Abstract
Chemical composition of secretions of skin glands in hominoid primates have apparently not been
analyzed previously, except for the axillary secretions of humans. This paper reports on skin
secretions of siamangs (Symphalangus syndactylus), a species of gibbons or small apes from
Southeast Asia. Secretions were collected and radioimmunoassays (RIA) were carried out in order to
check for the presence of the following three steroid hormones: Dehydroepiandrosterone (DHEA),
Androstenedione, and Testosterone. This study presents first evidence that high hormone
concentrations occurring especially in the sternal area cannot be the result of a simple filtration of
hormones out of the blood plasma, but must be the result of a more complex accumulation process.
Particularly androstenedione appears to be highly concentrated in the sternal gland. Our findings
further support the view that sternal glands in gibbons and axillary glands in humans and African apes
may fulfil similar functions, and shed some light on the origin of the axillary organ. We speculate that
the accumulation of steroid hormones in siamang skin glands may play a role in olfactory
communication.
Geissmann, T