Abstract
Abstract
The effects of several putative pineal hormones on prolactin (PRL) secretion from clonal pituitary cells were studied in vitro. The pituitary cells (2B8) were derived from Rathke's pouch epithelium of normal fetal rats, and they were shown earlier to produce only prolactin when grown in Ham's F-10 medium. The substances tested were: 5-HTP (5-hydroxytryptophan), serotonin (5-HT; 5-hydroxytryptamine), NA-5-HT (N-acetyl serotonin), melatonin, and the nonapeptide AVT (arginine—vasotocin). For comparison with the effects of AVT, oxytocin, and AVP (arginine—vasopressin), the neurohypophyseal hormones which are analogs of AVT were also used. After 6 hr of incubation in the presence of these agents, the cells were separated and the media were collected. The media were later assayed for prolactin by radioimmunoassay.
5-HTP, 5-HT, and NA-5-HT (each 10-11 to 10-6 M) had no direct effect on PRL secretion from the 2B8 clonal cells. In contrast, melatonin clearly enhanced PRL secretion over the range of concentrations used. AVT also stimulated PRL secretion in low concentrations (10-11 and 10-10 M), although it inhibited PRL secretion in much higher concentrations (10-8 to 10-6 M). In contrast, oxytocin and AVP did not evoke any response in PRL secretion from these cells. We conclude that the pineal hormones melatonin and AVT, in physiological concentrations, may have direct stimulatory roles in PRL secretion.
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