Evidence for catecholaminergic control of alpha-melanotropin (alpha-MSH) content in hypothalamic areas.
A possible catecholaminergic regulation of hypothalamic alpha-melanocyte-stimulating hormone (alpha-MSH) has been investigated in male rats by an in vivo approach. The hormone was measured by radioimmunoassay in three hypothalamic regions: medial basal hypothalamus, preoptic hypothalamic area and dorsolateral hypothalamus. The tyrosine hydroxylase inhibitor alpha-methyl-para-tyrosine (300mg/kg) increased the hypothalamic alpha-MSH content in medial basal hypothalamus and preoptic hypothalamic area when it was measured at 22:00 h. Diethyldithiocarbamate (600mg/kg), which inhibits dopamine beta-hydroxylase, as well as 2-3-dichloromethylbenzylamide (25mg/kg), which acts on the phenylethanolamine-NCH3 transferase also increased the alpha-MSH content in the above mentioned discrete areas. The alpha-adrenoceptor antagonist phenoxybenzamine (15mg/kg), as well as the alpha 1-adrenoceptor antagonist prazosin (1.0mg/kg), also increased the hypothalamic alpha-MSH content in medial basal hypothalamus and preoptic hypothalamic area. None of these agents modified alpha-MSH content in dorsolateral hypothalamus. Haloperidol (1.2mg/kg), a dopaminergic receptor antagonist, propranolol (6.0mg/kg) and yohimbine (10mg/kg) (non selective beta- and alpha 2-adrenergic antagonist drugs respectively) had no effect on the alpha-MSH in any of the hypothalamic areas studied. These results indicate that the catecholaminergic system is involved in the control of proopiomelanocortin derived hypothalamic alpha-MSH through an alpha 1-adrenoreceptor. The data suggest that the control mechanism in the two alpha-MSH hypothalamic pools are different.
Dpto de Farmacología, Facultad de Ciencias Químicas, Universidad Nacional de Córdoba, Argentina.
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Scimonelli
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Marucco
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Celis
D000316:Adrenergic alpha-Agonists / Q000494:pharmacology*; D000818:Animals; D007031:Hypothalamus / Q000737:chemistry*; D008297:Male; D008781:Methyltyrosines / Q000494:pharmacology*; D011863:Radioimmunoassay; D051381:Rats; D017207:Rats, Sprague-Dawley; D000521:alpha-MSH / Q000032:analysis*; D019805:alpha-Methyltyrosine
D000316:Adrenergic alpha-Agonists; D008781:Methyltyrosines; D000521:alpha-MSH; D019805:alpha-Methyltyrosine