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Changes in the circulating form of serum somatomedin-C during fetal life
Insights
Human serum somatomedin-C (Sm-C) changes form during development. Premature infants show a smaller 40,000 dalton Sm-C form, while full-term infants have a larger 150,000 dalton form.
Area of Science:
- Endocrinology
- Developmental Biology
- Biochemistry
Background:
- Somatomedin-C (Sm-C) is a crucial growth factor in human development.
- The molecular form of Sm-C in circulation can vary, particularly between fetal and postnatal stages.
Purpose of the Study:
- To investigate the developmental changes in the molecular weight of somatomedin-C (Sm-C) in human serum.
- To characterize the different forms of Sm-C present during fetal and postnatal development.
Main Methods:
- Gel chromatography was used to separate and analyze Sm-C in serum samples from infants of varying gestational ages.
- Radioimmunoassay techniques were employed to quantify immunoreactive Sm-C.
Main Results:
- Predominant Sm-C in postnatal serum elutes at ~150,000 daltons (150 K).
- Infants <27 weeks gestation predominantly show Sm-C eluting at ~40,000 daltons (40 K), while those >30 weeks show the 150 K form.
- A transitional pattern was observed in infants between 26-32 weeks gestation.
Conclusions:
- The 150 K form of Sm-C, likely bound to other proteins, appears to be acquired postnatally, possibly influenced by growth hormone or pituitary hormones.
- The 40 K form, found in fetal serum and in vitro fetal liver explants, may not be the primary gene product but rather a complex of Sm-C with other proteins.
Abstract:
The predominant form of somatomedin-C (Sm-C) in human postnatal serum elutes from gel chromatographic columns at an approximate molecular weight of 150,000 daltons (150 K). Nine of 10 infants of 30 weeks gestation or more had elution profiles similar to postnatal sera, while in 7 of 9 infants of 27 weeks or less, the immunoreactive Sm-C eluted predominantly at an apparent molecular weight of 40,000 daltons (40 K). Five infants between 26-32 weeks exhibited a transitional pattern. One 43 week gestation anencephalic infant exhibited only 40 K Sm-C, suggesting that the 150 K proteins which bind Sm-C are acquired in response to growth hormone or other pituitary hormones. Even though the 40 K form of Sm-C is the only form found in mid-gestation fetal serum and in media from in vitro fetal mouse liver explants, it probably does not represent the primary gene product. This is suggested by the observation that 40 K Sm-C also binds 125-I-Sm-C and can be dissociated by acid and, therefore, probably is a complex of Sm-C non-covalently bound to other proteins.