Bromocriptine and Hibernation

The Food and Drug Administration recently approved the drug bromocriptine mesylate for use in treating diabetes.

The drug works on dopamine receptors in the brain to produce the same effects as dopamine would produce. For this reason, it's been used in dopamine-deficiency diseases like Parkinson's disease for some time.

In other words, it's not a new drug. It's a new use of an old drug.

But why, you might wonder, would a drug that works on dopamine receptors in the brain do anything for diabetes, which is a disease that causes blood glucose (BG) levels to be too high?

This is because there is some evidence that insulin resistance and obesity are regulated in part by the brain.

One example of this is the phenomenon of hibernation or, in some species, what is called torpor, a shorter period of reduced temperature and slower metabolism. Animals that hibernate typically put on a lot of weight in the late summer and fall. They also have increased insulin resistance.

People who believe that obesity is simply a case of eating too much and not exercising enough, causing obesity that in turn causes insulin resistance, would say this is what is happening in hibernating animals. There's a lot of food in the late summer and fall so the animals pig out and get fat, and the fat causes the insulin resistance, they'd argue.

But here's the interesting part. Ground squirrels normally put on a lot of weight in the fall. They also eat a lot more. But if you keep the squirrels in the laboratory and don't let them eat any more than normal, they'll put on weight anyway, mostly fat.

In other words something, most likely hormonal signals triggered by changes in daylength, are telling the squirrels to store fat. Because they're storing the fat instead of letting it hang around in the blood to be burned for energy, they have an energy deficit, and this makes them hungry.

This is consistent with the theory of weight gain described by Gary Taubes in his book Good Calories, Bad Calories. He says the "energy balance" equation so beloved of dieticians who use it to say that the only thing that matters is calories in and calories out is true, but the cause and effect have been reversed. This equation says:

Change in weight = energy in - energy out.

The dieticians would say if you change the right hand side of the equation, reducing energy in or increasing energy out, your weight will change. To some degree, this is true in extremes or for the short term, when an animal or person has no access to enough food, as in starvation, or has super willpower because of a belief that the latest diet will really work. But when food is available, the drive to eat becomes overpowering and any lost weight will be regained.

Taubes and other argue that some external force, mostly likely hormones or nervous system signals (Taubes argues that it's insulin) affects the left-hand side of the equation. This causes extreme hunger or lethargy, or both, as the body tries to balance the equation.

In other words, the net energy change is not causing the weight change, but the weight change makes the body try to balance the equation by creating an overwhelming desire to eat and aversion to exercise.

When food is available, the animal or person will thus eat more than normal and exercise less. But if you don't let them eat more than normal, they'll still store the fat. They'll just be very hungry and lethargic.

Furthermore, animals are not machines. Energy in from the same food can differ depending on the efficiency of digestion, and energy out can vary with the efficiency of transforming food into forms of energy the body can use. Some people turn excess calories into heat instead of turning them into fat.

So where does bromocriptine come into all this?

Syrian hamsters normally become insulin resistant and gain a lot of weight before they hibernate; these effects are blocked by bromocriptine. Similar effects were seen in obese women: glucose and insulin levels decreased and energy expenditure and fat burning both increased, although body weight did not change in this 8-day experiment. And other researchers found that bromocriptine helped people with type 2 diabetes.

Some authors see hibernation as a model for insulin resistance, and the more we learn about what triggers the weight gain in hibernating animals, the more we'll know about what triggers insulin resistance and weight gain in obese humans.

They suggest that hibernators have a sliding set point. The concept of a set point is that the body has a certain weight that it wants to be, and if you go over or under that weight, you will have a strong urge to eat more if you're under the set point or eat less if you're over the set point. Instead of having one set point, hibernators have different set points depending on the time of year.

There are reasons to believe that bromocriptine might help people who have serious problems with obesity and insulin resistance. The drug has been around for a long time to treat other diseases, so we have a better idea of side effects than we do with brand-new drugs. And there are side effects.

The Mayo Clinic has a good outline of some of these side effects. They note that they're more apt to occur in older people, and can include confusion and hallucinations (the drug is an ergot alkaloid). This is a powerful drug, and I doubt that many physicians would prescribe it as the first choice when someone is diagnosed.

But for a person with a serious weight problem that isn't helped by other measures as well as uncontrolled BG levels, the drug might be worth a try, keeping a close watch to make sure no serious side effects occurred.