Cholinomimetic Activity Research Articles

Discovery of potent glycogen synthase kinase 3/cholinesterase inhibitors with neuroprotection as potential therapeutic agent for Alzheimer’s disease

In the present work, a novel series of pyridinethiazole bearing benzylpiperidine hybrids were designed and synthesized as dual-target inhibitors of GSK-3β/AChE. Among them, GD29 was the most promising candidate, with an IC50 value of 0.3 μM for hAChE and an IC50 value of 0.003 μM for hGSK-3β, respectively. The compounds exhibited good drug-like properties with optimal inhibitory enzyme activities. Moreover, GD29 showed anti-inflammatory properties at micromolar concentrations and displayed interesting neuroprotective profiles in an in vitro model of oxidative stress-induced neuronal death. Notably, the compounds also exhibited good permeability across the blood–brain-barrier (BBB) both in vitro. Central cholinomimetic activity was confirmed using a scopolamine-induced cognition impairment model in Institute of Cancer Research (ICR) mice upon oral administration. The current work identified optimized compounds and explored the therapeutic potential of glycogen synthase kinase 3/cholinesterase inhibition for the treatment of AD.

Pharmacological evaluation of the hydro-alcoholic extract of Campomanesia phaea fruits in rats.

Campomanesia phaea (Myrtaceae), popularly known as cambuci, is one of several species of plants producing comestible fruits, largely used in human nutrition. Despite its consumption and economic potential, limited scientific research is available on the Campomanesia, especially those related to its therapeutic benefits. It is reported by traditional medicine the use of the plant in the treatment of different disorders, such as cardiovascular and nervous system disturbances. So, the aim of this study was to carry out the pharmacological evaluation of the hydro-alcoholic extract (HAE) of Campomanesia fruits in rats by screening consisting of tests: a) neuropharmacological observation, b) test on the cardiovascular system. The HAE, prepared from the extraction of fruits with water/ethanol, was concentrated and freeze-dried. Behavioral responses in rats were investigated in open field test and the cardiovascular actions were investigated by a register of indirect blood pressure and the register of spontaneous beating rate right atrium. The results revealed that HAE induced grooming, hypotension and bradycardia. So, this study identified an action on the central nervous system, represented by grooming, and a cardiovascular activity of Campomanesia. The hypotension, attributed in part to bradycardia, was not related to a cholinergic effect, discarding a possible cholinomimetic action of the plant that could justify both cardiovascular and central actions.

Alkylphospholipids are Signal Transduction Modulators with Potential for Anticancer Therapy.

Alkylphospholipids (APLs) are synthetically derived from cell membrane components, which they target and thus modify cellular signalling and cause diverse effects. This study reviews the mechanism of action of anticancer, antiprotozoal, antibacterial and antiviral activities of ALPs, as well as their clinical use. A literature search was used as the basis of this review. ALPs target lipid rafts and alter phospholipase D and C signalling cascades, which in turn will modulate the PI3K/Akt/mTOR and RAS/RAF/MEK/ERK pathways. By feedback coupling, the SAPK/JNK signalling chain is also affected. These changes lead to a G2/M phase cell cycle arrest and subsequently induce programmed cell death. The available knowledge on inhibition of AKT phosphorylation, mTOR phosphorylation and Raf down-regulation renders ALPs as attractive candidates for modern medical treatment, which is based on individualized diagnosis and therapy. Corresponding to their unusual profile of activities, their side effects result from cholinomimetic activity mainly and focus on the gastrointestinal tract. These aspects together with their bone marrow sparing features render APCs well suited for modern combination therapy. Although the clinical success has been limited in cancer diseases so far, the use of miltefosine against leishmaniosis is leading the way to better understanding their optimized use. Recent synthetic programs generate congeners with the increased therapeutic ratio, liposomal formulations, as well as diapeutic (or theranostic) derivatives with optimized properties. It is anticipated that these innovative modifications will pave the way for the further successful development of ALPs.

Evaluation of the antinociceptive and anti-inflammatory activities of piperic acid: Involvement of the cholinergic and vanilloid systems

Piperin is the active compound of black pepper (Piper nigrum). From the piperine was obtained the molecule of the piperic acid (PAC). The objective of this study was to evaluate the antinociceptive and anti-inflammatory of the compound. The antinociceptive effects of PAC were evaluated by abdominal writhing, formalin, capsaicin and tail-flick tests; while the anti-inflammatory effects were evaluated by paw oedema and air pouch tests, and in vitro COX inhibition assay. The possible action mechanism of PAC was evaluated using naloxone, L-NAME, glibenclamide and atropine in tail flick test and by Cholinesterase activity assay and production of TNF-α and IL-1β. PAC significantly reduced the nociceptive effects induced by acetic acid or formalin in mice. PAC also demonstrated an antinociceptive effect in the tail-flick model. The muscarinic receptor antagonist, atropine reduced the antinociceptive effect of PAC in the tail-flick model. PAC was able to inhibit capsaicin-induced nociception, showing involvement of TRPV1. The compound did not alter the motor capacity of the animals, not interfering in the nociceptive response. PAC also showed anti- inflammatory activity by inhibiting the formation of carrageenan-induced paw oedema, leukocyte migration, and cytokine production / release. Atropine reduced the activity of PAC on leukocyte migration, and cytokine production. The compound showed to be able to reduce the cytokine production stimulated by capsaicin. PAC inhibited the COX activity. The results presented suggest that the possible cholinomimetic action and vanilloid agonist of the piperic acid may be responsible by antinociceptive and anti- inflammatory effects; these effects are devoid of toxicity.

An evaluation of neonicotinoids' potential to inhibit human cholinesterases: Protein–ligand docking and interaction profiling studies

Many so-called neuroactive insecticides target invertebrate neurotransmitter systems, including the cholinergic system. With their relatively low toxicity to vertebrates, neonicotinoids represent a new class of neuroactive insecticides that bind to nicotinic receptors for acetylcholine in the insect central nervous system and result in paralysis and eventual death due to receptor overstimulation. On the understanding that, today, cholinesterase inhibitors are used to obtain the symptomatic relief of Alzheimer disease (AD), the aforementioned direct cholinomimetic action of neonicotinoids could, perhaps, confer anti-AD drug-like attributes to these compounds. It is shown here, using protein–ligand docking and interaction profiling, that neonicotinoids penetrate deep into the active-site gorge of both acetylcholinesterase and butyrylcholinesterase and that they form relatively strong noncovalent bonds with multiple critical residues that normally bind/hydrolyze choline esters. With their gorge-spanning shape and dual-binding specificity, neonicotinoids (first-generation compounds in particular) represent promising leads for the development of reversible, mixed-type cholinesterase inhibitors in the fight against AD.

Vitexin with its Derivatives is Responsible for the Cholinomimetic Properties of Penianthus longifolius Extract which Stimulates Muscarinic Receptors

Background: Alzheimer’s disease is a neurodegenerative disease that affects about 47.5 million people worldwide, a number that is expected to double every 20 years. Available treatments are only palliative because none of the cholinomimetic agents is curative or preventive and they mostly come with severe side effects. The discovery of safer and more effective medications is an unmet healthcare need. Penianthus longifolius is an herbal medicine with strong cholinomimetic activity. Keywords: Alzheimer’s, cholinomimetic, P. longifolius, dementia, antioxidant, muscarinic.

Scopolamine-induced amnesia model: A possible anticholinergic mechanism with reversibility with statins and nootropic agents

Background: High cholesterol turnover is implicated in the pathogenesis of Alzheimer’s disease by causing β amyloid plaque deposition and selective degeneration of cholinergic neurons in brain whereas drugs currently used for the treatment of the same are based on mechanisms which are cholesterol independent. Aims and Objectives: The aim of the study is to find any cholesterol independent mechanisms such as antioxidant and cholinomimetic action of statins in a reversal of memory deficit in scopolamine-induced amnesia. Materials and Methods: Sixty young Swiss albino mice were divided equally into 10 groups, i.e., Group I to Group X. Group I–V and Group VI–X were subjected two exteroceptive behavioral models, i.e., passive avoidance paradigm and Morris water maze, (MWM) respectively. Group I and Group VI served as negative control. Carboxymethyl cellulose (CMC), atorvastatin, simvastatin (test drugs), and piracetam (standard drug), respectively, were given orally to Group II and VII, Group III and VIII, Group IV and IX, and Group V and X for 14 days before inducing amnesia using scopolamine (0.4 mg/kg body weight) injection i.p. Results: Step down latency of disease control group treated with CMC was significantly lower than that of the negative control group (42.5 ± 9.07 s vs. 147.5 ± 10.78 s) as well as that of statin and piracetam treated groups. Learning was good among all groups in MWM with a gradual decrease in escape latency from day 1 to day 4 but during memory retrieval test on day 5, CMC treated group performed poorly in comparison to others. There was no significant difference in plasma cholesterol levels among different groups whereas malondialdehyde was significantly lower among groups treated with statins or piracetam. Conclusion: Statins reversed the scopolamine-induced amnesia by some cholesterol independent mechanisms.

Contribution of Ryanodine Receptors in Forming Presynaptic Ca2+ Level and Cholinergic Modulation in Response to Single Potential in Frog Neuromuscular Junction

Ca2+ entering through voltage-gated Ca2+ channels plays a key role in the initiation of neurotransmitter secretion. However, intracellular Ca2+ storages such as endoplasmic reticulum (ER) can also contribute in the presynaptic Ca2+ level forming. Also ryanodine-dependent Ca2+-induced Ca2+ channels of endoplasmic reticulum may contribute in secretion inhibiting action of cholinomimetics. In this work, we use a photometric method for estimating the relative change in the level of presynaptic Ca2+ ions (Ca2+ transient). We have shown that during low-frequency stimulation Ca2+ release from the ER is involved in forming of presynaptic Ca2+ level. And more likely those effects of the cholinomimetics on Ca2+ transient are not related to Ca2+ release from the endoplasmic reticulum.

Novel multi-target-directed ligands for Alzheimer's disease: Combining cholinesterase inhibitors and 5-HT6 receptor antagonists. Design, synthesis and biological evaluation

As currently postulated, a complex treatment may be key to an effective therapy for Alzheimer's disease (AD). Recent clinical trials in patients with moderate AD have shown a superior effect of the combination therapy of donepezil (a selective acetylcholinesterase inhibitor) with idalopirdine (a 5-HT6 receptor antagonist) over monotherapy with donepezil. Here, we present the first report on the design, synthesis and biological evaluation of a novel class of multifunctional ligands that combines a 5-HT6 receptor antagonist with a cholinesterase inhibitor. Novel multi-target-directed ligands (MTDLs) were designed by combining pharmacophores directed against the 5-HT6 receptor (1-(phenylsulfonyl)-4-(piperazin-1-yl)-1H-indole) and cholinesterases (tacrine or N-benzylpiperidine analogues). In vitro evaluation led to the identification of tacrine derivative 12 with well-balanced potencies against the 5-HT6 receptor (Kb = 27 nM), acetylcholinesterase and butyrylcholinesterase (IC50hAChE = 12 nM, IC50hBuChE = 29 nM). The compound also showed good in vitro blood-brain-barrier permeability (PAMPA-BBB assay), which was confirmed in vivo (open field study). Central cholinomimetic activity was confirmed in vivo in rats using a scopolamine-induced hyperlocomotion model. A novel class of multifunctional ligands with compound 12 as the best derivative in a series represents an excellent starting point for the further development of an effective treatment for AD.

Anticholinesterase activity of prolactin: correlation with analgesia.

The possible inhibitory effect of prolactin on serum cholinesterase activity has been examined. Prolactin given to mice inhibited the enzyme's activity in a dose-related fashion. This inhibition was not reversed by naloxone. A significant correlation was observed between the anticholinesterase and analgesic activity of prolactin. The findings suggest that prolactin may exert its cholinomimetic activity by inhibition of cholinesterase. A significant contribution by the cholinergic activity, which was independent of the opioid system, was indicated in the analgesic effect.

Pharmacological and physiological characterization of the tremulous jaw movement model of parkinsonian tremor: potential insights into the pathophysiology of tremor.

Tremor is a cardinal symptom of parkinsonism, occurring early on in the disease course and affecting more than 70% of patients. Parkinsonian resting tremor occurs in a frequency range of 3–7 Hz and can be resistant to available pharmacotherapy. Despite its prevalence, and the significant decrease in quality of life associated with it, the pathophysiology of parkinsonian tremor is poorly understood. The tremulous jaw movement (TJM) model is an extensively validated rodent model of tremor. TJMs are induced by conditions that also lead to parkinsonism in humans (i.e., striatal DA depletion, DA antagonism, and cholinomimetic activity) and reversed by several antiparkinsonian drugs (i.e., DA precursors, DA agonists, anticholinergics, and adenosine A2A antagonists). TJMs occur in the same 3–7 Hz frequency range seen in parkinsonian resting tremor, a range distinct from that of dyskinesia (1–2 Hz), and postural tremor (8–14 Hz). Overall, these drug-induced TJMs share many characteristics with human parkinsonian tremor, but do not closely resemble tardive dyskinesia. The current review discusses recent advances in the validation of the TJM model, and illustrates how this model is being used to develop novel therapeutic strategies, both surgical and pharmacological, for the treatment of parkinsonian resting tremor.

Drug-induced parkinsonism

Drug-induced parkinsonism (DIP) is condition that mimics Parkinson's disease. Characterized mainly by rigidity and bradykinesia, it has less prominent tremor and gait instability. DIP is generally caused by lipophilic drugs that "block" dopamine D2 receptors in the brain, although presynaptic dopamine depletion, false transmitters, mitochondrial respiratory chain dysfunction, and overactivity in the gamma-aminobutyric acid (GABA)ergic system or cholinomimetic action have also been postulated as possible mechanisms. The onset of DIP is acute to subacute. It is more common in women and has a bimodal age distribution. Other diseases that can resemble DIP include neuropsychiatric conditions (eg, depression, negative symptoms of schizophrenia) and Wilson's disease. Physicians may be able to prevent DIP by prescribing neuroleptic agents appropriately and with caution. The risk of DIP is presumably lower with the use of "atypical" antipsychotic agents but it is not eliminated, especially in those most vulnerable to parkinsonism (eg, the elderly or cognitively impaired). The best treatment is discontinuation of the provoking medication. Prospective studies are needed to further define the mechanism of DIP, identify individual susceptibility, determine the impact of atypical antipsychotic agents, and develop further treatment options for those unable to stop the offending agent.

Effects of muscarinic agonists in the guinea‐pig prostate

1. The contractile response to transmural stimulation of the guinea-pig prostate is largely due to activation of noradrenergic neurons but there is a small contribution from cholinergic neurons. Carbachol and acetylcholine have been reported to act via muscarinic M(1) cholinoceptors to facilitate contractions produced by neuronal stimulation of the tissue. This action of cholinomimetics was further investigated in isolated ventral lobes of the prostate. 2. Oxotremorine-M, bethanecol, pilocarpine, xanomeline and McN-A-343 produced facilitation of the response to transmural stimulation of the prostate. When carbachol was applied as the first agonist, the facilitatory response to the latter four agonists above was absent or reduced, compared with the effect observed when the other agonist was applied first, indicating that the effect of these agonists is readily desensitized. Only oxotremorine-M was unaffected by prior exposure of the tissue to carbachol. When applied first, pilocarpine and xanomeline produced a smaller degree of facilitation than carbachol indicating they were partial agonists for the effect. The facilitation produced by McN-A-343, when applied as the first agonist, was variable. In some preparations the facilitation was less than that of carbachol but in others it exceeded that produced by a subsequent application of carbachol. 3. The release of endogenous choline from the prostate was measured at rest and during transmural stimulation using a chemiluminescent technique. A statistically significant negative correlation existed between pmol mg(-1) of endogenous choline released during transmural stimulation and the mass of the ventral lobe of the prostate. As the guinea-pig prostate is known to undergo postpubertal stromal hypertrophy the finding suggests that endogenous choline release from the prostate is largely from epithelial, rather than stromal tissue. 4. The possible involvement of facilitatory M(1) autoreceptors on cholinergic neurons in the effect of cholinomimetics was investigated. Tissue was incubated with (3)H-choline to label neuronal stores of acetylcholine and the subsequent release of (3)H-choline from the tissue was measured. Carbachol per se increased the release of (3)H-choline. 5. Transmural stimulation usually increased the release of (3)H-choline but in c. 30% of preparations there was a decrease. In the presence of carbachol there was a significant increase in the release of (3)H-choline during transmural stimulation of prostate lobes. However, there was no correlation between the two effects of carbachol; facilitating contractions produced by transmural stimulation and enhancing (3)H-choline release during transmural stimulation. The finding provides no evidence that facilitatory M(1) autoreceptors on cholinergic neurons play a major role in the facilitation of contractions.

Examination of nighttime sleep-related problems during double-blind, placebo-controlled trials of galantamine in patients with Alzheimer's disease

SUMMARYBackground: Acetylcholinesterase inhibitors (AChEI) are now widely used as treatment for Alzheimer's disease (AD). Their cholinomimetic action has the potential to influence sleep quality and donepezil has been associated with sleep-related adverse events. This study examined whether galantamine, an AChEI with nicotinic modulation, is associated with nighttime sleep-related problems.Methods: Using data combined from three randomized, double-blind trials, galantamine (GAL) and placebo-treated patients were compared on sleep-related adverse events and concomitant medications. Verbatim descriptions by patients, as recorded by physicians, were used to classify adverse events into insomnia/sleep problems and nightmares/dreams. New concomitant medications were counted when prescribed for sleep-related indications. Treatment arms were 705 subjects on GAL 24 mg (12 mg BID), 279 on GAL 16 mg (8 mg BID), and 714 on placebo.Results: Comparing GAL 24, GAL 16, and placebo arms, the respective rates for insomnia/ sleep problems were 2.6, 1.1, and 2.2% and for nightmares were 1.1, 0.4, and 0.1%. Comparisons between GAL arms and placebo were not significant, with the exception of GAL 24 for nightmares ( p = 0.02). However, due to the low frequency of nightmares in each group the clinical relevance of this difference is unknown. Rates of use for all concomitant medications indicated for sleep were 5.4, 2.9, and 4.6%, respectively, with no significant differences between GAL arms and placebo.Conclusion: These results support previous findings from double-blind, placebo-controlled studies that have shown maintenance of good sleep hygiene during treatment with galantamine.

Evaluation of the cholinomimetic actions of trimethylsulfonium, a compound present in the midgut gland of the sea hare Aplysia brasiliana (Gastropoda, Opisthobranchia).

Trimethylsulfonium, a compound present in the midgut gland of the sea hare Aplysia brasiliana, negatively modulates vagal response, indicating a probable ability to inhibit cholinergic responses. In the present study, the pharmacological profile of trimethylsulfonium was characterized on muscarinic and nicotinic acetylcholine receptors. In rat jejunum the contractile response induced by trimethylsulfonium (pD2 = 2.46 +/- 0.12 and maximal response = 2.14 +/- 0.32 g) was not antagonized competitively by atropine. The maximal response (Emax) to trimethylsulfonium was diminished in the presence of increasing doses of atropine (P<0.05), suggesting that trimethylsulfonium-induced contraction was not related to muscarinic stimulation, but might be caused by acetylcholine release due to presynaptic stimulation. Trimethylsulfonium displaced [3H]-quinuclidinyl benzilate from rat cortex membranes with a low affinity (Ki = 0.5 mM). Furthermore, it caused contraction of frog rectus abdominis muscles (pD2 = 2.70 +/- 0.06 and Emax = 4.16 +/- 0.9 g), which was competitively antagonized by d-tubocurarine (1, 3 or 10 microM) with a pA2 of 5.79, suggesting a positive interaction with nicotinic receptors. In fact, trimethylsulfonium displaced [3H]-nicotine from rat diaphragm muscle membranes with a Ki of 27.1 microM. These results suggest that trimethylsulfonium acts as an agonist on nicotinic receptors, and thus contracts frog skeletal rectus abdominis muscle and rat jejunum smooth muscle via stimulation of postjunctional and neuronal prejunctional nicotinic cholinoreceptors, respectively.

The effects of carbachol on the proximal and distal parts of frog motor nerve endings.

Cholinomimetics not only activate postsynaptic cholinoreceptors in neuromuscular synapses, but also alter the process of acetylcholine secretion from nerve endings. However, the mechanism of action of cholinomimetics on the secretory process remains unidentified. We approached the question of the mechanism of the presynaptic action of cholinomimetics in the present study by investigating the effects of the n,m-cholinomimetic carbachol on nerve ending currents and postsynaptic membrane currents. Carbachol induced decreases in the postsynaptic response, without affecting the duration and amplitude of the nerve ending current in both the central and distal part of the nerve ending. However, carbachol increased the time between the arrival of the presynaptic action potential and the start of transmitter secretion. This effect on synaptic delay was more marked in the distal parts of the ending. The action of another potential modulator, extracellular potassium, was accompanied by decreases in presynaptic currents and also by increases in synaptic delay. These data provide evidence for the suppressive effect of carbachol on acetylcholine secretion acting via presynaptic metabotropic cholinoreceptors which control the level and time course of secretion of neurotransmitter quanta.

Lithium does not synergize the peripheral action of cholinomimetics as seen in the central nervous system

Lithium is known to synergize the action of cholinomimetics in the CNS such that pilocarpine induces seizures in low concentration (1/13th of per se dose) in rats. The present study was undertaken to see if lithium priming also enhances the peripheral effects of acetylcholine and pilocarpine i.e. change in blood pressure in rats and contractions of the isolated guinea pig ileum. In anaesthetized rats the blood pressure was recorded from cannulated carotid artery connected through the pressure transducer to Coulbourn polygraph. The blood pressure response of pilocarpine was not different either in magnitude or in duration when administered 1, 2 and 4 h after lithium chloride (3meq/kg) pretreatment as compared to the control. Similarly acetylcholine effect remained unchanged after lithium chloride priming. In the isolated guinea pig ileum experiments, ileum was incubated for 1 h in different concentrations of lithium chloride and effect on acetylcholine induced contractions were observed. Lithium in concentration of 2.8 × 10 −3M had no effect on acetylcholine induced contractions while incubation with higher concentrations of 1.4 × 10 −2 M and 2.8 × 10 −2 M significant inhibition of acetylcholine contractions were observed. At this concentration, histamine induced contractions were also inhibited. The results indicate that lithium does not synergize the action of cholinomimetics in the periphery as that seen in the CNS. The inhibition of acetylcholine and histamine induced contractions in guinea pig ileum at high concentration of lithium seems to be non-specific effect.

Pharmacological Screening of a Methanol Extract from Mormodica charantia in Rodents

A methanol leaf extract of Mormodica charantia was evaluated for analgesic and contractile effects. The extract showed a significant reduction in writhing induced by acetic acid in mice and contractile effects on isolated rat stomach strip preparation, but reversed a dimethytubocurarine block of rat diaphragm muscle preparations, suggesting cholinomimetic and analgesic activities.

Arachidonoylcholine and N,N-dimethylaminoethyl arachidonate are new cholinergic compounds

Choline and N,N-dimethylaminoethyl esters of arachidonic and some other fatty acids were synthesized. Experiments on the embryos and larvae of sea urchins, sensitive to cholinergic compounds, showed that arachidonoylcholine exhibited cholinomimetic activity similar to that of nicotine whereas N,N-dimethylaminoethyl arachidonate acted as an acetylcholine antagonist. The corresponding esters of docosahexaenoic acid displayed similar biological properties.

EFFECTS OF CARNITINE AND ITS DERIVATIVES ON GASTRIC ACID SECRETION IN RATS

Carnitine is a natural substance that acts as a carrier of fatty-acids across the inner mitochondrial membrane for subsequent β-oxidation. Acetyl- L-carnitine is the acetyl derivative of L-carnitine that has been shown to possess a slight cholinomimetic activity. Its success in sports medicine is dependent on the fact that it is able to stimulate the central nervous system functions. This study aims to investigate the effects of L-carnitine (LC) and its derivatives—acetyl- L-carnitine (ALC) and propionyl- L-carnitine (PLC)—on gastric acid secretion in rats. A concentration-dependent relationship with both ALC or PLC was observed in experiments in vitrousing a rat isolated stomach. The addition of atropine to the perfusion bath only partially antagonized the effects of the two compounds. Stimulation of gastric acid secretion in a dose-dependent manner was also found when the tested compounds were administered i.v. to anaesthetized rats. To elucidate the mechanism of the gastric secretory response, assay for acetylcholine esterase activity using acetylthiocholine as substrate, was performed. It was found that ALC and PLC inhibited acetylcholine esterase, however, the IC 50for both compounds was about four times of magnitude greater than that of eserine. As the increase of the gastric acid secretion promoted by carnitines was blocked only partially by atropine both in vitroand in vivo, whilst it was completely abolished by experimental degeneration of the sympathetic neurons or by blockade of the postsynaptic sympathetic receptors, it is suggested that the effect of carnitines is determined by cholinergic and partly by adrenergic mechanisms.