Hypothalamic factors differentially affect the proportions of cells that secrete growth hormone or prolactin

Hypothalmic factors have been shown to regulate acutely the synthesis and release of adenohypophyseal hormones, yet few studies have investigated the long term effects of these agents on adenohypophyseal cell types. In the present study, we assessed the chronic influence of selected hypothalamic factors on the relative proportions of GH- and PRL-secreting cells in pituitary cultures derived from 5-day-old rats. Primary cultures were established and incubated for 6 days in the presence or absence of 0.1-microM doses of GH-releasing factor, LHRH, CRF, TRH, or vasoactive intestinal polypeptide and then subjected to reverse hemolytic plaque assays for analysis of the percentages of cells that released GH or PRL. In cultures from males, GH-releasing factor and LHRH treatment caused an increase in the proportion of PRL secretors and a commensurate decrease in the GH population. CRF increased PRL cells without affecting the GH secretors, while TRH reduced the percentages of both cell types, and vasoactive intestinal polypeptide had no effect. Virtually identical results were obtained for cells isolated from females. These results demonstrate that hypothalamic factors have the capacity to induce differential effects on the proportions of GH- and PRL-secreting cells. Surprisingly, our findings also show that hypothalamic factors that do not normally influence the acute release of GH or PRL can exert a chronic effect on the proportion of cells that secrete these hormones.