Inhibitory effect of [Asu1 . 7]-eel calcitonin on glucagon-induced glycogenolysis in perfused rat liver

In an attempt to elucidate the mechanism by which calcitonin modulates glucose metabolism, the effect of elcatonin ([Asu1 . 7]-eel calcitonin), a potent synthetic eel calcitonin analogue, on hepatic glycogenolysis was investigated by use of perfused liver from fed rats. Elcatonin, as infused into the portal vein at concentrations between 10 mU/ml and 200 mU/ml did not affect glucose output into the hepatic venous effluent. At concentrations higher than 100 mU/ml, it inhibited the glycogenolysis stimulated by submaximal concentrations of glucagon which was perfused concurrently. This aspect of elcatonin effect was reproduced by synthetic salmon calcitonin. Though elcatonin showed a marked inhibition of the glycogenolytic activity induced by glucagon at or less than 5.7 X 10(-11) M, the inhibitory effect became undetectable when higher concentrations of glucagon were employed. Elcatonin did not inhibit the glycogenolysis induced by dibutyryl cyclic AMP at near (0.5 microM) or less than half-maximally effective (0.2 microM) concentrations. In addition, it did not inhibit the glycogenolytic activity half-maximally stimulated by alpha-adrenergic agonist (phenylephrine, 0.4 microM) or vasopressin (0.2 mU/ml). Elcatonin inhibited the cyclic AMP production of the tissue induced by glucagon infusion. These data indicate that elcatonin modulates hepatic glycogenolysis by preventing the glucagon effect at a step before cyclic AMP production and with an apparently competitive kinetics. In view of the concept that Ca++ is involved in the glycogenolytic effect of alpha-adrenergic agonist and vasopressin, the fact that elcatonin did not influence the action of these agents suggests that Ca++ fluxes are not involved in the elcatonin effect on liver.

Different mode of action of cimetidine and prostaglandin on the rat gastric mucosa under stress loading by restrain and water-immersion

Gastric mucosal blood flow and oxygen tension in the corporal mucosa gradually declined after water immersion in the control animals. Neither cimetidine nor prostaglandin E2 had any influence on the decrease of the corporal mucosal blood flow or mucosal oxygen tension during seven hours of stress loading. The stress ulceration began to occur starting three hours after cold immersion in the control rats, and the deficit of energy metabolism was attributed to reduced oxidative phosphorylation from tissue hypoxia resulting from lowered blood flow and oxygen tension under stress. Cimetidine (4 mg/kg) maintained aerobic glycolysis, continued to produce high-energy phosphates and kept the energy charge unchanged in the gastric mucosa. In addition, PG E2-Me (100 micrograms/kg) showed similar, but less marked and shorter-lived effects on aerobic glycolysis and ATP production, whereas the energy charge of the adenosine pool decreased significantly from that produced by cimetidine. These results indicated that cimetidine significantly reduced energy requirements as compared with the control and PG E2 groups due to marked inhibition of gastric secretion and produced inhibition of mucosal ulceration by water immersion. On the other hand, increased energy requirements due to the rise of cytoprotective mucoprotein production and a resultant decrease of the energy charge were seen with PG E2 as compared with cimetidine.

Bypass anomaly of the vertebral artery associated with cerebral aneurysm and arteriovenous malformation

✓ In a series of 1107 patients with cerebrovascular disease studied by four-vessel angiography, the authors have found 10 cases of a bypass anomaly of the vertebral artery. Six of the cases also had cerebral aneurysms, and two cerebral arteriovenous malformations. The authors discuss the possible origins for this relationship.