Measurement of somatostatin release in rat brain by microdialysis

Abstract

We determined the most suitable conditions for measuring the somatostatin (SRIF) level by brain microdialysis and investigated its release from the hypothalamus. The relative recovery rate of SRIF was 8.4 ± 0.5%(mean ± SE) using a polycarbonate (PC) membrane with the push-pull method at a flow rate of 2 μl/min. Using tubes with an internal diameter of 0.28 mm and lengths of 5, 25, 50 and 100 cm, the relative recovery rates using a PC membrane with the push method were 8.2 ± 0.5%, 7.3 ± 0.6%, 6.2 ± 0.5% and 4.1 ± 0.6%, respectively. When using tubes with an internal diameter of 0.1 mm and lengths of 5, 25, 50 and 100 cm, the relative recovery rates were 7.3 ± 0.7%, 5.6 ± 1.0%, 3.5 ± 1.1% and 1.4 ± 0.7%, respectively. The relative recovery rate was 5.2 ± 0.5% with a polysulfone (PS-F, Fresenius) membrane, 4.5 ± 0.4% with a PS-H (Hospal) membrane, 2.6 ± 0.2% with an ethylenevinyl alcohol membrane (EVAL), 5.1 ± 0.8% with a polyvinyl alcohol (PVA) membrane and 10.4 ± 0.8% with a PS-K (Kaneka) membrane. With the push method, the extracellular SRIF level in rat pituitary was 42.8 ± 1.8 pg/ml with a PC membrane, 23.1 ± 2.9 pg/ml with an EVAL membrane at a flow rate of 2 μl/min. With the push-pull method, it was 52.7 ± 5.2 pg/ml using a PC membrane, 33.5 ± 2.8 pg/ml using a PVA membrane and 54.4 ± 3.2 pg/ml using a PS-K membrane. Intraperitoneal injection of urethane significantly increased SRIF from a basal level of 36.8 ± 10.6 pg/ml to 66.6 ± 12.5 pg/ml ( P < 0.05) after 1 h; however, pentobarbital decreased it from 44.7 ± 4.1 pg/ml to 16.0 ± 4.6 pg/ml after 1 h. These data, which give optimum microdialysis conditions for measuring SRIF release in the rat, were useful for measuring the physiological release of SRIF from the hypothalamus.