CHANGES IN SOMATOMEDIN‐LIKE ACTIVITY AND GROWTH HORMONE CONCENTRATIONS IN THE PLASMA OF THE DOMESTIC FOWL (GALLUS DOMESTICUS)

Abstract

Summary. Variations to immunoreactive growth hormone (GH) and bioassayable somatomedin-like activity (SLA) were determined in the plasma of the domestic fowl. The plasma concentralions of SLA (potency relative to a pooled serum standard) and GH were both inversely age-related in growing cockerels (Thornber 909) between 3 and 20 weeks of age (SLA, r = 0 454; P<0 01. GH. r = 0 548; P<0 01) and directly related to each other (r -0 54, P<0 01). In immature birds maintained on a photoperiod of 16 h light, 8 h darkness, plasma concentrations of SLA were highest during the first hour of darkness (I 19 ±: 0 18 units/ml (u/ml) mean ± S.E.M.. n = 6) and significantly lower 1 h after dawn (0 78 ± 0 07 u/ml n = 6). No diurnal variations in plasma concentralions of GH were observed. Deprivation of food in two strains of chickens (Thornber 909 and broiler) significantly reduced plasma concentrations of SLA in both strains and increased plasma concentrations of GH in the Thornber strain. Re-feeding fasted Thornber chickens caused the plasma concentrations of SLA and GH (o return to normal within 24 h but had no effect in broilers. Deprivation of water, which also reduces food intake, for 12. 18 and 24 h markedly reduced plasma concentrations of SLA but had no effect on plasma GH concentration in Thornber cockerels.

Plasma concentrations of somatomedin-C in hypophysectomized, dwarf and intact growing domestic fowl as determined by heterologous radioimmunoassay

“…However it is arguable whether a real discrepancy exists between the data obtained by bioassay and by radioimmunoassay. Falconer et al (1981) reported a significant 29% decrease in bioassayable somatomedin activity after a 24-h fast while, in the present study, starvation for 12-48 h was accompanied by a non-significant 20% decline in plasma IR-somatomedin-C concentrations. In rats, plasma concentrations of IR-somatomedin-C are found to be decreased by starvation for 24 h (Maes et al 1983).…”

“…This contrasts with the observed effect of starvation on plasma somatomedin bioactivity of young chicks (Falconer et al 1981). However it is arguable whether a real discrepancy exists between the data obtained by bioassay and by radioimmunoassay.…”

“…However, in the latter case, somatomedin was estimated by the in-vitro uptake of [35S]sulphate by porcine cartilage. The quantitative but not qualitative differences between the present study (together with that of Hoshino et al 1982) and that of Falconer et al ( 1981 ) are probably explicable in terms of the relative activities of the different somato¬ medins presumed to be present in chicken plasma in the various assay systems.…”

“…It is interesting that plasma concentrations of IR-somatomedin-C decreased by 33% between 6 and 18 weeks of age in control White Leghorn chicks in the present study while an almost identical reduction (34%) was previously observed in plasma somatomedin bioactivity (as determined by [35S]sulphate uptake by chick cartilage in vitro) between 7 and 20 weeks of age, also in White Leghorn chicks (Hoshino et al 1982). On the other hand, Falconer et al (1981) found a 70% decrease in somatomedin activity between 6 and 20 weeks of age in a similar strain of fowl. However, in the latter case, somatomedin was estimated by the in-vitro uptake of [35S]sulphate by porcine cartilage.…”

“…In addition, the variation of IR-somatomedin-C with age in various strains of chickens has been determined. Previous studies on somatomedins in the domestic fowl have examined changes in 'total' somatomedin-like biological activity during embryonic and posthatching development (Falconer, Harvey, Forbes & Scanes, 1981;Gaspard, Klitgaard & Wondergem, 1981;Hoshino, Wakita, Suzuki & Yamamoto, 1982).…”