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Glucose output was investigated in bivascularly perfused rat liver. Flow rate was 1 ml/min/g from hepatic artery and 2 ml/min/g from portal vein. Basal glucose output (130 +/- 30 microM/min) from bivascularly perfused liver was significantly (p less than 0.02) higher than that (80 +/- 20 microM/min) from usual monovascularly perfused (3 ml/min/g from portal vein) liver. However, glucagon-induced (1 ng/ml) increment in glucose output from bivascularly perfused liver 589 +/- 127 microM/30 min) was not significantly different from that (630 +/- 127 microM/30 min) of monovascularly perfused liver. These results suggest that glucagon-dependent glucose output was similar in monovascularly and bivascularly perfused rat liver, and that arterial blood supply may have some role in glycogenolysis in the perfused rat liver.

To evaluate the possible role of the adrenergic mechanism in hyperketonemia in hyperthyroidism and starvation, the plasma concentrations of FFA, acetoacetate (AcAc), and beta-hydroxybutyrate (BOHB) were measured in thyrotoxic and starved rats for 96 hours. Thyrotoxemia was induced in rats by a daily subcutaneous thyroxine (100 micrograms/kg/day) injection carried out for 7 days. Some of the thyrotoxic and starved rats were administered subcutaneous phentolamine (2 mg/kg, twice daily) or propranolol (0.1 mg/kg, twice daily). Plasma levels of FFA, AcAc, and BOHB were significantly increased in thyrotoxic and starved rats compared with the control rats. Phentolamine and propranolol administration did not alter plasma levels of FFA, AcAc, and BOHB in thyrotoxic rats. In starved rats, propranolol did not alter plasma levels of FFA, AcAc, and BOHB, however, phentolamine did increase plasma levels of FFA, AcAc, and BOHB. These results indicate that the adrenergic mechanism may not contribute to the hyperketonemia in thyrotoxic rats, but may have a slight inhibitory effect on ketogenesis in starvation probably due to alpha-antilipolytic action.

To determine the effect of maturation on glucose-induced insulin release after starvation, we investigated the insulin release from perfused pancreas of young adult rats after fasting for 18-20 hr. In the rats weighing 300-400 g (12-14 w) and 200-250 g (7-8 w), the glucose-induced insulin secretion from perfused pancreas of starved rats was similar to that of fed rats. While, in the rats weighing 100-150 g (4-5 w), both the first and the second phase of glucose-induced insulin secretion from perfused pancreas of starved rats was markedly decreased compared with that of fed rats. These results suggest that insulin response to glucose is not matured in young below 150 g (5 w).

1. 1. The quinidine-induced modification of intracellular Ca 2+ concentration ([Ca 2+ ] i ) was studied in guinea-pig myocardium using fura-2. Quinidine reduced the systolic fluorescence signal level for [Ca 2+ ] i and enhanced the end-diastolic signal level during a stimulation train. 2. 2. The diastolic decay of [Ca 2+ ] i fitted 2 exponential curves. Quinidine distorted the stimulation frequency-dependent acceleration of rapid [Ca 2+ ] i decay, and prolonged the mean time constant of rapid decay after 2 Hz stimulation, from 154.4 to 205.3 msec (20 μM), and to 259.7 msec (60 μM quinidine). The time constant of slow recovery from [Ca 2+ ] i accumulation after the stimulation train was not affected by stimulation frequency, or by quinidine, or caffeine. 3. 3. These results suggest that quinidine modulates [Ca 2+ ] i via a balance between the slowing of rapid [Ca 2+ ] i decay and the reduction of the systolic [Ca 2+ ] i . This effect may contribute to the anti-arrhythmic and pro-arrhythmic effects exerted by quinidine in some conditions.

To elucidate the effects of fatty acids on the uptake of glucose and insulin in the muscle, the effects of oleic and palmitic acids on the uptake of glucose and insulin were investigated in perfused hind-quarters of rats. In the absence of insulin, glucose uptake in the hindquarter was slightly, but not significantly, decreased by the addition of oleic and palmitic acids. In the presence of 100 or 500 microU/ml insulin, glucose uptake in the hindquarter (243 +/- 58 or 282 +/- 65 mumol/30 min) was significantly decreased by the addition of 1000 microM oleic acid and 500 microM palmitic acid (175 +/- 50 or 207 +/- 47 mumol/30 min). The decrease in insulin uptake rate, although not significant at 500 microU/ml insulin, is of similar magnitude to the decrease in glucose uptake. In the presence of 1000 microU/ml insulin, glucose and insulin uptake was not significantly altered by the addition of fatty acids. These results indicate that fatty acids directly inhibit the muscular glucose uptake via the decrease in muscular insulin uptake at a physiological concentration of insulin.

The use-dependent effects of cibenzoline, a new anti-arrhythmic drug, on the maximal rate of rise (Vmax) of the action potential and on conduction velocity, and their corresponding recovery kinetics were studied in isolated papillary muscles of guinea pigs under normal and hypoxic conditions. Standard microelectrode techniques were applied to monitor the action potential of the muscles and their conduction. Under control conditions, the amount of use-dependent block of Vmax, conduction velocity, and square of conduction velocity, induced by 10 mumol/L cibenzoline were 26.5 +/- 3.9, 13.8 +/- 1.4, and 25.6 +/- 2.4%, respectively; under hypoxic conditions, these values increased to 32.3 +/- 4.8, 19.7 +/- 1.2, and 35.5 +/- 2.0%, respectively. In the presence of 10 mumol/L cibenzoline, the mean values of time constants for the onset of the use-dependent inhibition of Vmax, conduction velocity, and the square of conduction velocity, during a 2-Hz stimulation, were 3.65 +/- 0.27, 2.77 +/- 0.33, and 2.56 +/- 0.26 seconds, respectively. Under hypoxic conditions, these values changed to 5.10 +/- 0.96, 3.05 +/- 0.44, and 2.84 +/- 0.39 seconds, respectively. The recovery time constants averaged 14.72 +/- 4.08 seconds (for Vmax), 22.23 +/- 3.78 seconds (for conduction velocity), and 23.17 +/- 13.38 seconds (for the square of conduction velocity) in the presence of 10 mumol/L cibenzoline, and 17.19 +/- 8.59 seconds (for Vmax), 15.77 +/- 2.37 seconds (for conduction velocity), and 16.82 +/- 2.61 seconds (for the square of conduction velocity) under hypoxic conditions.(ABSTRACT TRUNCATED AT 250 WORDS)

1. 1. The relationship between the negative inotropic and chronotropic effects of tocainide and 5 other class I antiarrhythmic drugs was evaluated in Langendorff-perfused guinea-pig hearts. 2. 2. All 6 drugs reduced the contractile force (Fc) and the heart rate (HR) of spontaneously beating guinea-pig hearts in a dose-dependent manner. The order of crude negative inotropic potency was: quinidine (Qui) = aprindine (Apr) > mexiletine (Mex) > lidocaine (Lid) > disopyramide (Dis) > tocainide (Toc); and the order of negative chronotropic effect was: Apr > Qui > Mex > Dis > Lid > Toc. 3. 3. The order of the negative inotropic potency relative to chronotropic effect (expressed as a ratio: ID 50 for Fc/ID 50 for HR) was Lid > Qui > Dis > Toc > Mex > Apr ( n = 6). 4. 4. For heart electrically stimulated at a constant rate, the order of crude negative inotropic potency was: Apr > Qui > Mex > Dis > Lid > Toc, and the order of negative inotropic potency (determined by the ratio: ID 50 for Fc in driven heart/ID 50 for spontaneously beating HR) was: Mex > Apr > Toc > Dis > Qui > Lid ( n = 6). 5. 5. There was a significant influence of negative chronotropic effect on the inotropic potency and the order was: Lid > Qui > Dis > Toc > Apr > Mex. The potency of various drugs is clinically useful in the choice of drugs when considering cardiac function and heart rate.

To elucidate the peripheral disposal of ketone bodies in hyperketonemia accompanied with starvation, hyperthyroidism, or diabetes mellitus, the uptake of acetoacetic acid (AcAc) and beta-hydroxybutyrate (BOHB) was investigated in the perfused hindquarter and kidney of starved, thyrotoxic, and diabetic rats. Thyrotoxicity was induced by daily subcutaneous injection of thyroxine (100 micrograms/kg/day) for 7 days, and diabetes mellitus was induced by intraperitoneal streptozotocin (50 mg/kg) injection. Plasma concentration of AcAc and BOHB was significantly higher in starved, thyrotoxic, and diabetic rats than in controls. The hindquarter or kidney of rats was perfused with synthetic medium containing 0.2 or 1.5 mM AcAc or BOHB for 30 min at a flow rate of 0.5 ml/g muscle wt/min or 3.2-3.5 ml/kidney/min, respectively. In perfused hindquarter, the uptake of AcAc and BOHB was significantly reduced in starved and diabetic rats, but not in thyrotoxic rats. In perfused kidney, the uptake of AcAc and BOHB was not significantly different between the experimental and control rats. These results suggest that in starvation or diabetes mellitus, disposal of AcAc and BOHB was impaired in the hindquarter but not in the kidney, and that disposal of AcAc and BOHB by hindquarter and kidney was not impaired in thyrotoxic rats.

The effects of hypoxia on the beta-adrenoceptor-mediated slow channel responses of guinea pig ventricular muscle in a potassium-rich (27 mM) solution containing Ba2+ were examined using microelectrode techniques. Isoproterenol produced a small depolarization of the resting membrane and also induced repetitive discharges of action potentials at higher concentrations, mainly due to a beta-adrenoceptor-mediated increase in the slow channel conductance. Two different threshold concentrations of isoproterenol, one for inducing depolarization and one for inducing automatic activity, were measured to assess myocardial responsiveness to catecholamines. During hypoxia, the electrically triggered slow upstroke action potentials of muscle were gradually depressed and catecholamine-induced membrane responses mediated by the beta-adrenoceptor/slow channel system were enhanced. The enhancement of the catecholamine effects was accelerated by acidosis and reversed by reoxygenation. Methyl xanthine-induced responses, similar to those induced by catecholamines, were also enhanced during hypoxia. It is suggested that not only changes of catecholamine-beta-adrenoceptor interaction, but also changes of intracellular metabolic processes, may be responsible, at least in part, for the enhancement of abnormal automatic activity mediated by the myocardial beta-adrenoceptor/slow channel system under hypoxic conditions.

Using the perfused liver and hindquarter of the rat, the uptake of glycosylated insulin and its effect on glucose output were investigated. Insulin was glycosylated in ambient high glucose concentration, and glycosylated insulin GI80 (insulin incubated with 0.08% glucose), GI350 (incubated with 0.35% glucose), and GI1000 (incubated with 1% glucose) were prepared. The liver and hindquarter were perfused with nonglycosylated insulin (N-GI) or glycosylated insulin at a concentration of 100 or 1000 microU/ml. There were no significant differences in the fractional uptake of insulin by perfused liver and hindquarter despite glycosylation. Insulin-induced decrement in glucose output was significantly lower in the liver perfused with GI1000 than that in the liver perfused with N-GI, GI80, and GI350 at an insulin concentration of 100 microU/ml. There were no significant differences in insulin-induced decrement in glucose output between the hindquarter perfused with N-GI, GI80, GI350, and GI1000. These results suggest that when insulin (100 microU/ml) is incubated with a markedly elevated concentration of glucose (1000 mg/dl) its biological activity is reduced in the liver, but not in the hindquarter.

To elucidate the peripheral ketone body uptake and the role of insulin in regulating peripheral ketone body utilization in starvation and diabetes mellitus, uptake of beta-hydroxybutyrate (BOHB) was investigated in the perfused hindquarter of starved (72 hour) or streptozotocin-induced (65 mg/kg, intraperitoneally) diabetic rats. Blood concentration of BOHB was significantly higher in diabetic (1,380 +/- 250 mumol/L) and starved (1,229 +/- 245 mumol/L) rats than in controls (104 +/- 8 mumol/L). The hindquarter was perfused with synthetic medium at a flow rate of 0.5 mL/g muscle weight/min. BOHB was added to the medium at a concentration of 0.1, 0.5, 2, or 10 mmol/L, and insulin was added at a concentration of 20, 100, or 500 microU/mL. In the hindquarter perfused with 0.1, 0.5, 2, or 10 mmol/L BOHB, fractional uptake of BOHB in the absence or presence of insulin was significantly lower in diabetic and starved rats than in controls. The addition of 100 or 500 microU/mL insulin significantly increased BOHB uptake in the perfused hindquarter of control rats; however, insulin addition did not significantly increase BOHB uptake in the perfused hindquarter of starved and diabetic rats. These results suggest that BOHB uptake is markedly reduced in the perfused hindquarter of starved and diabetic rats, and that physiological dose of insulin stimulates BOHB uptake in control rats, but not in starved and diabetic rats.

The electrophysiological effects of urapidil, a new alpha 1-adrenoceptor antagonist, were assessed in the reserpinized guinea-pig ventricular myocardium. Urapidil suppressed the maximal rate of rise (Vmax) of steady-state action potentials elicited by the fast responses at high concentrations independently of blockade of myocardial alpha-adrenoceptors, but not the Vmax of Ca(2+)-dependent slow action potentials of partially depolarized muscles in concentrations tested (up to 1.1 mM). Urapidil at high concentrations prolonged the action potential durations of the fast and slow responses in a manner similar to the quinidine-like antiarrhythmic drugs. These results suggest that the inhibitory effect of urapidil on the slow inward Ca2+ current and the Na+ current is in practice negligible.

Study objective – The aim was to investigate whether the use dependent effects of antiarrhythmic drugs on the Na+ current could be applied to explain their effects on impulse conduction. Design – Trains of rapid stimuli were applied to guinea pig papillary muscles via an electrode in the presence of quinidine (20 and 60 μmol·litre−1), and the conduction velocity was determined from the time difference between two signals of the maximal rate of rise (dV/dtmax) of the action potentials at two separate sites. The relationship of the time constants of the onset and recovery from the use dependent inhibition induced by quinidine was determined for the dV/dtmax and the conduction velocity. Experimental material – Six male Hartley guinea pigs weighing 200 to 300 g were killed by a blow to the head and the papillary muscles were rapidly excised from the right ventricles. The preparations were superfused with Tyrode solution. Measurements and main results – The rate of onset of the use dependent inhibition of conduction velocity and that of the square of conduction velocity were both faster than the simultaneously measured rate of onset of dV/dtmax inhibition induced by 20 μmol·litre−1 quinidine at high frequency stimulation. The relation between the rates of onset of the use dependent inhibition of conduction velocity (and the square of conduction velocity) and dV/dtmax became weak with low frequency stimulation and in the presence of 60 μmol·litre−1 quinidine. However, the recovery of conduction velocity (and the square of conduction velocity) from quinidine induced use dependent blockade, as measured by the extrastimulation method, appeared to be slower than the recovery of dV/dtmax. These results may be explained by a transient change in intracellular and intercellular conditions, such as an increase in internal resistance. Conclusions – The onset and recovery of the use dependent inhibition of conduction by antiarrhythmic drug may not always parallel the changes of the dV/dtmax of action potential in multicellular muscle preparations.

1. Effect of bunazosin, an alpha 1-adrenoceptor antagonist, upon the slow inward Ca2+ current (ICa) was studied in single ventricular myocytes of the guinea-pig using a whole-cell patch-clamp technique. 2. Bunazosin (10-100 microM) decreased ICa in a concentration-dependent manner with an IC50 of 60 microM during depolarization to + 10 mV from the holding potential of -40 mV. 3. As for the inactivation process of ICa, the steady-state inactivation (f infinity) curve was shifted toward more negative potentials from -12 mV to -17 mV and -21 mV at f infinity = 0.5, by 30 microM and 70 microM bunazosin. 4. Inhibition of ICa by the compound (10 microM) was also dependent on stimulation frequency, with greater block induced at 2 Hz (50%) than at 0.33 Hz (13%). 5. It is concluded that bunazosin possesses a direct Ca2+ channel-blocking (class 4) action in a rate-dependent fashion.

To elucidate the possible role of the stomach in enteroinsular axis, rats had both an inflow gastric cannula and an outflow diversion cannula and a duodenal inflow cannula. The effects of intragastric infusion of glucose (1 mL in 10% solution) or mannitol (1 mL in 10% solution) on blood glucose and plasma insulin responses to subsequent intraduodenal glucose (1.5 g/kg in 10% solution) or amino acids (1.0 g/kg in 10% solution) infusion were investigated. Blood glucose and plasma insulin responses to intraduodenal amino acids were not altered by intragastric infusion of glucose or mannitol. However, higher blood glucose and lower plasma insulin responses to intraduodenal glucose were observed in the rat with intragastric infusion of glucose or mannitol compared with controls (intragastric infusion of distilled water). This phenomenon was abolished in the rat with preadministration of phentolamine. These results suggest that intragastric tonicity may suppress glucose-induced insulin secretion, probably through the α-adrenergic mechanism in the rat.

To elucidate the effect of intestinal osmolality on insulin secretion, we investigated insulin response to a subsequent intravenous infusion of glucose or arginine after intragastric or intraduodenal mannitol or NaCl instillation in the rat. After anesthesia with intraperitoneal pentobarbital sodium, mannitol solution (10% or 20%) or 2.7% NaCl was instillated into the stomach or duodenum for 5 min at a flow rate of 0.5 ml/min, and 20% glucose (0.5 g/kg) or 10% L-arginine (0.5 g/kg) was infused bolus into the femoral vein 45 min after intestinal instillation. Insulin response to intravenous glucose was significantly higher in the rat with intragastric or intraduodenal mannitol or NaCl infusion than in control rats with intragastric or intraduodenal instillation of distilled water. Insulin response to intravenous arginine was almost the same in all groups. Subcutaneous preadministration of propranolol (0.4 mg/kg), atropine (1.2 mg/kg), or phentolamine (0.8 mg/kg) did not alter the present phenomenon. These results suggest that intestinal osmolality may enhance insulin release to intravenous glucose, but not to arginine in the rat.

Under whole cell patch conditions, 1389-S blocked the I Na in guinea-pig ventricular myocytes under steady state conditions (K d rest = 30 μ M, K d i = 2.4 μ M) with a shift of the inactivation curve to the hyperpolarizing direction. Both brief and long conditioning pulses could produce a use-dependent block of 1389-S. These results suggest that 1389-S had a higher affinity to the inactivated than to the rested state under steady state conditions and had a higher affinity to the activated state during train pulses as well as to the inactivated state, making channels unavailable for conduction upon activation.

1. The use-dependent effects of pirmenol, a new antiarrhythmic drug, on the maximal rate of rise (Vmax) of the action potential, conduction velocity, and their corresponding recovery kinetics were studied in isolated papillary muscles of guinea-pig. Standard microelectrode techniques were used to monitor the conduction and action potential characteristics of the muscles. 2. Pirmenol decreased Vmax and the overshoot of action potentials in a dose-dependent fashion. Also, doses of pirmenol greater than 1 mM abolished the generation of action potentials. Low concentrations of pirmenol (3 and 10 microM) prolonged the action potential duration, while concentrations greater than 0.1 mM shortened it markedly. 3. The resting block of Vmax in the presence of 10 and 30 microM pirmenol was 9.48 +/- 3.12 and 20.36 +/- 3.61%, and that of conduction velocity 2.87 +/- 1.52 and 6.58 +/- 2.09%, respectively. 4. The degree of use-dependent block induced by 10 and 30 microM pirmenol during 0.2, 1, 2 and 3 Hz stimulations was dose- and rate-dependent. 5. In the presence of 30 microM pirmenol, mean values of time constants for the onset of the use-dependent inhibition of Vmax and conduction velocity during a 2 Hz stimulation were 1.32 +/- 0.15 and 1.28 +/- 0.09 s, respectively. The recovery time constants averaged 15.83 +/- 2.14 (for Vmax) and 27.80 +/- 8.74 (for conduction velocity) s in the presence of 30 microM pirmenol. 6. These results showed that the characteristics of the use-dependent inhibition of Vmax and conduction velocity induced by pirmenol are similar to those of slow kinetic drugs such as disopyramide rather than of fast ones.

1. The electrophysiological effect of 9-amino-1,2,3,4-tetrahydroacridine (THA) on the rabbit sino-atrial node was studied using double-microelectrode voltage clamp methods. 2. THA (above 10 μM) caused statistically significant decreases in the maximum rate of rise, the action potential amplitude, the rate of diastolic depolarization, and increases in the spontaneous cycle length, the action potential duration at 50% repolarization. 3. On the current systems, THA obviously depressed the time-dependent outward K+ current. The compound also decreased the slow inward Ca2+ current and the hyperpolarization-activated inward current. 4. These findings indicate that THA exerts an inhibitory action on the automaticity of sino-atrial node via effects on both outward and inward current systems.

Study objective – To examine the effect of 9-amino-1,2,3,4-tetrahydroacridine (THA), a compound similar to the K+ blocker 4-aminopyridine, on potassium channels in the sinoatrial node. Design – The pace making portion of rabbit sinoatrial nodes was studied using the double microelectrode voltage clamp method in the presence of THA at various concentrations. Measurements and results – Above 1 μmol·litre−1, THA prolonged the spontaneous cycle length and the transmembrane action potential duration at 50% repolarisation. Above 10 μmol·litre−1, the compound also decreased the maximum rate of rise, the action potential amplitude, and the rate of diastolic depolarisation. Under voltage clamp conditions, THA reduced the time dependent K+ current (IK) in a dose dependent manner. Neither the decay process of IK nor its activation process were altered by THA. Conclusions – THA depresses sinoatrial node IK without changing its kinetics. Thus it may inhibit the open state of the potassium channels.

Using perfused liver of the rat, the hepatic uptake of glycosylated insulin (GI) and glucagon (GG) and its effects on hepatic glucose output were investigated. Insulin and glucagon were glycosylated in ambient high glucose concentration, and GI80 or GG80 (insulin or glucagon incubated with 0.08% glucose), GI350 or GG350 (incubated with 0.35% glucose), and GI1000 or GG1000 (incubated with 1% glucose) were prepared. The liver was perfused with the medium containing 1000 microU/ml insulin and 200 pg/ml glucagon or 200 microU/ml insulin and 1000 pg/ml glucagon. The fractional uptake of insulin or glucagon by perfused liver was not significantly altered by the glycosylation. In the liver perfused with 1000 microU/ml insulin and 200 pg/ml glucagon, glucose output was not changed by the glycosylation of the hormones, while in the liver perfused with 200 microU/ml insulin and 1000 pg/ml glucagon, GI1000 reduced its biological activity, as reflected by insulin-mediated decrease in glucose output. These results suggest that in the liver insulin incubated with markedly high concentration of glucose reduces its biological activity at a physiological concentration in the presence of high concentration of glucagon.

1. Effects of bepridil, a sodium-, calcium-, and potassium-antagonistic agent, on the Na+ current were studied by the whole cell voltage clamp technique (tip resistance = 0.5 MOhm, [Na]i and [Na]o 10 mmol l-1 at 20 degrees C). 2. Bepridil produced tonic block (Kdrest = 295.44 mumol l-1, Kdi = 1.41 mumol l-1; n = 4). 3. Bepridil (100 mumol l-1) shifted the inactivation curve in the hyperpolarization direction by 13.4 +/- 2.7 mV (n = 4) without change in the slope factor. 4. In the presence of 50 mumol l-1 bepridil, bepridil showed use-dependent block at 2 Hz, whereas changes in pulse duration did not significantly effect this use-dependent block (81% +/- 2% at 10 ms, 84% +/- 3% at 30 ms, 86% +/- 3% at 100 ms; n = 4). 5. After removal of fast inactivation of the Na+ current by 3 mmol l-1 tosylchloramide sodium, bepridil (50 mumol l-1) still showed use-dependent block which was independent of the holding potential. 6. The recovery time constant from the bepridil-induced use-dependent block was 0.48 s at holding potential of -100 mV and 0.51 s at holding potential of -140 mV. 7. These results indicate that bepridil could bind to the receptor in the sodium channel through the hydrophobic and the hydrophilic pathway and leave the receptor through the hydrophobic pathway in the lipid bilayer. The binding and dissociation kinetics of this drug were shown to be fast, and the accumulation of the drug in the sodium channel appeared to be small. Bepridil is presumed to be safe in terms of adverse effects that result from drug-accumulation in the sodium channel.

Summary 1. We investigated the cardiovascular effects of intracerebroventricularly administered (ICV) growth hormone-releasing factor (GRF) in both spontaneously hypertensive rats (SHR) and Wistar rats (WR) with reference to the involvement of adrenergic mechanisms and plasma AVP concentration. 2. The ICV GRF induced biphasic changes of mean arterial pressure (MAP) in SHR. In the first phase, maximum pressor response was observed 2–3 min after injection. In the second phase, maximum depressor response was observed 12–13 min after injection, and lasted up to 21–22 min. In WRY there were no significant changes in MAP. 3. ICV phentolamine attenuated the GRF-induced pressor response, but did not affect the depressor response. ICV bunazosine had no effect in both responses. ICV yohimbine attenuated the GRF-induced pressor response, but did not affect the depressor response. 4. In SHR, plasma AVP concentration was not affected by ICV GRF. 5. These data suggest that central GRF plays an important role in the maintenance of hypertension in SHR, since ICV GRF caused a significant depressor effect in SHR but not in WR. ICV GRF induced biphasic changes of MAP in SHR. The pressor response was mediated through central α2-adreno-ceptors. The depressor response was not mediated through central α-adrenoceptors. The depressor effect of ICV GRF was not mediated by the changes of plasma AVP concentration.

We found a TSH-dependent K + channel in the membrane of a rat thyroid cell line (FRTL-5 cell). This K + channel is activated by extracellular application of the thyroid stimulating hormone (TSH). Treatment of dibutyryladenosine cyclic monophosphate (Bt 2 cAMP) also activated the TSH-dependent K + channel. Intracellular application of protein kinase A activates this K + channel without the presence of free Ca 2+ . These findings indicate that the thyroid K + channel is activated through the TSH-cAMP-protein kinase A system. This is the first report of a polypeptide hormone activated K + channel and it should be useful for examining the effects of this K + channel on thyroid cell functions.

Gastric inhibitory polypeptide (GIP) and glucagon-like peptide-1(7-36) amide (GLP-1) are thought to be the most probable candidates for incretin. However, the precise mechanism of incretin effect is unclear. In the present study, to elucidate the possible role of the autonomic nervous system in incretin effect, the effects of atropine, propranolol, metoprolol, and phentolamine on GIP- or GLP-1-induced insulin release were investigated in the rat. The GIP-induced (2 or 20 micrograms) insulin release was partly inhibited by propranolol pretreatment (0.5 mg/kg subcutaneously [SC]), and GLP-1-induced (2 or 20 micrograms) insulin release was partly inhibited by propranolol or metoprolol (35 mg/kg SC). These results suggest that a beta-adrenergic mechanism may be involved in the incretin effect, probably through a modulating effect on GIP- or GLP-1-induced insulin secretion.

Using a bivascularly perfused rat liver, we investigated the hepatic extraction and hepatic action on glucose output of insulin, glucagon, and epinephrine. The liver was perfused for 70 min without recirculation via the portal vein and hepatic artery (3.0 ml/(min.g liver) from portal vein and 1.0 ml/(min.g liver) from celiac artery). Low and high concentration of insulin, glucagon, or epinephrine (450 and 4,500 pM, 21.5 and 215 pM, or 410 and 4,100 pM, respectively) was added to the perfusing medium via portal vein (P-liver), via celiac artery (H-liver), or via portal vein and celiac artery (H-P-liver). Hepatic extraction of insulin, glucagon, or epinephrine was not significantly different among H- (56 +/- 9 and 21 +/- 5%, 31 +/- 7 and 24 +/- 6%, or 22 +/- 8 and 17 +/- 5%), P- (50 +/- 10 and 23 +/- 6%, 32 +/- 9 and 23 +/- 7%, or 22 +/- 9 and 18 +/- 6%), and H-P-liver (55 +/- 11 and 24 +/- 6%, 30 +/- 9 and 26 +/- 8%, or 20 +/- 9 and 17 +/- 6%). Glucagon- or epinephrine-induced increase in glucose output was also similar in H- (245 +/- 47 and 498 +/- 82 mumol/30 min, or 112 +/- 21 and 215 +/- 38 mumol/30 min), P- (258 +/- 51 and 512 +/- 95 mumol/30 min, or 128 +/- 20 and 220 +/- 36 mumol/30 min), and H-P-liver (263 +/- 58 and 515 +/- 94 mumol/30 min, or 129 +/- 22 and 225 +/- 39 mumol/30 min).(ABSTRACT TRUNCATED AT 250 WORDS)

The effect of TYB-3823 on Ca2+ current (ICa) of guinea pig ventricular myocytes was investigated by means of whole-cell patch-clamp technique. TYB-3823 (100–1,000 μM) caused a concentration-dependent decrease in ICa. Furthermore, a reduction of ICa induced by TYB-3823 (1,000 μM) was progressively accentuated by repetitive membrane depolarization, indicating a rate-dependent block of ICa. However, the inhibitory potency on ICa was approximately 1 1000 of a Ca2+ antagonistic agent, verapamil hydrochloride. Considering evidence that 3–30 μM TYB-3823 decreased the maximum upstroke velocity of the action potential of guinea pig ventricular muscles, it is indicated that the drug does not show its Ca2+ antagonistic property in the usual concentration range as a class I antiarrhythmic agent.

To elucidate the direct effect of an intestinal osmolality on insulin release, we investigated the insulin response to intra-duodenal infusion of mannitol in rats. After the anesthesia with intraperitoneal pentobarbital sodium, one milliliter of mannitol solution (10% or 20%) was infused into the duodenum. Portal and femoral blood insulin concentrations significantly increased at 30, 60, and 120 min after intra-duodenal infusion of mannitol, although the blood glucose level did not change. Subcutaneous pre-administration of propranolol (0.4mg/kg) or metoprolol (25mg/kg) completely abolished this phenomenon. These results suggest that intestinal osmolality can directly enhance insulin secretion and that β 1 -adrenergic mechanism is involved in this phenomenon.

Aprindine is a class Ib antiarrhythmic agent. We studied effects of aprindine (3 mumol/l) on the Na+ current using whole cell voltage clamp (tip resistance = 0.5 M omega, [Na]i ando = 10 mmol/l at 18 degrees C). Aprindine revealed tonic block (Kdrest = 37.7 mumol/l, Kdi = 0.74 mumol/l; n = 4). Aprindine, shifted inactivation curve to hyperpolarizing direction by 11.4 +/- 3.5 mV (n = 4) without changes in slope factor. In the presence of 3 mumol/l aprindine, aprindine showed phasic block, i.e., duration-dependent block at 2 Hz (64% +/- 3% at 1.5 ms, 82% +/- 6% at 20 ms, 93% +/- 7% at 200 ms; n = 4). Short single prepulse also produced aprindine-induced phasic block (12% at 1.5 ms, 22% at 100 ms; n = 2). After removal of fast inactivation of Na+ current by 3 mmol/l tosylchloramide sodium, aprindine revealed phasic block, independent of holding potential. The recovery time constant from aprindine-induced phasic block was 4.8 s at holding potential = -100 mV and 5.0 s at holding potential = -140 mV. This use-dependent block of aprindine had pH dependency. Under acidic condition (pH 6.0), 3 mumol/l aprindine showed smaller use-dependent block (14% +/- 7% at 2 Hz; n = 4) comparing with either at pH 7.4 (68% +/- 13%; n = 4) or at pH 8.0 (90% +/- 12%; n = 4). The results suggest that aprindine could bind to the receptor via activation process through channel pore, resulting in decrease of Na+ current, and egress from the receptor through the lipid bilayer. These effects might be attenuated under acidic condition due to changes in intracellular ratio of charged to neutralized form of drug molecule.

1. Sodium current (INa) blockade by TYB-3823, a newly synthesized antiarrhythmic agent, was investigated in isolated single ventricular myocytes by use of the whole cell patch-clamp technique. 2. TYB-3823 blocked INa under steady-state conditions (Kd,rest = 500 microM, Kd,i = 4.9 microM), findings consistent with a shift in the steady state INa availability curve to more negative potentials. 3. TYB-3823 produced use-dependent block at 2 Hz in conjunction with increase in pulse duration (5-300 ms), that was markedly enhanced at less negative holding potentials. 4. The time course of the onset of block was accelerated and the degree of use-dependent block was decreased at more negative holding potential. The time course of the onset of block was accentuated with enhancing block at more positive holding potentials. 5. The time course of recovery from use-dependent block was accelerated at more negative holding potentials but was accentuated at more positive holding potentials. 6. These results suggest that both tonic block and use-dependent block of sodium channels in cardiac tissue might result from an interaction of TYB-3832 with sodium channels mainly in the inactivated channel states and the kinetics of the interaction between drug and receptor may be modulated by the inactivation gate.

1. The electrophysiological effects of midaglizole, a new oral hypoglycaemic agent which is an alpha 2-adrenoceptor antagonist, were assessed in the reserpinized ventricular myocardium of the guinea-pig. 2. Midaglizole suppressed the maximal rate of rise (Vmax) and the amplitude of action potentials (APA) of the fast and the slow responses in a concentration-dependent manner without influencing the resting potentials. 3. Voltage-dependency of the Vmax block of the action potentials by midaglizole (10 microM) did not appear in solutions containing various concentrations of KCl. 4. It is concluded that midaglizole has inhibitory effects on the fast Na+ and slow Ca2+ currents of the membrane independent of the blockade of myocardial alpha-adrenoceptors, and that these effects may be significant in some clinical uses of the drug.

To elucidate the possible role of adrenergic mechanism in thyroid hormone metabolism during starvation, serum thyrotropin (TSH), thyroxine (T4), and 3,5,3'-triiodothyronine (T3) levels and conversion of T4 to T3 in perfused liver were investigated in fasting (60 h) and fed rats. Propranolol (0.5 mg/kg), yohimbine (0.3 mg/kg) or phentolamine (5.0 mg/kg) was subcutaneously injected to the rat every 12 h. Serum levels of TSH, T4, and T3 were significantly lower in fasting rats than in fed rats. Although propranolol, yohimbine, and phentolamine administration did not significantly alter circulating TSH, T4 and T3 levels in fed rats, phentolamine partly inhibited the starvation-induced reduction in circulating TSH, T4, and T3. Thyroxine uptake and T3 production in perfused liver were significantly lower in fasting rats than in fed rats. Phentolamine treatment did not alter the T4 uptake and T3 production in perfused liver of fasting rats. These results suggest that alpha-adrenergic mechanism may have some role in starvation-induced reduction in circulating T4 and T3, and that phentolamine partly inhibited this phenomenon probably through the inhibitory effect on reduction in circulating TSH during starvation.

1. 1. Cibenzoline, a class 1 antiarrhythmic drug, was studied on the effects upon the myocardial slow inward Ca2+ current (ICa) and the contractile force, and was compared with verapamil. 2. 2. In voltage-clamp experiments with guinea-pig ventricular myocytes, cibenzoline caused a concentration-related inhibition of ICa (IC50 = 30 μM), whereas verapamil exerts a stronger effect (IC50 = 0.6 μM). 3. 3. Cibenzoline also produced a concentration-related decrease in contractile force of isolated papillary muscle preparation (IC50 = 30 μM), while IC50 of verapamil was 0.8 μM. 4. 4. Although the myocardial Ca2+ channel blocking effect of cibenzoline is about 1 50 compared to verapamil, cibenzoline possesses an inhibitory action on Ca2+ channel as well as on Na+ channel.

The electrophysiological effect of the antihypertensive drug pinacidil has been examined in preparations of guinea-pig papillary muscle and rabbit sino-atrial node using a standard microelectrode method. In papillary muscle preparations, pinacidil (> 30 μM) shortened the action potential duration (APD), whereas it did not affect the maximum rate of rise (Vmax). Pinacidil (> 1 μM) also decreased APD of slow action potentials evoked by high K+ (27 mM) solution containing 0.2 mM Ba2+. At 30 μM, the drug reduced the Vmax of slow action potentials. In the spontaneously beating sino-atrial node, pinacidil (> 30 μM) shortened APD. At 100 μM, it also decreased the heart rate, Vmax, action potential amplitude and the rate of diastolic depolarization. It is concluded that pinacidil modifies the electrical activity of myocardial cells probably due to an increase in the potassium conductance although in high concentrations the compound might also reduce Ca2+ influx through the cell membrane, which would contribute to an obvious negative chronotropic action.

To investigate the effects of insulin and sulfonylurea drug administration on islet A and B-cell functions, insulin and glucagon response was studied in normal rats treated with insulin (4 U/day subcutaneously) or glibenclamide (0.03 mg/kg intraperitoneally) for 8 weeks. In intravenous glucose tolerance test (0.5 g/kg), lower insulin response and impaired glucose tolerance were observed in insulin-treated rats and higher insulin response and impaired glucose tolerance were observed in glibenclamide-treated rats. In perfused pancreas, insulin response to glucose and arginine was significantly lower in insulin-treated rats and that was significantly higher in glibenclamide-treated rats. Glucagon response was not altered by insulin or glibenclamide treatment. These results suggest that hyperinsulinisation and glibenclamide administration strongly influence pancreatic B-cell function but not influence pancreatic A-cell function.

To elucidate the possible role of thyroid hormone in somatomedin-C (SmC)/insulin-like growth factor I regulation in diabetes mellitus and starvation, plasma SmC, liver SmC, and kidney SmC concentrations were measured in streptozotocin-induced (60 mg/kg) diabetic and starved (for 72 h) rats. Triiodothyronine (T3, 5.0 micrograms/kg every 24 h) was subcutaneously injected into diabetic rats for 7 days and into starved rats at 12, 36, and 60 h after starvation. Plasma T3, plasma SmC, liver SmC, and kidney SmC concentrations were significantly decreased in diabetic and starved rats. T3 administration restored plasma T3 levels to the normal value in diabetic and starved rats. Plasma SmC and kidney SmC concentrations were significantly increased in T3-treated starved rats, while they were not increased in T3-treated diabetic rats. These results suggest that thyroid hormone may have some role in SmC regulation during starvation, but may have no role in diabetes mellitus in the rat.

1. 1. The effects of the physiological levels of corticotropin-releasing factor (CRF) on isolated guinea-pig ventricular myocardium were studied using a force transducer and standard microelectrode techniques. 2. 2. CRF increased the contractile force of muscles concentration-dependently in normal Tyrode and a high-K + (27 mM) solution. The positive inotropic effect of CRF was associated with a significant enhancement of the slow action potentials of partially depolarized muscles in high-K + solution. CRF potentiated the effect of increasing Ca 2+ concentration of Tyrode solution. 3. 3. The inotropic effect of CRF was reduced in the presence of diltiazem, and suppressed by phentolamine, metoclopramide, and cimetidine, but was not affected by propranolol and cold condition. 4. 4. It is suggested that an increase in the slow inward Ca 2+ current induced by CRF plays an important role in its positive inotropic effect and that its effect differs from that of cardiotonic steroids.

This study was undertaken to elucidate the effect of thyrotropin (TSH) on the conversion of thyroxine (T4) to 3,5,3'-triiodothyronine (T3) in the isolated perfused rat kidney. The kidney was perfused with a synthetic medium containing 20 micrograms/dL T4 and the effect of constant infusion of bovine TSH (125 or 250 microU/mL) on the conversion of T4 to T3 was investigated. T4 uptake in the perfused kidney was not changed by the addition of TSH. However, the release of T3 (89 +/- 11 ng/g/30 min, mean +/- SD), tissue T3 (190 +/- 23 ng/g/30 min), net T3 production (227 +/- 37 ng/g/30 min), and the conversion rate of T4 to T3 (9.5 +/- 1.6%) in the kidney perfused with 250 microU/mL TSH were significantly (P less than 0.005) greater than those in controls (63 +/- 9, 143 +/- 15, 152 +/- 36 ng/g/30 min, and 6.3 +/- 1.9%), respectively. Degradation rate of T3 in perfused rat kidney was not changed by the addition of 250 microU/mL TSH. These results suggest that TSH may directly affect renal iodothyronine-monodeiodinating activity in rats in vitro.

To clarify the in vivo events following administration of steroid hormones, the effect of molybdate on the cytoplasmic glucocorticoid receptor (GR) translocation in rat livers after administration of glucocorticoids was examined. After injection of hydrocortisone-succinate (Hydro) (200 micrograms/150 g rat) into the inferior vena cava of adrenalectomized rats, 3H-dexamethasone (3H-Dex) binding in liver cytosol rapidly decreased within 5 min, followed by a rapid replenishment. This decrease in binding was partially prevented by pre-treating the animals with 20 mg of sodium molybdate (Mo), which was considered to inhibit GR activation. Administration of 200 micrograms/150 g body weight of hydrocortisone caused a rapid replenishment of the binding sites following the depletion. Administration of molybdate 5 min after the hydrocortisone injection did not influence the replenishment. The GR content was increased significantly 20 min after the administration of molybdate in intact rats but not in adrenalectomized rat. It is concluded that activation of the hormone receptor complex observed in vitro also occurs in vivo after administration of glucocorticoid to animals.

This study was undertaken to elucidate the effect of glibenclamide, one of sulfonylurea drugs, on thyroid hormone metabolism in vivo and on the conversion of thyroxine (T4) to 3,5,3'-triiodothyronine (T3) in the isolated perfused rat liver and kidney. Glibenclamide (0.2 mg/kg body weight) was intraperitoneally administered to normal and streptozotocin-induced (50 mg/kg) diabetic rats for 14 days. The liver and kidney of normal rats were perfused for 30 minutes with a synthetic medium containing 20 micrograms/dl T4 and glibenclamide (200 or 400 ng/ml), and production of T3 in the tissues was measured by radioimmunoassay. Serum T4 and T3 levels in control and streptozotocin-induced diabetic rats were not changed by daily intraperitoneal glibenclamide administration. The production of T3 (111 +/- 40 and 95 +/- 16 ng/g/30 min, mean +/- SD) and the conversion rate of T4 to T3 (11.1 +/- 2.9 and 10.2 +/- 2.3%) in the liver perfused with glibenclamide (200 and 400 ng/ml) were not significantly different from those in controls (109 +/- 41 ng/g/30 min and 12.8 +/- 5.4%). And those (120 +/- 33 and 99 +/- 19 ng/g/30 min, and 3.5 +/- 0.6 and 2.5 +/- 0.4%) in the kidney perfused with glibenclamide (200 and 400 ng/ml) were similar to those in controls (98 +/- 33 ng/g/30 min and 3.0 +/- 1.5%).

To clarify the contribution of gastrointestinal function to impaired oral glucose tolerance in hyperthyroidism, gastric emptying rate and portal and peripheral blood glucose responses to intragastric or intraduodenal glucose administration were investigated in experimental thyrotoxic rats. Glucose absorption from perfused intestine of thyrotoxic rats was also examined. Thyrotoxicosis was induced by subcutaneous (SC) thyroxine injection (50 micrograms/kg/d) for seven days. In intragastric glucose tolerance test, although insulin and glucagon responses were not significantly altered, increments in portal and peripheral blood glucose were significantly higher in thyrotoxic rats than in controls at 30 minutes. This phenomenon was almost normalized by the preadministration of phentolamine (2 mg/kg SC). In intraduodenal glucose tolerance test, blood glucose, insulin, and glucagon responses were similar in thyrotoxic and control rats. Gastric emptying rate in thyrotoxic rats was significantly higher than that in controls at 30 minutes, and that was also normalized by phentolamine administration. Absorption of glucose from perfused intestine was similar in thyrotoxic and control rats. These results suggest that an altered glucose tolerance to intragastric glucose load in thyrotoxic rats may primarily be due to rapid gastric emptying induced by increased alpha-adrenoceptor responses, and that glucose absorption from small intestine was not increased in short-term thyrotoxic rats.

To elucidate the possible role of insulin, glucagon, and epinephrine on glucose intolerance in thyrotoxicosis, the secretion of insulin and glucagon in vivo (glucose, arginine, and epinephrine infusion tests) and in perfused pancreas and the hepatic action of insulin, glucagon, and epinephrine in perfused liver were investigated in experimental thyrotoxic rats (induced by thyroxine injection, 20 micrograms/kg sc, for 7 days). In thyrotoxic rats, fasting blood glucose (87 +/- 5 mg/dl, mean +/- SD) and plasma insulin (16 +/- 3 microU/ml) were significantly (P less than 0.001) higher than those in controls (74 +/- 5 mg/dl and 8 +/- 1 microU/ml), respectively. In glucose infusion test (0.5 g/kg iv), blood glucose, plasma insulin, and glucagon responses in thyrotoxic rats were not significantly different from those in controls. In arginine infusion test (5 mg/min for 20 min iv), the increments in blood glucose and plasma insulin after arginine in thyrotoxic rats were not significantly different from those in controls. Plasma glucagon response was almost the same in both groups. In epinephrine infusion test (100 micrograms/kg iv), the increments in blood glucose and plasma insulin in thyrotoxic rats were significantly greater than those in controls. In perfused pancreas, insulin and glucagon secretions in response to 16.7 mM glucose or 6.4 mM arginine in the presence of 5.5 mM glucose in thyrotoxic rats were not different from those in controls.(ABSTRACT TRUNCATED AT 250 WORDS)

The effects of trimebutine maleate on electrical activity in guinea-pig isolated papillary muscles and rabbit sino-atrial nodes have been studied by means of a standard microelectrode method. In papillary muscles, trimebutine (above 10 μM) decreased the maximum rate of rise (V̇max) and the action potential duration at 90% repolarization (APD90), whereas the resting potential was not significantly altered. As to a decrease in V̇max, trimebutine produced a negative shift of the curve relating V̇max to the resting potential along the voltage axis. Trimebutine also depressed the slow action potentials of papillary muscles produced by 27 mM K and 0·2 mitt Ba. In spontaneously beating sino-atrial node preparations, trimebutine (above 10 μ) decreased the heart rate, V̇max and the rate of diastolic depolarization. These results indicate that trimebutine maleate possesses a depressant action on the electrical activities of the fast- and slow-response fibres of the heart mainly due to inhibitions of both fast Na+ and slow Ca2+ channels.

The changes in the cytosol glucocorticoid receptor (GR) content during a long-term administration of a glucocorticoid were studied to examine the mechanism of the development of steroid hormone resistance. Dexamethasone (Dex)(0.2μg/ml and 2.0μ/ml) was given to adrenalectomized rats, and the GR content was determined using the exchange assay 1, 10, 20 and 50 days after the start of administration. The activity of tyrosine aminotransferase (TAT) in the cytosol was also assayed as a measure of the biological responsiveness of these animals to the administered glucocorticoid. The dissociation constant (Kd) was elevated and the Bmaxs of the GR in the cytosol were decreased by the lower concentration of Dex. The Bmaxs decreased to 30% of the untreated controls within 24 h and this lower level was maintained as long as the hormone treatment continued. On the other hand, the cytosol obtained from animals treated with 2.0μg/ml of Dex for 20-24 days did not show any measurable amount of binding to 3H-Dex. The activity of TAT was elevated 24 h after the administration of Dex but decreased gradually and steadily with time during the experimental period. To examine the biological potency of remaining GR in the liver cytosol, 2.0μg/ml Dex was again administered after a long-term treatment. This treatment eliminated the remaining GR completely and induced TAT at almost the same rate as observed in the untreated control animals. The pattern of depletion and replenishment of the GR after a single injection of hydrocortisone in the animals that had received 2.0μg/ml Dex for 14 days followed by steroid free drinking fluid for 3 days was also determined and compared with those of the untreated control. No significant differences were observed between the two animal groups in the kinetics of depletion or replenishment of the GR. We concluded that the function of GR in the Rat liver was not distorted significantly during the course of the long-term Dex treatment.

The electrophysiological effects of bunazosin, a novel α-adrenoceptor antagonist, were examined on isolated spontaneously beating sinoatrial node preparations of the rabbit by means of a double-microelectrode voltage clamp method. Bunazosin (above 10 μM) reduced the beating frequency, and the maximum rate of rise and the amplitude of action potentials. The slope of the diastolic depolarization (phase 4) was also decreased by the drug whereas the action potential duration at 50% repolarization was prolonged. Bunazosin decreased the slow inward current (I si ) and the time-dependent potassium outward current (I K ). However, the major effect was the reduction of I si . The results indicate that bunazosin, an α-adrenoceptor antagonist, depresses the action potential and automaticity of the sinoatrial node by inhibition of Ca channels.

The inotropic effect of the physiological level of TRH on isolated guinea pig cardiac muscle was studied using a force transducer and standard microelectrode techniques. TRH increased the contractile force of muscles dose-dependently without changing the time course of contraction in normal Tyrode and a high K+ (27 mM) solution. The positive inotropic effect of TRH was associated with an augmentation of slow action potentials in high K+ solution and was reduced in the presence of diltiazem, verapamil, and manganese. TRH potentiated the response of contractile force to increasing extracellular Ca2+ concentration. The inotropic effect of TRH was suppressed by metoclopramide, phentolamine, and cimetidine, but was not affected by propranolol. TRH increased the contractile force even in the myocardium of reserpinized guinea pig. It is suggested that TRH has a positive inotropic effect at least partly due to an increase in the slow inward Ca2+ current. (Endocrinology 123: 2805–2811, 1988)

1. The effects of nizofenone fumarate were studied on the membrane potentials and currents of rabbit sino-atrial node preparations by means of the double-microelectrode voltage clamp method. 2. In spontaneously firing pacemaker cells, nizofenone (above 1 microM) decreased the heart rate. Above 3 microM, nizofenone reduced the maximum upstroke velocity, the amplitude of the action potential and the slope of the phase 4 depolarization, and prolonged the action potential duration at 50% repolarization. 3. Under voltage clamp conditions, nizofenone decreased the slow inward current and the time-dependent potassium outward current in a dose-dependent manner. 4. These findings suggest that nizofenone exerts an inhibitory action on the automaticity of sinoatrial node preparations via effects on both inward and outward currents.

The direct effect of methimazole (MMI) on FRTL-5 cell growth was examined. TSH, (Bu)2cAMP, calf serum, insulin-like growth factor I, and Graves' immunoglobulin (IgG) increased [3H]thymidine incorporation into DNA during 72-h incubation. MMI (10-3 M), which does not damage cell viability, significantly enhanced the increase in [3H]thymidine incorporation induced by TSH and (Bu)2cAMP. In contrast, MMI suppressed the increase in [3H]thymidine incorporation induced by calf serum, insulin-like growth factor I, and Graves' IgG. MMI had no effect on the production of cAMP by TSH. Accordingly, we concluded that MMI has opposite effects on cAMP- and non-cAMP-dependent cell growth pathways. Moreover, Graves' IgG, which has a modest effect on cAMP production, is believed to induce cell growth via the non-cAMP dependent cell growth pathway. (Endocrinology 124: 2046–2051, 1989)

To elucidate the mechanism of hyperinsulinemia and hyperglucagonemia in liver diseases, secretion of insulin and glucagon from perfused pancreas and extraction of insulin and glucagon by perfused liver were investigated in carbon tetrachloride inhalated liver injury rats. Fasting plasma insulin and glucagon levels and insulin and glucagon levels after arginine injection (0.25 g/kg) in liver injury rats were significantly higher than those in control rats. Glucagon levels after glucose injection (0.5 g/kg) were slightly increased in the liver injury group. Insulin responses to 16.7 mM glucose and 10 mM arginine from perfused pancreas were similar in liver injury rats and control rats. Glucagon response to 10 mM arginine from perfused pancreas was also similar in liver injury rats and control rats. Insulin extraction by perfused liver in liver injury rats (45 +/- 9%) was significantly (P less than 0.05) lower than that (64 +/- 11%) in control rats, and glucagon extraction by perfused liver was also significantly (P less than 0.05) decreased in liver injury rats (57 +/- 8%) compared with controls (73 +/- 9%). It is concluded that in carbon tetrachloride-induced liver injury rats, hyperinsulinemia and hyperglucagonemia may be dependent on decreased insulin and glucagon extraction by the liver.

To elucidate the physiological significance of ketone bodies on insulin and glucagon secretion, the direct effects of beta-hydroxybutyrate (BOHB) and acetoacetate (AcAc) infusion on insulin and glucagon release from perfused rat pancreas were investigated. The BOHB or AcAc was administered at concentrations of 10, 1, or 0.1 mM for 30 min at 4.0 ml/min. High-concentration infusions of BOHB and AcAc (10 mM) produced significant increases in insulin release in the presence of 4.4 mM glucose, but low-concentration infusions of BOHB and AcAc (1 and 0.1 mM) caused no significant changes in insulin secretion from perfused rat pancreas. BOHB (10, 1, and 0.1 mM) and AcAc (10 and 1 mM) infusion significantly inhibited glucagon secretion from perfused rat pancreas. These results suggest that physiological concentrations of ketone bodies have no direct effect on insulin release but have a direct inhibitory effect on glucagon secretion from perfused rat pancreas.