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What do body weight, the immune response and the growth of new blood vessels have in common? The answer, according to several recent studies, is a hormone called leptin.
Within the past few months, research groups at Yale and Imperial College London have discovered receptors for leptin - which was orig- inally identified through its link to obesity in mice - in newly sprouting capillaries and in the T cells of the immune system. The findings are changing scientists' views of the hormone and suggest that leptin might be involved in conditions as diverse as compromised immunity and cancer. In short, leptin may prove to be a multi-purpose hormone, and its role in weight regulation simply the tip of the iceberg.
For example, leptin may represent the body's way of reining in its ability to generate specific immune responses - which consume considerable metabolic energy - during times of starvation. It may also explain the old observation that vaccines are often ineffective in people who are experiencing famine.
In the meantime, early results are in from the ongoing clinical trials of leptin as a treatment for obesity. In June it was reported at an American Diabetes Association conference that eight moderately obese people who took the highest dose of leptin lost an average of 7.2kg (16lb) during a six-month study. But 37 others taking lower doses lost much less weight - some as little as 0.75kg (112lb) - even though all of them were on a calorie-restricted diet.
The thermosphere is falling
Chicken Licken had a point: part of the sky really is falling down. According to a recent paper in the Journal of Geophysical Research, the height of the Earth's upper atmosphere - the thermosphere, 295km (185 miles) above the Earth, and the ionosphere, 70km (43 miles) up - has dropped 8km (5 miles) in the past 38 years. The finding is based on more than 600,000 echo-sounding signatures taken by researchers at the British Antarctic Survey (BAS) and the Rutherford Appleton Laboratory. As the thermosphere cools, atmospheric pressure drops, which in turn lowers the level of the ionosphere. BAS attributes the cooling to increased greenhouse gas emissions, which trap heat in the lower atmosphere but help to radiate it away in the upper atmosphere. The environmental significance of these changes is not yet known.
Mini-mammal
When the Society of Vertebrate Paleontology met in October, Jonathan Bloch of the University of Michigan presented a very small find - in size, at least: a fossil jaw from the tiniest mammal ever discovered. A distant relative of the shrew, the creature named Batodonoides weighed no more than 1.3 grams. Its existence challenges earlier theories about the smallest body-size that can be supported by a warm-blooded physiology. Small bodies do not retain body heat as well as larger ones, because they have a relatively large surface area and radiate heat faster. Below a certain size, in theory, warm-bloodedness may be unfeasible. To compensate for heat loss, Batodonoides must have been extremely active for its size. Bloch came across the remains within limestone from the badlands in Wyoming that dates back between 37 and 65 million years.
! All items are adapted from `Scientific American' magazine. Visit Scientific American's website at www.sciam.com.
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