Who Should Be Consulted For Stage 4 Kidney Disease And Uncontrolled High Blood Pressure For Better Management?

I am very conserned about my brother he has stage 4 kidney disease & for the last year his GP has just kept increasing his blood pressure meds so he is on 50mg a day. But his BP is not coming down. The kidney consultant says it s his high NO that is making his kidneys leak more protein. So who should he be referrerd to.......?