Effect of initial combination therapy with sitagliptin, a dipeptidyl peptidase-4 inhibitor, and pioglitazone on glycemic control and measures of ß-cell function in patients with type 2 diabetes.

AIM/HYPOTHESIS: To assess the safety and efficacy of initial combination therapy with sitagliptin and pioglitazone compared with pioglitazone monotherapy in drug-naïve patients with type 2 diabetes. METHODS: A total of 520 patients were randomised to initial combination therapy with sitagliptin 100 mg q.d. and pioglitazone 30 mg q.d. or pioglitazone 30 mg q.d. monotherapy for 24 weeks. RESULTS: Initial combination therapy with sitagliptin and pioglitazone led to a mean reduction from baseline in A1C of -2.4% compared with -1.5% for pioglitazone monotherapy (p<0.001). Mean reductions from baseline were greater in patients with a baseline A1C≥10% (-3.0% with combination therapy vs. -2.1% with pioglitazone monotherapy) compared with patients with a baseline A1C<10% (-2.0% with combination therapy vs. -1.1% with pioglitazone monotherapy). Sixty percent of patients in the combination therapy group vs. 28% in the pioglitazone monotherapy group had an A1C of <7% at week 24 (p<0.001). Fasting plasma glucose decreased by -63.0 mg/dl (-3.5 mmol/l) in the combination therapy group compared with -40.2 mg/dl (-2.2 mmol/l) for pioglitazone monotherapy (p<0.001), and 2-h post meal glucose decreased by -113.6 mg/dl (-6.3 mmol/l) with combination therapy compared with -68.9 mg/dl (-3.8 mmol/l) for pioglitazone monotherapy (p<0.001). Measures related to ß-cell function also improved significantly with combination therapy compared with pioglitazone monotherapy. Combination therapy was generally well-tolerated compared with pioglitazone monotherapy, with similar incidences of hypoglycemia (1.1% and 0.8%, respectively), gastrointestinal adverse events (5.7% and 6.9%, respectively), and oedema (2.7% and 3.5%, respectively). CONCLUSION/INTERPRETATION: Initial combination therapy with sitagliptin and pioglitazone substantially improved glycemic control and was generally well-tolerated compared with pioglitazone monotherapy.

A clinical trial assessing the safety and efficacy of taranabant, a CB1R inverse agonist, in obese and overweight patients: a high-dose study.

OBJECTIVE: To evaluate the efficacy, safety and tolerability of taranabant in obese and overweight patients. DESIGN: Double-blind, randomized, placebo-controlled study. SUBJECTS: Patients were >or=18 years old, with body mass index of 27-43 kg m(-2), and 51% with metabolic syndrome (MS) randomized to placebo (N=417) or taranabant 2 mg (N=414), 4 mg (N=415) or 6 mg (N=1256) for 104 weeks. MEASUREMENTS: Key efficacy measurements included body weight, waist circumference (WC), lipid and glycemic end points. RESULTS: On the basis of risk/benefit assessments, the 6-mg dose was discontinued during year 1 (patients on 6 mg were down-dosed to 2 mg or placebo) and the 4-mg dose was discontinued during year 2 (patients on 4 mg were down-dosed to 2 mg). Changes from baseline in body weight at week 52 (all-patients-treated population, last observation carried forward analysis) were -2.6, -6.6 and -8.1 kg, respectively, for placebo and taranabant 2 and 4 mg (both doses P<0.001 vs placebo). For patients who completed year 1, changes from baseline in body weight at week 104 were -1.4, -6.4 and -7.6 kg for placebo and taranabant 2 and 4 mg, respectively (both doses P<0.001 vs placebo). The proportions of patients at weeks 52 and 104 who lost at least 5 and 10% of their baseline body weight were significantly higher and the proportions of patients who met criteria for MS were significantly lower for taranabant 2 and 4 mg vs placebo. The incidence of adverse experiences classified in the gastrointestinal, nervous, psychiatric, cutaneous and vascular organ systems were generally observed to be dose related with taranabant vs placebo. CONCLUSION: Taranabant at the 2- and 4-mg dose was effective in achieving clinically significant weight loss over 2 years and was associated with dose-related increases in adverse experiences. On the basis of these and other data, an assessment was made that the overall safety and efficacy profile of taranabant did not support its further development for the treatment of obesity.

Influence of the endothelium on the amplification by serotonin of vasoconstrictor responses to noradrenaline and sympathetic nerve stimulation in rabbit isolated ear artery.

The influence of the vascular endothelium on the amplifying effect of serotonin on steady-state responses to noradrenaline (NA) and sympathetic nerve stimulation (SNS) has been studied in the rabbit isolated ear artery. Removal of the endothelium abolished the dilator effect of acetylcholine (ACh, 1 microM) obtained in the presence of NA (0.3 microM). Responses to NA were increased after endothelium removal; however, responses to SNS were unaffected. Serotonin in a concentration which did not itself produce vasoconstriction (100 nM) increased responses of endothelium-intact preparations to NA and SNS and of endothelium-denuded preparations to SNS but had no effect on NA responses of endothelium-denuded preparations. If neuronal uptake was inhibited with cocaine (1 microM), serotonin markedly amplified responses to NA and SNS in both endothelium-intact and endothelium-denuded preparations. These results suggest that the endothelium influences the amplifying effect of serotonin on responses of rabbit ear artery to NA but not to SNS. Inhibition of removal of serotonin and NA by neuronal uptake may extend the facilitatory interaction between NA and serotonin to smooth muscle cells which are not subject to the inhibitory influence of an endothelium derived relaxing factor.

CCKA receptors mediate slow depolarizations in cultured mammalian sympathetic neurons.

The effect of cholecystokinin octapeptide (CCK-8) was examined in guinea-pig celiac ganglion (CG) neurons in primary culture using standard intracellular recording techniques. Sulfated CCK-8 (CCK-8S; 1 microM) evoked slow depolarizing responses in 94% of CG neurons tested. In contrast, membrane potential was not affected by nonsulfated CCK-8 (CCK-8NS; 1 microM), CCK tetrapeptide (CCK-4; 1 microM), or gastrin (1 microM). The selective CCKA receptor antagonist L 364,718 potently inhibited CCK-8S-induced slow depolarizations (IC50 2.9 pM). In contrast, the selective CCKB receptor antagonist L 365,260 was a weak inhibitor of CCK-8S-induced slow depolarizations (IC50 1.3 microM). The depolarizing responses to CCK-8S were associated with an average increase in cell input resistance of 61%. Single electrode voltage clamp experiments indicated that CCK-8S-induced depolarizations were associated with a slow inward shift in holding current. Thus, the present findings indicate that guinea-pig cultured CG neurons are endowed with excitatory CCKA receptors the activation of which elicits a decrease in membrane conductance, thereby resulting in slow depolarizations.

Involvement of Ca2+ mobilization in the amplifying effect of serotonin on responses of rabbit isolated ear artery to exogenous noradrenaline.

The present study examined the involvement of Ca2+ mobilization in the amplifying effect of serotonin on steady-state responses of rabbit isolated perfused ear artery to exogenous noradrenaline (NA; 0.001-3 mumol/l). In contrast to its marked amplifying effect on responses to NA, serotonin in the subconstrictor concentration of 100 nmol/l had no effect on responses to KCl. The Ca2+-entry blocking drug diltiazem (10 mumol/l) decreased responses to NA; in addition, the amplifying effect of serotonin on responses to NA was reduced by diltiazem. Lowering the concentration of Ca2+ in the Krebs-Henseleit perfusion solution from 2.5 to 0.25 mmol/l also reduced both responses to NA and the amplifying effect of serotonin. Using the method of Manzini et al. (1982), separate intra- and extracellular Ca2+-dependent responses to NA were obtained. Serotonin had no effect on intracellular Ca2+-dependent responses to NA but enhanced extracellular Ca2+-dependent NA responses. These results suggest that the amplifying effect of serotonin on responses of rabbit ear artery to exogenous NA involves a selective enhancement of the component of the NA response which is dependent on extracellular Ca2+; serotonin may increase NA-evoked entry of Ca2+ into the vascular smooth muscle cells through receptor-operated Ca2+ channels.

Electrophysiological studies on the interaction of 5-hydroxytryptamine with sympathetic transmission in the guinea pig inferior mesenteric artery and ganglion.

The interaction of 5-hydroxytryptamine (5-HT) with sympathetic transmission was investigated in the guinea pig inferior mesenteric artery (IMA) and ganglion (IMG). Intracellular recordings of membrane potential were made using glass microelectrodes. Superfusion of 5-HT (0.3 microM) reduced the amplitudes of stimulation-evoked excitatory junction potentials in the IMA. 5-HT had no effect on depolarizing responses to pressure-ejection of adenosine triphosphate or norepinephrine in the IMA. The inhibitory effect of 5-HT on excitatory junction potentials in the IMA was abolished by methysergide (3 microM), but was unaffected by the following antagonists: methiothepin (1 microM), MDL 72222 (3 microM), MDL 11939 (0.3 microM) or by phentolamine (10 microM). In the IMG, pressure-ejection of 5-HT (10 mM) evoked fast and slow depolarizing responses in 77% of neurons tested; the fast depolarizing responses to 5-HT were reduced in the presence of MDL 72222 (5 microM). Superfusion of 5-HT (0.3-3 microM) had no effect on stimulation-evoked fast excitatory postsynaptic potentials in the IMG. Thus, the results of the present study suggest that, depending on its site of interaction with postganglionic sympathetic neurons, 5-HT may have excitatory or inhibitory effects on sympathetic transmission. 5-HT may inhibit transmitter release through the activation of as yet unidentified 5-HT receptors on the sympathetic nerve endings in mesenteric blood vessels. Whereas, in the prevertebral ganglion, 5-HT may act to facilitate sympathetic transmission, in part, through activation of 5-HT3, receptors on the somata of principal neurons.

Interaction of the prejunctional inhibitory action of 5-hydroxytryptamine on noradrenergic transmission with neuronal amine uptake in rabbit isolated ear artery.

The interaction of the prejunctional inhibitory action of 5-hydroxytryptamine (5-HT) on noradrenergic transmission with the neuronal amine uptake mechanism has been studied in rabbit isolated ear artery preparations. Release of norepinephrine in response to stimulation of periarterial sympathetic nerves (30 pulses, 1 Hz) was deduced from the efflux of radioactivity which had been incorporated into the noradrenergic transmitter pool as [3H]norepinephrine. 5-HT (100 nM), applied alone, had no effect on the stimulation-induced efflux of radioactivity. However, in the presence of cocaine (1 microM), 5-HT reduced stimulation-induced efflux. The inhibitory effect of 5-HT, in the presence of cocaine, on stimulation-induced efflux was abolished by the nonselective 5-HT1/5-HT2 receptor antagonist, methiothepin (30 nM), but not by the selective 5-HT2 receptor antagonist, ketanserin (6 nM), or by the alpha adrenoceptor antagonist, phentolamine (30 nM). These findings indicate that the uptake of 5-HT into periarterial sympathetic nerves may limit its prejunctional "5-HT1-like" receptor-mediated inhibitory effect on noradrenergic transmission. In arteries which were incubated with 5-HT (1 microM) and the monoamine oxidase inhibitor, pargyline (10 microM), before loading the transmitter stores with [3H]norepinephrine, methiothepin (30 nM) enhanced stimulation-induced efflux markedly. The enhancing effect of methiothepin was not observed in arteries which were preincubated with cocaine (10 microM) together with 5-HT and pargyline. It is suggested that, following its uptake into periarterial sympathetic nerves, 5-HT may be coreleased with norepinephrine to activate prejunctional 5-HT1-like receptors and thereby mediate an autoinhibitory effect on transmitter release.

A capsaicin-sensitive inhibitory reflex from the colon to mesenteric arteries in the guinea-pig.

1. The present in vitro study examined the effect of distension of the distal colon on membrane potential in the inferior mesenteric artery of the guinea-pig. 2. Distension of the distal colon up to an intraluminal pressure of 25 cmH2O induced a hyperpolarization in the inferior mesenteric artery. The average amplitude of hyperpolarizations induced by 2 min distensions of the colon was 3 mV and their average duration was 268 s. 3. Distension-induced hyperpolarizations (DIHs) were abolished in the presence of tetrodotoxin or a low-Ca2+ (0.5 mM) superfusion solution. 4. Superfusion of capsaicin (10 microM) induced slow hyperpolarizing responses in mesenteric arteries. Following application of capsaicin (10 microM), DIHs were abolished. 5. These findings provide strong evidence that mesenteric arteries receive an inhibitory, capsaicin-sensitive sensory innervation from the distal colon which is activated during periods of colon distension to induce hyperpolarization of the arterial smooth muscle. This extramural inhibitory reflex pathway may play a physiological role in co-ordinating mesenteric blood flow with changes in gut motility.

Effects of serotonin on sympathetic noradrenergic transmission in rabbit isolated ear artery.

The amplifying effect of serotonin in subconstrictor concentrations on steady-state vasoconstrictor responses to norepinephrine (NE; 0.001-3 microM) and to stimulation of periarterial sympathetic nerves (SNS; 0.3-ms pulses, 0.1-3 Hz) has been studied in rabbit isolated ear artery. Ketanserin (30 nM by itself had no effect on responses to NE or SNS; however, the amplifying effect of serotonin (10 nM) on responses to NE was abolished; ketanserin also markedly reduced the amplifying effect of serotonin on responses to SNS. Idazoxan (100 nM) had no effect on responses to NE or SNS; furthermore, idazoxan had no effect on the amplifying effect of serotonin. Prazosin (10 nM) reduced responses to NE and SNS; however, prazosin had no effect on the amplifying effect of serotonin on responses to NE and SNS. Intraluminally applied serotonin increased responses to intraluminal and extraluminal NE and to SNS. Extraluminally applied serotonin increased responses to extraluminal NE but not to intraluminal NE or SNS; however, in the presence of cocaine (1 microM), an amplifying effect of extraluminal serotonin on responses to intraluminal NE and to SNS was also observed. It thus appears that the amplification by serotonin of the alpha 1-adrenoceptor-mediated responses to NE and SNS in rabbit ear artery involves postjunctional 5-HT2-receptor activation. Moreover, the neuronal uptake process appears to modify the amplifying effect of serotonin.

Capsaicin-sensitive nerves mediate inhibitory junction potentials and dilatation in guinea-pig mesenteric artery.

1. The present study examined the effects of repetitive nerve stimulation on membrane potential and on contractile responses to noradrenaline in the guinea-pig inferior mesenteric artery and its distal branches. 2. Repetitive stimulation of perivascular nerves evoked slow inhibitory junction potentials (IJPs) and dilator responses. Individual nerve shocks elicited excitatory junction potentials (EJP)s. 3. Stimulation-evoked IJPs were abolished in the presence of tetrodotoxin (0.3 microM) or a low-Ca2+ (0.5 mM) superfusion solution. 4. The amplitudes and durations of IJPs were dependent on the frequency and duration of repetitive nerve stimulation. Nerve stimulation delivered at 5 Hz for 5 s induced IJPs which had an average amplitude of 2 mV and an average duration of 130 s. When the time interval between successive stimulation periods was less than 4 min, the amplitudes of IJPs were reduced in a time-dependent manner. 5. Stimulation-evoked IJPs were unaffected following endothelium removal. Furthermore, stimulation-evoked IJPs were not affected by atropine (1 microM), indomethacin (20 microM), prazosin (0.5 microM), phentolamine (10 microM), propranolol (0.5 microM) or alpha,beta-methylene ATP (0.2 microM). 6. Pre-treatment of arteries with guanethidine (30 microM) or 6-hydroxydopamine (0.4 mM) abolished stimulation-evoked EJPs but had no effect on stimulation-evoked IJPs. 7. In a similar manner to repetitive nerve stimulation, capsaicin (10 microM) itself induced membrane hyperpolarization and dilatation in mesenteric arteries. Moreover, following application of capsaicin (10 microM), stimulation-evoked IJPs and dilator responses were abolished. 8. EJPs evoked during stimulation-induced IJPs were reduced in amplitude, compared to EJPs evoked under resting conditions. 9. These findings suggest that, in addition to an excitatory sympathetic innervation, mesenteric arteries receive an inhibitory, capsaicin-sensitive innervation which is activated by low-frequency repetitive stimulation.

Comparison of neurotransmission with nerve trunk and transmural field stimulation in guinea-pig mesenteric artery.

1. Intracellular electrical and contractile responses to sympathetic nerve trunk stimulation (NTS) and transmural electrical field stimulation (TMS) were compared in the guinea-pig mesenteric artery in vitro. 2. Step increases in voltage with NTS gave rise to excitatory junctional potentials (EJPs) which reached a plateau amplitude of 5-10 mV, whereas with TMS larger amplitude EJPs and sometimes action potentials were obtained. 3. EJPs of equal amplitude (1-7 mV) elicited with TMS and NTS had the same rise time, duration and decay half-time. 4. Slow depolarization obtained with repetitive stimulation was significantly greater in amplitude with TMS than with NTS. 5. Equal amplitude EJPs were obtained throughout the preparation with NTS. With TMS, the amplitude of responses declined substantially with distance from the stimulating electrodes. 6. Tetrodotoxin (TTX) completely blocked EJPs, slow depolarization and contraction with NTS; however, with TMS a TTX-resistant component was observed. The TTX-resistant response to TMS was abolished in the presence of a low-Ca2+ superfusion solution but was not affected by endothelium removal. 7. Phentolamine or prazosin abolished slow depolarization but not EJPs with NTS or TMS. Prazosin abolished contraction with NTS and reduced but did not abolish contraction with TMS. 8. alpha, beta-Methylene ATP abolished EJPs with NTS, whereas with TMS only EJPs obtained with low stimulus intensities were abolished. alpha, beta-Methylene ATP did not block contraction with either NTS or TMS. 9. Combined TTX, prazosin and alpha, beta-methylene ATP abolished EJPs initiated with TMS at all but the highest stimulus intensities (12-20 V, 0.3 ms duration). 10. It is concluded that responses obtained with NTS can be reliably attributed to the release of transmitter by the conduction of action potentials in paravascular nerves, whereas activation by TMS is a more complex phenomenon dependent upon stimulus strength and probably involving multiple forms of activation.