Calcitonin-induced anorexia in rats: A structure-activity study by intraventricular injections.

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Abstract
The anorectic potency of salmon, porcine and human calcitonins (sCT, pCT and hCT, respectively) and 2 sCT-fragments were compared in rats. Intraventricular injections of sCT (0.062 and 0.031 nmol/animal) significantly reduced the normal feeding and body weight. The effect appeared to be dose-dependent, reversible and lasted > 6 h. No anorexia ensued on injections of mammalian hormones although tested in relatively high doses (pCT, up to 3.7 nmol; hCT, 3.7 nmol). The C-terminal fragments of sCT, sCT (10-32) and sCT (22-32) were devoid of anorectic activity; but when administered with sCT, and longer fragment (1.2 nmol) significantly decreased the effect of sCT and even the shorter one (18 nmol) tended to act as an antagonist. This property was not recorded with pCT and hCT in the doses examined. These results indicate a novel specificity of the anorectic receptor in rat brain, and on the other hand, they also strongly argue against the hypothesis that in mammals thyroidal calcitonin secreted postprandially might participate in the regulation of subsequent feeding, unless the presence of the sCT-like molecule can be detected in mammals. The antagonistic property of the sCT fragment may have use in clarifying the physiological significance of the anorectic receptor which is possibly in the hypothalamus.

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