Giving young blood to old people can increase their lifespan ???

Recently an experiment was performed in the mice in which young and old mice were surgically connected such that they shared blood circulation for three months, it was discovered that the longevity of the older mice was not greatly increased. But the younger mice that shared the blood with the older one was found with the decreased lifespan compared to the mice that shared it's blood with the other younger mice.

 

This whole experiment was based on Heterochronic parabiosis.  

Parabiosis, which is derived from two Greek words "para" (next to) and "bios" (life), describes when two completely living creatures are surgically linked and grow a single, shared circulatory system. The method, which can involve the transplantation of cells, tissues, or entire body parts like limbs or other appendages from one creature to another, is essentially a more thorough version of "transbiosis."

Since each animal can be seen as an equal partner in the coupling and each parabiont influences the other parabiont, unlike transbiosis, parabiosis does not have a formal donor and host. Conjoined twins, whether they be human or nonhuman, and parabionts are frequently compared, with the latter being the product of faulty developmental processes. While the physiology of conjoined twins may be instructive in relation to some experimental questions addressed by parabiosis, it is evident that the experimental approaches provided by parabiosis, particularly the joining of two animals that differ genetically or physiologically, greatly expand the types of biological phenomena related to the circulatory milieu that may be investigated.

The use of heterochronic parabiosis models has been used to show how blood-borne circulating components contribute to the systemic consequences of aging. Old mice have previously exhibited favorable benefits of heterochronic parabiosis in a variety of organs. A recent study indicated that young mice's muscle development and neurogenesis were significantly harmed by old blood. In this study, heterochronic parabiosis was utilized to test the idea that the loss in mitochondrial bioenergetic activity, a recognized biological indicator of aging, is mediated by circulating substances. We looked at the mitochondrial morphology, expression of mitochondrial complexes, and respiration in skeletal muscle from heterochronic pairs of mice, as well as young and elderly isochronic controls. In comparison to young isochronic controls, young heterochronic mice exhibited considerably reduced total mitochondrial content and, on average, smaller mitochondria.

In comparison to young isochronic controls, young heterochronic mice exhibited considerably reduced total mitochondrial content and, on average, smaller mitochondria. Complex IV expression displayed a similar pattern of expression, with young heterochronic mice showing a tendency for reduced expression in comparison to young isochronic controls. Furthermore, respirometric studies show that young heterochronic mice exhibited considerably reduced complex I, complex I + II, and maximal mitochondrial respiration, as well as a tendency for lower complex II-driven respiration, compared to young isochronic controls. Interesting results show the profoundly negative impacts of circulating components from elderly animals on mitochondrial structure and function since significant improvements in old heterochronic mice compared to old isochronic controls were not seen.

They discovered no discernible differences between the young and old heterochronic mice, showing that circulating variables can be a driving force behind changes in mitochondrial structure and function that are connected to aging.

This heterochronic parabiosis experiment was performed in two sets of mice in which one set was a pair of old mice and young mice sharing the blood together and another pair was the pair of two young mice. After three months the results were obtained and the results were interesting

After they disconnected the mice and studied the results on the blood plasma and the life span of the experimented mice . They found the shockingly interesting result that is the significant decrease in the lifespan of the young mice from the heterochronic  probiotic pair.

This result supports that the  old blood contains factors capable of inducing aging in young ones.

Result 

When it came to lengthening longevity, older mice did not considerably gain from the blood of younger mice. However, the lifetime of younger mice that were exposed to the blood of older mice was significantly decreased.