Plasma growth hormone, somatostatin, insulin and glucagon inter-relationships during infusion of human pancreatic growth hormone-releasing factor in young and adult ducks (Anas platyrhynchos)

Abstract

Human pancreatic GH-releasing factor (hpGRF) increased the concentrations of plasma GH when infused i.v. into immature ducks. A dose-dependent increase in plasma GH was observed within 10 min of the start of infusion and was maintained during the 30-min infusion period. Simultaneous infusion of somatostatin S-14 prevented the increase in plasma GH induced by hpGRF, but when the infusion had finished there was a rebound increase in plasma GH. Infusion of the highest dose of hpGRF (800 ng/kg per min) in adult ducks had no significant effect on plasma GH. Plasma somatostatin concentrations were reduced during the infusion of hpGRF in young but not in adult ducks. This observation suggests that the stimulatory effect of hpGRF on GH secretion may be partly due to its inhibitory effect on somatostatin secretion. Infusion of hpGRF in ducklings also increased the concentrations of glucagon and decreased levels of insulin in the plasma. Peripheral plasma glucagon and insulin levels in adult ducks were unaffected by hpGRF infusion. These results indicate that in ducklings, hpGRF increases plasma GH and glucagon concentrations and lowers plasma somatostatin and insulin levels. In the adult, these hormonal responses to hpGRF are not maintained. The highly stimulatory effect of hpGRF on GH secretion in ducklings may explain why plasma GH concentrations are high in these birds.

In-vitro control of growth hormone secretion by synthetic releasing factors in young and adult ducks (Anas platyrhynchos)

“…A direct dose-dependent effect of GRF on in-vitro GH secretion has also been observed in young chickens (Leung & Taylor, 1983;, rats (Vale, Vaughan, Yamamoto et al 1983;Arimura, Culler, Turkelson et al 1983) and humans (White, Daniels, Kendall-Taylor et al 1985). The GH profile obtained in vitro from both young and adult ducks is similar to that previously observed in vivo (Foltzer-Jourdainne et al 1987).…”

“…In contrast to TRH, the GH response to GRF is maintained both in vivo (Foltzer-Jourdainne et al 1987) and in vitro (Fig. 6) during and sometimes after, the period of GRF challenge.…”

“…Although specific GH-releasing factors have not been characterized in the avian hypothala¬ mus, synthetic GH-releasing factors increase plasma GH concentrations in chickens , turkeys (Proudman, 1984) and young ducks (Foltzer-Jourdainne, Harvey, Karmann & Mialhe, 1987), and hypothalamic sites regulating GH release have been detected in the ventromedial and arcuate nuclei of the domestic fowl (Rabii, Knapp, De La Guardia et al 1984). Thyrotrophin-releasing hor¬ mone (TRH) also appears to be physiologically important as a GH-releasing factor in birds, increas¬ ing the circulating GH level in young chickens Klandorf, Harvey & Fraser, 1985), ducklings (Pethes, Scanes & Rudas, 1979;Harvey, Foltzer-Jourdainne, Karmann & Mialhe, 1988) and turkey poults (Proudman, 1984).…”

“…Thyrotrophin-releasing hor¬ mone (TRH) also appears to be physiologically important as a GH-releasing factor in birds, increas¬ ing the circulating GH level in young chickens Klandorf, Harvey & Fraser, 1985), ducklings (Pethes, Scanes & Rudas, 1979;Harvey, Foltzer-Jourdainne, Karmann & Mialhe, 1988) and turkey poults (Proudman, 1984). Somato¬ statin (SRIF), in contrast, has been demonstrated in the avian hypothalamus (Calas, Dubois & Assenmacher, 1975;Blahser, 1984;Foltzer, Harvey & Mialhe, 1987) and has inhibitory effects on in-vivo GH secretion in immature birds (Strosser, Harvey, Foltzer & Mialhe, 1984Harvey, Lam & Hall, 1986).…”

“…However, in adult ducks, GRF, TRH and SRIF have no effect on GH concentrations in peripheral plasma (Strosser et al 1985; Foltzer-Jourdainne et al 1987;Harvey, Foltzer-Jourdainne, Karmann & Mialhe, 1988). In adult chickens, the effect of GRF is much reduced and TRH stimulates GH secretion only in anaesthetized birds Scanes, Carsia, Lauterio et al 1984; .…”