scholarly journals Direct effects of progesterone on rat islets of Langerhans in vivo and in tissue culture

Diabetologia ◽  
1977 ◽  
Vol 13 (6) ◽  
pp. 579-583 ◽  
Author(s):  
S. L. Howell ◽  
Margaret Tyhurst ◽  
Irene C. Green
Keyword(s):  
Tissue Culture ◽  
Islets Of Langerhans ◽  
Direct Effects ◽  
Rat Islets ◽  
Rat Islets Of Langerhans

scholarly journals ISOLATION AND PROPERTIES OF SECRETORY GRANULES FROM RAT ISLETS OF LANGERHANS

1969 ◽  
Vol 41 (1) ◽  
pp. 167-176 ◽  
Author(s):  
S. L. Howell ◽  
D. A. Young ◽  
P. E. Lacy
Keyword(s):  
Islets Of Langerhans ◽  
Secretory Granules ◽  
Sodium Deoxycholate ◽  
Rat Islets ◽  
The Matrix ◽  
Effects Of Ph ◽  
The Stability ◽  
Rat Islets Of Langerhans ◽  
Specific Insulin

A partially purified secretory granule fraction, isolated from rat islets of Langerhans by differential centrifugation, was used for investigating the stability of the beta granules during incubation in various conditions. Effects of pH, temperature, and time were studied; the granules possessed optimal stability at 4° and pH 6.0, and could be solubilized at pH 4.0 or 8.5, or in the presence of sodium deoxycholate, but not by phospholipase c, ouabain, or alloxan. Incubation with glucose or some of its metabolites, or with tolbutamide, ATP, or cyclic 3',5'-AMP did not alter the stability of the beta granules Exogenous insulin-131I was not bound by the isolated granules under the conditions used; no specific insulin-degrading activity could be detected in subcellular fractions of the islets. These findings indicate that intracellular solubilization of the granules with subsequent diffusion of the insulin into the extracellular space is not a likely mode of insulin secretion in vivo, and suggest that a crystalline zinc-insulin complex may exist in the matrix of the beta granules.

Effects of cyclic AMP on DNA replication and protein biosynthesis in fetal rat islets of Langerhans maintained in tissue culture

1982 ◽  
Vol 2 (11) ◽  
pp. 867-876 ◽  
Author(s):  
I. Swenne
Keyword(s):  
Tissue Culture ◽  
Dna Replication ◽  
Cyclic Amp ◽  
Islets Of Langerhans ◽  
Protein Biosynthesis ◽  
Insulin Production ◽  
Rat Islets ◽  
Fetal Rat ◽  
Rat Islets Of Langerhans ◽  
Stimulation Of

The regulatory role of cyclic AMP (cAMP) in the growth and insulin production of the islet organ in vitro has been investigated. The effects of dibutyryl cyclic AMP (dbcAMP), theophylline, and 3-isobutyl-1-methylxanthine (IBMX) on DNA replication and on the biosynthesis of RNA and insulin in fetal rat islets of Langerhans maintained in tissue culture have been studied. Raising the glucose concentration from 2.7 mM to 16.7 mM caused a two-fold increase in DNA replication. Both dbcAMP and theophylline markedly inhibited the DNA replication at all glucose Concentrations studied. Low concentrations of IBMX stimulated DNA synthesis. However, at higher concentrations of this drug, known to considerably increase the islet cAMP levels, a marked inhibition of islet DNA replication was observed. Both (pro)insulin and total protein biosynthesis were stimulated by glucose, whereas dbcAMP stimulated only the (pro)insulin biosynthesis. Since glucose is known to raise islet intracellular levels of cAMP, which is known to be an inhibitor of cellular proliferation, the observed glucose stimulation of both islet-cell DNA replication and insulin production appeared conflicting. It is suggested that this dual effect of glucose may depend on a stimulation of proliferation in a limited pool of islet cells which may not exhibit an increase in cAMP.

Preservation of the Effects of Pregnancy on Rat Islets of Langerhans in Tissue Culture

1979 ◽  
Vol 10 (1) ◽  
pp. 37-43 ◽  
Author(s):  
Irene C. Green ◽  
Simon L. Howell ◽  
David Perrin
Keyword(s):  
Tissue Culture ◽  
Islets Of Langerhans ◽  
Rat Islets ◽  
Rat Islets Of Langerhans

Opioid peptides in rat islets of Langerhans. Immunoreactive met- and leu-enkephalins and BAM-22P

Diabetes ◽  
1986 ◽  
Vol 35 (1) ◽  
pp. 52-57 ◽  
Author(s):  
K. I. Timmers ◽  
N. R. Voyles ◽  
C. King ◽  
M. Wells ◽  
R. Fairtile ◽  
...  
Keyword(s):  
Islets Of Langerhans ◽  
Opioid Peptides ◽  
Rat Islets ◽  
Rat Islets Of Langerhans

Effects of epicatechin on rat islets of Langerhans

Diabetes ◽  
1984 ◽  
Vol 33 (3) ◽  
pp. 291-296 ◽  
Author(s):  
C. S. Hii ◽  
S. L. Howell
Keyword(s):  
Islets Of Langerhans ◽  
Rat Islets ◽  
Rat Islets Of Langerhans

scholarly journals CYTOCHEMICAL LOCALIZATION OF ADENYL CYCLASE ACTIVITY IN RAT ISLETS OF LANGERHANS

1972 ◽  
Vol 20 (11) ◽  
pp. 873-879 ◽  
Author(s):  
S. L. HOWELL ◽  
MARGARET WHITFIELD
Keyword(s):  
B Cells ◽  
Islets Of Langerhans ◽  
Adenosine Triphosphate ◽  
Adenyl Cyclase ◽  
Cyclase Activity ◽  
Cytochemical Localization ◽  
Adenyl Cyclase Activity ◽  
Rat Islets ◽  
Rat Islets Of Langerhans ◽  
A And B Cells

A cytochemical method has been used to investigate the localization of adenyl cyclase activity in A and B cells of isolated rat islets of Langerhans. Adenosine triphosphate was initially utilized as substrate, the pyrophosphate liberated being precipitated by lead ions at its site of production. The specificity of the method was increased by the use of adenylyl-imidodiphosphate as an alternative substrate; this adenosine triphosphate analogue was not hydrolyzed by adenosine triphosphatase but provided an effective substrate for adenyl cyclase. Adenyl cyclase activity, which was found to retain its glucagon and fluoride sensitivity in glutaraldehyde-fixed tissue, was found exclusively and almost uniformly in the plasma membranes of A and B cells. Storage granule membrane, incorporated into the plasma membrane during secretion of the granule content by exocytosis, appeared to be devoid of adenyl cyclase activity.

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