.1 μM) significantly displaced the NS-004 concentration-response curve to the right of control with no change in maximum response. In contrast, glibenclamide (1.0 μM), apamin (0.1 μM) and dofetilide (1.0 μM) each failed to modify the responses to NS-004 on spontaneous tone in guinea-pig trachea. These results suggest that relaxations in guinea-pig tracheal smooth muscle to the substituted benzimidazolone, NS-004, involve the activation of BK_Ca channels.     

Tonic block of the Na+ current in single atrial and ventricular guineapig myocytes, by a new antiarrhythmic drug, Ro 22-9194

Summary— Ro 22-9194 reduced the Na⁺ current in the atrial myocytes as well as ventricular myocytes in a tonic block fashion. Ro 22-9194 had a higher affinity to the inactivated state Na⁺ channels (Kd₁ = 3.3 μM in atrial myocytes, Kd₁ = 10.3 μM in ventricular myocytes) than to those in the rested state (Kd_R = 91 μM in atrial myocytes, Kd_R = 180 μM in ventricular myocytes), which indicated that Ro 22-9194 had a higher affinity to the Na⁺ channels in atrial myocytes than in ventricular myocytes. Ro 22-9194 shifted the inactivation curve in the hyperpolarized direction in both atrial and ventricular myocytes. These findings suggest that Ro 22-9194 more strongly inhibited the Na⁺ channel of the atrial myocytes of the diseased hearts with the depolarized membranes potentials than the Na⁺ channels in ventricular myocytes.     

Effect of serotonin and calcium in normal and sensitized guinea pig isolated trachea

Summary— Tracheal strips from normal and actively sensitized guinea pigs were studied to determine the responses to serotonin (5-hydroxytryptamine, 5-HT; 1 nM – 0.1 mM) and ouabain (0.1 μM – 0.1 mM), and the effects of increasing the extracellular calcium (Ca_o) concentration on tonic contractions elicited by 5-HT. Sensitized trachea exhibited an increased responsiveness and sensitivity to 5-HT and ouabain. Increases in Ca_o to achieve final concentrations of 5, 10 and 20 mM caused concentration-related relaxations of normal and sensitized tissues contracted to a similar plateau level with 5-HT. Inhibition of the Na⁺/K⁺-ATPase by ouabain (10 μM) reversed the effects of Ca_o from relaxation to contraction in normal and sensitized tissues contracted with 5HT. Sensitized preparations showed reduced relaxations in response to Ca_o (10–20 mM), and sensitized, ouabain-treated, trachea showed augmented contractions to Ca_o (10–20 mM) when compared to normal tissues. These results demonstrate a decreased membrane-stabilizing effect of Ca_o in sensitized trachea and the implication of the Na⁺/K⁺-ATPase in the regulation of membrane stability by Ca_o, suggesting a possible relevance to those mechanisms underlying airway hyperreactivity.     

CHANGES IN PLATELET FREE Ca2+ CONCENTRATION AFTER CHRONIC DIGOXIN TREATMENT

Summary— Cell Na+ and Ca²⁺ concentrations control each other by various mechanisms. In excitable cells from various origins, Ca²⁺ extrusion from the cell and its entry are dependent for a large part on the activity of the Na+, Ca²⁺-countertransport system. Cytosolic free Ca²⁺ concentration is also controlled by the Na+–H+ exchange activity. To analyze the changes in cytosolic Ca²⁺ concentration accompanying the reduction of the membrane Na+ gradient, cytosolic free Ca²⁺ concentration ([Ca²⁺]_i) was measured by fluorescent dyes in platelets and erythrocytes from healthy subjects, before and during digoxin treatment (0.25 mg/day for 6 days). [Ca²⁺]_i was increased in platelets from 169±30 to 321±61 nmol/l ( n = 7, P <0.02) and unchanged in erythrocytes (121±6 and 104±7 nmol/l). This increase in platelet [Ca²⁺]_i was not accompanied by a change in serotonin content (5.43±0.67 vs 5.49±0.61 10⁻⁷ mol per 10¹¹ cells) and could not be reproduced by in vitro addition of 10⁻⁴ mol/l ouabain (198±33 vs 186±73 nmol/l). The enhanced [Ca²⁺]_i in platelets is thus not a short-term consequence of a reduced membrane Na+ gradient, but reflects either the overload of intracellular Ca²⁺ stores or an enhanced in vivo stimulation by hormones or neurotransmitters.     

Y27632, a Rho-activated kinase inhibitor, normalizes dysregulation in alpha1-adrenergic receptor-induced contraction of Lyon hypertensive rat artery smooth muscle

RhoA-activated kinase (ROK) is involved in the disorders of smooth muscle contraction found in hypertension model animals and patients. We examined whether the α1-adrenergic receptor agonist-induced ROK signal is perturbed in resistance small mesentery artery (SMA) of Lyon genetically hypertensive (LH) rats, using a ROK antagonist, Y27632. Smooth muscle strips of SMA and aorta were isolated from LH and Lyon normotensive (LN) rats. After Ca²⁺-depletion and pre-treatment with phenylephrine (PE), smooth muscle contraction was induced by serial additions of CaCl₂. In LH SMA Ca²⁺ permeated cells to a lesser extent as compared with LN SMA, while CaCl₂-induced contraction of LH SMA was greater than that of LN SMA, indicating a higher ratio of force to Ca²⁺ in LH SMA contraction (Ca²⁺ sensitization). No hyper-contraction was observed in LH aorta tissues. Treatment of LH SMA with Y27632 restored both Ca²⁺ permeability and Ca²⁺-force relationship to levels seen for LN SMA. In response to PE stimulation, phosphorylation of CPI-17, a phosphorylation-dependent myosin phosphatase inhibitor protein, and MYPT1 at Thr853, the inhibitory phosphorylation site of the myosin phosphatase regulatory subunit, was increased in LN SMA, but remained unchanged in LH SMA. These results suggest that the disorder in ROK-dependent Ca²⁺ permeability and Ca²⁺-force relationship is responsible for LH SMA hyper-contraction. Unlike other hypertensive models, the ROK-induced hyper-contractility of LH SMA is independent of MYPT1 and CPI-17 phosphorylation, which suggests that ROK-mediated inhibition of myosin phosphatase does not affect SMA hyper-contractility in LH SMA cells.     

A single isoform of the Na+/K+-ATPase α-subunit in Diptera: evidence from characterization of the first extracellular domain

The first extracellular domain of the α-subunit of the Na⁺/K⁺-ATPase (sodium/potassium pump) is functionally important, affecting sensitivity of the enzyme to cardiac glycosides (e.g. ouabain) and being implicated in the transport of K⁺. This domain is also variable among mammalian isoforms of the α-subunit. Using PCR, we have isolated from seven insect species with contrasting physiologies a DNA fragment containing this region, in order to help determine whether tissue-specific expression might be associated with isoforms encoded by a gene family, as it is in mammals. A single sequence (with one ORF) characteristic of Na⁺/K⁺-ATPase was obtained from genomic DNA of each species. Only the fragment from Manduca sexta contained an intron, but at a location different to that found in mammals. For all Diptera so far characterized, the species phylogeny is the same as the α-subunit gene phylogeny (based on the sequences of the first extracellular domain and flanking transmembrane domains). The results strongly indicate a single, ouabain-sensitive isoform of the α-subunit of Na⁺/K⁺-ATPase is present in Diptera.     

The cytoplasmic Ca2+ response to glucose as an indicator of impairment of the pancreatic β-cell function

Abstract. The effects of glucose on the cytoplasmic Ca²⁺ concentration (Ca²⁺_i) regulating insulin release were investigated using pancreatic β-cells representative for the normal and diabetic situations. Increase of the glucose concentration resulted in a slight lowering of Ca²⁺_i followed by a rise, often manifested as high amplitude oscillations. The Ca²⁺_i-lowering component in the glucose action associated with suppression of insulin release became particularly prominent when the β-cells were already depolarized by tolbutamide. Glucose-induced inhibition of insulin release was observed also in experiments with rats made diabetic with streptozotocin or alloxan. Other studies indicated lowering of plasma insulin after intravenous glucose administration in patients with insulin- and noninsu-lin-dependent diabetes mellitus. Brief exposure of β-cells to 2–2 mmol 1^-1 streptozotocin resulted in impairment of the response to glucose, manifested as disappearance of the cyclic variation of Ca²⁺_i. The results indicate that glucose-induced depolarisation is a vulnerable process, the disturbance of which may contribute to insulin secretory defects in diabetes mellitus.     

Transforming growth factor β1 modulates angiotensin induced calcium influx in vascular smooth muscle

Abstract. The modulatory effects of transforming growth factor β₁ (TGF β₁) on the angiotensin II (Ang II)-induced increase in cytosolic free calcium concentration ([Ca²⁺]_i) were investigated in vascular smooth muscle cells (VSMC) from spontaneously hypertensive rats (SHR) and normotensive Wistar-Kyoto rats (WKY). [Ca²⁺]_i in VSMC was measured using the fluorescent dye fura-2. When TGF β₁ was applied 30 s prior to Ang II, the Ang II-induced [Ca²⁺]_i increase was significantly enhanced in VSMC from SHR ( P < 0.05 compared to control), whereas after the preincubation with TGF β₁ for 30 min, the Ang II-induced [Ca²⁺]_i increase was significantly reduced in VSMC from both strains. Using the manganese-quenching technique, it was confirmed that short-term exposure to TGF β₁ enhanced the Ang II-induced trans-plasma-membrane calcium influx in SHR. The inhibition of protein kinase C by calphostin C abolished the stimulatory effect of TGF β₁ on the Ang II-induced [Ca²⁺]_i increase. It is concluded that TGF β₁ modulates the Ang II-induced calcium handling in VSMC.     

Dynamics of the cationic and secretory responses to A-4166 in perifused pancreatic islets

Summary— The dynamics of the cationic and secretory response to A-4166, a hypoglycemic meglitinide analogue, was investigated in rat islets prelabelled with either ⁸⁶Rb or ⁴⁵Ca and placed in a perifusion system. In the absence of D-glucose, A-4166 (10 μM) provoked an immediate, sustained and rapidly reversible inhibition of ⁸⁶Rb outflow, this contrasting with a short-lived stimulation of insulin release. In the presence of 6 mM D-glucose, A-4166 provoked a rapid, sustained and rapidly reversible stimulation of both insulin release and ⁴⁵Ca efflux. The latter cationic response was suppressed in the absence of extracellular Ca²⁺, in which case A-4166 even caused a modest decrease in effluent radioactivity.
These findings support the view that A-4166 acts mainly in the islet B-cell by closing ATP-responsive K⁺ channels, leading to subsequent depolarization of the plasma membrane and gating of voltage-sensitive Ca²⁺ channels. Independently of the latter effect, A-4166 may also affect the intracellular distribution of Ca²⁺ ions. The present data further indicate that A-4166 belongs to those hypoglycemic agents that cause rapidly reversible changes in cationic and secretory events, at variance with highly potent sulfonylureas such as glibenclamide or glimepiride.     

Blockers of NMDA-operated channels decrease glutamate and aspartate extracellular accumulation in striatum during forebrain ischaemia in rats

Summary— Brain microdialysis was used to study changes in the glutamate and aspartate extracellular concentrations in the striatum of conscious rats submitted to 30 minutes cerebral ischaemia, using the four-vessel occlusion model. Perfusion of the N-methyl-D-aspartate (NMDA) receptor channel blockers, dizocilpine (MK-801; 75 μM) and Mg²⁺ (2.5 mM), inhibited the ischaemia-induced accumulation of glutamate and aspartate. The AMPA/kainate receptor antagonist, 2,3-dihydroxy-6-nitro-7-sulfamylbenzo (F) quinoxaline (NBQX; 15 μM and 450 μM) had no effect on glutamate and aspartate levels during ischaemia. On the other hand, omission of Ca²⁺ from the perfusing solution did not alter the increases in glutamate and aspartate induced by ischaemia. These results suggest that the glutamate and aspartate accumulation in four-vessel occlusion ischaemia is mediated by activation of NMDA receptors in a Ca²⁺ independent manner.     

Potentiating effects of nicorandil on the adenosine A2 receptor-mediated vasodepression in rats: potential role for KATP channels

Summary— The effects of nicorandil on systemic blood pressure (SBP) and heart rate (HR) responses to adenosine were compared with those to N⁶-cyclopentyladenosine (CPA), a selective adenosine A, receptor agonist, and 5'-(N-cyclopropyl)-carboxamidoadenosine (CPCA), a selective adenosine A₂ receptor agonist, in anesthetized rats. When injected intravenously (iv), single bolus doses of CPCA (0.01–1.0 μg/kg), like adenosine (30 μg/kg), elicited dose-dependent decreases in SBP scarcely affecting HR, while CPA (0.03–1.0 μg/kg) produced only reduction of HR without influencing SBP. The enhancement of the vasodepressor response to CPCA, like adenosine, was induced by the iv infusion of either nicorandil (10 μg/kg per min) or cromakalim (0.1 μg/kg per min), but the response to CPA in HR remained unmodified during the infusion of nicorandil as well as cromakalim. After iv treatment with glibenclamide (20 mg/kg), an adenosine triphosphate (ATP)-sensitive K⁺ channel blocker, or 3,7-dimethyl-1-propargylxanthine (DMPX) (1 mg/kg), a selective antagonist of adenosine A₂ receptor, not only CPCA action but also the enhancement of CPCA action by nicorandil and cromakalim were significantly attenuated. Similar results were obtained in the case of single bolus iv adenosine. The present result indicates that the augmentation of the adenosine action by nicorandil appears to be mediated by activation of ATP-sensitive K⁺ channels, closely linked with stimulation on A₂ receptors by adenosine.     

Cloning and sequence of a gene for a homologue of the C subunit of the V-ATPase from the salivary gland of the tick Amblyomma americanum (L.)

A 1084 base pair partial cDNA showing similarity to the C subunit of the vacuolar ATPase (V-ATPase) was isolated on a clone from a cDNA library made from salivary glands from 3-day-old feeding adult Amblyomma americanum (L.) female ticks. The 5' end was completed using primer extension and the two pieces joined to form a complete cDNA of 1373 bp. This mRNA is expressed in embryos and the salivary glands of unfed adults and adult females at all stages of feeding. Specific inhibitors of the V-ATPase decrease the rate of dopamine-stimulated secretion of isolated salivary glands, but not as much as ouabain, an inhibitor of the Na⁺, K⁺ ATPase, indicating that a V-ATPase may participate in the mechanism of salivary fluid secretion in A. americanum , but the volume of saliva secreted is more dependent on an active Na⁺, K⁺ ATPase.     

Electrophysiological Remodeling in Human Atrial Fibrillation

Atrial fibrillation (AF) is a progressive disease characterized by cumulative electrophysiological and structural remodeling of the atria. Cellular electrophysiological studies have revealed marked reductions in the densities of the L-type voltage-gated Ca²⁺ current, I_Ca,L, the transient outward K⁺ current, I_TO, and the ultra-rapid delayed rectifier K⁺ current, I_Kur, in atrial myocytes from patients in persistent or permanent AF. The density of the muscarinic K⁺ current (I_KACh) is also reduced, however the inward rectifier K⁺ current (I_K1) density is increased. The net shortening or lengthening of the action potential is dependent on the balance between changes in inward and outward currents. The prominent reduction in I_Ca,L appears to be sufficient to explain the observed decreases in action potential duration and effective refractory period that are characteristic of the fibrillating atria. Earlier studies have shown that calcium overload and perturbations in calcium handling play prominent roles in AF induced atrial remodeling. More recently, we have shown that AF is associated with evidence of oxidative injury to atrial tissue, and suggested that oxidative stress may directly contribute to the pathophysiology of AF. It is anticipated that insights gleaned from mechanistic studies will facilitate the development of improved pharmacological approaches to treat AF and to prevent the progression of arrhythmia. (PACE 2003; 26[Pt. II]:1572–1575)     

Erythrocyte Na+–H+ exchanger kinetics and Na+–Li+ countertransport activity in essential hypertensive patients

The authors measured Na⁺–H⁺ exchanger kinetics together with Na⁺–Li⁺ countertransport V _max in the erythrocytes of 21 subjects with essential hypertension and 16 normotensive control subjects. Na⁺–H⁺ exchanger V _max appeared to be increased in patients with essential hypertension, while the Na⁺–H⁺ exchanger affinity for intracellular proton sites ( K _50%) proved to be unchanged and the index of cooperativity among intracellular proton binding sites as measured by Hill's coefficient (Hill's n ) decreased as compared with normotensive control subjects. Na⁺–Li⁺ countertransport V _max appeared to be higher in patients with essential hypertension than in control subjects. The authors were unable to find any correlations between Na⁺–H⁺ exchanger kinetic parameters and metabolic variables such as parameters of insulin resistance and plasma lipids. On the basis of the data obtained, erythrocyte Na⁺–H⁺ exchanger activity was found to be abnormal in two kinetic variables in essential hypertensive patients and showed no simple linear correlations with the main variables of glucose metabolism, plasma lipids, renin or aldosterone.     

Interactions of calcium, magnesium and atropine on exocrine pancreatic secretion in man

Abstract. The effects of the intravenous administration of atropine or magnesium on pancreatic secretion which has been stimulated by secretin and induced hypercal-caemia have been studied in man.
In the presence of secretin (0.5 CU/kg.h) the infusion of Ca²⁺ (0.3 mmol/kg.105 min) resulted in an increase in secretion of enzymes by 100–200%, and in that of Ca²⁺ and Mg²⁺ by 50–100% without affecting fluid and bicarbonate secretion.
The additional injection of atropine (0.5 mg i.v. and 0.5 mg s.c.) were followed by a prompt fall in enzymes but not in Ca²⁺ and Mg²⁺ to the secretin-stimulated values.
The additional infusion of Mg²⁺ (0.12 mmol/kg.45 min) to the Ca²⁺-infusion did not alter the secretion of enzymes, Ca²⁺ or Mg²⁺ compared with the calcium infusion alone.
It is suggested that the hypercalcaemic stimulus depends on an intact innervation of the acinar cells.
In these experiments the secretion of Ca²⁺ and Mg²⁺ seem to originate mainly from extracellular fluxes.     

Transport ATPases of Cardiac Sarcolemma in 20, 25-Diazacholesterol Induced Myopathy

Abstract. 20, 25-Diazacholesterol, known to induce myotonia in skeletal muscle, also affects cardiac muscle as can be concluded from the development of cardiomegaly. At the same time (Na⁺, K⁺) ATPase of cardiac sarcolemmal membranes of the 20, 25-diazacholesterol treated rats showed an increased activity as compared with control animals (91 % and 46 % stimulation respectively). The Ca⁺⁺ stimulated ATPase showed the same tendency (96 % and 64 % stimulation).
In the plasma of the treated rats creatine phosphokinase activity was found to be elevated whereas the amount of protein-bound iodine was decreased, a finding that is common in myotonic dystrophy.