The clinical pharmacogenetics implementation consortium guideline for SLCO1B1 and simvastatin-induced myopathy: 2014 update

Simvastatin is among the most commonly used prescription medications for cholesterol reduction. A single coding single-nucleotide polymorphism, rs4149056T>C, in SLCO1B1 increases systemic exposure to simvastatin and the risk of muscle toxicity. We summarize evidence from the literature supporting this association and provide therapeutic recommendations for simvastatin based on SLCO1B1 genotype. This article is an update to the 2012 Clinical Pharmacogenetics Implementation Consortium guideline for SLCO1B1 and simvastatin-induced myopathy.

A common functional promoter variant links CNR1 gene expression to HDL cholesterol level

CB₁ receptor blockers increase HDL-C levels. Although genetic variation in the CB₁ receptor – encoded by the CNR1 gene – is known to influence HDL-C level as well, human studies conducted to date have been limited to genetic markers such as haplotype tagging SNPs. Here we identify rs806371 in the CNR1 promoter as the causal variant. We resequenced the CNR1 gene and genotype all variants in a DNA biobank linked to comprehensive electronic medical records. By testing each variant for association with HDL-C level in a clinical practice-based setting, we localize a putative functional allele to a 100bp window in the 5′-flanking region. Assessment of variants in this window for functional impact on electrophoretic mobility shift assay identified rs806371 as a novel regulatory binding element. Reporter gene assays confirm that rs806371 reduces HDL-C gene expression, thereby linking CNR1 gene variation to HDL-C level in humans.

Characterization of statin dose response in electronic medical records

Efforts to define the genetic architecture underlying variable statin response have met with limited success, possibly because previous studies were limited to effect based on a single dose. We leveraged electronic medical records (EMRs) to extract potency (ED50) and efficacy (Emax) of statin dose-response curves and tested them for association with 144 preselected variants. Two large biobanks were used to construct dose-response curves for 2,026 and 2,252 subjects on simvastatin and atorvastatin, respectively. Atorvastatin was more efficacious, was more potent, and demonstrated less interindividual variability than simvastatin. A pharmacodynamic variant emerging from randomized trials (PRDM16) was associated with Emax for both. For atorvastatin, Emax was 51.7 mg/dl in subjects homozygous for the minor allele vs. 75.0 mg/dl for those homozygous for the major allele. We also identified several loci associated with ED50. The extraction of rigorously defined traits from EMRs for pharmacogenetic studies represents a promising approach to further understand the genetic factors contributing to drug response.

The effect of novel promoter variants in MATE1 and MATE2 on the pharmacokinetics and pharmacodynamics of metformin

Interindividual variation in response to metformin, first-line therapy for type 2 diabetes, is substantial. Given that transporters are determinants of metformin pharmacokinetics, we examined the effects of promoter variants in both multidrug and toxin extrusion protein 1 (MATE1) (g.-66T → C, rs2252281) and MATE2 (g.-130G → A, rs12943590) on variation in metformin disposition and response. The pharmacokinetics and glucose-lowering effects of metformin were assessed in healthy volunteers (n = 57) receiving metformin. The renal and secretory clearances of metformin were higher (22% and 26%, respectively) in carriers of variant MATE2 who were also MATE1 reference (P < 0.05). Both MATE genotypes were associated with altered post-metformin glucose tolerance, with variant carriers of MATE1 and MATE2 having an enhanced (P < 0.01) and reduced (P < 0.05) response, respectively. Consistent with these results, patients with diabetes (n = 145) carrying the MATE1 variant showed enhanced metformin response. These findings suggest that promoter variants of MATE1 and MATE2 are important determinants of metformin disposition and response in healthy volunteers and diabetic patients.

Electronic medical records as a tool in clinical pharmacology: opportunities and challenges

The development and increasing sophistication of electronic medical record (EMR) systems hold the promise of not only improving patient care but also providing unprecedented opportunities for discovery in the fields of basic, translational, and implementation sciences. Clinical pharmacology research in the EMR environment has only recently started to become a reality, with EMRs becoming increasingly populated, methods to mine drug response and other phenotypes becoming more sophisticated, and links being established with DNA repositories.

The clinical pharmacogenomics implementation consortium: CPIC guideline for SLCO1B1 and simvastatin-induced myopathy

Cholesterol reduction from statin therapy has been one of the greatest public health successes in modern medicine. Simvastatin is among the most commonly used prescription medications. A non-synonymous coding single-nucleotide polymorphism (SNP), rs4149056, in SLCO1B1 markedly increases systemic exposure to simvastatin and the risk of muscle toxicity. This guideline explores the relationship between rs4149056 (c.521T>C, p.V174A) and clinical outcome for all statins. The strength of the evidence is high for myopathy with simvastatin. We limit our recommendations accordingly.

Optimizing drug outcomes through pharmacogenetics: a case for preemptive genotyping

Routine integration of genotype data into drug decision making could improve patient safety, particularly if many relevant genetic variants can be assayed simultaneously before prescribing the target drug. The frequency of opportunities for pharmacogenetic prescribing and the potential adverse events (AEs) mitigated are unknown. We examined the frequency with which 56 medications with known outcomes influenced by variant alleles were prescribed in a cohort of 52,942 medical home patients at Vanderbilt University Medical Center (VUMC). Within a 5-year window, we estimated that 64.8% (95% confidence interval (CI): 64.4-65.2%) of individuals were exposed to at least one medication with an established pharmacogenetic association. Using previously published results for six medications with severe, well-characterized, genetically linked AEs, we estimated that 383 events (95% CI, 212-552) could have been prevented with an effective preemptive genotyping program. Our results suggest that multiplexed, preemptive genotyping may represent an efficient alternative approach to current single-use ("reactive") methods and may also improve safety.

Operational implementation of prospective genotyping for personalized medicine: the design of the Vanderbilt PREDICT project

The promise of "personalized medicine" guided by an understanding of each individual's genome has been fostered by increasingly powerful and economical methods to acquire clinically relevant information. We describe the operational implementation of prospective genotyping linked to an advanced clinical decision-support system to guide individualized health care in a large academic health center. This approach to personalized medicine entails engagement between patient and health-care provider, identification of relevant genetic variations for implementation, assay reliability, point-of-care decision support, and necessary institutional investments. In one year, approximately 3,000 patients, most of whom were scheduled for cardiac catheterization, were genotyped on a multiplexed platform that included genotyping for CYP2C19 variants that modulate response to the widely used antiplatelet drug clopidogrel. These data are deposited into the electronic medical record (EMR), and point-of-care decision support is deployed when clopidogrel is prescribed for those with variant genotypes. The establishment of programs such as this is a first step toward implementing and evaluating strategies for personalized medicine.

The emerging role of electronic medical records in pharmacogenomics

Health-care information technology and genotyping technology are both advancing rapidly, creating new opportunities for medical and scientific discovery. The convergence of these two technologies is now facilitating genetic association studies of unprecedented size within the context of routine clinical care. As a result, the medical community will soon be presented with a number of novel opportunities to bring functional genomics to the bedside in the area of pharmacotherapy. By linking biological material to comprehensive medical records, large multi-institutional biobanks are now poised to advance the field of pharmacogenomics through three distinct mechanisms: (i) retrospective assessment of previously known findings in a clinical practice-based setting, (ii) discovery of new associations in huge observational cohorts, and (iii) prospective application in a setting capable of providing real-time decision support. This review explores each of these translational mechanisms within a historical framework.

High-density lipoprotein (HDL) cholesterol: leveraging practice-based biobank cohorts to characterize clinical and genetic predictors of treatment outcome

Over the past decade, large multicenter trials have unequivocally demonstrated that decreasing low-density lipoprotein (LDL) cholesterol can reduce both primary and secondary cardiovascular events in patients at risk. However, even in the context of maximal LDL lowering, there remains considerable residual cardiovascular risk. Some of this risk can be attributed to variability in high-density lipoprotein (HDL) cholesterol. As such, there is tremendous interest in defining determinants of HDL homeostasis. Risk prediction models are being constructed based upon (1) clinical contributors, (2) known molecular determinants and (3) the genetic architecture underlying HDL cholesterol levels. To date, however, no single resource has combined these factors within the context of a practice-based data set. Recently, a number of academic medical centers have begun constructing DNA biobanks linked to secure encrypted versions of their respective electronic medical record. As these biobanks combine resources, the clinical community is in a position to characterize lipid-related treatment outcome on an unprecedented scale.

Mapping genes that predict treatment outcome in admixed populations

There is great interest in characterizing the genetic architecture underlying drug response. For many drugs, gene-based dosing models explain a considerable amount of the overall variation in treatment outcome. As such, prescription drug labels are increasingly being modified to contain pharmacogenetic information. Genetic data must, however, be interpreted within the context of relevant clinical covariates. Even the most predictive models improve with the addition of data related to biogeographical ancestry. The current review explores analytical strategies that leverage population structure to more fully characterize genetic determinants of outcome in large clinical practice-based cohorts. The success of this approach will depend upon several key factors: (1) the availability of outcome data from groups of admixed individuals (that is, populations recombined over multiple generations), (2) a measurable difference in treatment outcome (that is, efficacy and toxicity end points), and (3) a measurable difference in allele frequency between the ancestral populations.

The Pathway Less Traveled: Moving from Candidate Genes to Candidate Pathways in the Analysis of Genome-Wide Data from Large Scale Pharmacogenetic Association Studies

The candidate gene approach to pharmacogenetics is hypothesis driven, and anchored in biological plausibility. Whole genome scanning is hypothesis generating, and it may lead to new biology. While both approaches are important, the scientific community is rapidly reallocating resources toward the latter. We propose a step-wise approach to large-scale pharmacogenetic association studies that begins with candidate genes, then uses a pathway-based intermediate step, to inform subsequent analyses of data generated through whole genome scanning. Novel computational strategies are explored in the context of two clinically relevant examples, cholesterol synthesis and lipid signaling.

Healthy People 2010 disease prevalence in the Marshfield Clinic Personalized Medicine Research Project cohort: opportunities for public health genomic research

OBJECTIVES

The purpose of this study was to estimate the prevalence of Healthy People 2010 disease conditions in a large population-based cohort in central Wisconsin (WI, USA) and to consider how these conditions can be prioritized for research based on the use of healthcare services, the prevalence of various disease states and the resulting study power.

METHODS

Healthy People 2010 diagnoses were estimated for participants in the Personalized Medicine Research Project (PMRP), a large population-based biobank for residents aged 18 years and older living in central Wisconsin. By interrogating the electronic medical record, three parameters were calculated for each diagnosis: mean number of concomitant diagnoses, mean number of annual clinic visits before diagnosis and mean number of clinic visits after diagnosis.

RESULTS

A total of 18,239 adults enrolled in PMRP from September 2002 to May 2005 and were included in the study. They had a mean age of 49 years (standard deviation: 18.5), ranging from 18-98 years; 57% were female. At least one Healthy People 2010 disease was diagnosed in 86.4% of the participants; 13.6% had never been diagnosed with any of these conditions. The median number of diagnoses per subject was three (range: 1-15). The median number of annual visits after diagnosis was lowest for chronic obstructive pulmonary disease (9.1) and highest for sleep apnea (17.9). Subjects with a diabetic retinopathy diagnosis had the highest number of concomitant diagnoses (mean: 6.8).

DISCUSSION

All of the diseases within the Healthy People 2010 list are purported to have at least some genetic component, with the exception of injuries. The PMRP cohort is large enough that diseases of public health importance can be studied in the context of a variety of clinical and environmental covariates. This database is being developed as a national resource and is particularly useful where the estimated disease prevalence is 5% or greater. For less common diseases, additional cases can be recruited from throughout the Marshfield Clinic system of care, with population-based controls selected from the main PMRP study cohort.

Are pesticides really endocrine disruptors?

In recent years, a considerable amount of basic laboratory investigation has been targeted toward understanding the relationship between environmental contaminants and cellular endocrine function. A number of environmental contaminants are now known to alter endocrine physiology without acting as classic toxicants. Hence, a new field of inquiry has emerged within the discipline of environmental toxicology, the study of endocrine disrupting chemicals (EDCs). Pesticides represent one of the better studied groups of EDCs. As the tools of molecular biology become increasingly sophisticated, our ability to understand the endocrine effects of these compounds continues to broaden at a remarkable rate. Still, clinical data linking them to derangements in human endocrine function have been quite limited. While the scientific community awaits further epidemiological assessment of the impact of pesticides on public health, responsible land management practices should be employed in an effort to reduce the burden of these chemicals ultimately reaching our water supply.

Membrane-delimited coupling between sigma receptors and K+ channels in rat neurohypophysial terminals requires neither G-protein nor ATP

Receptor-mediated modulation of ion channels generally involves G-proteins, phosphorylation, or both in combination. The sigma receptor, which modulates voltage-gated K+ channels, is a novel protein with no homology to other receptors known to modulate ion channels. In the present study patch clamp and photolabelling techniques were used to investigate the mechanism by which sigma receptors modulate K+ channels in peptidergic nerve terminals. The sigma receptor photoprobe iodoazidococaine labelled a protein with the same molecular mass (26 kDa) as the sigma receptor protein identified by cloning. The sigma receptor ligands pentazocine and SKF10047 modulated K+ channels, despite intra-terminal perfusion with GTP-free solutions, a G-protein inhibitor (GDPbetaS), a G-protein activator (GTPgammaS) or a non-hydrolysable ATP analogue (AMPPcP). Channels in excised outside-out patches were modulated by ligand, indicating that soluble cytoplasmic factors are not required. In contrast, channels within cell-attached patches were not modulated by ligand outside a patch, indicating that receptors and channels must be in close proximity for functional interactions. Channels expressed in oocytes without receptors were unresponsive to sigma receptor agonists, ruling out inhibition through a direct drug interaction with channels. These experiments indicate that sigma receptor-mediated signal transduction is membrane delimited, and requires neither G-protein activation nor protein phosphorylation. This novel transduction mechanism is mediated by membrane proteins in close proximity, possibly through direct interactions between the receptor and channel. This would allow for more rapid signal transduction than other ion channel modulation mechanisms, which in the present case of neurohypophysial nerve terminals would lead to the enhancement of neuropeptide release.

Novel human TEF-1 isoforms exhibit altered DNA binding and functional properties

The transcriptional enhancer factor-1 (TEF-1) is a member of the TEA/ATTS domain family. TEF-1 binds to GT-IIC (GGAATG), SphI (AGTATG), SphII (AGCATG), and M-CAT (GGTATG) response elements and is involved in the transactivation of a variety of genes, including the SV40 large T antigen, mammalian muscle-specific genes, and human chorionic somatomammotropin genes. Also, TEF-1 acts as a transcriptional repressor in placental cells, possibly through interaction with the TATA binding protein (TBP), preventing TBP binding to the TATA box. Here we describe the cloning, tissue-specific expression pattern, and functional characterization of two novel TEF-1 isoforms, TEF-1beta and TEF-1gamma. These isoforms most likely arise from alternative splicing of mRNA transcribed from a single gene and involve substitutions and/or insertions in a region immediately following the DNA binding domain. TEF-1beta appears to be widely distributed like the prototypic TEF-1, designated TEF-1alpha, whereas TEF-1gamma exhibits a narrower tissue-specific expression pattern that includes pancreas, kidney, and skeletal and heart muscle. The relatively limited sequence alterations among these isoforms cause significant changes in their DNA binding and transcriptional activities. TEF-1beta and TEF-1gamma bind to GT-IIC sequences with higher affinity and repress hCS promoter more efficiently than TEF-1alpha. These results suggest that each TEF-1 isoform may play unique regulatory roles in various tissues.

Accessory spleens in the thoracic and abdominal cavities after a relapse of idiopathic thrombocytopenic purpura: a case report

This case report presents a highly unusual finding of ectopic splenic tissue in both the thoracic and abdominal cavities in a patient with recurrent idiopathic thrombocytopenic purpura (ITP).

Sigma receptor photolabeling and sigma receptor-mediated modulation of potassium channels in tumor cells

Recent work has indicated that sigma receptor ligands can modulate potassium channels. However, the only sigma receptor characterized at the molecular level has a novel structure unlike any other receptor known to modulate ion channels. This 26-kDa protein has a hydropathy profile suggestive of a single membrane-spanning domain, with no apparent regions capable of G-protein activation or protein phosphorylation. In the present study patch clamp techniques and photoaffinity labeling were used in DMS-114 cells (a tumor cell line known to express sigma receptors) to investigate the role of the 26-kDa protein in ion channel modulation and probe the mechanism of signal transduction. The sigma receptor ligands N-allylnormetazocine (SKF10047), ditolylguanidine, and (+/-)-2-(N-phenylethyl-N-propyl)-amino-5-hydroxytetralin all inhibited voltage-activated potassium current (IK). Iodoazidococaine (IAC), a high affinity sigma receptor photoprobe, produced a similar inhibition in IK, and when cell homogenates were illuminated in the presence of IAC, a protein with a molecular mass of 26 kDa was covalently labeled. Photolabeling of this protein by IAC was inhibited by SKF10047 with half-maximal effect at 7 microM. SKF10047 also inhibited IK with a similar EC50 (14 microM). Thus, physiological responses to sigma receptor ligands are mediated by a protein with the same molecular weight as the cloned sigma receptor. This indicates that ion channel modulation is indeed mediated by this novel protein. Physiological responses were the same when cells were perfused internally with either guanosine 5'-O-(2-thiodiphosphate) or GTP, indicating that signal transduction is independent of G-proteins. These results demonstrate that ion channels can be modulated by a receptor that does not have seven membrane-spanning domains and does not employ G-proteins. Sigma receptors thus modulate ion channels by a novel transduction mechanism.

K+ channel modulation in rodent neurohypophysial nerve terminals by sigma receptors and not by dopamine receptors

1. Sigma receptors bind a diverse group of chemically unrelated ligands, including pentazocine, apomorphine (a dopamine receptor agonist) and haloperidol (a dopamine receptor antagonist). Although sigma binding sites are widely distributed, their physiological roles are poorly understood. Here, the whole-terminal patch-clamp technique was used to demonstrate that sigma receptors modulate K+ channels in rodent neurohypophysis. 2. Previous work suggested that dopamine type 4 (D4) receptors modulate neurohypophysial K+ current, so this study initially tested the role of dopamine receptors. Experiments using transgenic mice lacking D2, D3 or D4 receptors indicated that the reduction of K+ current by PPHT and U101958 (ligands thought to be selective for dopamine receptors) is not mediated by dopamine receptors. The sensitivity of the response to U101958 (a drug that binds to D4 receptors) was the same in both wild-type and D4 receptor-deficient mice. 3. Experiments with other ligands revealed a pharmacological signature inconsistent with any known dopamine receptor. Furthermore, dopamine itself (at 100 microM) had no effect. Thus, despite the activity of a number of putative dopamine receptor ligands, dopamine receptors play no role in the modulation of neurohypophysial K+ channels. 4. Because of the negative results regarding dopamine receptors, and because some of the dopamine receptors ligands used here are known to bind also to sigma receptors, experiments were conducted to test for the involvement of sigma receptors. In rat neurohypophysis the sigma receptor ligands SKF10047, pentazocine, and ditolylguanidine all reversibly inhibited K+ current in a concentration-dependent fashion, as did haloperidol and apomorphine (ligands that bind to both dopamine and sigma receptors). The activity of these and other ligands tested here matches the reported binding specificity for sigma receptors. 5. Fifteen candidate endogenous sigma receptor ligands, including biogenic amines (e.g dopamine and serotonin), steroids (e.g. progesterone), and peptides (e.g. neuropeptide Y), were screened for activity at the sigma receptor. All were without effect. 6. Haloperidol reduced K+ current proportionally at all voltages without shifting the voltage dependence of activation and inactivation. Sigma receptor ligands inhibited current through two distinct K+ channels, the A-channel and the Ca2+-dependent K+ channel. In rat, all drugs reduced current through both channels proportionally, suggesting that both channels are modulated by a single population of sigma receptors. In contrast, mouse peptidergic nerve terminals either have two receptors which are sensitive to these drugs, or a single receptor that is differentially coupled to ion channel function. 7. The inhibition of voltage-activated K+ current by sigma receptors would be expected to enhance the secretion of oxytocin and vasopressin from the neurohypophysis.

Membrane excitability in the neurohypophysis

The application of patch clamp technology to the neurohypophysis has contributed significantly to our understanding of the membrane events governing neuropeptide secretion. Nerve terminals within the posterior pituitary are now known to contain three distinct K+ channel subtypes, a rapidly inactivated channel (responsible for A current), a Ca(2+)-activated K+ channel, and a delayed rectifier channel. Activation of a D2 subtype dopamine receptor reduces both the A-current and current through the Ca2+ activated K+ channels. These actions can be expected to enhance neuropeptide release. Release of nitric oxide reduces the amplitude of the A-current but enhances current through the Ca(2+)-activated K+ channel, and this would provide mechanisms for more complex modes of regulation of release. Neurohypophysial nerve terminals also express at least two types of Ca2+ channels. The first is a dihydropyridine-sensitive, "L-type" channel. The second resembles the "N-type" Ca2+ channel. Patch clamp recordings have shown that tissue culture medium conditioned by exposure to T-cells enhances this Ca2+ current. This may represent a mechanistic link between activation of the immune system and functional membrane changes within the neurohypophysis. GABA-activated Cl- channels have also been described within the neurohypophysis, and these receptors can be modulated by neuroactive steroids. One of these, the progesterone derivative allopregnanolone, changes dramatically during female reproductive transitions. Such an interaction could represent a pivotal mechanistic step in the onset of parturition, and the neurohypophysial GABA receptor may hold promise as a target of therapeutic intervention in clinical cases of preterm labor.

Dopamine D4 receptor mediated inhibition of potassium current in neurohypophysial nerve terminals

Dopamine influences the release of neurohypophysial peptides in vivo. However, the extent to which this effect is caused by a direct dopaminergic action within the neurohypophysis remains unclear. With use of the patch-clamp technique on thin slices of rat posterior pituitary glands, we now provide evidence that dopaminergic agonists inhibit potassium current (IK) in neurohypophysial nerve terminals. Superfusion with the dopamine receptor agonist, (+/-)-2-(N-phenylethyl-N-propyl)-amino-5-hydroxytetralin (PPHT), causes a reversible inhibition of whole-terminal IK under voltage clamp. This effect is concentration-dependent, with a maximal inhibition of 40 +/- 5% and an EC50 of 1.8 +/- 1.0 microM. It can be blocked with either a nonselective D2-like antagonist (100 microM eticlopride) or with the highly selective D4 antagonist, RBI-257 (10 microM). U101958 (a derivative of RBI-257) exhibits agonist activity similar to PPHT. Neither SKF 38393 (a D1/D5 agonist) nor quinpirole (a D2/D3 agonist) had any effect on whole-terminal IK in this preparation. Kinetic analysis demonstrated that the amplitude of both the rapidly and slowly inactivating phases of neurohypophysial IK are reduced by D4 receptor activation. These two separate current components have previously been shown to represent current through two distinct potassium channels, an A-current channel and a high-conductance Ca++-activated K+ channel. Thus, both channel types can be modulated by D4 receptors. This effect is likely to enhance the release of neurohypophysial peptides in vivo.

Decreased adrenal medullary catecholamine release in spontaneously diabetic BB-Wistar rats. Role of hypoglycemia

We have demonstrated previously that spontaneously diabetic BB-Wistar rats exhibit decreased adrenal medullary catecholamine secretion in response to splanchnic nerve terminal stimulation. We hypothesized that this abnormality is caused by changes in the sensitivity of the adrenomedullary chromaffin cells to acetylcholine (ACh). To study this hypothesis, we isolated adrenal glands from control and spontaneously diabetic BB-Wistar rats, perfused them with ACh, and measured catecholamine secretion. Adrenal catecholamine release in response to ACh was significantly decreased at 2, 8, and 16 weeks after the onset of diabetes compared with age-matched, nondiabetic control rats. Catecholamine release in response to perfusion with 20 mM K+ was the same in adrenals from diabetic and control rats. The decreased responsiveness of diabetic rat adrenals to perfusion with ACh was significantly correlated with a decrease in the release of catecholamines in response to splanchnic nerve stimulation. A similar defect in catecholamine secretion was also seen in adrenals harvested from nondiabetic BB-Wistar rats following a 3-h period of acute hypoglycemia; however, the adrenal response to potassium was also decreased as was the catecholamine content of the adrenal. Conversely, nondiabetic BB-Wistar rats made diabetic with streptozocin (STZ) and maintained in a hyperglycemic state did not exhibit catecholamine hyposecretion 2 weeks after STZ administration. Collectively, the data describe decreased adrenomedullary response to cholinergic stimulation in spontaneously diabetic rats as early as 2 weeks after the onset of diabetes and that a similar, although more severe, hyposecretion occurs after acute, severe hypoglycemia.

Decreased catecholamine secretion from the adrenal medullae of chronically diabetic BB-Wistar rats

Many humans with IDDM eventually lose the capacity to secrete epinephrine from their adrenal medullae. The mechanism for this pathological change is unknown. We hypothesized that this abnormality is attributable to neuropathic changes in the greater splanchnic nerves or in the chromaffin cells that they innervate. To study this hypothesis, we isolated rat adrenal glands, perfused them ex vivo, and measured the epinephrine content of the perfusate under various conditions of stimulation. We used transmural electrical stimulation (20-80 V, at 10 Hz) to induce epinephrine secretion indirectly by selectively activating residual splanchnic nerve terminals within the isolated glands. Under these conditions, epinephrine secretion was severely attenuated in glands from female BB-Wistar rats with diabetes of 4 mo duration compared with their age-matched, nondiabetic controls. These perfused diabetic adrenal medullae also demonstrated decreased catecholamine release in response to direct chromaffin cell depolarization with 20 mM K+, evidence that a functional alteration exists within the chromaffin cells themselves. Nonetheless, total catecholamine content of adrenal medullae from these diabetic rats was not significantly different from controls, indicating that the secretory defect was not simply attributable to a difference in the amount of catecholamines stored and available for release. Herein, we also provide histological evidence of degenerative changes within the cholinergic nerve terminals that innervate these glands.

Histochemical discrimination of fibers in regenerating rat infraorbital nerve

In rat dorsal root ganglia, histochemical staining of carbonic anhydrase (CA) and cholinesterase (CE) yields a reciprocal pattern of activity: Sensory processes are CA positive and CE negative, whereas motor processes are CA negative and CE positive. In rat infraorbital nerve (a sensory peripheral nerve), we saw extensive CA staining of nearly 100% of the myelinated axons. Although CE reactivity in myelinated axons was extremely rare, we did observe CE staining of unmyelinated autonomic fibers. Four weeks after transection of infraorbital nerves, CA-stained longitudinal sections of the proximal stump demonstrated 3 distinct morphological zones. A fraction of the viable axons retained CA activity to within 2 mm of the distal extent of the stump, and the stain is capable of resolving growth sprouts being regenerated from these fibers. Staining of unmyelinated autonomic fibers in serial sections shows that CE activity was not retained as far distally as is the CA sensory staining.

Effect of KT-362, a putative intracellular calcium antagonist, on norepinephrine-induced contractions and inositol monophosphate accumulation in canine femoral artery

The purpose of the present study was to determine if the intracellular calcium antagonist, KT-362, inhibits norepinephrine- (NE) induced contractions and inositol monophosphate (IP) accumulation in canine femoral arteries preincubated with [3H]inositol. Norepinephrine dose-dependently increased contractile tension and produced a parallel stimulation of inositol phospholipid hydrolysis as measured by IP accumulation. This stimulation was inhibited by the selective alpha 1 adrenoceptor antagonist, prazosin (0.1 microM), indicating that the NE-induced stimulation of inositol phospholipid hydrolysis is coupled to alpha 1 adrenoceptor activation in canine femoral artery. Pretreatment with nitroglycerin (100 microM), 8-Br cyclic guanosine monophosphate (cGMP) (1 microM), or diltiazem (40 microM) inhibited contractile responses produced by NE; however, these agents had no significant effect on NE-induced IP accumulation. In contrast, pretreatment with KT-362 (10-100 microM) greatly inhibited both the NE-induced contractions and IP accumulation. KT-362 also produced a marked inhibition of NE-induced contractions in normal as well as zero calcium buffer, whereas diltiazem (40 microM) had no effect in zero calcium buffer. These results indicate that the mechanism of action of KT-362 differs from diltiazem, nitroglycerin, and 8-Br cGMP, and these data suggest that one of the mechanisms by which KT-362 antagonizes NE-induced vasoconstrictor responses is by decreasing inositol phospholipid hydrolysis in canine femoral artery.