THERMAL AND NUTRITIONAL INFLUENCES ON TISSUE-LEVELS OF INSULIN-LIKE GROWTH FACTOR-I MESSENGER-RNA AND PEPTIDE

1. The influence of environmental temperature on tissue levels of IGF-I mRNA and peptide has been investigated in 8 week old pigs living under conditions of controlled energy intake. Animals were acclimated to 35 or 10-degrees-C on a high (H) or low (L) energy intake (where H = 2L) and there were thus 4 treatment groups: 35H, 35L, 10H and 10L. 2. The warm temperature was associated with greater levels of IGF-I peptide in plasma and all tissues investigated (liver, kidney, skeletal muscle and heart). Temperature had significant but contrasting influences on IGF-I mRNA in liver and kidney: at 35 compared with 10-degrees-C, levels were increased in liver but reduced in kidney. Despite marked differences in growth and protein deposition, there was no effect of temperature on muscle IGF-I mRNA. 3. A high energy intake was associated with increased levels of IGF-I peptide in plasma and tissues. However, although there was a tendency for liver IGF-I mRNA to be elevated in the 35H compared with the 35L group, there was no overall effect of energy intake on IGF-I mRNA in any issue. 4. It is concluded that ambient temperature and energy intake can significantly affect the concentration of IGF-I peptide in tissues and that regulation may occur at either transcriptional or translational levels. The probability is that the effects of temperature are mediated via its influence on energy balance.