Indirect pathway of liver glycogen synthesis in humans is predominant and independent of beta-adrenergic mechanisms.

The relative contribution of the direct and indirect pathways to liver glycogen formation was assessed in humans by using a combined tracer-hepatic vein catheterization technique. An oral glucose load (75 g) labelled with 1-14C-glucose was administered to five subjects (control group) and 4.5 h later hepatic glycogen was flushed with glucagon and analysed to determine the randomization of 14C. The specific activity (SA) of the glycogen derived glucose (1-14C-glucose SA+recycled 14C-glucose SA) was 61 +/- 7% of the mean blood glucose SA of the interval 0-180 min after the oral glucose load. The relative values due to 1-14C-glucose and recycled 14C-glucose were 33 +/- 7 and 28 +/- 3%, respectively. The data indicate that the indirect pathway of glycogen formation is not only active in humans but contributes substantially (at least 50%) to liver glycogen formation. In order to investigate whether the basal adrenergic tone plays a role in the maintenance of the indirect pathway, the same protocol was also performed in a second group of subjects (n = 5) who received propranolol before the oral glucose load (propranolol group). The SA of the glycogen-derived glucose was considerably smaller than that of the control group (18 +/- 5 vs. 61 +/- 7%, P < 0.001), suggesting lesser glycogen formation. However, the ratio of 1-14C to recycled-14C in the glucose molecule was similar in the control (1.3 +/- 0.4) and propranolol group (1.9 +/- 1.2). We conclude that the basal adrenergic tone does not play any role in the operation of the indirect pathway of liver glycogen synthesis.

Atrial natriuretic factor potentiates forearm reflex vasoconstriction induced by cardiopulmonary receptor deactivation in man.

Previous evidence suggests that atrial natriuretic factor (ANF) interferes with the autonomic control of circulation. In the present study we investigated whether ANF modulates forearm vasoconstriction reflexly induced by cardiopulmonary receptor unloading in man. For this purpose, the hemodynamic response to -20 mm Hg lower body negative pressure (LBNP) was assessed under control conditions and during the constant infusion of alpha-human ANF (0.5 micrograms/kg bolus followed by 0.05 micrograms/kg/min) in seven normal subjects. ANF infusion resulted in a slight reduction in blood pressure and right atrial pressure, did not modify heart rate or forearm vascular resistance, but significantly potentiated the reflex increase in forearm vascular resistance during LBNP (+25 +/- 9% under control conditions vs +40 +/- 12% during ANF, p less than .05). In an attempt to clarify the mechanisms underlying the enhanced reflex vasoconstriction during infusion of ANF, in five additional subjects we demonstrated that there was a comparable vascular reflex response to LBNP under control conditions and during nitroglycerin infusion at a dose that induced a reduction in atrial pressure comparable to that observed during ANF. Finally, in seven additional subjects we found that ANF infusion did not alter the reflex hemodynamic responses elicited by carotid baroreceptor unloading induced by a +60 mm Hg increase in external neck pressure. We conclude that during the infusion of a pharmacologic dose of ANF the reflex forearm vasoconstriction in response to selective cardiopulmonary receptor unloading is potentiated. This effect does not seem to be related to the hemodynamic actions of the peptide or to interference with the sympathetic control of peripheral circulation.

[Limitation of the area of necrosis induced by quinacrine after coronary occlusion in the dog]. / Limitazione dell'area di necrosi indotta dalla chinacrina dopo occlusione coronarica nel cane.

Phospholipase activation has been suggested to represent one of the most relevant biochemical steps toward irreversible myocardial injury during ischemia. Accordingly, the time-course of myocardial phospholipid degradation was studied in 167 rats surviving coronary artery occlusion randomly divided into 83 controls and 84 treated with the phospholipase inhibitor quinacrine (75 mg/Kg s.c. every 8 h). The animals were sacrificed at different times ranging from 2 to 48 h post-occlusion and phospholipids and creatine kinase activity (CK) were measured on the supernatant of the left ventricular homogenates. In control animals a rapid fall in phospholipid concentration (from 1.33 +/- 0.12 to 0.67 +/- 0.05 microgram P/mg of protein) and CK activity (from 9.84 +/- 0.49 to 6.93 +/- 0.60 IU/mg of protein) was observed within 4 hours post-occlusion; these parameters remained almost unchanged throughout the rest of the study. In quinacrine-treated animals left ventricular phospholipids and CK also fell during the first hours post-occlusion; however, 24 and 48 h after the occlusion they were significantly higher than in controls (phospholipids: 0.99 +/- 0.05 vs 0.62 +/- 0.04 microgram P/mg of protein, p less than 0.001, and CK: 7.76 +/- 0.54 vs 4.99 +/- 0.37 IU/mg of protein, p less than 0.001, at 48 h). The effect of quinacrine on the extent of necrosis was then assessed in 13 anesthetized dogs undergoing ligation of the left anterior descending coronary artery. To measure the area at risk (RZ), 99Tc-PP labeled albumin microspheres were injected into the left atrium 5 min after coronary occlusion.(ABSTRACT TRUNCATED AT 250 WORDS)