Dopaminergic involvement in the mechanism of action of pentazocine

Sigma-1 Receptor Signaling: In Search of New Therapeutic Alternatives for Cardiovascular and Renal Diseases

Cardiovascular and renal diseases are among the leading causes of death worldwide, and regardless of current efforts, there is a demanding need for therapeutic alternatives to reduce their progression to advanced stages. The stress caused by diseases leads to the activation of protective mechanisms in the cell, including chaperone proteins. The Sigma-1 receptor (Sig-1R) is a ligand-operated chaperone protein that modulates signal transduction during cellular stress processes. Sig-1R interacts with various ligands and proteins to elicit distinct cellular responses, thus, making it a potential target for pharmacological modulation. Furthermore, Sig-1R ligands activate signaling pathways that promote cardioprotection, ameliorate ischemic injury, and drive myofibroblast activation and fibrosis. The role of Sig-1R in diseases has also made it a point of interest in developing clinical trials for pain, neurodegeneration, ischemic stroke, depression in patients with heart failure, and COVID-19. Sig-1R ligands in preclinical models have significantly beneficial effects associated with improved cardiac function, ventricular remodeling, hypertrophy reduction, and, in the kidney, reduced ischemic damage. These basic discoveries could inform clinical trials for heart failure (HF), myocardial hypertrophy, acute kidney injury (AKI), and chronic kidney disease (CKD). Here, we review Sig-1R signaling pathways and the evidence of Sig-1R modulation in preclinical cardiac and renal injury models to support the potential therapeutic use of Sig-1R agonists and antagonists in these diseases.

Sigmar1's Molecular, Cellular, and Biological Functions in Regulating Cellular Pathophysiology

The Sigma 1 receptor (Sigmar1) is a ubiquitously expressed multifunctional inter-organelle signaling chaperone protein playing a diverse role in cellular survival. Recessive mutation in Sigmar1 have been identified as a causative gene for neuronal and neuromuscular disorder. Since the discovery over 40 years ago, Sigmar1 has been shown to contribute to numerous cellular functions, including ion channel regulation, protein quality control, endoplasmic reticulum-mitochondrial communication, lipid metabolism, mitochondrial function, autophagy activation, and involved in cellular survival. Alterations in Sigmar1’s subcellular localization, expression, and signaling has been implicated in the progression of a wide range of diseases, such as neurodegenerative diseases, ischemic brain injury, cardiovascular diseases, diabetic retinopathy, cancer, and drug addiction. The goal of this review is to summarize the current knowledge of Sigmar1 biology focusing the recent discoveries on Sigmar1’s molecular, cellular, pathophysiological, and biological functions.

Cardiac Dysfunction in the Sigma 1 Receptor Knockout Mouse Associated With Impaired Mitochondrial Dynamics and Bioenergetics

Background The Sigma 1 receptor (Sigmar1) functions as an interorganelle signaling molecule and elicits cytoprotective functions. The presence of Sigmar1 in the heart was first reported on the basis of a ligand-binding assay, and all studies to date have been limited to pharmacological approaches using less-selective ligands for Sigmar1. However, the physiological function of cardiac Sigmar1 remains unknown. We investigated the physiological function of Sigmar1 in regulating cardiac hemodynamics using the Sigmar1 knockout mouse (Sigmar1-/-). Methods and Results Sigmar1-/- hearts at 3 to 4 months of age showed significantly increased contractility as assessed by left ventricular catheterization with stimulation by increasing doses of a β1-adrenoceptor agonist. Noninvasive echocardiographic measurements were also used to measure cardiac function over time, and the data showed the development of cardiac contractile dysfunction in Sigmar1 -/- hearts as the animals aged. Histochemistry demonstrated significant cardiac fibrosis, collagen deposition, and increased periostin in the Sigmar1 -/- hearts compared with wild-type hearts. Ultrastructural analysis of Sigmar1-/- cardiomyocytes revealed an irregularly shaped, highly fused mitochondrial network with abnormal cristae. Mitochondrial size was larger in Sigmar1-/- hearts, resulting in decreased numbers of mitochondria per microscopic field. In addition, Sigmar1-/- hearts showed altered expression of mitochondrial dynamics regulatory proteins. Real-time oxygen consumption rates in isolated mitochondria showed reduced respiratory function in Sigmar1-/- hearts compared with wild-type hearts. Conclusions We demonstrate a potential function of Sigmar1 in regulating normal mitochondrial organization and size in the heart. Sigmar1 loss of function led to mitochondrial dysfunction, abnormal mitochondrial architecture, and adverse cardiac remodeling, culminating in cardiac contractile dysfunction.

Interactions of opioids with caffeine: evaluation by ambulatory activity in mice

Morphine (up to 10 mg kg-1), buprenorphine (up to 0.1 mg kg-1), pentazocine (30 mg kg-1) and caffeine (up to 10 mg kg-1), significantly increased mouse ambulation. The combination of morphine, buprenorphine and pentazocine with caffeine generally enhanced the effect. Dopamine D1- and D2-receptor bockade, depletion of stored dopamine, and inhibition of dopamine synthesis could reduce the ambulation increased by single administration of morphine, buprenorphine and caffeine, and by combined administration of morphine and buprenorphine with caffeine. Although naloxone (0.1-3 mg kg-1) itself did not change mouse ambulation, at 3 mg kg-1, it reduced the effect of caffeine. The repeated administration of morphine (10 mg kg-1) induced a sensitization to the ambulation-increasing effect, and was inhibited by the combination of caffeine (10 mg kg-1) in the repeated administration schedule. The repeated administration of caffeine (10 mg kg-1) with buprenorphine (0.3 mg kg-1) resulted in a decrease in the effect to the level of caffeine alone. The development of cross-sensitization to morphine (10 mg kg-1) by the repeated treatment with buprenorphine (0.3 mg kg-1) was inhibited by caffeine (10 mg kg-1). Our results suggest that the dopaminergic systems are involved in the enhanced interaction of opioids having agonistic action on mu- or sigma-receptors with caffeine. However, it is also considered that, following the repeated administration, caffeine acts to reduce the sensitivity to the ambulation-increasing effect of opioids, probably inducing up-regulation of adenosinergic systems.

Non-competitive N-methyl-D-aspartate antagonists are potent activators of ventral tegmental A10 dopamine neurons

The response of ventral tegmental (VTA) A10 dopamine neurons to a series of compounds covering the spectrum from high-affinity phencyclidine receptor ligands (MK-801, PCP) to high-affinity sigma-receptor ligands [+)-pentazocine, DTG) was measured using single-unit extracellular recording techniques in the rat. Dose-response comparisons revealed that MK-801 was 3, 6, 19 and 119 times more potent at activating A10 neurons than PCP, (+)-SKF-10,047, ketamine and (+)-pentazocine, respectively. DTG (1,3-di-o-tolylguanidine), the most selective sigma-ligand, and U50,488H, a kappa-opiate, failed to produce any stimulation of firing. Also, pretreatment with haloperidol, a potent sigma-receptor ligand, did not prevent MK-801-induced excitations. Thus, the activation of the A10-mesolimbic-mesocortical dopamine pathways by PCP, PCP-like drugs and sigma-psychotomimetics is mediated by the PCP receptor, not the haloperidol-sensitive sigma-receptor, with potencies directly correlated to their activity as non-competitive N-methyl-D-aspartate (NMDA) antagonists.

Effects of repeated administration of pentazocine on ambulatory activity in mice: comparison with the effects of morphine and methamphetamine

Effects of single and repeated administration of pentazocine (5 times at intervals of 3-4 days) were compared with those of morphine and methamphetamine by means of ambulatory activity in mice. The interactions among these 3 drugs were also investigated. Pentazocine (25 mg/kg, s.c.), morphine (10 and 20 mg/kg, s.c.) and methamphetamine (2 mg/kg, s.c.) significantly increased the activity, and the effect progressively enhanced (defined here as development of reverse tolerance) during the repeated administration schedule. The induction of reverse tolerance to pentazocine was less dependent on the environmental conditions, and it was abolished within 2 months. A cross reverse tolerance was demonstrated from methamphetamine to pentazocine and to morphine, and from morphine to pentazocine. However, no significant cross reverse tolerance was induced from pentazocine to morphine and to methamphetamine, and from morphine to methamphetamine. The present results suggest that pentazocine possesses an ambulation-increasing effect, although the characteristics are different from that of either morphine or methamphetamine.

Abuse of pentazocine combined with tripelennamine: an interaction of pharmacological and demographic characteristics

Abuse of pentazocine (Talwin) and tripelennamine (Pyrabenzamine) (P and T) was studied in a group (N = 16) of inpatients. They were queried about subjective effects and their drug preferences. P and T use was associated with more anxiety than was the opiate or drug-free state. P and T use did not produce euphoria, and users preferred this drug next to last among other abused drugs. P and T use was further studied in outpatients (N = 628) using Client Oriented Data Acquisition Process information. These patients were younger and more often male, Black, and single or separated when compared with opiate users. They began using the drug later and had many fewer years invested in its use.

Morphine may mimic the apomorphine cue by inhibiting dopaminergic autoinhibition

Rats were trained to discriminate the cue produced by 0.25 mg/kg apomorphine from that produced by saline, using a two-lever, drug discrimination task. This cue was blocked by haloperidol but not by DPI, ergometrine, bromocriptine, sulpiride, naloxone or naltrexone; none of these agents substituted for (mimicked) apomorphine. Morphine and levorphanol did, however, mimic apomorphine, whereas dextrorphan did not; pentazocine induced responding unlike either apomorphine or saline. The substitution of morphine for apomorphine was blocked by naltrexone or bromocriptone, and was partially antagonized by a low of ergometrine, but was unaffected by haloperidol or sulpiride. To explain these results, it was proposed that morphine mimics apomorphine by inhibiting dopaminergic autoregulation involving D2-receptors.

Effects of pentazocine and other opiates on shock detection in the rat: involvement of opiate and dopamine receptors

The hypothesis that the antinociceptive effects of pentazocine, a mixed agonist-antagonist opiate of the benzomorphan class, are mediated by a dual opiate-dopaminergic mechanism was tested using a two-choice procedure in which rats were required to discriminate the presence or absence of shock. The results showed that pentazocine decreased shock sensitivity and speed of responding, effects that were qualitatively similar to those of morphine. However, while the antinociceptive effect of both pentazocine and morphine could be antagonized by opiate receptor blockage, that of pentazocine, but not of morphine, could also be antagonized by dopamine receptor blockade. Observations with levorphanol and phenazocine suggested further that dopamine, as well as opiate receptor agonism may be characteristic of the benzomorphans.