Cysteamine Acts Immediately to Inhibit Prolactin Release and Induce Cellular Changes in Estradiol-Primed Male Rats

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Abstract
Cysteamine (CSH) has an inhibitory effect on the secretion of PRL, GH and TSH. The purpose of the present study was twofold: (1) to examine the short-term effects of CSH on PRL secretion, and (2) to elucidate the mechanism of action of CSH. CSH (100 mg/kg) was injected as an intra-atrial bolus to both normal and estradiol-primed male Sprague-Dawley rats. Blood samples were drawn every 2 min for 1 h and assayed for PRL. To determine if the actions of CSH involved PIF release or PIF receptors, a dopamine receptor blocking agent, pimozide (100 µg/kg) was given intra-atrially 1 h after the CSH injection and PRL concentration was monitored. Within 6 min after the CSH injection PRL levels in estradiol-primed rats began to fall, and by 30 min postinjection the levels were well below baseline values. Blocking the dopamine receptors with pimozide did not result in increased PRL levels, indicating that CSH was acting through some mechanism not directly involving dopaminergic PIF receptors. In a separate study, 6 min after the injection of CSH the rats were decapitated and their anterior pituitaries were removed and processed for electron microscopy. Only mammotrophs from estradiol-primed rats treated with CSH showed an extensive rearrangement of rough endoplasmic reticulum (RER) in concentric whorls around the periphery of the cells. These studies show that the inhibition of PRL secretion by CSH begins within 6 min, and is appreciable only when basal PRL levels are increased by estrogen priming. The inhibition by CSH is not mediated through stimulation of PIF release, or PIF receptors or cellular degeneration, but appears to involve rearrangement of RER into a physical obstacle.