Flight effects on plasma glucose, lactate, catecholamines and corticosterone in homing pigeons

Significant increase in the circulating levels of glucose, lactate, adrenaline (A) and noradrenaline (NA) was observed in homing pigeons after a flight of 48 km, lasting 60-80 min. There was, however, no change in plasma corticosterone concentrations. The increase in lactate has been attributed mainly to the activity of the white glycolytic fibres in the flight muscles. The increase in A and NA indicated increased sympathetic activity. It is suggested that the flight-induced increase in A stimulated the release of glucagon which could account for the increase in plasma glucose. The lack of any increase in plasma corticosterone implied that the birds were not under any serious stress during the flight and that these results represent the normal changes that may be expected in pigeons during a free flight of the specified distance and duration.     

Effect of vagotomy on plasma levels of growth hormone, free fatty acids and glucose in the pigeon

Plasma levels of growth hormone (GH), free fatty acids (FFA) and glucose were measured in vagotomized (VgX) and sham-operated (VgS) control pigeons. In VgX pigeons, GH level was significantly lower whereas FFA and glucose levels were higher than in VgS pigeons. The depression in GH level in VgX pigeons has been attributed to the significantly high levels of norepinephrine (NE) and corticosterone in these Birds. The higher plasma FFA concentration in VgX pigeons was therefore due to adipokinetic hormonal action other than of GH. It has been suggested that the adrenocorticotrophic hormone (ACTH) and/or NE could have produced the increase in plasma FFA in VgX pigeons. The pronounced hyperglycemia seen in VgX pigeons has been attributed to catecholamine action in the absence of the vagal tone.     

Different acute in vivo effects of bacterial derived and pituitary growth hormone preparations on plasma levels of glucagon, insulin and free fatty acids in rabbits

Intravenous injection of high doses of bacterial derived growth hormone (1 and 2 mg Somatonorm) did not affect the plasma levels of glucagon, insulin and free fatty acids in fasted and fed rabbits. On the other hand, 1 and 2 mg human extracted growth hormone (Crescormon) had stimulatory effects on plasma levels of glucagon, insulin and free fatty acids. These results indicate that the observed stimulatory effects in the rabbits were not due to the growth hormone molecule itself. It was shown by gel filtration and SDS electrophoresis that Crescormon contained constituents that were not present in Somatonorm. The differences in the observed metabolic effects of bacterial derived and pituitary growth hormone preparations in the rabbits could possibly be attributed to a human pituitary lipid-mobilizing factor LMF.     

Effect of thermal stress and dehydration on plasma levels of glucose, free fatty acids and growth hormone in the pigeon.

Pigeons were subjected to high ambient temperature and water deprivation for 3 days (28 degrees C, 31 degrees C and 36.5 degrees C respectively). After 3 days of heat stress and dehydration, the plasma levels of glucose, free fatty acids (FFA) and growth hormone (GH) were measured. Although the level of plasma glucose was not significantly altered, FFA and GH were found to be significantly increased. The possible mediation of the neurohypophysial hormone, vasotocin, in the syndhronous rise in plasma GH and FFA, is suggested.     

The effect of vasotocin on plasma glucose, free fatty acids and growth hormone in the frog, Rana catesbeiana

Injections of arginine vasotocin into bullfrogs had no effect on plasma glucose after 30 min. but caused hyperplycemia after 120 min. Plasma levels of growth hormone were elevated earlier (30 min.) and returned to control levels after 120 min. Plasma free fatty acids were unaltered following vasotocin administration. It is suggested that the hyperglycemic effect of vasotocin may be mediated via growth hormone.     

Oxytocin decreases plasma levels of thyroid-stimulating hormone and thyroid hormones in rats

Oxytocin (OXT) administered to rats induces several long-lasting physiological and metabolic effects. The aim of the present study was to investigate the effects of oxytocin treatment on plasma levels of thyroid-stimulating hormone (TSH), free thyroxine (fT4) and free triiodothyronine (fT3). For this purpose, oxytocin or NaCl was administered intracerebroventricularly (i.c.v.) (0.3 micro g) or subcutaneously (s.c.) (1 mg/kg) once a day for 5 days to male rats. Five or ten days after the last injection, rats were decapitated, blood was collected and hormone levels were analyzed by fluoroimmunoassay. The oxytocin treatment i.c.v. decreased plasma levels of TSH (p<0.05), fT3 (p<0.01) and fT4 (p<0.05) when measured at day 5 after oxytocin treatment, whereas the effect was abolished when measured at day 10. Oxytocin treatment s.c. did not affect plasma levels of TSH, fT3 or fT4. Thus, the effect seems to have been mediated within the central nervous system, and TSH and the thyroid hormones may be involved in some of the metabolic effects in response to oxytocin.     

The effect of pinealectomy on plasma levels of thyroid hormones in pigeons reared under different photoperiods

The effects of pinealectomy on plasma T3, T4 and free T4 concentrations were studied for about 10 weeks in pigeons maintained either under a constant short photophase or in a regime where a long photophase was replaced by a short one during the experiments. The results indicate that, regardless of the photoperiod, no clear functional relationship can be found between the avian pineal gland and thyroid function, although a transitory increase in T4 levels was seen in both pinealectomized and sham-operated birds shortly after the operations.     

Metabolic regulation of growth hormone by free fatty acids, somatostatin, and ghrelin in HIV-lipodystrophy

Human immunodeficiency virus (HIV)-lipodystrophy is a syndrome characterized by changes in fat distribution and insulin resistance. Prior studies suggest markedly reduced growth hormone (GH) levels in association with excess visceral adiposity among patients with HIV-lipodystrophy. We investigated mechanisms of altered GH secretion in a population of 13 male HIV-infected patients with evidence of fat redistribution, compared with 10 HIV-nonlipodystrophic patients and 11 male healthy controls similar in age and body mass index (BMI). Although similar in BMI, the lipodystrophic group was characterized by increased visceral adiposity, free fatty acids (FFA), and insulin and reduced extremity fat. We investigated ghrelin and the effects of acute lowering of FFA by acipimox on GH responses to growth hormone-releasing hormone (GHRH). We also investigated somatostatin tone, comparing GH response to combined GHRH and arginine vs. GHRH alone with a subtraction algorithm. Our data demonstrate an equivalent number of GH pulses (4.1 +/- 0.6, 4.7 +/- 0.8, and 4.5 +/- 0.3 pulses/12 h in the HIV-lipodystrophic, HIV-nonlipodystrophic, and healthy control groups, respectively, P > 0.05) but markedly reduced GH secretion pulse area (1.14 +/- 0.27 vs. 4.67 +/- 1.24 ng.ml(-1).min, P < 0.05, HIV-lipodystrophic vs. HIV-nonlipodystrophic; 1.14 +/- 0.27 vs. 3.18 +/- 0.92 ng.ml(-1).min, P < 0.05 HIV-lipodystrophic vs. control), GH pulse area, and GH pulse width in the HIV-lipodystrophy patients compared with the control groups. Reduced ghrelin (418 +/- 46 vs. 514 +/- 37 pg/ml, P < 0.05, HIV-lipodystrophic vs. HIV-nonlipodystrophic; 418 +/- 46 vs. 546 +/- 45 pg/ml, P < 0.05, HIV-lipodystrophic vs. control), impaired GH response to GHRH by excess FFA, and increased somatostatin tone contribute to reduced GH secretion in patients with HIV-lipodystrophy. These data provide novel insight into the metabolic regulation of GH secretion in subjects with HIV-lipodystrophy.     

Serum glucose and free fatty acids modulate growth hormone and luteinizing hormone secretion in the pig

Two experiments were conducted to determine the effect of free fatty acids (FFA) and glucose treatment on growth hormone (GH) and luteinizing hormone secretion in the pig. In Experiment (Exp) 1, 15 prepuberal gilts received an intravenous infusion of FFA (n = 5; 3 ml of 10% Liposyn II/kg), glucose (n = 5; 1 g/kg), or saline (n = 5; 3 ml of 0.9%/kg). Jugular blood samples were collected every 15 min for 2 hr before and 3 hr after intravenous infusion of saline, FFA, and glucose. Synthetic [Ala15]-h growth hormone-releasing factor-(1-29)NH2 (1 microgram/kg) and gonadotropin-releasing hormone (0.2 micrograms/kg) were administered 30 min after infusion (Time 0 = infusion). In Exp 2, eight prepuberal gilts received either FFA (n = 4) or saline (n = 4) as described in Exp 1, except that treatments were given every hour ove a 10-hr period. Blood samples were collected every 15 min from 1 hr before to 10 hr after the start of FFA or saline infusion. In Exp 1, the peak GH response to growth hormone-releasing factor was delayed by 45 min (P less than 0.01) by glucose treatment and suppressed (P less than 0.01) by FFA treatment. The luteinizing hormone response to gonadotroph-releasing hormone was suppressed (P less than 0.03) by glucose and enhanced (P less than 0.03) by FFA. In Exp 2, the number of GH pulses was increased (P less than 0.05) by FFA infusion and GH concentrations were positively correlated (r = 0.58, P less than 0.0003) with FFA concentrations, while luteinizing hormone pulse amplitude was greater (P less than 0.01) in FFA gilts than in saline gilts. These results indicate that FFA are more effective modulators of GH secretion than acute hyperglycemia, while metabolic status can alter pituitary responsiveness to gonadotropin-releasing hormone.     

Effect of sympathomimetic compounds with beta-adrenergic effects on plasma free fatty acids in man

Nine sympathomimetic compounds were infused intravenously in man, and their effects on the level of plasma free fatty acids, pulse rate, and blood pressure were recorded. Each compound raised the level of plasma free fatty acids. Its activity in this respect could be correlated with its activity in producing Beta-adrenergic effects on the circulation; both effects were abolished by pretreatment with propranolol. It is concluded that sympathomimetic compounds that stimulate -receptors will raise the plasma concentration of free fatty acids.     

The role of insulin, glucagon and growth hormone in the regulation of plasma glucose and free fatty acid levels in anorexia nervosa

It is well established that glucagon plays an important role in the regulation of fuel supplies as its plasma level increases during the first days of a complete fast. However, it is not certain that glucagon is involved in the adaptation to chronic starvation. In the present study, this problem was investigated by the determination of the changes in the plasma glucagon level elicited by an i.v. glucose tolerance test followed by an i.v. arginine perfusion in 26 self starved patients suffering from anorexia nervosa (AN) and 14 control patients having only minor neurotic disorders. The basal plasma glucagon level tended to be higher in the AN patients than in the controls; but the difference was not statistically significant. Glucagon responses to glucose and arginine observed in the AN patients were not significantly different from those seen in the control patients. In the AN patients, the insulin response to both loads was reduced and the plasma GH level increased paradoxically after the glucose load, whereas it rose normally after the arginine load. It may be concluded that in chronic starvation by AN the regulation of fuel supplies depends mainly on decreased insulin and increased growth hormone secretion. The role of glucagon seems to be of minor importance in this condition.