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In vitro insulin-like actions of the growth factor from the tapeworm, Spirometra mansonoides
1Department of Biochemistry, University of Nebraska Medical Center, Omaha 68105.
Abstract:
In vitro actions of purified plerocercoid growth factor (PGF) were compared with those of insulin and human growth hormone (hGH) in adipose tissue from normal male rats. Insulin-like effects were measured by the ability of PGF, insulin, or hGH to stimulate oxidation of [U-14C]glucose to 14CO2, to stimulate lipogenesis, and to inhibit epinephrine-induced lipolysis. PGF and insulin stimulated significant increases in glucose oxidation and lipogenesis in adipose tissue that had not been preincubated as well as in tissue that had been preincubated. hGH stimulated insulin-like effects only in tissue that had been preincubated for 3 hr. Insulin, hGH, and PGF inhibited epinephrine-induced lipolysis of preincubated (3 hr) adipose tissue. hGH produced a dramatic lipolytic response in tissue freshly removed from normal rats but no dose of PGF was lipolytic. PGF did not displace 125I-insulin from its receptors on adipocytes but did competitively inhibit 125I-hGH binding to adipocytes. These results suggest that PGF has direct insulin-like actions which are initiated by binding a GH receptor, but PGF had no anti-insulin action and the insulin-like activity of PGF was unaffected by refractoriness of adipose tissue to GH.
Insights
Plerocercoid growth factor (PGF) exhibits direct insulin-like actions in rat adipose tissue by binding to growth hormone (GH) receptors. Unlike insulin, PGF
Area of Science:
- Endocrinology
- Metabolic Research
- Molecular Biology
Background:
- Plerocercoid growth factor (PGF) is a protein with poorly understood biological functions.
- Insulin and human growth hormone (hGH) play critical roles in regulating glucose and lipid metabolism.
- Adipose tissue is a key metabolic organ responsive to hormonal signaling.
Purpose of the Study:
- To compare the in vitro metabolic actions of PGF with insulin and hGH in rat adipose tissue.
- To investigate the receptor binding characteristics of PGF in adipocytes.
- To elucidate the mechanism of PGF's insulin-like effects.
Main Methods:
- In vitro incubation of rat adipose tissue with PGF, insulin, and hGH.
- Measurement of [U-14C]glucose oxidation to 14CO2.
- Assessment of lipogenesis and inhibition of epinephrine-induced lipolysis.
- Competitive binding assays using 125I-insulin and 125I-hGH.
Main Results:
- PGF and insulin significantly stimulated glucose oxidation and lipogenesis in adipose tissue.
- hGH showed insulin-like effects only after preincubation, unlike PGF and insulin.
- PGF inhibited epinephrine-induced lipolysis, similar to insulin and hGH.
- PGF did not displace 125I-insulin but competitively inhibited 125I-hGH binding.
Conclusions:
- PGF possesses direct insulin-like actions mediated through growth hormone receptors.
- PGF's insulin-like activity is independent of insulin receptors and is not affected by GH refractoriness.
- PGF does not exhibit anti-insulin effects, distinguishing its metabolic profile.