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

Abstract

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.

Somatostatin binding to chicken adenohypophysial membranes

“…Exogenous SRIF also inhibits basal plasma GH concentrations in chickens and ducks (Strosser, Harvey, Foltzer & Mialhe, 1984;Foltzer, Strosser, Harvey & Mialhe, 1985;Harvey & Scanes, 1987;Scanes & Harvey, 1989) and blocks the in-vivo (Harvey & Scanes, 1987;Scanes & Harvey, 1989) and in-vitro (Perez, Malamed & Scanes, 1987;Foltzer-Jourdainne, Har¬ vey & Mialhe, 1988) GH response to GH-releasing factor or thyrotrophin-releasing hormone (TRH). These effects are likely to be mediated by specific SRIF receptors on pituitary somatotrophs, as ob¬ served on tumorous somatotrophs (Schonbrunn 8c Tashjian, 1980; Moyse, Le Dafniet, Epelbaum et al 1985) and healthy pituitary tissue (Leitner, Rifkin, Maman & Sussman, 1979;Srikant & Patel, 1982; Lewis & Williams, 1987) in mammals.…”