Rat hypophyseal hormone profiles in response to metabolic stress



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The effects of altered carbohydrate metabolism on the growth hormone and prolactin content of the anterior pituitary was studied in the adult male rat. Alterations in carbohydrate metabolism were induced by starvation, insulin hypoglycemia, and alloxan diabetes. In addition, changes in nucleic acid and protein content of the pars distalis in response to these metabolic stresses were measured. Fasting caused a biphasic response in the total growth hormone content, decreasing at 24 hours, returning to control values at 48 hours and decreasing again at 72 hours. The adenohypophyseal relative growth hormone content demonstrated a similar response to fasting at 24 and 48 hours, however remaining at control values at 72 hours. The prolactin content of the pars distalis remained stable at 24 hours of fasting, then increased to supracontrol levels at 48 and 72 hours. Pars distalis DNA content remained at control levels and the RNA, RNA/DNA ratio, and protein content decreased progressively during 72 hours of fasting. Insulin hypoglycemia produced an increase in the total and relative adenohypophyseal growth hormone content at 5 1/2 hours of insulin treatment, then returning to control values at 24 hours, a biphasic prolactin response, an increasing trend in the protein content of the anterior pituitary while decreasing the RNA content and RNA/DNA ratio and causing no changes in DNA content. Alloxan diabetes decreased the total adenohypophyseal growth hormone content, and prolactin content (decreasing relative content also), decreased DNA, RNA, and RNA/DNA ratio, and protein levels of the anterior pituitary. The results of this study suggest that the growth hormone and prolactin content of the anterior pituitary are responsive to alterations in carbohydrate metabolism, probably being associated with homeostatic mechanisms directed toward providing adequate (alternate) energy supplies to the organism during periods of inadequate carbohydrate availability.