Effect of starvation on hepatic glycogen metabolism and glucose homeostasis.

The effects of starvation on the hepatic glycogen synthase and phosphporylase systems were sequentially assessed in fed and 24-120-hr-fasted rats. Enzymic changes before and after glucose were correlated with simultaneous measurements of hepatic cyclic AMP and glycogen concentrations and glucose, insulin, and glucagon concentrations in the portal vein plasma. Fasting caused parallel changes in plasma glucose and hepatic glycogen concentrations with decreases by 24 hr and subsequent increases, which correlated with increases in hepatic synthase l and decreases in phosphorylase activites. Hepatic cyclic AMP levels increased as 24-48 hr, decreased below fed levels at 96 hr, and increased again at 120 hr. Fasting caused progressive impairment of glucose disposal, decreased basal and postglucose insulin concentrations, and decreased basal glucagon levels at 48-72 hr. Hepatic synthase l increments following glucose were exaggerated in 48-120-hr-fasted rats, although consistent phosphorylase decrements were seen only in fed rats. There was no clearcut relationship between synthase activation and phosphorylase inactivation following glucose in fed or fasted rats.     

Quinidine for ventricular arrhythmias: value of electrophysiologic testing

Quinidine was evaluated during serial electrophysiologic testing with programmed ventricular stimulation in 89 patients with life-threatening ventricular arrhythmias. In 30 of the 89 patients, quinidine therapy prevented the initiation of ventricular tachycardia (VT) during programmed ventricular stimulation. In 8 additional patients no single drug tested was effective, and quinidine in combination with either mexiletine (7 patients) or propranolol (1 patient) prevented the initiation of VT during electrophysiologic testing. The mean serum concentrations of quinidine in the patients who responded and those who failed to respond were 2.9 +/- 0.8 and 2.8 +/- 1.1 micrograms/ml, respectively; however, but nonresponders were characterized by more severe congestive heart failure and an increased incidence of digitalis use. During chronic therapy (24 +/- 3 months) with quinidine either alone or in combination with a second antiarrhythmic drug in the 38 patients whose arrhythmia had been suppressed during electrophysiologic testing, 32 (84%) remain symptom-free while 3 have had recurrent arrhythmia and 3 discontinued quinidine because of adverse effects. These data demonstrate that quinidine, when selected on the basis of electrophysiologic testing, provides effective long-term prophylaxis against recurrent ventricular arrhythmia and that approximately 40% of patients tested are likely to respond either to quinidine alone or quinidine in combination with another antiarrhythmic agent.     

Effect of coronary collateral circulation on regional myocardial perfusion assessed with quantitative thallium-201 scintigraphy

The functional role of the coronary collateral circulation in patients with coronary artery disease has yet to be clarified. Because the distribution of thallium in the myocardium after its intravenous injection is proportional to regional blood flow, quantitative thallium scintigraphy was employed to assess noninvasively the effect of collateral vessels on regional myocardial perfusion at rest and after exercise stress. Sixty-two patients with significant (greater than 50 percent stenosis of luminal diameter) coronary artery disease had after exercise thallium imaging and 35 patients underwent imaging at rest. Delayed redistribution images were obtained after exercise and at rest. Images were divided into six segments for analysis and interpreted using computer-assisted quantitative techniques. In patients undergoing exercise stress, collateral vessels did not significantly influence thallium uptake patterns in segments associated with electrocardiographic Q waves. In segments without Q waves, thallium uptake was more frequently abnormal (p <0.001) in segments with than in segments without collateral vessels whether or not such vessels were jeopardized. The presence or absence of collateral channels did not affect the frequency of occurrence of thallium redistribution. In patients undergoing serial imaging at rest, the prevalence of segments with normal thallium uptake was greater in segments with nonjeopardized than in those with jeopardized collateral vessels (p <0.05).It is concluded that (1) coronary collateral vessels are an indicator of severe coronary arterial obstruction and do not protect against exercise-induced hypoperfusion or affect the occurrence of redistribution, and (2) non-jeopardized collateral vessels appear to augment perfusion at rest in some segments to the degree that normal thallium uptake at rest is observed.     

Interactions of the trophoblast and maternal tissues in three closely related primate species

The confluence of maternal and fetal tissues to form the placenta causes a wide variety of alterations in cells of both origins. Three closely related primate species were studied for similarities and differences in the interrelationships formed during various stages of placental development in the areas of implantation, decidualization, and trophoblastic involvement in the spiral arteries. Although certain similarities exist among the three species a surprising number of distinct differences were found to shed doubt on the common practice of assuming species-to-species similarity, particularly among primates.     

Ratio of transverse to longitudinal resistivities of isolated cardiac muscle fiber bundles

The ratio of transverse to longitudinal resistivities (рt/р1) of isolated cat cardiac muscle bundles (papillary muscles and ventricular trabeculae) composed of parallel fibers was measured and compared with frog sartorius muscles. Similar measurements made on a physical model representing such bundles of parallel fibers, consisting of layers of glass rods orderly packed with Ringer solution filling the interstices, gave a рt/р1 of 7. This ratio averaged 11 for cardiac muscle and 21 for skeletal muscle, indicating that in both muscles the transverse conductivity and effective diffusion coefficient are much less than the longitudinal values. Equilibration of cardiac muscle in ten-fold diluted Ringer (sucrose to isotonicity) to raise the resistance of the interstitial fluid (ISF) 8.5-fold raised р1 6.3-fold, but hardly affected р1, so that рt/р1 was markedly reduced to 2.0. In sartorius, the high-resistance solution had much less of an effect on р1 or on рt/р1. Equilibration in hypertonic Ringer (2 X isotonicity with sucrose) raised р1 and lowered рt slightly in both types of muscles, resulting in a small decrease in рt/р1. Calculations of the ratio of the resistance of the cellular pathway to that of the extracellular pathway averaged 20 for cardiac muscle compared to only 0.82 for skeletal muscle. The data indicate that the longitudinal current path through the myocardial cells is high in resistance compared to that through the ISF, suggesting that the intercalated disks are high-resistance membranes. The resistivity of the disk membranes averages 576 Ω-cm², assuming a 6.4-fold increase in surface area due to convolutions; this value approaches that of the sarcolemma, and is much higher than the maximum (2 Ω-cm²) allowable for significant DC electrical coupling to occur between contiguous cells. The fact that the extracellular fluid of a parallel-fibered muscle bundle itself acts as a cable could account for the observation that measurements of the tissue length constant by extracellular application of current give large values; thus, such measurements cannot be used to determine the resistance of the cell junctions in muscles composed of short cells.