Given an abstract, generate a keyword (a noun phrase) that best describes the focus or contribution of the paper. Such keywords can be directly from the given abstract or outside it.
Example: Abstract: Some patients converted from ventricular fibrillation to organized rhythms by defibrillation - trained ambulance technicians(EMT - Ds) will refibrillate before hospital arrival.The authors analyzed 271 cases of ventricular fibrillation managed by EMT - Ds working without paramedic back - up.Of 111 patients initially converted to organized rhythms, 19(17 % ) refibrillated, 11(58 % ) of whom were reconverted to perfusing rhythms, including nine of 11(82 % ) who had spontaneous pulses prior to refibrillation.Among patients initially converted to organized rhythms, hospital admission rates were lower for patients who refibrillated than for patients who did not(53 % versus 76 % , P = NS), although discharge rates were virtually identical(37 % and 35 % , respectively).Scene - to - hospital transport times were not predictively associated with either the frequency of refibrillation or patient outcome.Defibrillation - trained EMTs can effectively manage refibrillation with additional shocks and are not at a significant disadvantage when paramedic back - up is not available.
Example solution: Ventricular Fibrillation
Example explanation: This term is directly present in the abstract and it is one of the main topic in it. So can be chosen as the medical subject heading.

Problem: Abstract: A peptide that is recognized by antibodies to human somatomedin-C/insulin-like growth factor I (Sm-C/IGF-I) has been partially purified from cultured Sertoli cells prepared from sexually immature rats. The mol wt of this peptide is about 25,000, as determined by gel filtration chromatography and immunoblot analysis of samples resolved by polyacrylamide gel electrophoresis. Isoelectric focusing indicated that the isoelectric point of this peptide was near neutrality. However, a smaller peptide of mol wt 8,000 that cross-reacted with antibodies to Sm-C/IGF-I, was released after gel filtration in acetic acid. Similarly, reverse phase HPLC on a C18 column under acidic conditions released a Sm-C/IGF-I immunoreactive peptide of 8,000 mol wt. This smaller species apparently resulted from the dissociation of this peptide from a binding protein. Unlike the larger neutral form, the isoelectric point of the smaller peptide was 9.8. This pI is similar to the GH-dependent Sm-C/IGF-I peptide isolated from rat serum. The small peptide, unlike the larger form, reacted in a parallel manner to human Sm-C/IGF-I in the Sm-C/IGF-I RIA and radioreceptor assays. In addition, the 8,000 mol wt peptide behaved as a progression factor in the BALB/c-3T3 assay and competed with [125I]Sm-C/IGF-I for binding to the type I Sm-C/IGF-I receptor from cultured rat Sertoli cells. In summary, results of this study demonstrate that rat Sertoli cells in culture secrete a peptide that is the rat equivalent of human Sm-C/IGF-I.
Solution: Age Factors