Dopamine modulation of pathological human chromaffin tissue.
To evaluate the presence of dopamine-2(DA2) binding sites in pheochromocytoma tissue, we performed binding studies and light microscopy autoradiography on sections of 7 different tumors. 3-H-Spiroperidol, a DA2 ligand, bound specifically to tumor sections with a (mean +/- SD) Kd value of 1.93 +/- 0.62 nmol/L. Binding site density (Bmax) was 29.16 +/- 2.33 fmol/mg tissue. Light microscopy autoradiography showed a nonhomogenous localization of silver grains within chromaffin cells. The specific binding was about 50% of total. To investigate whether DA2 binding sites found on pheochromocytoma cells might modulate catecholamine (CA) release, we studied the effects of oral bromocriptine (2.5 mg) on circulating CA of 5 patients with pheochromocytoma. In these patients bromocriptine caused a decrease in blood pressure (P less than .05) but no significant change in plasma CA. Our study shows the presence of DA2 binding sites on tumoral chromaffin tissue. As bromocriptine, a DA2 receptor agonist, was not able to modify tumor CA secretion, the functional role, if any, played by these binding sites on tumor secretion is still to be clarified.
Mannelli
M
M
Endocrinology Service, University of Florence, Italy.
Pupilli
C
C
Lanzillotti
R
R
Ianni
L
L
Amenta
F
F
Ricci
A
A
Serio
M
M
D000310:Adrenal Gland Neoplasms / Q000378:metabolism*; D001345:Autoradiography; D001665:Binding Sites; D001971:Bromocriptine / Q000494:pharmacology; D002395:Catecholamines / Q000097:blood / Q000378:metabolism; D002838:Chromaffin System / Q000378:metabolism*; D004298:Dopamine / Q000378:metabolism / Q000502:physiology*; D005260:Female; D006801:Humans; D008297:Male; D010673:Pheochromocytoma / Q000378:metabolism*; D011954:Receptors, Dopamine / Q000378:metabolism; D017448:Receptors, Dopamine D2; D013134:Spiperone / Q000378:metabolism
D002395:Catecholamines; D011954:Receptors, Dopamine; D017448:Receptors, Dopamine D2; D001971:Bromocriptine; D013134:Spiperone; D004298:Dopamine