Pulsatile Growth Hormone and Prolactin: Effects of (+) Butaclamol, a Dopamine Receptor Blocking Agent

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Abstract
Growth hormone (rGH) and prolactin (rPRL) secretory profiles were obtained before and after treatment with a dopamine receptor blocking agent, (+) butaclamol in 10 male rats chronically implanted with right atrial cannulae. Mean rGH plasma concentrations, determined by planimetry, were reduced (202 .+-. 20 ng/ml vs. 135 .+-. 20 ng/ml, P < .01), but the basic configuration and periodicity of rGH secretory bursts were unaltered. Mean rPRL plasma concentrations were elevated (11.1 .+-. 2.1 ng/ml vs. 65.5 .+-. 8.1 ng/ml, P < .0005), but rPRL episodic secretion was still apparent. Dopaminergic neurons probably have a minor role in facilitating episodic rGH secretion. Furthermore, persisting episodic rPRL secretion in rats administered a dopamine antagonist suggests that rPRL feedback inhibition does not inactivate the neural mechanism generating episodic rPRL secretion.