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Biomedical subjects

G A Robison

Publications and source records attributed to G A Robison.

At least 19 recordsLinked to original sources
PubMed1979

Insulin inhibition of lipolysis of human adipocytes: the role of cyclic adenosine monophosphate.

To gain information on the manner in which insulin suppresses lipolysis in man, isolated adipocytes, prepared from subcutaneous adipose tissue, were incubated with insulin (100 microunits/ml) alone and in combination with isoproterenol (10(-7) M or 10(-8) M). Cyclic AMP concentration was measured at 60 min; glycerol release, used as an index of lipolysis, was determined at 45 and 75 min. Insulin consistently reduced both basal and stimulated cyclic AMP and glycerol release: the degree of suppression of each was comparable. In subsequent experiments, the ability of insulin to suppress glycerol release stimulated by isoproterenol, theophylline, and dibutyryl cyclic AMP (dbcAMP), respectively, was compared. Insulin substantially reduced the raised levels of cyclic AMP and glycerol release prompted by isoproterenol and theophylline, but it had little effect on increases caused by dbcAMP. These findings support the view that reduction in cyclic AMP is an important component in the regulation of fat mobilization by insulin.

Adipose Tissue↗
PubMed1979

The effect of fasting on the adrenergic receptor activity of human adipocytes.

To assess the influence of fasting of the alpha- and beta-adrenergic receptor activities of human adipocytes, subcutaneous adipose tissue was obtained from normal obese subjects in the fed state and after 3 days of fasting. Isolated cells prepared from the adipose tissue were incubated with epinephrine, 10(-6)M, and in the presence of the alpha-blocker phentolamine, 10(-5)M, and the beta-blocker propranolol, 10(-5)M, respectively; intracellular cyclic AMP levels and glycerol released into the buffer were measured. Consistent with past observations, epinephrine stimulated cyclic AMP and glycerol release when incubated with cells from fed subjects. Phentolamine enhanced this action and propranolol reduced it below the basal level. In contrast, epinephrine suppressed cyclic AMP and lipolysis when incubated with adipocytes from fasted individuals. This reversal in the effect of epinephrine on adipocy.se in alpha-activity. Additional studies suggest that this change in alpha- and beta-adrenergic receptor balance occurred after 1 day of fast and was not significantly exaggerated when fast was prolonged to 8 days. These findings are consistent with the view that in the fasting state the sympathetic nervous system and circulating catecholamines act to conserve adipose tissue triglyceride.

Adipose Tissue↗
PubMed1978

Loss of lymphocyte cyclic AMP dependent protein kinase activity in malignant melanoma.

Cyclic AMP dependent protein kinase activity was depressed in whole thymus and spleen as well as isolated splenic lymphocytes from B16 melanoma bearing C57B1/6J mice as compared to control animals. A similar loss of enzyme activity was observed in human peripheral blood lymphocytes from melanoma bearing patients as compared to normal subjects. An unaltered level of activity in the heart of tumor bearing mice suggested some specificity for the lymphoid system. This depressed enzyme activity was the result of a diminished Vmax for cAMP stimulated calf histone phosphorylation. The tumor bearing state in the mouse was also accompanied by a depletion of small lymphocytes from both thymus and spleen and it is hypothesized that the losses of lymphocytes and cAMP dependent protein kinase activity are related.

Animals↗
PubMed1978

Inhibition of GH1 rat pituitary tumor cell adenylyl cyclase activity by somatostatin.

Somatostatin inhibits basal and chlorpromazine stimulated adenylyl cyclase activity in homogenates of GH1 rat pituitary tumor cells. The Dtryp8-Dcys14 analogue is more potent than tyrosyl somatostatin as an inhibitor of both basal and chlorpromazine-stimulated adenylyl cyclase. Somatostatin had no effect on sodium fluoride or quanylyl-imidodiphosphate-stimulated cyclase in GH1 cell homogenates or on basal, epinephrine or prostaglandin E1 stimulated cyclase activity in sonicated BHK fibroblasts. These results indicate a specific effect of somatostatin to inhibit pituitary adenylyl cyclase activity.

Adenylyl Cyclase Inhibitors↗
PubMed1977

In-vitro observations on isolated adipose tissue cells from hyperobese subjects.

Isolated adipose tissue cells were prepared from subcutaneous samples obtained from nine morbidly obese subjects weighing from 187 to 306% of ideal body weight. The responsiveness of these adipocytes to a number of test substances was determined by measuring cellular cyclic AMP concentration at one-half hour and glycerol release at four hours. Theophylline (10(-3) M) and epinephrine (10(-5) M) stimulated lipolysis; theophylline stimulated an increase in cyclic AMP, while epinephrine failed to prompt a significant change in the nucleotide. Neither the alpha blocker, phentolamine (10(-5) M), nor the beta blocker, propranolol (3 X 10(-5) M), affected lipolysis or cyclic AMP; when these agents were incubated in combination with epinephrine, changes occurred indicative of the presence of both alpha and beta adrenergic receptor sites. Insulin significantly reduced both basal and stimulated lipolysis but failed to affect cyclic AMP. With minor exceptions, adipocytes from hyperobese subjects behaved similarly to cells from unselected donors; at the concentration used, there was no evidence of resistance to insulin.

Adipose Tissue↗
PubMed1977

Sonication as a tool for the study of adenylyl cyclase activity.

The technique of sonication was applied in studying adenylyl cyclase activity of cultured fibroblasts. Exposure of BHK 21 c/13 to brief periods of low power sonication gives cell preparations with greater basal, fluoride and hormone sensitive adenylyl cyclase activites than those of broken cell preparations of homogenized cells. The sonicated cells provide a convenient method to study adenylyl cyclase since they are added directly to the adenylyl cyclase reaction vessels without further processing. Maximal epinephrine stimulated activity in sonicated cells is nearly equivalent to that activated by sodium fluoride, but the apparent affinity of the enzyme system is similar to that of broken cell preparations. Furthermore, broken cell preparations of sonicated cells possess greater adenylyl cyclase activity than broken cell preparations of unsonicated cells. This procedure may provide a useful tool for the analysis of the hormonal regulation of adenylyl cyclase activity of isolated cells.

Adenylyl Cyclases↗