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.
One 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.
Solution is here: Ventricular Fibrillation
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.

Now, solve this: Abstract: Developmental changes and sexual differences in the lactotrope population were studied with a reverse hemolytic plaque assay for detection and measurement of PRL secretion from individual cells in conjunction with PRL immunocytochemistry (ICC). Pituitary glands from both sexes at different ages were monodispersed with 0.1% trypsin. Freshly dispersed cells were incubated in Cunningham chambers for measurement of the fraction of plaque-forming cells and the size of plaques formed, or attached to glass slides for measurement of the fraction of cells staining for PRL by ICC. The percentage of plaque-forming cells in both sexes gradually increased with age from about 5% of the total anterior pituitary cell population at 5 days of age to the adult levels of about 54% in the females at proestrus and about 37% in the males. Sexual differences in the percentage of plaque-forming cells were consistently seen at 40 days of age and thereafter. The mean size of plaques in both sexes also increased with age from about 1,100 microns 2 at 5 days of age to a peak level of about 15,600 microns 2 in the females at proestrus and about 6,700 microns 2 in the males at 60 days of age; then fell to the adult levels of about 5,500 microns 2 in the females at proestrus and about 3,200 microns 2 in males. Sexual differences first appeared at 40 days of age and were estrogen-dependent. The results from ICC closely matched those from the plaque assay, except at 5 days of age and in the adult males. At 5 days, the fraction of cells staining for PRL was twice that of cells forming plaques. In adult male rats there were about 47% immunostained PRL cells but only about 39% plaque-forming cells. This difference, however, disappeared after estrogen treatment. These results demonstrate that sexual differences in the lactotrope population develop around puberty in rats and appear to be estrogen dependent.
Solution:
Age Factors