Effect of treatment with vitamin D3 on the responses of the duodenum of spontaneously hypertensive rats to bradykinin and to potassium

1 The diet of spontaneously hypertensive rats (SHR) and normotensive Wistar‐Kyoto (WKY) and Wistar (NWR) rats was supplemented with either 2% calcium lactate in the drinking water or 12.5 μg vitamin D3 100 g−1 body weight daily by gavage, for 14 days. 2 The blood pressure of the SHR treated with either calcium or vitamin D decreased to the same levels as that of WKY and NWR. 3 The response to bradykinin of the SHR isolated duodenum, which is predominantly contractile, upon treatment with vitamin D (but not with calcium), became predominantly relaxant, approaching the normal behaviour of the WKY and NWR duodenum. 4 The relaxant responses of the SHR and WKY duodenum to potassium were smaller than those of NWR, but treatment with vitamin D increased the response in all three rat strains. 5 It is concluded that, besides sharing the hypotensive effect of calcium, vitamin D treatment of SHR has an effect on the duodenum smooth muscle which might be due to calmodulin‐dependent activation of calcium‐dependent potassium channels.