During stress, blood flow to the kidney is almost completely blocked via constriction of the relevant arteries. therefore, the blood pressure in the capillaries of the kidney during stress is very low, virtually zero. on the other hand, we learned that constriction increases resistance, and therefore increasing blood pressure. how can it be that blood pressure increases and decreases at the same time?

Yes, it is possible that the blood pressure increases and decreases at the same time.

Explanation:

As given that, during stress the blood flow to the kidney is almost completely blocked via constriction (tightening or narrowing) of the relevant arteries. Therefore the blood pressure of the capillaries of the kidney in the stress becomes low, virtually zero.

But as well as when the constriction increases that results in the narrowness and tightness due to which the resistance increases. Consequently, the systematic blood pressure, that is measured by measuring the pressure exerted by the arteries during the contraction of heart, is increases.

That's how the blood pressure increases and decreases at the same time but the references are different.