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The origin of young star clusters represents a major challenge for modern stellar astrophysics. While stellar rotation partially explains the colour spread observed along main-sequence turn-offs, i.e. where stars leave the main-sequence after the exhaustion of hydrogen in their core, and the multiple main sequences in the colour-magnitude diagrams of stellar systems younger than approximately 2 Gyr, it appears that an age difference may still be required to fulfill the observational constraints. Here we introduce an alternative approach that exploits the main-sequence turn-on, i.e. the point alongside the colour-magnitude diagram where pre-main-sequence stars join the main-sequence, to disentangle between the effects of stellar rotation and age to assess the presence, or lack thereof, of prolonged star formation in the approximately 40-Myr-old cluster NGC1818. Our results provide evidence for a fast star formation, confined within 8 Myr, thus excluding age differences as responsible for the extended main-sequence turn-offs, and leading the way to alternative observational perspectives in the exploration of stellar populations in young clusters., (© 2022. The Author(s).)

Objective: To evaluate the urinary levels of inositol phosphates (InsPs) in rats that received different salts of myo-inositol hexaphosphate (InsP6) by gavage or by oral administration., Methods: Thirty rats received AIN-76A diet (in which InsPs are undetectable) for 15 days. Then, 12 rats received InsP6 by gavage as a Na salt or a Ca/Mg salt; after 4 days, the Na or Ca/Mg InsP6 was administered with water containing 15 g/L sucrose and urine samples were collected. The other 18 rats received oral InsP6, in which 0.5 g of sugar was combined with InsP6 as a Na salt, a Ca/Mg salt, or a Na salt with CaCO3; daily urine samples were collected. Urine levels of InsPs were determined using a nonspecific method and a specific method (polyacrylamide gel electrophoresis, PAGE), and different InsPs were identified by mass spectroscopy (MS)., Results: After 15 days of the InsP6-free diet, the non-specific method detected no urinary InsPs, and MS detected only InsP2. After administration of Na-InsP6 by gavage, the non-specific method indicated more urinary InsPs than the amount of InsP6 determined by PAGE. MS indicated the presence of urinary InsP2, InsP3, InsP4, InsP5, and InsP6 in these rats, with notable variations among animals. Use of the same treatment to administer Ca/Mg-InsP6 led to a lower overall content of urinary InsPs and a lower level of InsP6. Oral administration of InsP6 as a sugar pill led to lower urinary levels of InsPs than administration of InsP6 by gavage, and administration as a Ca/Mg pill or a Ca/Mg pill with CaCO3 led to lower levels than administration as a Na pill., Conclusion: Administration of InsP6 to rats leads to the excretion of a mixture of different InsPs. Rats more effectively absorb InsP6 when supplied without dietary components that interfere with its uptake, such as the Ca ion and sugar., Competing Interests: The authors have declared that no competing interests exist.

Aims: Previous studies demonstrated a remarkable increase of urinary InsP 6 by topical administration. However, the methodology used for InsP 6 analysis was not specific. The aim of this paper is to measure urinary inositol phosphates InsPs using more advanced methodologies and to compare the results with those obtained by the non-specific method., Materials and Methods: We fed 12 female rats with a diet without InsP 6 for 16days. Then, we administered a topical InsP 6 gel at high doses for 7days (50mgInsP 6 /day) or at low doses for 28days (20mgInsP 6 /day). We measured urine levels InsPs using a nonspecific method (based on the ability of InsPs to complex Al 3+ ) and levels of InsP 6 by a specific method (using polyacrylamide gel electrophoresis). Identification of different InsPs was performed by MS., Key Findings: At baseline, after dietary deprivation of InsP 6 , rats only excreted InsP 2 in their urine, and there was no detectable InsP 6 or other InsPs. Rats given the high dose treatment for 7days had abundant urinary InsP 6 , but also had other InsPs in their urine; cessation of InsP 6 administration led to decreased levels of urinary InsPs. Rats given the low dose treatment for 28days had increasing levels of urinary InsPs over time. The maximum urinary InsP 6 was at 21days, after which InsPs excretion decreased., Significance: We conclude that the skin can absorb InsP 6 from a topical gel, and that InsP 6 is excreted in the urine, along with other InsPs (InsP 5 , InsP 4 , InsP 3 , and InsP 2 )., (Copyright © 2017 Elsevier Inc. All rights reserved.)