Ascorbic acid diabetogenesis in the domestic fowl

Production and growth related disorders and other metabolic diseases of poultry – A review

In humans, metabolic complaints may be associated with a failure in one of the body hormone or enzyme systems, a storage disease related to lack of metabolism of secretory products because of the lack of production of a specific enzyme, or the breakdown or reduced activity of some metabolic function. Some of these disorders also occur in poultry, as do other important conditions such as those associated with increased metabolism, rapid growth or high egg production that result in the failure of a body system because of the increased work-load on an organ or system. These make up the largest group of poultry diseases classified as metabolic disorders and cause more economic loss than infectious agents. Poultry metabolic diseases occur primarily in two body systems: (1) cardiovascular ailments, which in broiler chickens and turkeys are responsible for a major portion of the flock mortality; (2) musculoskeletal disorders, which account for less mortality, but in broilers and turkeys slow down growth (thereby reducing profit), and cause lameness, which remains a major welfare concern. In addition, conditions such as osteoporosis and hypocalcaemia in table-egg chickens reduce egg production and can kill.

Effect of ascorbic acid and cooling during egg incubation on hatchability, culling, mortality, and the body weights of broiler chickens

Five experiments involving 3,100 settable eggs with living embryos of commercial broiler parent stock were conducted to determine the effect of ascorbic acid (AA) and cooling during egg incubation on embryonic weight, hatchability, percentage of cull chicks, embryonic mortality, and body weights of the hatched chicks. The treatments were carried out at 15, 15, 17, 11 and 19 d of incubation for Experiments 1, 2, 3, 4, and 5, respectively. The treatments for the experiments were as follows: 1) eggs injected with 0.1 mL of sterile saline solution; 2) eggs injected with saline containing 0.5, 1, 3, and 12 mg of AA per egg; and 3) control for Experiment 1; 1) eggs injected with 3 mg of AA per egg; 2) eggs cooled at 22 C for 24 h; and 3) control for Experiments 2 and 3; 1) eggs injected with 3 mg AA per egg; and 2) control for Experiments 4 and 5. Ascorbic acid at a dose of 3 mg during egg incubation improved hatchability and body weight, and decreased number of cull chicks, whereas a dose of 12 mg decreased embryo weight and hatchability and increased the number of cull chicks and embryonic mortality. Injection of AA hatchability improved when injected on Days 11 and 15 of incubation; effects diminished if AA was injected on Day 19 of incubation. Cooling eggs at 22 C for 24 h had no significant effect on any of the variables studied when compared with controls. Comparison of AA injection at a dose of 3 mg per egg and egg cooling to 22 C for 24 h at 15 to 17 d of incubation led to the conclusion that AA had two advantages over cooling. These advantages were 1) low embryonic death and 2) greater chick weight at hatch and on Days 15 and 17 of incubation.

Ascorbate-induced free radical toxicity to isolated islet cells

Ascorbate is known to be cytotoxic by generating free oxygen radicals, a property shared with the diabetogenic drug alloxan. Some reports indicate that also ascorbate may be diabetogenic. In this study the cytotoxicity of ascorbate on isolated mouse islet cells has been investigated. Ascorbate (0.5-2.0 mmol/l) induced a concentration-dependent increase of trypan blue uptake by the cells, indicating an increase of membrane permeability to the dye. Trypan blue uptake induced by 2.0 mmol/l ascorbate was inhibited by concomitant incubation of the cells with 200 mg/l superoxide dismutase, 200 mg/l catalase, 3.0 mmol/l cytochrome-c or 50 mumol diethylenetriaminepentacetic acid (DTPA), but not by 50 mmol/l D-mannitol. The results indicate that ascorbate is cytotoxic to islet cells by metal-catalysed free radical generation.

Adrenergic regulation of insulin secretion from the chicken pancreas in vitro

Adrenergic regulation of insulin secretion in the chicken was studied using a perifused pancreas fragment preparation. Beta-adrenergic stimulation by 50 microM isoproterenol potentiated theophylline-stimulated insulin secretion. Glucose at 19.5 mM did not stimulate insulin secretion, a finding consistent with previous reports of chicken pancreas sensitivity in vitro. Pretreatment with 50 microM isoproterenol did not alter this glucose insensitivity. Alpha-adrenergic stimulation by 50 microM epinephrine in the presence of beta blockade by sotalol or by 50 microM phenylephrine did not alter insulin secretion. Inhibition of insulin secretion by somatostatin could be demonstrated, however. Epinephrine, 50 and 0.164 microM, potentiated theophylline-stimulated insulin release and at 50 microM stimulated insulin secretion as an off-response even in the absence of theophylline. It is concluded that adrenergic regulation of insulin secretion in the chicken is primarily mediated through beta-adrenergic receptors, resulting in stimulation of insulin secretion.

Adrenergic regulation of avian pancreatic polypeptide secretion in vitro

Adrenergic regulation of avian pancreatic polypeptide (APP) secretion from perifused microfragments of chicken pancreas was investigated with catecholamines and adrenoreceptor-specific analogues added to avian Krebs-Ringer perifusion medium containing 11.1 mM glucose. APP release was stimulated by the alpha-adrenoreceptor agonist phenylephrine (threshold 5 microM; maximum effective concn, 50 microM) and the beta-adrenoreceptor agonist isoproterenol (threshold 5 microM; maximum effective concn, 50 microM). Epinephrine (0.164 microM) and 50 microM norepinephrine also stimulated APP release. The results obtained suggest that APP secretion from chicken pancreas is regulated by dual, complementary alpha- and beta-adrenoreceptor mechanisms.