Jane Myers, MSc, and Stuart Myers
Horse Pasture
Nice Pasture
I have received several questions regarding a possible connection between high potassium intake and high insulin in horses. Spoiler: It's not true.
Pastures have high potassium, especially in Spring, but this is not causing high insulin.
It's true that insulin stimulates cells to take up potassium. The circulating glucose levels trigger a baseline secretion of insulin, even when fasting. This insulin works with the kidneys to keep blood potassium in the normal range.
In a normal, healthy pancreas inside the body, generous levels of potassium inside the insulin-secreting beta cells keeps the cells in a stable/polarized state where they do not secrete insulin. When glucose comes along and enters the cells, the channels that allow potassium in are closed, calcium enters the cell and triggers insulin release. The maintenance of high potassium levels inside cells is a common scenario in all cells.
If you take the pancreas out of the body and expose it to high concentrations of potassium, it will secrete insulin. I suppose this is where the idea of high-potassium hay or pasture stimulating insulin originated. It's not that simple.
The levels needed to release insulin are at least 300% higher than normally found in the blood. This never happens in a live horse, even on a high potassium diet or with electrolyte supplements. In fact, blood potassium that high would kill the horse. High potassium intake stimulates the release of the hormone aldosterone, which enhances the removal of potassium by the kidneys. This is why potassium blood levels stay in the normal range even on high potassium intake.
To summarize, the levels of potassium found inside a horse's blood do not stimulate the release of insulin. It takes at least three times upper normal levels of potassium to cause insulin release. However, potassium levels are tightly regulated as high levels cause potentially fatal arrhythmias in the heart.
Hay and pasture contain two to four times more potassium than the horse needs but it has nothing to do with insulin.
For more information about insulin, EMS, and Insulin resistance see www.ecirhorse.org.
References
Chanut F, Potassium Channels Rule over Insulin Release with an Ion Fist. PLoS Biol. 2006 Feb; 4(2): e53. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC1334240/
Epstein G, Fanska R, Grodsky, G, The Effect of Potassium and Valinomycin on Insulin and Grlucagon Secretion in the Perfused Rat Pancreas. Endocrinology, Volume 103, Issue 6, 1 December 1978, Pages 2207–2215, https://doi.org/10.1210/endo-103-6-2207