Regulation of growth hormone-releasing hormone and somatostatin from perifused, bovine hypothalamic slices. II. Dopamine receptor regulation.
An in vitro perifusion system for bovine hypothalamic tissue was utilized to examine the role of D1 and D2 dopamine receptors in the regulation of somatostatin (SRIF) and growth hormone-releasing hormone (GHRH) release. Up to three sagittal slices (600 microns) of bovine hypothalamus, immediately parallel to the midline, were cut in an oxygenated balanced salt solution at 4 degrees C, placed in 5 cc syringes, and perifused at 37 degrees C with oxygenated minimum essential medium-alpha 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 D1 receptor 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 D1 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 D2 receptor agonist, and haloperidol, which blocks D2 receptors, did not affect release of SRIF or GHRH. We concluded that activation of D1 dopamine receptors, but not D2 dopamine receptors, stimulates release of SRIF and inhibits release of GHRH from the bovine hypothalamus.
West
C R
CR
Department of Animal Science, Michigan State University, East Lansing 48824-1225, USA.
Lookingland
K J
KJ
Tucker
H A
HA
D015647:2,3,4,5-Tetrahydro-7,8-dihydroxy-1-phenyl-1H-3-benzazepine / Q000494:pharmacology; D000818:Animals; D001552:Benzazepines / Q000494:pharmacology; D002417:Cattle / Q000502:physiology*; D018491:Dopamine Agonists / Q000494:pharmacology; D018492:Dopamine Antagonists / Q000494:pharmacology; D013007:Growth Hormone-Releasing Hormone / Q000378:metabolism*; D006220:Haloperidol / Q000494:pharmacology; D006706:Homeostasis; D007031:Hypothalamus / Q000187:drug effects / Q000378:metabolism*; D066298:In Vitro Techniques; D007700:Kinetics; D011804:Quinolines / Q000494:pharmacology; D011954:Receptors, Dopamine / Q000502:physiology*; D017447:Receptors, Dopamine D1 / Q000187:drug effects / Q000502:physiology; D017448:Receptors, Dopamine D2 / Q000187:drug effects / Q000502:physiology; D013004:Somatostatin / Q000378:metabolism*
D001552:Benzazepines; D018491:Dopamine Agonists; D018492:Dopamine Antagonists; D011804:Quinolines; D011954:Receptors, Dopamine; D017447:Receptors, Dopamine D1; D017448:Receptors, Dopamine D2; D013004:Somatostatin; D015647:2,3,4,5-Tetrahydro-7,8-dihydroxy-1-phenyl-1H-3-benzazepine; D013007:Growth Hormone-Releasing Hormone; D006220:Haloperidol; C047726:quinelorane