Pengaruh durasi pemberian kombinasi ekstrak akar kucing acalypha indica linn dan pegagan centella asiatica terhadap perubahan aktivitas spesifik katalase dalam ginjal tikus pascahipoksia = The effect of the duration of using extract combination between akar kucing acalypha indica linn and pegagan centella asiatica on the specific change of catalase enzyme activity in hypoxic rats kidney