Effects of Cysteamine Administration on thein VivoIncorporation of [35S]Cysteine into Somatostatin-14, Somatostatin-28, Arginine Vasopressin, and Oxytocin in Rat Hypothalamus*

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Abstract
The effect of cysteamine injection on the in vivo incorporation of [35S]cysteine into somatostatin-14 (SRIF-14), SRIF-28, arginine vasopressin (AVP), and oxytocin (OXT) in rat hypothalamus was studied. [35S]Cysteine was injected into the third ventricle 1 h, 4 h, or 1 week after cysteamine (300 mg/kg, sc) injection; animals were killed 4 h later. The drug was found to substantially reduce immunoreactive SRIF levels, but not OXT or AVP, 4 h after its injection. Cysteamine also caused large reductions in label incorporation into SRIF-14, SRIF-28, and OXT 1 and 4 h after drug injection. However, [35S]cysteine incorporation into AVP was increased substantially at these time points, while that into acid-precipitable protein was normal. One week after cysteamine injection, label incorporation into all hypothalamic peptides was normal. Cysteine specific activity was also measured afer [35S]cysteine injection and was found to be similar in treatment and control groups. The results suggest that cysteamine inhibits the synthesis of SRIF-14, SRIF-28, and OXT and stimulates that of AVP.

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