Spraying urine on vertical objects by raising the tail is a commonly observed functional behavior for chemical communication in felids, including domestic cats (Felis silvestris catus). The sprayed urine is recognized as a chemical signal for territorial ownership of their habitats. Previous studies reported that sprayed urine emits a more pungent odor than urine excreted from a squatting position. However, little is known about how sprayed urine acts as a strong scent mark in the environment. New research shows that sprayed urine originates only from bladder urine without any secretions, but it can effectively emit volatile organic compounds when smeared on vertical objects due to its strong adhesion.
Uenoyama et al. improve our understanding of the mechanism of scent marking via the spraying of urine for chemical communication in cats.
In the study, lead author Professor Masao Miyazaki from Iwate University and colleagues initially compared the chemical profiles of volatile organic compounds emitted from sprayed urine, normal urine, and bladder urine collected using ureteral catheters.
Chemical analyses revealed a high degree of similarity in these profiles within the same individuals.
Behavioral analyses further demonstrated that cats perceived the sprayed urine and urine remaining in the bladder after spraying as similar odors, whereas the odors of another cat’s urine were perceived as different.
“The data indicate that the sprayed urine originates from bladder urine without supplementation with chemicals from other secretory glands,” Professor Miyazaki said.
Given the high degree of similarity of volatile chemical profiles between sprayed urine and naturally normal urine, the researchers examined why sprayed urine emits a pungent odor from another perspective.
They observed that cat urine samples easily adhered to the inner surface of plastic syringes when they transferred the samples into glass vials for urinary volatile analyses.
“This observation prompted us to explore the underlying mechanisms,” said first author Dr. Reiko Uenoyama, a researcher at Iwate University.
Twenty years ago, Professor Miyazaki discovered that healthy cats excrete a substantial amount of an urinary protein named cauxin, which contributes to the production of sulfur-containing odorants responsible for the distinct catty smell.
“Generally, the wettability of a liquid on solid surface increases as the surface tension decreases,” Dr. Uenoyama said.
“Based on this knowledge, we hypothesized that the high protein concentration in cat urine might reduce the surface tension of cat urine, enhancing the emission of urinary volatile compounds from the large vertical surface area that was spread over the urine.”
As anticipated, the surface tension was reduced with increasing concentrations of the urinary protein cauxin.
At the same protein concentration, the wettability was higher in the cauxin solution than in the control solution containing albumin, a major protein contained in mammalian blood.
When comparing the surface tension of cat urine with and without proteins, the authors confirmed that urine with proteins exhibited significantly lower surface tension than deproteinized urine.
Interestingly, the urine with proteins also demonstrated greater adhesion to vertically positioned glass plates than the deproteinized urine.
In the observations, odorants responsible for the distinctive catty smell were detectable in an artificial miniature garden designed to mimic natural environments in which a block sprayed with tomcat urine was placed.
In contrast, no such odorant was below the detection limit in another garden where the same urine was poured directly into sandy soil and then covered.
“The difference in environmental odors between the two gardens, despite using the same urine sample, can be explained by most of the urinary volatile chemicals being trapped in the porous structure of the sandy soil,” Professor Miyazaki said.
“This phenomenon did not occur in the urine adhering to the surface of the block.”
“Additionally, liquid droplets of sprayed urine can easily dry on the surface of the block, resulting in greater emissions of volatile chemicals from the scent mark rapidly as compared to from normal urine.”
In conclusion, feline sprayed urine originates solely from the bladder, without any contribution from other secretions.
However, despite this exclusive source, sprayed urine emits a strong and pungent odor owing to enhanced adhesion on vertical surfaces.
“The specific urinary protein, cauxin, plays a crucial role in scent marking by not only producing cat-specific odorants, but also by enhancing the emission of urinary volatile chemicals by increasing the wettability of the sprayed urine,” the scientists said.
“Our study may provide insights into addressing the distinct smell associated with sprayed urine.”
The team’s results were published in the Journal of Chemical Ecology.
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R. Uenoyama et al. Sprayed Urine Emits a Pungent Odor due to its Increased Adhesion to Vertical Objects via Urinary Proteins Rather Than to Changes in its Volatile Chemical Profile in Domestic Cats. J Chem Ecol, published online March 18, 2024; doi: 10.1007/s10886-024-01490-1