Nitrogen-13 glutamate uptake and perfusion in Walker 256 carcinosarcoma before and after single-dose irradiation

Nitrogen-13 (13N) glutamate uptake was recorded in 18 anesthetized rats, both before and at least once after intervention. Each investigation was immediately followed by imaging of blood flow distribution using [11C]butanol. All animals had Walker 256 carcinosarcoma implants in one hind leg. Tumors were locally irradiated with a dose of 800 rad in 14 rats; in four rats, the vasoactive substance 5-hydroxytryptamine (5-HT) was administered. Prior to interventions, the [13N]glutamate tumor-to-muscle uptake showed a linear correlation with blood flow close to identity (y = 0.117 + 0.915x, r = 0.97). After irradiation, a discordant pattern was observed: blood flow tended to increase, while [13N]glutamate tumor-to-muscle uptake dropped from 4.30 +/- 0.66 (s.e.m.) to 3.06 +/- 0.36 (p less than 0.005) during 30 min and attained 4.04 +/- 0.67 2 days later. If [13N]glutamate tumor-to-muscle uptake was related to that of [11C] butanol in each individual animal, this index dropped from 0.93 +/- 0.03 (s.e.m.) to 0.62 +/- 0.04 (p less than 0.001) 30 min after irradiation and attained 0.90 +/- 0.09 after 2 days. In animals treated with 5-HT, [13N]glutamate and [11C]butanol showed a parallel drop from 6.60 +/- 0.84 to 2.10 +/- 0.60 (p less than 0.05) and from 6.8 +/- 0.78 to 2.08 +/- 0.74 (p less than 0.05), respectively. Thus, single-dose irradiation causes [13N]glutamate uptake to be uncoupled with respect to flow, while [13N]glutamate uptake in untreated tumors is flow-limited and responds together with flow on vasomotion.