Phase 1 trial of dichloroacetate (DCA) in adults with recurrent malignant brain tumors.

BACKGROUND: Recurrent malignant brain tumors (RMBTs) carry a poor prognosis. Dichloroacetate (DCA) activates mitochondrial oxidative metabolism and has shown activity against several human cancers. DESIGN: We conducted an open-label study of oral DCA in 15 adults with recurrent WHO grade III - IV gliomas or metastases from a primary cancer outside the central nervous system. The primary objective was detection of a dose limiting toxicity for RMBTs at 4 weeks of treatment, defined as any grade 4 or 5 toxicity, or grade 3 toxicity directly attributable to DCA, based on the National Cancer Institute's Common Toxicity Criteria for Adverse Events, version 4.0. Secondary objectives involved safety, tolerability and hypothesis-generating data on disease status. Dosing was based on haplotype variation in glutathione transferase zeta 1/maleylacetoacetate isomerase (GSTZ1/MAAI), which participates in DCA and tyrosine catabolism. RESULTS: Eight patients completed at least 1 four week cycle. During this time, no dose-limiting toxicities occurred. No patient withdrew because of lack of tolerance to DCA, although 2 subjects experienced grade 0-1 distal parasthesias that led to elective withdrawal and/or dose-adjustment. All subjects completing at least 1 four week cycle remained clinically stable during this time and remained on DCA for an average of 75.5 days (range 26-312). CONCLUSIONS: Chronic, oral DCA is feasible and well-tolerated in patients with recurrent malignant gliomas and other tumors metastatic to the brain using the dose range established for metabolic diseases. The importance of genetic-based dosing is confirmed and should be incorporated into future trials of chronic DCA administration.

Postsynaptic mechanisms of excitotoxicity: Involvement of postsynaptic density proteins, radicals, and oxidant molecules.

Traditional models of neuronal excitotoxicity focused on the overactivation of receptors such as the ionotropic N-methyl-D-aspartate (NMDA)-subtype glutamate receptor. Recent developments have shifted focus to downstream neurotoxic signaling molecules with exciting implications to specific strategies for treating excitotoxic disorders. This review outlines these developments and introduces newly emerging evidence implicating the involvement of the melastatin subfamily in anoxic neuronal death. Both of these converge on the production of reactive oxygen species (ROS), including superoxide, nitric oxide (NO) and the oxidant peroxynitrite.

Lactic acid and protein interactions: implications for the NMR visibility of lactate in biological systems.

The addition of bovine serum albumin (BSA) to a solution of lactate and alanine resulted in the disappearance of the 1H-NMR resonances from lactate but not alanine. As temperature is increased lactate becomes increasingly NMR visible and after heating above 65 degreesC and cooling to 25 degreesC lactate binding is reduced. With a concentration of 0.2 mM BSA, there was a linear relationship between NMR visible lactate versus total lactate over a range of lactate concentrations of 0.2-35 mM (slope 0.384+/-0.003) indicating that approx. 60% of the added lactate is not visible in the 1H-NMR spectrum. With a 0.1 mM BSA solution, however, the slope was markedly higher indicating that under these conditions only 25-30% of the lactate was NMR invisible. The results from this study indicate that decreased NMR visibility of lactate in proteinaceous solutions is due to non-specific binding which is dependent on the tertiary structure of the protein. This has important implications not only for the interpretation of in vivo 1H-NMR experiments but also for 13C, and 14C studies of metabolism.

The porcine forelimb as a model for human flexor tendon surgery.

Technical skills have been shown to transfer very well from bench models to practical use. The central two rays of 30 forelimbs of pigs were dissected and anatomical observations were made. The rays contained deep and superficial flexor tendons enclosed in a fibro-osseous tunnel and these were present in all 60 specimens. The fibrous part of the tunnel had specific constant condensations in annular and oblique directions which were present in all 60 rays. The anatomy of the porcine forelimb digital flexor tendon system is sufficiently similar to the human system to be used as a model for surgeons wishing to master the technical aspects of zone II flexor tendon repair. This paper proposes the porcine forelimb as a bench model for zone II flexor tendon repair.

Preferential inhibition of lactate oxidation relative to glucose oxidation in the rat heart following diabetes.

OBJECTIVE: Alterations in myocardial metabolism occur early after the onset of diabetes suggesting that they may play a role in the development of cardiac dysfunction. Inhibition of myocardial pyruvate dehydrogenase (PDH), glucose transport and glycolysis have all been reported following diabetes. In vivo lactate is also a potential source of energy for the heart and its oxidation should not be affected by changes in glucose transport and glycolysis. Therefore, the objective of this study, was to test the hypothesis that following diabetes the inhibition of glucose oxidation would be greater than the inhibition of lactate oxidation. METHODS: Hearts from control and one-week-old diabetic rats were perfused with [1-13C]glucose (11 mmol/l) alone, [1-13C]glucose plus lactate (0.5 mmol/l) or glucose plus [3-13C]lactate (0.5 or 1.0 mmol/l) as substrates. Glucose and lactate oxidation rates were determined by combining 13C-NMR glutamate isotopomer analysis of tissue extracts with measurements of oxygen consumption. RESULTS: In diabetic hearts perfused with glucose alone, glucose oxidation was decreased compared to controls (0.31 +/- 0.08 vs. 0.71 +/- 0.11 mumoles/min/g wet weight; p < 0.05). Surprisingly, in hearts perfused with glucose plus 0.5 mmol/l lactate, there was no difference in glucose oxidation between control and diabetic groups (0.20 +/- 0.05 vs. 0.16 +/- 0.04 mumoles/min/g wet weight respectively). However, under these conditions lactate oxidation was markedly reduced in the diabetic group (0.89 +/- 0.18 vs. 0.24 +/- 0.05 mumoles/min/g wet weight; p < 0.05). At 1.0 mmol/l lactate oxidation was still significantly depressed in the diabetic group. CONCLUSION: There was a greater decrease in lactate oxidation relative to glucose oxidation in hearts from diabetic animals. These results demonstrate that diabetes leads to a specific inhibition of lactate oxidation independent of its effects on pyruvate dehydrogenase.

Acute L-triiodothyronine administration potentiates inotropic responses to beta-adrenergic stimulation in the isolated perfused rat heart.

OBJECTIVE: Acute inotropic effects of triiodothyronine (T3) have been reported, employing both in vivo experimental animal models and in vitro isolated heart perfusions. However, the mechanisms responsible for these acute inotropic effects remain unclear. The aim of this study, therefore, was to delineate the role of the beta-adrenergic receptor system in these acute responses. METHODS: The hearts from both euthyroid and hypothyroid (treated with 0.05% PTU in drinking water) male Sprague-Dawley rats were used in 5 experimental study protocols. Hearts from euthyroid rats were perfused with buffer containing either T3(10(-7) M) or control while continuously recording left ventricular function for 10 min ('acute effects'). Two-hour perfusions ('subacute effects') and cardiac responses following increasing doses of isoproterenol (10(-10) to 10(-6) M) in the presence or absence of T3-containing buffer (acute interaction) were also determined. In hypothyroid rats, the subacute responses and the acute interactions were investigated. RESULTS: In the presence of T3, an acute, significant potentiation of the inotropic responses following beta-adrenergic stimulation with isoproterenol was observed in both rat cohorts, which was more pronounced in hearts from euthyroid rats. An acute (< 40 s), but transient (79 +/- 8 s), direct inotropic response was observed in hearts from euthyroid rats. No cardiac responses were seen during a 2-h perfusion in hearts from either euthyroid or hypothyroid rats. CONCLUSIONS: The acute inotropic effects of T3 in non-ischemic myocardium probably result from an acute interaction between T3 and catecholamines rather than through a direct inotropic effect of T3 alone.

Normal T-cell response and in vivo magnetic resonance imaging of T cells loaded with HIV transactivator-peptide-derived superparamagnetic nanoparticles.

The present study analyzed the feasibility of using magnetic resonance imaging (MRI) to monitor T-cell homing in vivo after loading T cells with superparamagnetic iron oxide (CLIO) nanoparticles derivatized with a peptide sequence from the transactivator protein (Tat) of HIV-1. T cells were isolated from C57BL/6 (B6) mice and loaded with 0, 400, 800, 1600, or 8000 ng/ml of FITC conjugated CLIO-Tat (FITC-CLIO-Tat). There was a dose-dependent uptake of FITC-CLIO-Tat by T cells. Stimulation of FITC-CLIO-Tat loaded T cells with anti-CD3 (0.1 microg/ml) plus IL-2 (5 ng/ml) elicited normal activation and activation-induced cell death (AICD) responses, and normal upregulation of CD69, ICAM-1 (CD54), L-selectin (CD62L), and Fas. The FITC-CLIO-Tat loaded T cells (3 x 10(7)) were transferred intravenously (i.v.) into B6 mice and the in vivo MRI of mice was acquired using a spin-echo pulse sequence at 4.7 T with a Bruker Biospec system. Homing of T cells into the spleen was observed by a decrease in MRI signal intensity within 1 h after the transfer, which remained decreased for 2-24 h after transfer. These homing data were confirmed by FACS analysis and biodistribution analysis using 125I-CLIO-Tat. Thus, T cells can be efficiently loaded with FITC-CLIO-Tat without interfering with their normal activation and AICD, or homing to the spleen, and the biodistribution of FITC-CLIO-Tat loaded T cells can be monitored in vivo over time by MRI.

The effect of hypothermic ischemia on recovery of left ventricular function and preload reserve in the neonatal heart.

Neonatal and adult myocardium respond differently to ischemia. In addition, the neonatal heart possesses a limited preload reserve. The effect of uninterrupted hypothermic ischemia on recovery of left ventricular function and preload reserve was studied in two groups of isolated rabbit hearts: group 1 (neonates, n = 8), 7 to 10 days old; group 2 (adults, n = 15), 6 to 12 months old. Peak left ventricular systolic pressure, the first derivative of left ventricular systolic pressure, and heart rate were measured at left ventricular pressures of 0, 5, 10, and 15 mm Hg before and after 120 minutes of global ischemia at 27 degrees C. Before ischemia, left ventricular systolic pressure increased significantly at each increment of left ventricular end-diastolic pressure for both groups of hearts. After hypothermic ischemia, recovery of left ventricular systolic pressure was significantly reduced at each level of left ventricular end-diastolic pressure among neonatal hearts (range 75% to 79% of control values). The postischemic recovery of left ventricular systolic pressure in the adult hearts was markedly reduced from baseline values (range 43% to 53% of control values) and was significantly worse than that of neonatal hearts at each level of left ventricular end-diastolic pressure (p less than 0.001). Both groups were able to respond to increasing preload after ischemia. The slope of the curve describing the relationship between left ventricular end-diastolic pressure and percent recovery of left ventricular systolic pressure was not different from zero for neonatal hearts but was significantly greater than zero among the adults (0.22 +/- 0.21 versus 0.73 +/- 0.07, p = 0.0056). After ischemia, the first derivative of left ventricular systolic pressure fell significantly from control values among neonatal hearts (71% of control values). The reduction was considerably greater, however, among the adult hearts (54% of control values). These data indicate that the neonatal heart recovers systolic function better than the adult heart after global ischemia with moderate hypothermia.

Mental health: market power and governance.

This paper is concerned with the pricing behaviour of providers of residential care for people with mental health problems. Two aspects of pricing were considered. First, are there differences between providers' market power and their actual mark-up rates (e.g. due to differences in motivation)? Second, do the different governance arrangements used in sectors of the industry, such as unified public and non-profit organisation and private bilateral contracting, affect pricing behaviour? A theoretical model was developed to underpin the empirical analysis of 496 residents in 112 mental health care facilities. Private, bilateral organisation was found to be associated with comparatively lower potential price-cost mark-up but a greater propensity to use this power to make profits/surpluses.

Contracts and purchaser-provider relationships in community care.

This paper considers the incentives embodied in contracts between purchasers and providers of residential care for frail elderly people. The paper begins with an assessment of current contractual arrangements. A theoretical inquiry generates propositions that some contracts create incentives for providers to misrepresent users' characteristics. These propositions are found to be supported by sample data. The paper then turns to a theoretical consideration of optimal governance structures and, in particular, the use of incentive contracts. These contracts, it is claimed, may go some way to curbing cost-exaggerating behaviour without providing strong incentives to cream-skim or shirk on quality.

A comparison of the cost-effectiveness of sertraline versus tricyclic antidepressants in primary care.

There has been considerable debate concerning the cost-effectiveness of selective serotonin re-uptake inhibitors (SSRIs) versus tricyclic antidepressants (TCAs) thus far using crude prescription price comparisons or reductionist decision-analytic models. This paper employs a retrospective quasi-experimental design where data on service utilisation, use of medication and informal care were collected for two groups of patients in general practice settings. The mean cost of treatment was marginally greater for those people receiving TCA medication due to greater use of psychiatric services. Factors such as age, previous depression and concomitant physical illness are all associated with greater treatment costs. Further analysis using a prospective design is recommended.

Movement and change: independent sector domiciliary care providers between 1995 and 1999.

Promoting the development of a flourishing independent sector alongside good quality public services was a key objective of the community care reforms of the last decade. This paper charts some of the ways the independent domiciliary care sector is changing, as local authorities shift the balance of their provision toward independent sector providers and away from a reliance on in-house services. Two surveys of independent domiciliary care providers were carried out in 1995 and 1999. The aims of the studies were to describe the main features of provider organisations, such as size of business, client group and funding sources; to examine the nature of provider motivations and their past and future plans; to consider how local authorities manage the supply side of social care markets; and to examine the effects on providers of the development of the mixed economy. The first survey in 1995 was conducted in eight local authority areas, which by 1999 had increased to 11 because of the creation of three new unitary authorities. The findings are based on 261 postal surveys together with 111 interviews between the two studies. The research illustrates a domiciliary care market that is still relatively young with many small but growing businesses. There are considerable differences in the split between in-house and independent sector services in individual authorities and a common perception among independent providers that in-house services receive favourable treatment and conditions. Spot or call-off contracts continue to be the most common form of contract although there are moves toward greater levels of guaranteed service and more sophisticated patterns of contracting arrangements. There remains an ongoing need to share information between local authorities and independent providers so that good working relationships can develop with proven and competent providers.

A NOVEL INTRINSIC UNSCENTED KALMAN FILTER FOR TRACTOGRAPHY FROM HARDI*

The unscented Kalman filter (UKF) was recently introduced in literature for simultaneous multi-tensor estimation and tractography. This UKF however was not intrinsic to the space of diffusion tensors. Lack of this key property leads to inaccuracies in the multi-tensor estimation as well as in tractography. In this paper, we propose an novel intrinsic unscented Kalman filter (IUKF) in the space of symmetric positive definite matrices, which can be used for simultaneous recursive estimation of multi-tensors and tractography from diffusion weighted MR data. In addition to being more accurate, IUKF retains all the advantages of UKF for instance, multi-tensor estimation is only performed in the places where it is needed for tractography, which would be much more efficient than the two stage process involved in methods that do tracking post diffusion tensor estimation. The accuracy and effectiveness of the proposed method is demonstrated via real data experiments.

Outcomes of social care for adults: developing a preference-weighted measure.

OBJECTIVE: The aim of this study was to develop a measure of social care outcome, an equivalent to the quality-adjusted life year (QALY) in health, which could be used in a range of circumstances. DESIGN: The project drew on previous and parallel work developing the Adult Social Care Outcome Toolkit and the national Adult Social Care Survey. We developed and tested an instrument designed to reflect service users' social care-related quality of life (SCRQoL) and tested it with 30 service users from a variety of user groups and 300 older home care service users. In parallel, we explored discrete choice experiment (DCE) and best-worst scaling (BWS) approaches to preference elicitation with 300 members of the general population, and cognitively tested these with service users. We also cognitively tested a computer-aided time trade-off (TTO) exercise using SCRQoL attributes with members of the general population. In the second phase, using the finalised instruments, BWS interviews were conducted with 500 members of the general population, TTO interviews with a follow-up sample of 126 of these respondents, and BWS interviews with 458 people using equipment services. MAIN OUTCOME MEASURES: The final measure had eight domains: personal cleanliness and comfort, accommodation cleanliness and comfort, food and drink, safety, social participation and involvement, occupation, control over daily life and dignity. In addition to measuring current SCRQoL, the instrument includes questions used to establish service users' views of their 'expected' SCRQoL in the absence of services. The difference between a person's current and 'expected' SCRQoL provides an indicator of service impact. RESULTS: There was good evidence for the validity of the descriptive system and the validity of the current, expected and SCRQoL gain scales. The DCE and BWS approaches yielded similar results and, once introductions made clear, were understood by service users. BWS was used for the main stages, as it had technical and cognitive advantages. The computer-aided approach to TTO worked well, and respondents found questions acceptable and understandable. There were no substantive differences in the preferences of service users and the general population. The key domain was control over daily life, with the lowest and highest levels strongly estimated in all models. After allowing for observable heterogeneity, service users' preferences appeared to be more closely associated with their own SCRQoL than with those of the general population. The consistency of the results with the results of a previous study allowed the final model to be based on the preferences of 1000 members of the general population. A formula based on the relationship between TTO and BWS values was estimated for a social care QALY, with '0' equivalent to 'being dead' and '1' being the 'ideal' SCRQoL state. Members of the population experienced significantly higher SCRQoL than service users. CONCLUSIONS: Although further work is needed, particularly to develop an equivalent measure for informal carers and to explore the links with health QALYs, the measure has considerable potential. A number of methodological advances were achieved, including the first application of TTO in a social care context and use of BWS to establish service user preferences. FUNDING: The National Institute for Health Research Health Technology Assessment programme.

The price of placements in residential and nursing home care: the effects of contracts and competition.

A variety of contract types are used in the placement of elderly people in residential and nursing care homes in the UK. Contracts vary according to how and when providers are paid. Among other things, prices can be made contingent on the total quantity of service to be purchased and on production cost characteristics. They can be determined at the time of placement or in advance. The primary objective of this paper is to assess the impact of contract choices on the price of placements. Regression analysis was conducted on a final sample of 1780 publicly funded placements made in 18 local authorities in the UK over a 6-month period ending in early 1996. Controlling factors included in the price analysis were production cost indicators and those measuring market competitiveness. Choices of both quantity and cost contingent contracts were found to be significantly associated with placement prices. The findings support the hypothesis that contract payment arrangements have different risk, insurance and information properties, and so have implications for the performance of residential care providers.

Plasma membrane calcium flux, protein kinase C activation and smooth muscle contraction.

Isolated perfused rabbit ear arteries contract when treated with 12-O-tetradecanoylphorbol-13-acetate (TPA), an activator of the calcium-activated, phospholipid-dependent protein kinase or C-kinase. Under conditions where the calcium concentration in the perfusate is 1.5 mM and the potassium concentration is 4.8 mM, there is a latent period of 70 +/- 19 min (mean +/- S.E.M., n = 10) between TPA addition and the onset of the contractile response. Once initiated, the contractile response is progressive and sustained. When perfusion conditions are altered in such a way as to modify calcium flux across the plasma membrane (i.e., raising the extracellular calcium concentration to 2.5 mM Ca++, raising the extracellular potassium concentration to 10 mM, and/or preincubating the tissues in media containing 100 nM Bay K 8644, a potent calcium channel agonist), the latency period between TPA addition and initiation of the contractile response is significantly reduced (2.5 mM Ca++, 37 +/- 7 min; 10 mM K+ and 2.5 mM Ca++, 11 +/- 3 min; 100 nM Bay K 8644 and 1.5 mM Ca++, 20 +/- 7 min; 100 nM Bay K 8644 and 2.5 mM Ca2+, 8.5 +/- 1.7 min; 10 mM K+ and 100 nM Bay K 8644, 11 +/- 5 min). Likewise, the combination of 2.5 mM calcium, 100 nM Bay K 8644, and 3.3 microM ouabain results in a contractile response 4.5 +/- 2.0 min after TPA addition (means +/- S.E.M., n = 4). Control tissues (absence of TPA addition) run simultaneously show no contractile responses to the various Ca++ flux regulators even after 90 min of incubation.(ABSTRACT TRUNCATED AT 250 WORDS)

A 13C-NMR study of glucose oxidation in the intact functioning rat heart following diabetes-induced cardiomyopathy.

A causative factor in the development of diabetes-induced heart dysfunction may be abnormalities in myocardial energy metabolism. Using 13C-NMR spectroscopy, we investigated the effects of experimentally induced diabetes (streptozotocin 65 mg/kg, i.v.) on glucose metabolism and contractile function in the isolated perfused rat heart. Hearts from streptozotocin-treated and untreated control rats were perfused with 11 mM [1-13C]glucose as substrate and 1H-decoupled 13C-spectra recorded for up to 90 min. Incorporation of label from [1-13C]glucose into lactate and glutamate was observed in hearts from control animals, consistent with metabolism through glycolysis and TCA cycle, respectively. Diabetic hearts did not incorporate label into lactate or glutamate. Addition of insulin (0.05 U/ml) to the buffer resulted in the appearance of [3-13C]lactate, although glutamate labeling was not observed. Addition of insulin plus dichloroacetate (2 mM) resulted in incorporation of label from [1-13C]glucose into 2-, 3- and 4-13C-glutamate, indicating glucose entry into the TCA cycle. Addition of insulin, or insulin plus dichloroacetate to control hearts did not alter labeling of either lactate or glutamate. Cardiac function in hearts from the diabetic group was depressed compared to controls and declined significantly over the duration of the experiment. These studies show that concomitant with a decrease in cardiac function, glucose oxidation is profoundly inhibited following the induction of diabetes with streptozotocin. These observations are consistent with a combination of decreased glucose transport and a decrease in pyruvate dehydrogenase activity.

Metabolic compartmentation of lactate in the glucose-perfused rat heart.

Several studies using exogenous pyruvate as substrate have suggested that there are separate intracellular pyruvate pools in cardiac cells. Such heterogeneity in intracellular pyruvate has important implications for our understanding of both oxidative and nonoxidative glucose metabolism. Because pyruvate is not a major substrate for the heart in vivo, we wished to determine if there was pyruvate compartmentation with glucose as substrate. Hearts were isolated from male Sprague-Dawley rats and retrogradely perfused (Langendorff) with a modified Krebs-Henseleit buffer containing [1-13C[glucose for 5-115 min. At the end of each experiment, hearts were freeze-clamped and extracted for determination of the fractional enrichment of alanine, lactate, and acetyl CoA using 1H- and 13C-nuclear magnetic resonance spectroscopy. The fractional enrichment of alanine at the C-3 position was significantly higher than that for lactate at 55 min [43.6 +/- 2.8 vs. 27.2 +/- 4.6% (SD), n = 5, P < 0.003]. The differences in steady-state enrichment between lactate and alanine were not due to differences in the rate of labeling of these metabolites. The mean steady-state lactate enrichment was higher in the perfusate samples compared with the tissue samples from the same experiments (46.6 +/- 2.2 vs. 30.5 +/- 2.5%, n = 3, P < 0.005). Because fractional enrichment of alanine, acetyl CoA, and perfusate lactate are similar, we suggest that there is a separate nonexchanging pool of lactate rather than cytosolic compartmentation of pyruvate that has been previously proposed.

Relationship between cardiac function and substrate oxidation in hearts of diabetic rats.

The effects of streptozotocin-induced diabetes on myocardial substrate oxidation and contractile function were investigated using 13C nuclear magnetic resonance (NMR) spectroscopy. To determine the consequences of diabetes on glucose oxidation, hearts were perfused with [1-13C]glucose (11 mM) alone as well as in the presence of insulin (to stimulate glucose transport) and dichloroacetate (to stimulate pyruvate dehydrogenase). The contribution of glucose to the tricarboxylic acid (TCA) cycle was significantly decreased in hearts from diabetic animals compared with controls, with glucose alone and with insulin; however, the addition of dichloroacetate significantly increased the contribution of glucose to the TCA cycle. Contractile function in hearts from diabetic animals was significantly depressed with glucose as the sole substrate, regardless of the presence of insulin or dichloroacetate (P < 0.0005). To determine whether diabetes had any direct effects on beta-oxidation and the TCA cycle, hearts were perfused with glucose (11 mM) plus [6-13C]hexanoate (0.5 mM) as substrates. In control hearts, with glucose plus hexanoate as substrates, hexanoate contributed 98.9 +/- 2% of the substrate entering the TCA cycle; this was significantly decreased to 90.7 +/- 0.6% in the diabetic group (P < 0.02). The addition of hexanoate to the perfusate resulted in a significant increase in peak systolic pressure in the diabetic group (P < 0.001) such that contractile function was indistinguishable from controls.

TPA-induced contraction of isolated rabbit vascular smooth muscle.

Myosin light chain phosphorylation may not regulate the sustained phase of vascular smooth muscle contraction. Another, unidentified, calcium-dependent pathway may be involved in this process. TPA, an activator of C-kinase, at concentrations of 10 to 333 nM induces a calcium-dependent contraction of vascular smooth muscle which develops slowly but progressively to reach values of 50-300 mm Hg. Arteries exposed to the ionophore A23187, in a calcium-free medium, display a uniform series of contractile responses when exposed to 1.5 mM Ca2+ for 2 min once every 10 min. Exposure to 100 nM TPA as well as ionophore leads to a progressive enhancement of these calcium-induced, contractile responses. Arteries stimulated by brief (10 sec), repetitive (every 3 min) electrical pulses, respond with a series of comparable phase 1 responses. Prior exposure of vessels to 10 nM TPA, causes a progressive increase in the magnitude of these responses to repetitive electrical stimulation. Addition of 25 microM forskolin, an activator of adenylate cyclase, to TPA-treated, partially-contracted muscle leads to the immediate inhibition of the TPA-induced contraction. These data suggest that the activation of C-kinase plays a significant role in regulating vascular smooth muscle contraction.