No abstract

To describe the mechanisms of action of Corwin (ICI 118,587), a new cardioselective beta-adrenoceptor partial agonist, ten cardiac patients with mild to moderate functional cardiac impairment were studied. Hemodynamic measurements were made at rest and during three consecutive levels of submaximal exercise, before and 10 min after intravenous administration of 0.2 mg/kg of the drug. At rest, Corwin increased heart rate (HR) from 75 to 88 bpm and mean systemic blood pressure (BP) and decreased mean pulmonary capillary wedge pressure (PCWP); the resting cardiac output (CO) tended to increase in patients with a slow control HR. During exercise of low intensity (control HR: 103 bpm), the drug had no significant effect, except for a slight decrease in BP. During exercise of moderate and heavy intensity (control HR: 121 and 149 bpm), Corwin decreased HR (-10 and -24 bpm), BP and PCWP; at the heaviest exercise level, CO also decreased after Corwin. Thus, at rest, when the sympathetic tone is low, Corwin acts mainly as a beta-adrenoceptor agonist. As the sympathetic tone progressively increases with the intensity of the exercise, the beta-adrenoceptor antagonist action of Corwin becomes apparent and is most evident at the highest exercise level. In contrast to a full antagonist, these effects of Corwin appear to be less marked and they are accompanied by an unchanged or decreased PCWP. Corwin has thus interesting hemodynamic properties which deserve further investigation.

No abstract

To test the ability of ketone bodies to inhibit myocardial fatty acid oxidation in vivo, the myocardial clearance kinetics of [1-11C]palmitate was assessed with positron emission tomography in six fasted volunteers and six instrumented dogs, studied repeatedly before and during infusion of 3-hydroxybutyrate (17 mumol.kg-1 x min-1). With the use of multiexponential fitting of tissue time-activity curves, the size, half time (T1/2), and index of the early rapid phase of 11C myocardial clearance, reflecting palmitate oxidation, were calculated. In humans, the relative size (-28%, P < 0.001) and index (-37%, P < 0.01) of the early rapid phase decreased significantly during infusion of 3-hydroxybutyrate, consistent with decreased fatty acid oxidation. Paradoxically, T1/2 decreased from 10.1 +/- 1.6 to 7.4 +/- 1.1 min (P < 0.01). To elucidate possible mechanisms, multiple coronary arteriovenous samples were obtained from the dogs to assess the efflux of oxidized and nonmetabolized tracer. Infusion of 3-hydroxybutyrate resulted in decreased myocardial [11C]CO2 production (-40%, P < 0.05) and reduced palmitate retention (-38%, P < 0.05). In three dogs, the arteriovenous difference in radiolabeled palmitate became negative 10 min after injection, indicating backdiffusion of nonmetabolized tracer from the myocardium. Thus a steady-state infusion of 3-hydroxybutyrate, resulting in physiological plasma levels, alters [1-11C]palmitate kinetics in vivo by decreasing myocardial long-chain fatty acid oxidation and by increasing backdiffusion of nonmetabolized tracer.

Indium-111 pentetreotide scintigraphy was performed in two patients for the localization of recurrent medullary thyroid carcinoma treated by surgery and external radiotherapy 1 and 10 years earlier. A marked uptake of the radiopharmaceutical was demonstrated in the lung areas that had been irradiated. These cases strongly suggest that this uptake is related to pulmonary fibrosis, a well-known complication of radiotherapy, even long after the irradiation. Therefore, attention must be paid to the avoidance of false-positive interpretation of somatostatin receptor scintigraphy in patients previously treated by radiotherapy.