Lessons in comparative physiology: lactose intolerance

Lessons in comparative physiology: lactose intolerance

L.J. Filer

In the mid-1950s, one of the authors (L.J.F.) received a telephone call from Dr. Norman Kretchmer regarding a potential source of a lactose-free formula to feed California Golden Sea Lion pups. Kretchmer was investigating the otogeny of gut disaccharidases in a variety of species. He was aware of the fact that the sea lion was lactose intolerant and that young sea lions did not have lactase in their gut mucosa.

When it became evident that Kretchmer was asking for help and not pulling my leg, I suggested that he contact Dr. Robert Stewart, Director of Research and Development of the Gerber Company, and request a supply of lactose-free Gerber meat-based infant formula. At that time, the Gerber Company research laboratories were located in Oakland, California, and their meat-based formula was prescribed by a number of California pediatric allergists; thus, the logistics of supply would be minimized. Drs. Stewart and Kretchmer worked out a means to provide a lactose-free formula for these young sea lions, and I learned that sea lion milk, unlike most other mammalian milks, contained little or no lactose. This brief experience proved valuable some 30 years later.

In 1984, the Summer Olympics were held in Los Angeles, and the Peoples Republic of China (PRC) sent two Giant Panda Bears, a juvenile female and a juvenile male, to the Los Angeles Zoo as a gesture of goodwill and the opportunity for many Olympic attendees to see a panda. The pandas were only on loan and were to return to the PRC after a brief stay in San Francisco enroute home.

In the late summer of 1984, Dr. Reynolds, at that time Chancellor of the State University System of California, telephoned regarding her concerns that the male panda might not survive long enough to return to China. Dr. Reynolds described an apathetic panda with chronic diarrhea, weight loss, and an unkempt coat. The panda was off feed, eating little in the way of its basal diet or fresh bamboo shoots. Stool examinations were negative for ova and parasites.

My initial impression was a sprue-like syndrome, perhaps complicated with folic acid and/or vitamin B12 deficiency, and I suggested a complete blood count and smear for the panda. Dr. Reynolds reminded me that the panda was a bear with long claws and sharp teeth. To further complicate the picture, the Chinese veterinarian who was caring for the animals was under strict orders not to allow anyone to examine them or take so much as a blood sample.

At dietary history indicated that the basal diet was a gruel of rice, cooked hamburger, powdered milk, and unknown supplements of Chinese origin. Fresh bamboo was provided daily.

At some 2000 miles from Los Angeles, I decided any recommendation I made would be empirical rather than based upon more detailed clinical information. Knowing that diarrhea in infants is frequently followed by lactose intolerance and that such infants respond to the feeding of lactose-free formulas, and recalling the California Golden Sea Lion pups, I suggested that the panda be fed a lactose-free enteral formula such as Ensure [R]. Dr. Reynolds was on the Board of Directors of Abbott Laboratories, and its Ross Laboratories Division produced Ensure. I had no idea if this suggestion would work, how much the panda would eat, or how long he would need a lactose-free diet. Dr. Reynolds acted upon this empirical approach and procured Ensure. The male panda readily ate the Ensure, preferring it to the meal gruel, and preferred one flavor of Ensure above the others. The panda recovered to be on exhibition and was maintained on Ensure. Later, he and the female panda went on to San Francisco and then returned to China in apparent good health.

This, however, is not the end of the story. In January 1995, Ann and I had dinner in Cancun with Konrad Bloch, Nobel laureate. Dr. Bloch had just published a paper on lactose intolerance, a topic he had been interested in since his student days at the Technische Hochschule, Munich, Germany.[1] This led Ann and me to relate our panda experience and stimulated me to read again a paper by Jenness and Sloan on the composition of mammalian milks.[2] By now, I knew that the panda was a bear, a member of the family Ursidas.

As shown in Table 1, relative to human milk and cow milk, bear milk is low in lactose content, as is the milk of the sea lion. Jenness and coworkers have shown a marked difference in the lactose content of bear milk between wild bears and those raised in captivity. The lactose content of milk from the latter animals ranges from 1.9 to 3.2%.[3] Jenness and coworkers speculated that some environmental factor may be controlling the lactose concentration of bear milk.

Table 1 The Lactose Content of Varoius Mammalian Milks

Mammalian milk Percentage

Human 7.0

Pig 5.5

Cow 4.8

Dog 3.1

Black bear (wild) 0.4

Grizzly bear (wild) 0.6

California sea lion 0.0

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