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Biomedical subjects

K J Long

Publications and source records attributed to K J Long.

23 records · Page 2Linked to original sources
PubMed1981

Growth hormone stimulation of lipolysis and cyclic AMP levels in perifused fat cells.

A rapid, sustained lipolytic response to growth hormone (GH; 20 microgram/ml) was observed in experiments using the perifused fat cell system. No lipolytic response to this agent was observed when fat cells were incubated by the traditional flask incubation method, although isoproterenol stimulated lipolysis in this preparation. In experiments using flask incubated fat cells, isoproterenol increased cyclic AMP content while GH had no effect. However, in the presence of theophylline, isoproterenol and GH significantly increased cyclic AMP levels. In perifused fat cells, both isoproterenol and GH significantly increased cyclic AMP levels in the absence of theophylline. The presence of adenosine deaminase resulted in significant increases in the lipolytic response to isoproterenol and unmasked a lipolytic response to GH when the flask-incubated fat cell system was used. The antilipolytic action of adenosine was determined in perifused fat cells. It was found that the lipolytic response to GH was at least 10 times as sensitive to the inhibitory action of adenosine as was the lipolytic response to isoproterenol. It is concluded that the lipolytic response to GH in the flask-incubation method is prevented by the accumulation of adenosine. This rapid lipolytic response is unmasked in the perifused fat cell system because adenosine fails to accumulate as it is washed from the cell population by the constantly flowing buffer.

Adenosine↗
PubMed1981

Relationship among isoproterenol, cyclic AMP, cyclic AMP-dependent protein kinase and lipolysis in perfused fat cells.

By using perfused fat cells the effect of isoproterenol on adenosine 3':5'-monophosphate (cAMP) levels, cAMP-dependent protein kinase activity and lipolysis was studied. An infusion of isoproterenol (10(-7) M) resulted in a time-dependent increase in cAMP levels and protein kinase activity in the fat cells. Both parameters reached maximum values after 5 min of drug infusion, then declined to steady-state values by 10 min. At 60 min, cAMP levels were still significantly (P less than .05) elevated over basal. Dose-response curves were determined for isoproterenol on cAMP levels, protein kinase activity and glycerol release. All three parameters were increased by isoproterenol over the same concentration range (10(-9)--10(-7) M). A plot of cAMP levels or protein kinase activity ratios vs. glycerol release resulted in linear relationship with high degrees of correlation (r = 0.98). The rates at which cAMP levels and glycerol release decline after termination of isoproterenol infusion were studied. Half-life values of 5.8 and 6.9 min were obtained for cAMP levels and glycerol release, respectively. These results support the hypotheses that cAMP, acting through protein kinase, is an intracellular mediator of the lipolytic response to isoproterenol. It is concluded that cAMP is not formed in great excess of that necessary to maximally increase lipolysis.

Adipose Tissue↗
PubMed1979

Characterization of the multiple-chamber perifused fat cell system.

A multiple-chamber perifused fat cell system is described. Six chambers containing fat cells were perifused in parallel with buffer. Perifusate was collected for assay of glycerol as an index of lipolytic rates and cells in each chamber can be taken for analysis of biochemical intermediates. The system is so designed that drugs can be infused into the buffer and equally distributed in each chamber or can be individually infused into the buffer to one chamber, allowing for six different conditions to be tested in the same population of fat cells. The time and distribution characteristics of infused material are described. Time relationships are described for isoproterenol and glycerol release and for cyclic AMP levels in the fat cells, and the dose-response relationship between isoproterenol and glycerol release is shown.

Adipose Tissue↗