Dexamethasone effects on vascular volume and tissue hematocrit in experimental RG-2 gliomas and adjacent brain

Summary We have studied the effects of dexamethasone, a corticosteroid commonly used to treat brain tumors, on vascular volume and tissue hematocrit in RG-2 experimental rat gliomas.¹²⁵I-RISA (radioiodinated serum albumin) was used to measure tissue plasma vascular volume (V_p) and⁵¹Cr labeled red cells were used to measure tissue red cell volume (V_rbc). Quantitative autoradiography was used to obtain local measurements of V_p and V_rbc in different brain and tumor regions. From these experimentally measured values, we calculated the tissue vascular volume (V_v), tissue hematocrit (THct) and systemic arterial hematocrit (AHct). The value reported primarily reflect capillary and small vessel volumes since blood drained from larger vessels during tissue processing and large vascular structures were avoided during analysis of the autoradiographic images. A total of 110 tumors were studied in 29 animals. There was a consistent trend for V_p and V_v to be reduced in all tumor regions after dexamethasone treatment, although a significant decrease was seen only in tumor center. Dexamethasone did not affect V_p or V_v in tumor-free brain regions. Dexamethasone appeared to have little effect on V_rbc in any brain or tumor region. THct was consistently, although not significantly, higher in tumors after treatment with dexamethasone; THct in tumor-free brain regions was unaffected by dexamethasone treatment.