Regulation of growth hormone-releasing hormone and somatostatin from perifused, bovine hypothalamic slices. II. Dopamine receptor regulation

Abstract

Listen

Translate article

An in vitro perifusion system for bovine hypothalamic tissue was utilized to examine the role of D 1 and D 2 dopamine receptors in the regulation of somatostatin (SRIF) and growth hormone-releasing hormone (GHRH) release. Up to three sagittal slices (600 μm) of bovine hypothalamus, immediately parallel to the midline, were cut in an oxygenated balanced salt solution at 4° C, placed in 5 cc syringes, and perifused at 37° C with oxygenated minimum essential medium-α at a flow rate of 0.15 ml/min. Five experiments were conducted, and medium 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 (AUC), adjusted by covariance for pretreatment values, were calculated from samples collected during the treatment/post-treatment period. Activation of D 1 receptors with 10 −8 M and 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 ineffective. Relative to controls, release of GHRH was decreased 50% in the 10 −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 38393-induced release of SRIF and SKF 38393-induced suppression of GHRH. In contrast, quinelorane, a D 2 receptor agonist, and haloperidol, which 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 dopamine receptors, stimulates release of SRIF and inhibits release of GHRH from the bovine hypothalamus.