The Effects of Glucagon on Plasma Concentrations of Insulin. Growth Hormone, Glucose and Free Fatty Acids in Sheep: Comparison with the Effects of Catecholamines

Abstract

Glucagon, adrenaline, and isoprenaline were administered to adult sheep by intravenous infusion at a rate of 5 p.g/min for 2 hr.Plasma glucose concentration increased more rapidly during glucagon infusion than during infusion of either adrenaline or isoprenaline.Plasma insulin concentration increased rapidly during glucagon infusion, but the increase was less than that observed during infusion of isoprenaline. There was almost no increase in plasma insulin during infusion of adrenaline despite marked hyperglycaemia.Plasma growth hormone concentration increased during glucagon infusion, but high levels were not maintained. Both adrenaline and isoprenaline decreased growth hormone concentration.Plasma free fatty acid concentrations decreased during glucagon infusion. Plasma sodium and potassium concentrations also decreased but the plasma concentration of urea nitrogen was not altered during glucagon infusion.Intravenous infusion of glucagon at rates of 0·5 and O· 1 p.g/min for 2 hr also significantly increased plasma glucose, insulin, and growth hormone concentration and decreased plasma free fatty acid concentration. Infusion of glucagon at lower rates (0·05 and 0·01 p.g/min) had no significant effects.

Physiological changes during feeding and rumination in cows

“…In this study, we used the automated blood sampling system to collect blood samples every 5 min without diluting the blood with saline containing heparin sodium. However, in ruminants glucose concentration decreases after consumption of meals, as previously reported in steers (Veira et al 1994), sheep (Bassett 1971) and lactating ewes (Thye et al 1970). To our knowledge, this is the first report on physiological changes during rumination.…”

“…In non-ruminants, chewing behavior is used Table 1 Area under the curve (AUC)of non-esterified fatty acid (NEFA) and glucose before and after feeding as a synonym for feeding behavior, because feeding behavior is thought to increase plasma glucose concentrations due to the digestion and absorption of carbohydrates. However, in ruminants glucose concentration decreases after consumption of meals, as previously reported in steers (Veira et al 1994), sheep (Bassett 1971) and lactating ewes (Thye et al 1970). In ruminants, such a decrease most probably results from an increased tissue uptake of glucose stimulated by the postprandial increase in insulin secretion coupled with a low portal absorption of glucose.…”

The Regulation of Insulin Secretion by the Ovine Foetus in Utero

“…Studies of insulin secretion by isolated pancreas from foetal rats and rabbits (Vecchio et al 1967;Asplund, Westman & Hellerstrom, 1969;Milner, 1969) indicate that glucose alone may be unable to stimulate insulin secretion but it has been shown that glucagon and tolbutamide can stimulate insulin secretion by the pancreas of the foetal rat, and that in their presence glucose can also stimulate insulin secretion (Vecchio et al 1967). Glucagon and isoprenaline are both potent stimulators of insulin secretion in adult sheep (Bassett, 1970(Bassett, , 1971). However, the infusion of glucagon into foetal lambs did not stimulate insulin secretion or increase the effect of glucose when infused with it, even though the amount of glucagon used caused significant insulin secretion in the ewe when infused into the maternal circulation.…”

“…The experiments reported here were carried out to clarify whether glucose or fructose stimulate insulin secretion in foetal lambs and to examine whether other known stimulators of insulin secretion in sheep, such as isoprenaline or glucagon (Bassett, 1970(Bassett, , 1971, are also effective in foetal lambs.…”

Revue bibliographique : Variations quantitatives et métabolisme des lipides dans les tissus adipeux et le foie au cours du cycle gestation-lactation 2e partie : chez la brebis et la vache

“…Le glucagon n'a que peu ou pas d'effet lipolytique chez les ruminants in vivo Bassett, 1971 ;Luthman et Jonson, 1972a ;Brockman, 1978 ;Vernon, 1980) ou in vitro (Etherton et al, 1977). Cette hormone intervient en premier lieu pour stimuler la néoglucogenèse hépatique, ce qui va de pair avec une faible action sur les tissus périphériques (Bassett, 1975).…”