REGULATION OF GROWTH HORMONE-RELEASING HORMONE AND SOMATOSTATIN FROM PERIFUSED, BOVINE HYPOTHALAMIC SLICES .2. DOPAMINE-RECEPTOR REGULATION

An in vitro perifusion system for bovine hypothalamic tissue was utili zed to examine the role of D-1 and D-2 dopamine receptors in the regul ation of somatostatin (SRIF) and growth hormone-releasing hormone (GHR H) release. Up to three sagittal slices (600 mu m) of bovine hypothala mus, immediately parallel to the midline, were cut in an oxygenated ba lanced salt solution at 4 degrees C, placed in 5 cc syringes, and peri fused at 37 degrees C with oxygenated minimum essential medium-alpha a t a flow rate of 0.15 ml/min. Five experiments were conducted, and med ium effluent was collected every 20 min before (two samples), during ( one or three samples), and after (six samples) treatment. Areas under SRIF and GHRH response curves (AUG), adjusted by covariance for pretre atment values, were calculated from samples collected during the treat ment/post-treatment period. Activation of D, receptors with 10(-8) M a nd 10(-6) M SKF 38393 increased AUC for SRIF from 5.6 (control) to 420 and 500 +/- 57.8 ng . ml(-1) min, but 10(-10) M SKF 38393 was ineffec tive. Relative to controls, release of GHRH was decreased 50% in the 1 0(-6) M SKF 38393 group. Blockade of D-1 receptors with SCH 23390 had no effect on basal release of either SRIF or GHRH, but prevented SKF 3 8393-induced release of SRIF and SKF 38393-induced suppression of GHRH . In contrast, quinelorane, a D-2 receptor agonist, and haloperidol, w hich blocks D-2 receptors, did not affect release of SRIF or GHRH. We concluded that activation of D-1 dopamine receptors, but not D-2 dopam ine receptors, stimulates release of SRIF and inhibits release of GHRH from the bovine hypothalamus. (C) Elsevier Science Inc. 1997.