The “Free Hormone Hypothesis” posits that only free, unbound hormone is biologically active and available to tissues. Conventional biomedical wisdom proposes that corticosteroid-binding globulin (CBG) normally binds 90-95% of blood glucocorticoid (GC), rendering it unavailable to tissues. Under chronic stress, GC levels greatly exceed binding capacity resulting in impaired bodily function and reduced fitness. However, under normal conditions in northern and southern flying squirrels, less than 10% of GC is bound, presenting a major challenge to the hypothesis. To assess the extent of variation in these properties among vertebrates, I compared all species (88) with known GC and CBG and levels. 92% conform reasonably to known convention. Flying squirrels appear as extreme species, as do New World monkeys, yet both groups evolved from ancestors that followed normal convention. I speculate as to how this state evolved and persisted through time.
| Identifer | oai:union.ndltd.org:TORONTO/oai:tspace.library.utoronto.ca:1807/30571 |
| Date | 07 December 2011 |
| Creators | Desantis, Lanna |
| Contributors | Boonstra, Rudy |
| Source Sets | University of Toronto |
| Language | en_ca |
| Detected Language | English |
| Type | Thesis, Dataset |
Page generated in 0.0014 seconds