Effect of captopril on lymphocytic beta-adrenergic receptors in normal and hypoxic conditions

Regulation of atrial contraction by PKA and PKC during development and regression of eccentric cardiac hypertrophy

ANG II plays a major role in development of cardiac hypertrophy through its AT1receptor subtype, whereas angiotensin-converting enzyme (ACE) inhibitors are effective in reversing effects of ANG II on the heart. The objective of this study was to investigate the role of PKA and PKC in the contractile response of atrial tissue during development and ACE inhibitor-induced regression of eccentric hypertrophy induced by aortocaval shunt. At 1 wk after surgery, sham and shunt rats were divided into captopril-treated and untreated groups for 2 wk. Then isometric contraction was assessed by electrical stimulation of isolated rat left atrial preparations superfused with Tyrode solution in the presence or absence of specific inhibitors KT-5720 (for PKA) and Ro-32-0432 (for PKC) and high Ca2+. Peak tension developed was greater in shunt than in sham hearts. However, when expressed relative to tissue mass, hypertrophied muscle showed weaker contraction than muscle from sham rats. In sham rats, peak tension developed was more affected by PKC than by PKA inhibition, whereas this differential effect was reduced in the hypertrophied heart. Treatment of shunt rats with captopril regressed left atrial hypertrophy by 67% and restored PKC-PKA differential responsiveness toward sham levels. In the hypertrophied left atria, there was an increase in the velocity of contraction and relaxation that was not evident when expressed in specific relative terms. Treatment with ACE inhibitor increased the specific velocity of contraction, as well as its PKC sensitivity, in shunt rats. We conclude that ACE inhibition during eccentric cardiac hypertrophy produces a negative trophic and a positive inotropic effect, mainly through a PKC-dependent mechanism.

Characterization of beta-adrenergic receptors in fish and amphibian lymphoid organs

Cells from goldfish and amphibian lymphoid organs, mainly leukocytes, express high affinity beta-adrenergic receptors specific for beta-adrenergic ligands (agonists: adrenaline, noradrenaline, terbutaline, and fenoterol; antagonists: CGP-12177, dihydroalprenolol, propranolol, atenolol, and butoxamine). The rank order of ligand potency does not allow their being classified into any known mammalian subtype. Among features that distinguish them from mammalian beta1 and beta2-adrenoceptors is much lower affinity for (-)-CGP-12177, obtained in both saturation and kinetic experiments (about 25 nM for goldfish head kidney cells). The density of receptors on goldfish and anuran cells is organ-dependent and comparable to that estimated on mammalian leukocytes. The extraordinarily high receptor density on salamander splenic cells (about 183,000) correlates with the large size of urodele cells. The competition experiments on goldfish cells with propranolol and CGP-12177 suggest the existence of yet another binding site, which may be either another beta-AR subtype, or a serotonergic receptor.

A new method to measure cardiac inositol levels in intact animals

Inositol levels have been studied in cellular cultures and recently by perfusion of isolated hearts. The study was aimed to assess inositol turnover in rabbit hearts from intact animals. Thirty rabbits were injected i.v. three times (every 12 hr) with 25 microCi/kg of myo-3H-inositol. The rabbits 12 hr after the last injection were killed and the hearts perfused according to Langerdorff technique. Systolic and diastolic ventricular pressures (SVP, DVP), dp/dt, and coronary flow (CFl) were measured. The hearts (n = 14) were perfused under aerobic conditions and 16 hearts under ischemic conditions for 30 min. In addition, 5 hearts were perfused under aerobic conditions for 10 min, and 6 hearts were perfused under ischemic conditions for 10 min. Samples of myocardial tissue were taken from both groups at the end of 10-min and 30-min period of perfusion, and cAMP and inositol phosphates were assayed. The hearts subjected to ischaemia showed changes of cAMP and 3H-inositol. The cAMP was higher in the ischaemic (10 min and 30 min) than the control hearts, 0.22 +/- 0.09 and 0.21 +/- 0.08 versus 0.41 +/- 0.12 and 0.49 +/- 0.11 pmol 10(6) cells, respectively (p < .05, p < .001. The inositol trisphosphate was higher in control than ischemic hearts (10 min, 30 min), 0.42 +/- 0.02 and 0.39 +/- 0.01 versus 0.31 +/- 0.01 and 0.23 +/- 0.02 (percent of radioactivity) respectively, p < .001. Our data suggest that 3H-inositol may be studied by i.v. administration to intact animals. The ischemia was performed to verify the validity of this new technique.

Effects of the administration of captopril, metoprolol and of the captopril-metoprolol combination as adjuvant therapy during thrombolysis in acute myocardial infarction

The aim of the study was to verify, during thrombolysis in patients with anterior acute myocardial infarction, the safety and effects of beta-blockers or ACE-inhibitors and their combination in the short and long term. One-hundred sixty-six patients hospitalized within 4 h from the onset of the symptoms (first episode), eligible for thrombolysis, Killip class I-II, were randomized (single blind) into four groups. Group A (42 patients) received 6.25 mg captopril (orally) 15 min before thrombolysis and metoprolol (i.v.) not later than 1 h, and orally afterwards. Group B (42 patients) received 6.25 mg captopril 15 min before thrombolysis. Group C (37 patients) received metoprolol not later than 1 h. Group D (45 patients) received thrombolysis only. Later (day 3), groups C and D also received captopril. We checked ventricular arrhythmias (first 2h) from thrombolysis, creatine kinase peak, creatine kinase peak normalization time, late ventricular arrhythmias at Holter test pre-discharge (Lown's class > 2). At follow-up (mean 30.5 +/- 2 months), mortality was evaluated for reinfarction and ventricular failure. Age and sex were similar.

RESULTS

Early ventricular arrhythmias: Group A, five cases; Group B, five cases; Group C, 15 cases; Group D, 16 cases. Creatine kinase peak: Group A, 1875 +/- 220 U/l; Group B, 1566 +/- 168 U/l; Group C, 2274 +/- 212 U/l; Group D 2103 +/- 232 U/l. Creatine kinase peak normalization time: Group A, 57.7 +/- 3 h; Group B, 58.1 +/- 3 h; Group C, 72.7 +/- 3 h; Group D, 69.5 +/- 2 h (P < 0.05).(ABSTRACT TRUNCATED AT 250 WORDS)