Increased protein intake during recovery from zinc deficiency is accompanied by alterations in hypothalamic growth hormone releasing factor and somatostatin

To determine if alterations in growth hormone releasing factor (GRF) and somatostatin (SRIF) occur during recovery from zinc deficiency and to examine the relationship between these peptides and the increased protein intake observed during zinc repletion, both the hypothalamic release and mRNA levels of GRF and SRIF were measured during zinc deficiency and zinc repletion. Groups of male rats (n = 4-8 each) were provided 3-choice macronutrient diets made either zinc adequate (Zn+) or deficient (Zn-; 30 vs. I mg Zn/kg diet). Pair fed, calorie restricted (PF) rats were also maintained. After 28 days, Zn- rats were repleted with Zn+ diets for 2 days and one PF group was allowed free access to the same Zn+ diets for 2 days. Additionally, groups of Zn- and PF rats were repleted 2 days with Zn+ carbohydrate and fat diets but no protein. Hypothalamic GRF and SRIF release was measured in vitro. Basal GRF secretion was not significantly different between Zn-, PF, or Zn+ groups although there was a significant increase (P <0.05) during zinc repletion. PF and Zn- rats repleted 2 days with diets devoid of protein had highest GRF secretion (P <0.01) compared to other groups. There were no differences in GRF mRNA levels among groups. Basal SRIF secretion was significantly lower in Zn- and PF groups compared to Zn+, and SRIF mRNA levels were significantly higher in zinc repleted groups compared to Zn-. These results demonstrate that during zinc repletion, GRF and SRIF secretion and SRIF gene expression are altered concomitantly with protein intake. The present data support involvement of GRF in protein intake changes during zinc repletion.