COVID-19 vaccine effectiveness against severe disease from SARS-CoV-2 Omicron BA.1 and BA.2 subvariants - surveillance results from southern Sweden, December 2021 to March 2022.

We compared vaccine effectiveness against severe COVID-19 between December 2021 and March 2022 when Omicron BA.1 and BA.2 were the dominating SARS-CoV-2 variants in Scania county, Sweden. Effectiveness remained above 80% after the transition from BA.1 to BA.2 among people with at least three vaccine doses but the point estimate decreased markedly to 54% among those with only two doses. Protection from prior infection was also lower after the transition to BA.2. Booster vaccination seems necessary to maintain sufficient protection.

Risk of severe COVID-19 from the Delta and Omicron variants in relation to vaccination status, sex, age and comorbidities - surveillance results from southern Sweden, July 2021 to January 2022.

We compared the risk of severe COVID-19 during two periods 2021 and 2022 when Delta and Omicron, respectively, were the dominating virus variants in Scania county, Sweden. We adjusted for differences in sex, age, comorbidities, prior infection and vaccination. Risk of severe disease from Omicron was markedly lower among vaccinated cases. It was also lower among the unvaccinated but remained high (> 5%) for older people and middle-aged men with two or more comorbidities. Efforts to increase vaccination uptake should continue.

Pharmacokinetics of mometasone furoate delivered via two dry powder inhalers.

BACKGROUND: QMF149 is an inhaled fixed-dose combination of indacaterol acetate and mometasone furoate (MF) delivered via Breezhaler®, under development for once-daily treatment of asthma. MF delivered via Twisthaler® is approved as Asmanex® Twisthaler® for the treatment of asthma. Bridging of MF delivered via Twisthaler® to MF delivered via Breezhaler® was undertaken as part of QMF149 development to enable dose comparisons between the devices. Pharmacokinetics (PK) of MF were characterized in two studies; a single dose PK study in healthy volunteers and a pharmacokinetic/pharmacodynamic (PK/PD) study in asthma patients. OBJECTIVES: The PK study in healthy volunteers evaluated the PK of single doses of MF via Breezhaler® (50-400 µg) and compared systemic exposure of MF following administration via Breezhaler® and Twisthaler® 400 µg (2 inhalations of 200 µg). The study in patients with asthma characterized the MF PK profile following once-daily inhalation of MF via Breezhaler® and Twisthaler® devices for 4 weeks. METHODS: In the open-label, single-dose, crossover study, healthy subjects sequentially received MF via Twisthaler® (400 µg, medium-dose inhaled corticosteroid [ICS]) and escalating doses via Breezhaler® (50, 100, 200, 400 µg). PK data were obtained up to 72 h post-dose. In the double-blind, double-dummy, parallel-group study, asthma patients were randomised to receive either MF 80 µg (low-dose ICS) or 320 µg (high-dose ICS) via Breezhaler®, or 200 µg (low-dose ICS) or 800 µg (2 inhalations of 400 µg; high-dose ICS) via Twisthaler® once daily for 4 weeks. PK sampling was performed on Days 1 and 28 at pre-dose and up to 24 h post-dose. RESULTS: In the healthy volunteer PK study, 20 healthy subjects completed all treatments. Dose-normalised AUClast of MF was 1.8-1.9-fold higher when delivered via Breezhaler® versus Twisthaler®. AUC and Cmax of MF increased in a dose-proportional manner over the range of 50-400 µg via Breezhaler®. Results from this study guided dose selection of MF via Breezhaler® for the asthma study. In the asthma study, in a subset of 96 patients, mean systemic exposure (AUClast and Cmax) for MF 80 and 320 µg via Breezhaler® was comparable with MF 200 and 800 µg via Twisthaler®, respectively, on Day 28. CONCLUSION: PK characterization in a healthy volunteer PK study and subsequently an asthma study enabled selection of 80 µg (low), 160 µg (medium), and 320 µg (high) delivered via Breezhaler® as MF doses comparable to the 200 µg, 400 µg and 800 µg doses delivered by Twisthaler®, respectively, as part of QMF149 formulation development.

PERson-centredness in hypertension management using information technology (PERHIT): a protocol for a randomised controlled trial in primary health care.

Purpose: For primary health care (PHC), hypertension is the number one diagnosis for planned health care visits. The treatment of high blood pressure (BP) and its consequences constitutes a substantial economic burden. In spite of efficient antihypertensive medications, a low percentage of patients reach a well-controlled BP. The PERson-centredness in Hypertension management using Information Technology (PERHIT) Study is a multicentre randomised controlled trial. PERHIT is designed to evaluate the effect of supporting self-management on systolic blood pressure by the use of information technology in Swedish primary health care.Materials and Methods: After inclusion, 900 patients from 36 PHC centres are randomised to two groups. In the intervention group, patients are provided with a self-management support system including a home-BP monitor and further requested to perform self-reports and measure BP every evening for eight consecutive weeks. In the control group, patients receive treatment as usual.Results: The primary outcome will be the change in systolic blood pressure in patients with hypertension. In addition, person-centredness, daily life activities, awareness of risk and health care costs will also be evaluated.Conclusion: The results of this randomised controlled trial with assessment of blood pressure and same-day self-reports will provide patients a tool to understand the interplay between blood pressure and lifestyle applicable to primary health care. The self-management support system may be of importance for improved adherence to treatment and persistence to treatment recommendations.

Distribution of intranasal naloxone to potential opioid overdose bystanders in Sweden: effects on overdose mortality in a full region-wide study.

OBJECTIVES: Distribution of take-home naloxone is suggested to reduce opioid-related fatalities, but few studies have examined the effects on overdose deaths in the general population of an entire community. This study aimed to assess the effects on overdose deaths of a large-scale take-home naloxone programme starting in June 2018, using an observational design with a historic control period. DESIGN: From the national causes of death register, deaths diagnosed as X42 or Y12 (International Classification of Diseases, 10th revision, ICD-10) were registered as overdoses. Numbers of overdoses were calculated per 100 000 inhabitants in the general population, and controlled for data including only individuals with a prior substance use disorder in national patient registers, to focus on effects within the primary target population of the programme. The full intervention period (2019-2021) was compared with a historic control period (2013-2017). SETTING: Skåne county, Sweden. PARTICIPANTS: General population. INTERVENTIONS: Large-scale take-home naloxone distribution to individuals at risk of overdose. PRIMARY AND SECONDARY OUTCOME MEASURES: Decrease in overdose deaths per 100 000 inhabitants, in total and within the population with substance use disorder diagnosis. RESULTS: Annual average number of overdose deaths decreased significantly from 3.9 to 2.8 per 100 000 inhabitants from the control period to the intervention period (a significant decrease in men, from 6.7 to 4.3, but not in women, from 1.2 to 1.3). Significant changes remained when examining only prior substance use disorder patients, and decreases in overdose deaths could not be attributed to a change in treatment needs for opioid use disorders in healthcare and social services. CONCLUSIONS: The present study, involving 3 years of take-home naloxone distribution, demonstrated a decreased overdose mortality in the population, however, only in men. The findings call for further implementation of naloxone programmes, and for further studies of potential effects and barriers in women. TRIAL REGISTRATION NUMBER: NCT03570099.

Previous SARS-CoV-2 infections and their impact on the protection from reinfection during the Omicron BA.5 wave - a nested case-control study among vaccinated adults in Sweden.

Objectives: We evaluated the protection afforded by SARS-CoV-2 infection-induced immunity against reinfection among working-age vaccinated individuals during a calendar period from June to December 2022 when Omicron BA.5 was the dominating subvariant in Scania County, Sweden. Methods: The study cohort (n = 71,592) mainly consisted of health care workers. We analyzed 4144 infected cases during the Omicron BA.5 dominance and 41,440 sex- and age-matched controls with conditional logistic regression. Results: The average protection against reinfection was marginal (16%, 95% confidence interval [CI] 7-23%) during the study period but substantially higher for recent infections. Recent infection (3-6 months) with Omicron BA.2 and BA.5 offered strong protection (86%, 95% CI 68-94% and 78%, 95% CI 69-84%), whereas more distant infection (6-12 months) with Omicron BA.1, BA.2, and the variants before Omicron offered marginal or no protection. Conclusions: These findings suggest that infection-induced immunity contributes to short-term population protection against infection with the subvariant BA.5 among working-age vaccinated individuals but wanes considerably with time, independent of the virus variant.

Determination of nicotine absorption from multiple tobacco products and nicotine gum.

INTRODUCTION: Snus is a smokeless tobacco product traditionally used in Scandinavia and available in pouched or loose forms. The objective of this study was to determine nicotine absorption for current pouched and loose snus products in comparison with a cigarette and an over-the-counter nicotine gum. METHODS: We conducted an open-label, randomized, 6-way, crossover study involving 20 healthy snus and cigarette users. One of 6 products (2 pouched snus, 2 weights of loose snus, a cigarette, and a nicotine gum) was administered at each of 6 visits. Blood samples were taken at intervals over 120 min and sensory perception assessed by questionnaire. RESULTS: For the 4 smokeless tobacco products and the nicotine gum, blood plasma levels of nicotine were ranked according to total nicotine content as follows: loose snus (27.1 mg nicotine) > pouched snus (14.7 mg nicotine) > loose snus (10.8 mg nicotine) = pouched snus (10.7 mg nicotine) > nicotine gum (4.2 mg nicotine). The area under the plasma concentration-time curve (AUC) and maximum plasma concentration (C(max)) of nicotine ranged from 26.9 to 13.1 ng.h/ml and 17.9 to 9.1 ng.h/ml, respectively across all the products. Nicotine was absorbed more rapidly from the cigarette but systemic exposure was within the range of the smokeless tobacco products (AUC = 14.8 ng.h/ml; C(max) = 12.8 ng.h/ml). CONCLUSIONS: This study has generated new information on comparative nicotine absorption from a cigarette, loose snus, and pouched snus typical of products sold in Scandinavia. The similar nicotine absorption for 1 g portions of loose and pouched snus with approximately 11 mg of nicotine indicate that absorption kinetics were dependent on quantity of tobacco by weight and total nicotine content rather than product form.

High level of protection against COVID-19 after two doses of BNT162b2 vaccine in the working age population - first results from a cohort study in Southern Sweden.

BACKGROUND: Vaccine effectiveness against COVID-19 needs to be assessed in diverse real-world population settings. METHODS: A cohort study of 805,741 residents in Skåne county, Southern Sweden, aged 18-64 years, of whom 26,587 received at least one dose of the BNT162b2 vaccine. Incidence rates of COVID-19 were estimated in sex- and age-adjusted analysis and stratified in two-week periods with substantial community spread of the disease. RESULTS: The estimated vaccine effectiveness in preventing infection ≥7 days after second dose was 86% (95% CI 72-94%) but only 42% (95% CI 14-63%) ≥14 days after a single dose. No difference in vaccine effectiveness was observed between females and males. Having a prior positive test was associated with 91% (95% CI 85-94%) effectiveness against new infection among the unvaccinated. CONCLUSION: A satisfactory effectiveness of BNT162b2 after the second dose was suggested, but with possibly substantially lower effect before the second dose.

Within-session reproducibility of forced oscillometry.

BACKGROUND: The forced oscillation technique (FOT) provides detailed information about the mechanics of the respiratory system, while requiring minimal co-operation by the patient. FOT may be abnormal in subjects with normal spirometry and appears to be more closely related to airway symptoms. It is, therefore, attractive in epidemiological studies, where a large number of different examinations are made in each subjects in a short period of time. Current technical standards recommend the mean of three consecutive measurements to be used, but there is limited information regarding within-session variability of FOT measurements. OBJECTIVE: The purpose of this study was to examine the within-session variability in FOT measurements in a large, population-based sample. METHODS: We performed three consecutive FOT measurements in 700 subjects using the impulse oscillometry system. The first measurement was compared to the mean of three measurements for resistance at 5 and 20 Hz (R5 and R20, respectively), R5-R20, reactance at 5 Hz (X5) and resonant frequency (fres ). RESULTS: The differences between the first and the mean of three measurements (median, interquartile range) were minimal, for example 0.002, -0.008 to 0.014 kPa L-1  s for R5 and -0.001, -0.008 to 0.005 kPa L-1  s for X5. Findings were numerically similar for men and women as well as for subjects with and without airflow obstruction at spirometry. CONCLUSIONS: We conclude that, whereas in clinical situations, three FOT measurements are to be preferred, a single measurement may suffice in epidemiological studies.

Association of coronary calcium score with endothelial dysfunction and arterial stiffness.

BACKGROUND AND AIMS: The aim of the study was to determine potential associations between endothelial dysfunction and arterial stiffness, measured by peripheral arterial tonometry, and coronary artery calcium score (CACS) assessed by computed tomography (CT). METHODS AND RESULTS: The BIG3 study is a prospective longitudinal, non-interventional, pulmonary-cardiovascular cohort study exploring the three major smoking-induced diseases: cardiovascular disease, chronic obstructive pulmonary disease, and lung cancer, in a 45-75 aged cohort (mean 62 years), enriched in smokers. Computed tomography of the chest with assessment of CACS was performed in a selected subset of the participants (n = 2080). Peripheral arterial tonometry (EndoPAT) was used to assess endothelial function and arterial stiffness measured as reactive hyperaemia index (RHI) and augmentation index (AI), respectively. We observed significant associations of CACS, endothelial dysfunction, and arterial stiffness with several risk factors for coronary heart disease including age, sex, BMI, diabetes mellitus, and blood pressure. There was significant association of CACS, classified into three levels of severity, with RHI and AI (p = 0.0005 and p = 0.0009, respectively). For groups of increasing CACS (0, 1-400 and > 400 Agatston score), RHI decreased from median 1.89 (1.58-2.39), and 1.93 (1.62-2.41) to 1.77 (1.51-2.10). AI increased from median 14.3 (5.7-25.2), and 16.4 (8.1-27.6) to 18.0 (9.1-29.2). RHI, but not AI, remained significantly associated with CACS after risk factors adjustment. CONCLUSIONS: In this large study of coronary artery calcium and vascular function, we found an association between CACS and both endothelial dysfunction and arterial stiffness, indicating that they may reflect similar mechanisms for development of cardiovascular disease.

Thiopental pharmacokinetics in newborn infants: a case report of overdose.

UNLABELLED: Thiopental may be used for sedation before intubation in newborn infants. A boy, born at 33 weeks of gestation (gw); birth weight 2435 g, was prescribed thiopental 3 mg/kg before intubation. He developed temporary hypotension and oxygen desaturation, and remained unconscious for longer than expected with a suppressed electroencephalography for 48 h. Serum thiopental concentration was 82, 59, 42 and 32 micromol/L after 20 min and 6, 24 and 68 h respectively. Serum concentrations from five newborn infants at the same time points after intubation with the same thiopental dose were used as reference values, and indicated a 10-fold overdose in the index case. The cause of the overdose could not be identified. The infant recovered; cerebral magnetic resonance imaging at the age of 42 gw and psychomotor development at 2 years were normal. These results show that thiopental concentrations are variable in neonates and there is a high risk of dosage error as no specific paediatric formulation is available. CONCLUSION: Well-designed procedures and continuous education are required to prevent errors and adverse events during drug delivery to newborn infants. To develop a safe method of administration for thiopental, an extended pharmacokinetic and pharmacodynamic study in neonates is warranted.

Muscular exercise can cause highly pathological liver function tests in healthy men.

WHAT IS ALREADY KNOWN ABOUT THIS SUBJECT: The occurrence of idiosyncratic drug hepatotoxicity is a major problem in all phases of clinical drug development and the leading cause of postmarketing warnings and withdrawals. Physical exercise can result in transient elevations of liver function tests. There is no consensus in the literature on which forms of exercise may cause changes in liver function tests and to what extent. WHAT THIS STUDY ADDS: Weightlifting results in profound increases in liver function tests in healthy men used to moderate physical activity, not including weightlifting. Liver function tests are significantly increased for at least 7 days after weightlifting. It is important to impose relevant restrictions on heavy muscular exercise prior to and during clinical studies. AIM: To investigate the effect of intensive muscular exercise (weightlifting) on clinical chemistry parameters reflecting liver function in healthy men. METHODS: Fifteen healthy men, used to moderate physical activity not including weightlifting, performed an 1 h long weightlifting programme. Blood was sampled for clinical chemistry parameters [aspartate aminotransferase (AST), alanine aminotransferase (ALT), lactate dehydrogenase (LD), gamma-glutamyl transferase (gamma GT), alkaline phosphatase (ALP), bilirubin, creatine kinase (CK) and myoglobin] at repeated intervals during 7 days postexercise and at a follow-up examination 10-12 days postexercise. RESULTS: Five out of eight studied clinical chemistry parameters (AST, ALT, LD, CK and myoglobin) increased significantly after exercise (P < 0.01) and remained increased for at least 7 days postexercise. Bilirubin, gamma GT and ALP remained within the normal range. CONCLUSION: The liver function parameters, AST and ALT, were significantly increased for at least 7 days after the exercise. In addition, LD and, in particular, CK and myoglobin showed highly elevated levels. These findings highlight the importance of imposing restrictions on weightlifting prior to and during clinical studies. Intensive muscular exercise, e.g. weightlifting, should also be considered as a cause of asymptomatic elevations of liver function tests in daily clinical practice.

Novel subgroups of adult-onset diabetes and their association with outcomes: a data-driven cluster analysis of six variables.

BACKGROUND: Diabetes is presently classified into two main forms, type 1 and type 2 diabetes, but type 2 diabetes in particular is highly heterogeneous. A refined classification could provide a powerful tool to individualise treatment regimens and identify individuals with increased risk of complications at diagnosis. METHODS: We did data-driven cluster analysis (k-means and hierarchical clustering) in patients with newly diagnosed diabetes (n=8980) from the Swedish All New Diabetics in Scania cohort. Clusters were based on six variables (glutamate decarboxylase antibodies, age at diagnosis, BMI, HbA1c, and homoeostatic model assessment 2 estimates of ß-cell function and insulin resistance), and were related to prospective data from patient records on development of complications and prescription of medication. Replication was done in three independent cohorts: the Scania Diabetes Registry (n=1466), All New Diabetics in Uppsala (n=844), and Diabetes Registry Vaasa (n=3485). Cox regression and logistic regression were used to compare time to medication, time to reaching the treatment goal, and risk of diabetic complications and genetic associations. FINDINGS: We identified five replicable clusters of patients with diabetes, which had significantly different patient characteristics and risk of diabetic complications. In particular, individuals in cluster 3 (most resistant to insulin) had significantly higher risk of diabetic kidney disease than individuals in clusters 4 and 5, but had been prescribed similar diabetes treatment. Cluster 2 (insulin deficient) had the highest risk of retinopathy. In support of the clustering, genetic associations in the clusters differed from those seen in traditional type 2 diabetes. INTERPRETATION: We stratified patients into five subgroups with differing disease progression and risk of diabetic complications. This new substratification might eventually help to tailor and target early treatment to patients who would benefit most, thereby representing a first step towards precision medicine in diabetes. FUNDING: Swedish Research Council, European Research Council, Vinnova, Academy of Finland, Novo Nordisk Foundation, Scania University Hospital, Sigrid Juselius Foundation, Innovative Medicines Initiative 2 Joint Undertaking, Vasa Hospital district, Jakobstadsnejden Heart Foundation, Folkhälsan Research Foundation, Ollqvist Foundation, and Swedish Foundation for Strategic Research.

Complete Removal of Extracellular IgG Antibodies in a Randomized Dose-Escalation Phase I Study with the Bacterial Enzyme IdeS--A Novel Therapeutic Opportunity.

UNLABELLED: IdeS is a streptococcal protease that cleaves IgG antibodies into F(ab')2 and Fc fragments with a unique degree of specificity, thereby providing a novel treatment opportunity of IgG-driven autoimmune conditions and antibody mediated transplant rejection. Here we report the results from a first in man, double blinded and randomized study with single ascending doses of IdeS in healthy, male subjects. Twenty healthy subjects were given intravenous single ascending doses of IdeS. With impressive efficacy IdeS cleaved the entire plasma IgG-pool only minutes after dosing. IgG reached nadir 6-24 hours after dosing and then slowly recovered. The half-life of IdeS was 4.9 (±2.8) hours at 0.24 mg/kg with the main fraction eliminated during 24 hours. Already two hours after IdeS-dosing, the phagocytic capacity of IgG/IgG-fragments was reduced to background levels. Importantly, IdeS has the capacity to inactivate Fc-mediated effector function in vivo, was considered safe with no serious adverse events, and without dose limiting toxicity in this study. The complete, rapid, but temporary removal of IgG provides a new potent therapeutic opportunity in IgG-mediated pathogenic conditions. TRIAL REGISTRATION: ClinicalTrials.gov NCT01802697.

Clinical efficacy and pharmacokinetic profiles of intranasal and oral cetirizine in a repeated allergen challenge model of allergic rhinitis.

BACKGROUND: Intranasal and oral antihistamines are effective in treating allergic rhinitis. Studies comparing these routes of administration of an antihistamine regarding efficacy and pharmacokinetic profile are lacking. OBJECTIVE: To compare topical and oral routes of administration of cetirizine regarding efficacy, plasma exudation, and systemic drug levels in a repeated allergen challenge model of allergic rhinitis. METHODS: Oral cetirizine dihydrochloride, 10 mg once daily, and topical cetirizine dinitrate in a dose corresponding to 4.4 mg of the dihydrochloride salt twice daily were given to grass pollen-sensitive individuals for 12 days in a double-blind, placebo-controlled, crossover design. Timothy grass pollen allergen challenges were given once daily for 7 days using a nasal spray device. Nasal symptoms and peak inspiratory flow were recorded in the morning, 10 minutes after allergen challenge, and in the evening. The pharmacokinetics of the treatments was monitored in 8 patients. The remaining 28 patients were challenged topically with histamine 12 and 24 hours after the final topical and oral cetirizine doses, respectively. Nasal lavage levels of alpha2-macroglobulin were determined to evaluate histamine-induced mucosal plasma exudation. RESULTS: During the last 3 days of the repeated allergen challenge model, chronic symptoms were established. Both treatments reduced symptoms 10 minutes after allergen challenge (P < .001 vs placebo). Neither treatment reduced morning and evening symptoms or nasal peak inspiratory flow. Topical, but not oral, cetirizine reduced histamine-induced plasma exudation (P < .01 vs placebo) when systemic drug levels were similar in the 2 treatment regimens. CONCLUSIONS: Topical and oral cetirizine reduced acute nasal symptoms produced by allergen challenges in patients with established chronic symptoms. There were also antihistaminic effects of topical cetirizine not related to systemic drug levels.

Female pig urethral tone is dependent on Rho guanosine triphosphatases and Rho-associated kinase.

PURPOSE: Circular smooth muscle of the urethra generates spontaneous myogenic tone of relevance for the maintenance of continence. We tested if Rho guanosine triphosphatases (GTPases) and Rho-associated kinase (ROK) are involved in the generation of urethral tone. MATERIALS AND METHODS: Small circular strips of female pig urethra were dissected out and mounted for recording isometric force. The effect of pharmacological agents known to modulate the activity of Rho GTPases or ROK was examined. The intracellular calcium concentration was measured using fura-2. RESULTS: Urethral tone was abolished by removing extracellular calcium or by adding the calcium antagonist felodipine. The decrease in force was closely related to a decrease in intracellular calcium concentration, indicating that tone depends on membrane associated mechanisms. Toxin B, which inactivates Rho GTPases, and Y 27632, which inhibits ROK, completely abolished tone in the female pig urethra. The latter effect occurred without any change in the intracellular calcium concentration. CONCLUSIONS: The results suggests that urethral tone depends on activity in G-protein coupled pathways and inhibition of this activity is sufficient for urethral tone relaxation. Thus, to our knowledge a new pathway in the generation of urethral tone, which might be acted on by autonomic nerves during micturition, has been identified.

Cardiac myosin isoforms from different species have unique enzymatic and mechanical properties.

The mammalian heart contains two cardiac myosin isoforms: beta-myosin heavy chain (MHC) is found predominantly in the ventricles of large mammals, and alpha-MHC is expressed in the atria. The sequence identity between these isoforms is approximately 93%, with nonidentical residues clustered in discrete, functionally important domains associated with actin binding and ATPase activity. It is well-established that rabbit alpha-cardiac myosin has a 2-fold greater unloaded shortening velocity than beta-cardiac myosin but a 2-fold lower average isometric force. Here, we test the generality of these relationships for another large mammal, the pig, as well as for a small rodent, the mouse, which expresses alpha-MHC in its ventricles throughout adulthood. Hydrophobic interaction chromatography (HIC) was used to purify myosin from mouse, rabbit, and pig hearts. The superior resolving power of HIC made it possible to prepare highly homogeneous, enzymatically active myosin from small amounts of tissue. The movement of actin filaments by myosin was measured in an in vitro motility assay. The same assay could be used to determine average isometric force by loading the actin filaments with increasing concentrations of alpha-actinin to stop filament motion. We conclude that myosin from the mouse has significantly higher velocities for both alpha and beta isoforms than myosin from rabbits and pigs, even though the 2-fold difference in velocity between isoforms is maintained. Unlike the larger mammals, however, the small rodent generates the same high isometric force for both alpha and beta isoforms. Thus, nature has adapted the function of cardiac myosin isoforms to optimize power output for hearts of a given species.

Sustained norepinephrine contraction in the rat portal vein is lost when Ca(2+) is replaced with Sr(2+).

Agonist-induced activation of smooth muscle involves a rise in intracellular Ca(2+) concentration and sensitization of myosin light chain phosphorylation to Ca(2+). Sr(2+) can enter through Ca(2+) channels, be sequestered and released from sarcoplasmic reticulum, and replace Ca(2+) in activation of myosin light chain phosphorylation. Sr(2+) cannot replace Ca(2+) in facilitation of agonist-activated Ca(2+)-dependent nonselective cation channels. It is not known whether Sr(2+) can replace Ca(2+) in small G protein-mediated sensitization of phosphorylation. To explore mechanisms involved in alpha-receptor-activated contractions in smooth muscle, effects of replacing Ca(2+) with Sr(2+) were examined in rat portal vein. Norepinephrine (NE) at >3.0 x 10(-7) M in the presence of Ca(2+) resulted in a strong sustained contraction, whereas this sustained component was absent in the presence of Sr(2+); only the amplitude of phasic contractions increased. Pretreatment with low (approximately 0.05 mM) free Ca(2+) followed by 2.5 mM Sr(2+) resulted in a sustained component of the NE response. In beta-escin-permeabilized preparations, phenylephrine in the presence of GTP or guanosine 5'-O-(3-thiotriphosphate) alone induced sensitization to Sr(2+). In conclusion, a Ca(2+)-regulated membrane/channel process is required for the sustained component of NE responses in rat portal vein. Sensitization alone is not responsible for the sustained phase of the NE contraction.

Stretch-induced contractile differentiation of vascular smooth muscle: sensitivity to actin polymerization inhibitors.

Signaling mechanisms for stretch-dependent growth and differentiation of vascular smooth muscle were investigated in mechanically loaded rat portal veins in organ culture. Stretch-dependent protein synthesis was found to depend on endogenous release of angiotensin II. Autoradiography after [(35)S]methionine incorporation revealed stretch-dependent synthesis of several proteins, of which SM22 and actin were particularly prominent. Inhibition of RhoA activity by cell-permeant C3 toxin increased tissue mechanical compliance and reduced stretch-dependent extracellular signal-regulated kinase (ERK)1/2 activation, growth, and synthesis of actin and SM22, suggesting a role of the actin cytoskeleton. In contrast, inhibition of Rho-associated kinase by Y-27632 did not reduce ERK1/2 phosphorylation or actin and SM22 synthesis and did not affect tissue mechanical compliance but still inhibited overall growth. The actin polymerization inhibitors latrunculin B and cytochalasin D both inhibited growth and caused increased tissue compliance. Whereas latrunculin B concentration-dependently reduced actin and SM22 synthesis, cytochalasin D did so at low (10(-8) M) but not at high (10(-6) M) concentration. The results show that stretch stabilizes the contractile smooth muscle phenotype. Stretch-dependent differentiation marker expression requires an intact cytoskeleton for stretch sensing, control of protein expression via the level of unpolymerized G-actin, or both.