Browsing by Subject "Insulin-like growth factor"

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Wachstum und Wachstumsregulation beim Schwein
(1995) Weiler, Ulrike; Claus, Rolf
The endocrine regulation of growth was studied in wild and domestic pigs by systematic measurements of growth hormone (GH), IGF-I (Insulin-like growth factor-I), insulin and steroid hormones. In some of the studies measurements of osteocalcin were included to monitor the anabolic activity of osteoblasts under different physiological situations. The following results were obtained. Age dependent changes in the secretion of GH- und IGF-I were studied in growing boars, barrows and gilts and compared to growth parameters. IGF-I reflected age dependent changes in the growth potential and were closely correlated with daily gain and protein accretion. Osteocalcin concentrations were always correlated to IGF-I, the age dependent decrease, however, was more pronounced for osteocalcin than for IGF-I, reflecting the allometric predominance of skeletal growth in very young pigs. Osteocalcin concentrations were always correlated to IGF-I, the age dependent decrease was more pronounced for osteocalcin than for IGF-I, reflecting the allometric predominance of bone growth in very young pigs. Additionally a clear rhythm of IGF-I secretion was obvious with a period length of two to three weeks. This rhythm was similarly found for cortisol secretion and peripheral osteocalcin and might be related to allometric growth phenomena, as described for skeletal growth in other species. Regulation of GH-secretion includes interactions with hormones involved in the regulation of reproduction. At the pituitary level such interactions were demonstrated for Gn-RH and GH-RH. Gonadal steroids directly influence the release of GH and IGF-I secretion. The analysis of physiological situations as well as application studies revealed that testosterone had only a minor effect on both hormones. In contrast, low concentrations of estradiol clearly stimulated GH- and IGF-I secretion as well. Further increasing estradiol concentrations were still stimulatory for IGF-I but inhibited GH-secretion. Progesterone tended to lower both, GH and IGF-I secretion. Additionally Large White, Meishan and European wild boar were studied for differences in growth performance and the endocrine regulation during the first year of life. The studies revealed, that the high growth potential of LW is related both, to high levels of anabolic IGF-I and concomitantly low levels of catabolic cortisol. In Meishan and wild boars cortisol levels were high, but in Meishan boars additionally high concentrations of gonadal steroids were measured, which may explain the higher growth rate in MS when compared to wild boars. IGF-I concentrations were even higher in wild boars than in LW. Thus it is assumed that selection for growth potential led to a concomitant change in the level of catabolic glucocorticoids. The influence of the season and photoperiod on endocrine parameter, food intake and growth was investigated in wild and domestic boars. A seasonal influence on IFG-I secretion was obvious in wild and LW boars, but not in Meishan boars. It was further proven by the application of a reverse light programme that the pattern is mainly due to the influence of the photoperiod. In the wild boar three distinct metabolic periods were obvious, which were also found in domestic pigs, but less pronounced. In addition to the photoperiod food intake and food composition modulate GH and IGF-I secretion in the pig. Several experiments revealed, that IGF-I secretion is predominantly influenced by the energy supply and only to a lower extend by protein and tryptophane content of the ration.