Influence of Insulin and Glucagon on Secretion of Growth Hormone in Growing Ducks (Anas Platyrhynchos)

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Variations in the concentrations of plasma and pituitary GH were determined in ducks for 66 and 87 days after hatch, and compared with somatostatin-like immunoreactivity (SLI) in the plasma, hypothalamus and neural lobe. Plasma GH levels gradually decreased during growth, while pituitary GH content increased. The concentration of pituitary GH increased during the first 3 weeks of age and remained relatively constant thereafter. The decline in plasma GH concentration was paralleled by a similar fall in the level of plasma SLI. While the content of hypothalamic SLI increased during development, the SLI concentration was maximal at 14 days of age and lowest in adults. The content and concentration of SLI in the neural lobe, in contrast, increased progressively during development. Gel filtration of hypothalamic and neural lobe extracts demonstrated that both young and older birds had two main peaks of SLI, corresponding to somatostatin-14 and somatostatin-28, and a third, larger form. The elution pattern of plasma SLI was similar in young and older birds and was principally composed of a large molecular species ('big' somatostatin), although an additional small peak eluting between somatostatin-28 and somatostatin-14 was eluted from a large pool of plasma from 90-day-old ducks. These results suggest that increased plasma GH levels in young birds do not result from a hypothalamic somatostatin deficiency nor from variations in molecular forms of SLI, and that the age-related decline in plasma GH concentration is not due to a deficiency in pituitary GH content. The decline in the circulating GH level during growth is probably due to an increase in hypothalamic somatostatin release.

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Somatostatin-like immunoreactivity in duck plasma, hypothalamus and neural lobe during post-hatch growth: comparison with plasma and pituitary growth hormone concentrations

Foltzer¹,

Harvey²,

Mialhe³

1987

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“…Concentrations of GH, immunoreactive insulin (IRI), glucagon-like im¬ munoreactivity (GLI) and free fatty acids (FFA) in juvenile ducks, during and after the infusion (INF) of (a) oleic acid (6 mg/kg per min) (circles), oleic acid (6 mg/kg per min) 4-somatostatin-14 (800 ng/kg per min) (triangles) or plasma (squares) and (b) oleic acid (9 mg/kg per min) (stars), somatostatin-14 (800 ng/kg per min) (squares) or oleic acid (9 mg/kg per min) + somatostatin-14 (800 ng/kg per min) (diamonds (Tsushima, Matsuzaki & Irie, 1970), although a decrease in plasma FFA induces an increase in GH levels (Irie, Sakuma, Tsushima et al 1967;Tsushima et al 1970;Hertelendy & Kipnis, 1973;Reynaert, De Paepe, Marcus & Peeters, 1975). In juvenile ducks, plasma FFA may act directly at the level of the hypothalamus or pituitary gland to stimulate GH secretion since plasma GLI, which de¬ presses GH in ducks (Foltzer et al 1981), was not depressed during infusion of 6 mg oleic acid/kg per min (Fig. la).…”

Section: Resultsmentioning

confidence: 99%

“…In addition, the inhibitory effects of injections of S-14 on the release of GH from the pituitary gland may be modified by concomitant changes in plasma FFA, GLI and immunoreactive insulin (IRI). Glucagon and in¬ sulin inhibit GH secretion in ducklings (Foltzer, Harvey, Strosser & Mialhe, 1981) but the effect of a fall in plasma FFA levels on GH secretion is unknown. However, GH is important in the control of lipid meta¬ bolism in ducks, since after hypophysectomy plasma FFA drop by 50% while replacement therapy with bovine GH restores normal levels of plasma FFA (Foltzer & Mialhe, 1976).…”

Section: Introductionmentioning

confidence: 99%

Control of plasma levels of growth hormone, glucagon and insulin in ducklings: roles of free fatty acids and somatostatin

Foltzer¹,

Strosser²,

Harvey³

et al. 1985

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The effects of plasma free fatty acids (FFA) and somatostatin-14 (S-14) on concentrations of plasma GH, glucagon and insulin were investigated in juvenile ducks. Oleic acid, S-14 or both were infused into 4- to 7-week-old birds and plasma GH, glucagon-like immunoreactivity (GLI), immunoreactive insulin (IRI) and FFA were measured. An increase in plasma GH and a decrease in GLI but no change in IRI was observed after infusion of 9 mg oleic acid/kg per min. A decrease in plasma GH, FFA and IRI and an increase in plasma GLI was seen after infusion of 800 ng S-14/kg per min. These effects of S-14 on IRI and GLI were abolished when S-14 was infused simultaneously with oleic acid. It is concluded that FFA have a direct stimulatory effect on GH secretion and an inhibitory effect on glucagon secretion. Somatostatin-14 directly inhibits the secretion of GH and its stimulatory effect on the secretion of glucagon is mediated by a depression in concentrations of plasma FFA. Finally, S-14 has no effect on plasma insulin when basal levels of plasma FFA are maintained.

“…Consequently, the decrease in plasma SLI concentrations during growth may be due to a decrease in pancreatic SLI secretion following a decrease in pancreatic SLI con¬ tent. In contrast to SLI, no concomitant age-related variations in plasma immunoreactive insulin (IRI) and glucagon-like immunoreactivity (GLI) were observed in ducks during post-hatch growth (Foltzer, Harvey, Strosser & Mialhe, 1981). Small variations in pancreatic GLI and IRI concentrations may ensure a constant secretion rate of both hormones leading to stable plasma GLI and IRI levels and to blood glucose homeostasis during post-hatch growth.…”

Section: Introductionmentioning

confidence: 99%

Pancreatic somatostatin, glucagon and insulin during post-hatch growth in the duck (Anas platyrhynchos)

Foltzer¹,

Harvey²,

Mialhe³

1987

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Pancreatic somatostatin-like immunoreactivity (SLI), immunoreactive insulin (IRI) and glucagon-like immunoreactivity (GLI) were measured during growth in ducks. The content of each hormone increased progressively but at different rates in the dorsal, ventral and splenic lobes of the pancreas. In the almost fully grown duck, the splenic lobe contained 80 and 63% of the total content of GLI and SLI respectively but low levels of IRI (23%), which were highest in the dorsal lobe (53%). In contrast to the hormonal content, only total GLI concentrations increased during development, the SLI concentrations remaining stable and IRI concentrations declining during growth. Gel filtration of pancreatic extracts indicated that most of the SLI in the pancreas of young and adult birds was somatostatin-14, although somatostatin-28 was present in the ventral lobe of young birds and larger molecular forms were present in the ventral and dorsal lobes. These changes in pancreatic hormonal content and concentration are dissimilar to age-related changes in SLI, GLI and IRI previously observed in the plasma of ducks. Plasma levels of pancreatic hormones may thus be controlled by hormonal and/or neutral factors during post-hatch growth.