Calcium as mediator of isoproterenol-induced myocardial necrosis

Isoproterenol (ISO), a drug which causes an increased strength of myocardial contraction when administered to animals in mug/kg doses, causes myocardial necrosis when given mg/kg doses. Previous studies suggested that necrosis might be due to flooding of the heart muscle cells by calcium. To determine if this is true, and to distinguish between flooding due to release of Ca from sequestered intramyocardial compartments and increased influx from the blood, we have measured total myocardial calcium ([Ca](m)) after ISO administration. The concentration of myocardial calcium, measured by atomic absorption spectroscopy after dry ashing, increased within 10 minutes of the intraperitoneal injection of ISO in rats. After 10 minutes the [Ca](m) remained constant at its new level for at least 50 minutes if the dose of ISO was 10(2) mug/kg or less but continued to rise at a slower rate than noted during the first 10 minutes if the ISO dose was 10(3) mug/kg or more. As measured 1 hour after ISO administration, the increase in [Ca](m), was proportional to the dose, up to 10(2) mug/kg. At higher doses there was no further increase until the dose exceeded 2 x 10(3) mug ISO/kg. Since the amount of necrosis is proportional to dose from about 10(2) to 10(5) mug/kg, while the changes in [Ca](m) are not proportional to dose over this entire range, it is concluded that ISO-induced myocardial necrosis is not mediated exclusively by flooding of heart muscle with plasma-derived calcium, although this is undoubtedly an important factor. This conclusion was further supported by experiments showing that propranolol, at doses which completely suppressed the increase in [Ca](m) due to ISO, did not completely prevent necrosis.

Immunofluorescent localization of secretin in the canine duodenum

The endocrine polypeptide (APUD) cells responsible for the production and storage of secretin have been demonstrated, in canine duodenum, by the application of an indirect immunofluorescence technique, using anti-pure porcine secretin, to carbodiimide-fixed cryostat sections. The cells are identified, by the use of parallel cytochemical and ultrastructural preparations, as the small granular S cells. These are essentially restricted to the transitional zone of the duodenal mucosa, with whose lumen their apical projections probably always make contact. There is no need to alter the title of the cells since S can now stand for secretin instead of for small.

Immunofluorescent localization of enteroglucagon cells in the gastrointestinal tract of the dog

Localization of the endocrine polypeptide cells responsible for ;glucagon-like immunoreactivity' in the gastrointestinal tract of the dog has been achieved with an immunofluorescent technique using antibodies raised against porcine pancreatic glucagon. The cells, for which we prefer the term ;enteroglucagon', could only be demonstrated by this technique in tissues fixed in carbodiimide. The enteroglucagon cells possess cytological, cytochemical, and ultrastructural characteristics in common with those of the pancreatic alpha(2) cell and they are equivalent in the stomach to the A cell and in the intestine to the L cell of the Wiesbaden terminology. Their distribution, predominantly in fundus and jejunum, correlates precisely with the distribution of glucagon-like immunoreactivity by radioimmunoassay and bioassay. The storage form of enteroglucagon differs in many respects from that of pancreatic glucagon although there are some close resemblances between the two forms of specific hormone-containing granule. Elucidation of the role of enteroglucagon should be assisted by the ability to demonstrate enteroglucagon cells.

Spontaneous rhythmic contraction of separated heart muscle cells

Muscle cells that conitract spontaneously and rhythmically can be obtained from adult mouse myocardium. Contractions are observed immediately after homogenization in a solution that is ionically similar to intracellular fluid. Contraction frequency varies directly with temperature and decreases as a function of time after homogenization. At 16 degrees C rhythmic relaxation and contraction occur for about 20 minutes. Contractions are dependent on the presence of adenosine triphosphate in the homogenization medium.

Myocytolysis and mitochondrial calcification in rat myocardium after low doses of isoproterenol

Images