16 May 2005: Falling under a smell

An eggy whiff could be the scent of things to come in the operating theatre if the promise of recent research is realised. US researchers have found that hydrogen sulfide (H₂S) gas can send mice into a hibernation-like state. Driving tissues or even the body into suspended animation could improve the outcome of many surgical interventions, they suggest.

The response of mice to small concentrations of H₂S is striking. Metabolism slows down immediately, and after six hours’ exposure to the gas, CO₂ output and oxygen consumption have crashed to just 10 per cent of normal levels, report Mark Roth and colleagues at the University of Washington in Seattle. Breathing rate also drops from around 120 breaths per minute to less than 10 and core-body temperature falls to just a couple of degrees above ambient, they note. Crucially, the mice seemed to return to normal after the experiment. 

H₂S is a specific, potent and reversible inhibitor of cytochrome c oxidase, the last enzyme complex in the energy-generating mitrochondrial electron transport chain. Consequently, Roth reasoned that inhibition of this complex might reduce metabolic rate in mammals.

This is certainly a logical hypothesis, says Hannah Carey, professor of veterinary medicine at the University of Wisconsin. Although there is no evidence that inhibition of cytochrome c oxidase is a mechanism that natural hibernators use to slow their metabolism, this possibility now needs to be explored, she says.

This discovery could be of great medical benefit, say Roth’s team. ’Lowering metabolic demand in this way could be used to reduce physiological damage resulting from trauma,’ they report. However, surgeons will be pleased to note that the characteristic odour of the hospital is not about to be replaced by one of rotten eggs. ’Most operating rooms do a good job of scavenging volatile anaesthetics and could do the same with H₂S,’ says Roth. 

Henry Nicholls