It depends on the kind of exercise you are referring to. High level (a lot of muscle activity) resemble the valvalva manouevre (like in heavy lifting). Literature shows this increases blood pressure.

It is to be explored what the effect is of low level stabilisation exercises.

Some researches supports that Isometric exercises raise the Blood pressure where as others states that there is no change in the blood pressure on application of Isometric. Need to be explored well..

Twelve minutes, three to four times a week is prescribed for pre or mild hypertension. and is contraindicated in severe hypertension.