ADRENALINE RELEASE BY THE 5-HT1A RECEPTOR AGONIST 8-OH-DPAT IS PARTLYRESPONSIBLE FOR PITUITARY ACTIVATION

In male Wistar rats the effect of adrenalectomy on pituitary activatio n by the 5-HT1A receptor agonist. 8-hydroxy-2-(di-n-propylamino)tetral in (8-OH-DPAT), was studied. Rats were injected intravenously with 8-O H-DPAT (0.10 mg/kg) in their home cages. Blood samples were withdrawn from freely moving cannulated rats for determination of plasma adrenal ine and plasma adrenocorticotropin hormone (ACTH). Adrenalectomized ra ts showed almost no measurable amounts of plasma adrenaline, but these animals had elevated baseline plasma ACTH levels as compared to sham- operated rats. 8-OH-DPAT treatment led to a large plasma adrenaline re sponse in the sham-operated animals, which was abolished after adrenal ectomy. The plasma ACTH response to 8-OH-DPAT was significantly dimini shed in the adrenalectomized rats as compared to sham animals. This bl unted ACTH response in adrenalectomized rats, however, was still consi derable in magnitude. The present data thus indicate that the plasma A CTH response to 8-OH-DPAT is due to at least two different mechanisms. First, via 5-HT1A receptor-mediated adrenaline release, which may con sequently stimulate the pituitary. Second, a direct action of 8-OH-DPA T on hypothalamic 5-HT1A receptors is assumed, independent of peripher al adrenaline release.