A men's locker room might be termed an olfactorally challengedenvironment. The smell of sweaty bodies does not arise from thesweat per se. Perspiration is primarily odorless saline solution.
Rather, the rank message that enters the nostrils and impacts on theolfactory nerves derives from microorganisms that inhabit mainly theapocrine glands in the axillary regions of the body _ that is, theunderarm areas.
Why there in particular?
Organic chemist George Preti, of the Monell Chemical Senses Centerin Philadelphia, offers an explanation:
"Way back when we humans were hairier, and our knuckles scrapedon the ground more than they do now," Preti told BioWorld Today,"we may have had wider distribution of apocrine glands thatproduced a much stronger odor over our entire body. This odor mayhave characterized us as individuals, regulated reproductive events inour mates, things like that.
"Now," he continued, "most of this is limited to the hairier parts ofour body, particularly, to apocrine glands in the underarm region, inthe genital region, and around the nipples in the breasts of males andfemales.
"But the only place that smells like the underarm is the underarm, andthat's because it's occluded, it's moister than other areas, and canbuild up a population of lipophilic diphtheroids. These aerobicbacteria appear to have some unique properties, because they canproduce this odor from its precursors, found in apocrine secretions, alot faster than other bacteria can."
Preti, who also is an adjunct professor at the University ofPennsylvania School of Medicine, has been studying the molecularbasis of underarm odor for many years. His group's latest paperappears in today's Proceedings of the National Academy of Sciences(PNAS), titled: "A human axillary odorant is carried byapolipoprotein D."
"Our overall goal," Preti said, "is to find out the biogenesis ofunderarm odor, and how it arrives on the skin surface. We've nowelucidated one of the two carrier proteins, apolipoprotein D [apo D].No one has actually identified an in vivo ligand for it. We have, byidentifying the protein first, then liberating the ligand from this 169-amino acid molecule. It's an important step in elucidating thechemistry of odor production and the precursors to those odors."
"Our apo D," Preti continued, "is specific to the non-odorousapocrine glands of the axilla, where it is synthesized, and from whichit carries its payload, E-3-methyl-2-hexenoid acid (E-3M2H) to theskin surface."
E-3M2H is the most abundant odor component in males.
The factor that forwards these strong odors from the apocrine glandsis strong emotions. "They are released generally under control of thehormone norepinephrine," Preti went on, "because apocrine glandsrelease their contents more under emotional stress than, say, thermalstress. That's why a person builds up a stronger odor under stress."
To measure human axillary odor release in vivo, Preti and his co-authors recruited 47 healthy male paid volunteers, ages 21 to 40, asunderarm secretion donors. Over a two-year period, they donatedeight separate collections.
To stimulate release, each volunteer received shots of epinephrinesimulating an emotional charge.
"In terms of the research's global reach," Preti observed, "we comeinto the area of reproductive control of the menstrual cycle _ whichis where ultimately our work is going _ to examine what compoundsfound in the underarm can control the length and timing of themenstrual cycle."
He observed that "odoriferous constituents are qualitatively verysimilar chemically amongst males and females. Exposing females tomale or female underarm extracts of whole secretions can alter thelength and timing of their menstrual cycles."
He added: "So that's why I think our work may have a very importantpotential at some future point, as a novel way for fertilityenhancement and control with a putative active ingredient from underthe arm." He pointed out that irregular menstrual cycles diminishfertility.
"The effect of commercial deodorants and anti-perspirants," Pretisaid, "is to inhibit the production of this odor, and to cover it overwith a nice fragrance. But despite the fact that we Americans allperfume and deodorize ourselves fairly well, this alteration ofmenstrual cycles cannot overcome the menstrual synchrony effect,where women who are grouped together _ close friends, roommates_ tend to menstruate within a certain period of each other. Even incorporate situations, where you get a very well-groomed, perfumed,deodorized group of women, this phenomenon still occurs."
A pair of papers elsewhere in today's PNAS describe: "Chemicalbasis of courtship in a beetle (Neopyrochroa flabellata): Cantharidinas precopulatory `enticing' agent." Its principal author is organicchemist Jerrold Meinwald at Cornell University in Ithaca, N.Y.
Cantharidin is the chemical name for the reputed aphrodisiac,"Spanish fly."
Preti asserted that he has "no proof" of human underarm secretionshaving any effect on libido, and added: "That beetle paper is notrelated to anything we see in our work."
He concluded: "Most of the stuff about Spanish fly is based infolklore and the imagination of young men. I don't know that there'sever been a really good study done on whether it has any kind ofaphrodisiac activity in a human, or not." n
-- David N. Leff Science Editor
(c) 1997 American Health Consultants. All rights reserved.