"Smells are surer than sights or sounds to make your heart stringscrack."

When Rudyard Kipling penned these poetic words a century ago, hemay or may not have thought to relate those heart strings to the wayof humans. But in mammals, humans included, there is a specialconnection between the sense of smell and the urge to sexualreproduction.

The molecules that mediate this come-on between males and femalesare pheromones _ airborne ectohormones secreted by individuals ofone sex to turn on significant others, which inhale them. The port ofentry for these particular smells is a special kind of olfactory system,the vomeronasal organ behind the nostrils.

This fine horizontal canal in the mucous membrane of the nasalseptum conducts special nerves to project on various regions of thebrain, notably the limbic system and amygdala, which are known tobe involved in sexual behavior.

The pheromones' purposeful, though subliminal, odor activates thevomeronasal organ. The role of these pheromones in species survivalis thus self-evident.

Less apparent, until the advent of various hybridization blots andpolymerase chain reaction, has been the evolutionary relationships ofpheromone nucleic acids from species to species. A paper in thecurrent Proceedings of the National Academy of Sciences, datedMarch 14, contributes to filling this gap. Its title: "cDNA sequenceand expression pattern of the putative pheromone carrier aphrodisin."

The article's first author is molecular biologist Hans-Jrgen Mgert,leader of the DNA and gene-expression group at the Lower SaxonyResearch Institute in Hannover, Germany. He told BioWorld Todaythat "Ten years ago, Alan Singer and his co-workers at New YorkUniversity were the first to succeed in purifying the aphrodisinprotein, which they discovered in the vaginal discharge of hamsters.They were looking for a substance _ the so-called pheromones _that induces copulatory behavior in male hamsters."

Because of this pheromone's aphrodisiacal affect on male hamsters,Singer named the protein after Aphrodite, the Greek goddess of love.

Now Mgert and his co-authors have characterized hamsteraphrodisin's gene structure, and are exploring its homology withsimilar secretions in other lower mammals, so far, rats and tupaia(primitive primates), where they found it to be very active.

"In humans," Mgert said, "it's a little bit degenerated, but mostrecent results show it to be active also.

"By means of this hamster aphrodisin cDNA," he explained, "wethought we would be able to find other related genes in highermammalian forms. We have not yet succeeded; its a little bit morecomplicated than we thought. The genomic divergence of this class ofsubstances is very high. They are not so conserved as we hoped."

One clue they are now pursuing is "a hint from Singer's last resultsthat aphrodisin itself is not the pheromone, but just its carrier."Mgert added, "Perhaps by isolating a similar substance from othermammals, we might find the ligand that is the real pheromone, andhas the activity of stimulating copulatory behavior."

As a distant goal, he suggests that "This might make sense in animalbreeding, and maybe even for therapy of impotence in humans."

One of the German group's latest findings, by Northern blothybridization, confirmed by Western blot monoclonal antibodies, isof aphrodisin secreted in the salivary glands of female hamsters, butstrangely, not in males. Mgert hypothesizes that "Perhaps thisinvolves self-stimulation by the females to lower a little bit theaggressive behavior of males. But we must still test this."n

-- David N. Leff Science Editor

(c) 1997 American Health Consultants. All rights reserved.

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