A new study suggests gut bacteria play a more active role in digestion than previously understood. The research indicates that these microbes recycle hormones that help keep the colon moving.
Study Details
The study, published in Nature Neuroscience, found that androgen signaling, specifically testosterone, to neurons in the enteric nervous system is needed for normal intestinal movement in mice. This signaling depends on the microbiome to work. The enteric nervous system is a network of neurons in the gut wall. A specific group of neurons, called NOS1+ enteric neurons, appear to be key for regulating movement in the colon. A separate group of spinal afferent neurons also play a role.
When researchers used broad-spectrum antibiotics to deplete the gut microbiome in mice, androgen receptor expression in enteric neurons dropped. Serum testosterone levels also fell, and intestinal transit slowed. Restoring androgen signaling helped fix the movement problems. This suggests the hormone pathway is a meaningful driver of the effect.
Hormone Recycling
The body uses testosterone, then the liver deactivates it and sends it to the gut. Certain gut bacteria produce enzymes that reactivate the testosterone. The reactivated hormone can then bind to receptors in gut neurons. The researchers confirmed this mechanism directly. The bacteria were performing a specific biochemical function that the gut neurons depend on.
The study also found that NOS1+ enteric neurons increase androgen receptor expression after puberty. This change happens at the same time as shifts in bacterial enzyme activity. This timing suggests the microbiome and the hormonal system develop together in a coordinated way.
Antibiotic Disruption
Broad-spectrum antibiotics can eliminate the specific bacterial populations that produce the needed enzymes. Without those enzymes, the testosterone recycling loop breaks down. Androgen receptor expression in enteric neurons falls, serum testosterone drops, and the colon slows. The researchers found that androgens were necessary for antibiotics to affect movement. When androgen signaling was already absent, antibiotics had less additional impact on movement. This suggests the disruption of digestion caused by antibiotics is partly due to this hormone pathway.
This finding offers a more precise explanation for a common observation. Patients and doctors have noted that digestion can slow after antibiotic use. The study provides a biological mechanism for that effect.
Broader Implications
The research adds to evidence that the microbiome is an active participant in hormone metabolism. Gut bacteria have been found to synthesize or break down androgens in conditions like prostate cancer and depression. This study shows that microbial hormone reactivation also plays a role in healthy, everyday gut function. The researchers found that human colonic enteric neurons express androgen receptors in both males and females. Human gut bacteria also produce the same enzymes that can metabolize androgen glucuronides.
The findings suggest the microbiome is doing more than fermenting fiber and fighting pathogens. It may be actively maintaining the hormonal environment that gut neurons need to function. This level of interaction between gut bacteria and the body’s hormone systems is an area of ongoing scientific study. The research points to a deeper connection between gut health and hormone health than was previously understood. The study was conducted in mice, but the presence of similar receptors and enzymes in humans suggests the findings may have relevance for human health.
