What is the scientific basis behind attributing birds' high blood sugar to the different "switch" GCGR?

Well, the scientific basis behind attributing birds' high blood sugar to the different "switch" GCGR is quite interesting. First, in humans, GCGR is like a "switch" that controls the release of glucose from the liver for blood sugar regulation. When people are hungry, glucagon signals GCGR to "open" and raise blood sugar, and insulin works like a "pump" to lower it when blood sugar is high. But in birds, GCGR has constitutive activity, which means it's like a "faucet that's always on" even without glucagon further "turning it on", constantly making the liver release a lot of glucose.
Also, compared to other vertebrates, although non-mammalian vertebrates like fish and amphibians also have GCGR with constitutive activity, they don't have high blood sugar like birds. The reason is that birds have a high expression level of GCGR in the liver. A high expression level of constitutive activity GCCR in the liver is like installing a lot of "open faucets" on the "water tank", so the "water output" is fast and efficient. While for non-constitutive activity GCGR, even with a high expression, it still needs glucagon or insulin to "turn the faucet on or off" to precisely regulate blood sugar.
Moreover, the research team found that the constitutive activity of GCGR in birds can increase the basal metabolic rate of mice, and it plays a role in sugar, lipid and energy metabolism. Birds' high blood sugar maintained by constitutive activity GCGR can quickly provide energy for the flight burst stage. And it also promotes lipid metabolism during endurance flight, which is an adaptation to high-energy-consuming flight. So, in general, the combination of the constitutive activity and high expression level of GCGR in birds is the scientific basis for their high blood sugar.

Well, let me tell you about the scientific basis linking birds' high blood sugar to the distinct "switch" GCGR.
First off, in the animal kingdom, the GCGR receptor family is crucial for blood sugar regulation, and its genes are quite similar and functionally conserved among vertebrates. But birds have a unique situation. Their GCGR shows constitutive activity. Think of GCGR as a switch. In most cases, like in humans, this switch needs a signal from glucagon to turn on and release glucose from the liver. But in birds, this switch is kind of stuck in a semi - on position, constantly allowing the liver to release glucose even without a strong push from glucagon.
Secondly, the research team found that it's not just the constitutive activity of GCGR that matters. The expression level of GCGR in the liver is also key. They checked the GCGR expression in the livers of various vertebrates. Birds have a high expression level of GCGR in their livers. It's like having a bunch of open faucets (GCGR with constitutive activity) in a place (the liver) where there are a large number of these faucets due to high expression. In contrast, in most non - mammalian vertebrates, even though their GCGR might have some constitutive activity, the low expression level in the liver means there aren't enough of these "open faucets" to cause a significant increase in blood sugar.
Moreover, through a series of experiments on different vertebrates like zebrafish, lizards, chickens, and mice, the team verified that when the constitutive activity GCGR is highly expressed, it can increase blood sugar levels and regulate sugar - lipid metabolism. They also found that in the process of flight, which is a high - energy - consuming activity for birds, this unique GCGR system helps. For short - distance, high - intensity flight like a chicken's short take - off, the high blood sugar maintained by the special GCGR provides quick energy. And for long - distance, endurance flight, the high - expressed constitutive activity GCGR promotes lipid metabolism to support the long - term energy demand. So, all these findings together form the scientific basis for why we attribute birds' high blood sugar to this different "switch" GCGR.