Butyrate, a Gut Bacterial Metabolite, Lowers Intraocular Pressure in Normotensive But Not in Hypertensive Rats

Background:Accumulating evidence supports a role of gut bacterial metabolites in arterial blood pressure (BP) regulation. Since the mechanisms controlling intraocular pressure (IOP) and BP overlap, we hypothesized that butyrate, a bacterial metabolite, might affect both IOP and BP.Methods:IOP, BP, and heart rate (HR) were measured at baseline and after the intraperitoneal administration of either butyrate or a vehicle (0.9% NaCl) in anaesthetized normotensive Wistar-Kyoto rats (WKY) and spontaneously hypertensive rats (SHR).Results:At baseline, there was no significant difference between WKY and SHR in IOP and HR, whereas BP was significantly higher in SHR. In WKY administration of butyrate produced a significant decrease in IOP and BP, which lasted throughout the experiment. IOP response to butyrate was similar between sham WKY and WKY, which had undergone unilateral superior cervical ganglion excision. In contrast, in SHR butyrate treatment did not affect IOP and produced only a transient decrease in BP. WKY showed no significant changes in HR whereas SHR exhibited an increase in HR.Conclusions:Butyrate, a gut bacterial metabolite, lowers IOP in normotensive but not in hypertensive rats. The effect is independent of ocular sympathetic innervation. Given that changes in BP followed a different pattern than changes in IOP it seems that butyrate lowers IOP independently of BP changes.