Effect of thyroid hormone on concentrations of plasma calcitonin in broiler chicks.

The purpose of these studies was to determine the effect of thyroidectomy (Tx), and thyroid hormone (T3/T4) treatment on concentrations of plasma CT in chicks. In addition, the turnover of CT in Tx- and T3/T4-treated chicks was estimated using a novel nonradioactive salmon CT preparation. One-week-old broiler chicks (Gallus domesticus) (n = 75) were divided into three groups. Group I was sham-injected daily (i.m. saline), Group II was injected with 50 micrograms/day of T3/T4 while Group III was injected with the goitrogen, methimazole, (150 mg/kg BW per day) for 8 weeks. Chicks (8-9 weeks old) were implanted with catheters in the brachial wing vein and administered ruthenium-labeled salmon CT. Blood samples were collected at 30 s, 1, 2, 4, 8, 20 min, and 3 h after injection. Results showed that concentrations of plasma CT were decreased in T3/T4-injected birds. There was no significant effect of methimazole on circulating concentrations of plasma CT. The half-life of CT was significantly increased (P < 0.05) in both T3/T4-injected (n = 6; 1.34 +/- 0.16 min) and goitrogen-treated birds (n = 2; 5.81 +/- 2.83 min) compared to controls (n = 7; 54 +/- 3 s) The results demonstrate that changes in concentrations of plasma thyroid hormones can significantly affect concentrations of plasma CT.

T-Helper 1 and T-helper 2 cytokine responses in gut-associated lymphoid tissue following enteric reovirus infection.

Enteric infection of mice with reovirus serotype 1 elicits antibody and cytotoxic T-lymphocytes in gut-associated lymphoid tissue (GALT). This led to the hypothesis that T-helper 1 (Th1) and T-helper 2 (Th2) responses develop in GALT. Reverse transcriptase-polymerase chain reactions on RNA from Peyer's patches (PP), intraepithelial lymphocytes (IEL), and lamina propria (LP) lymphocytes demonstrated that interferon (IFN)-gamma message was increased in PP and IEL, but not in LP following infection. No increase in mRNA for interleukin (IL)-4, IL-5, or IL-6 was detected. IFN-gamma, IL-5, and IL-6 were produced in in vitro cultures of PP 4-10 days postinfection. PP and spleen lymphocytes from infected mice produced IFN-gamma, but no IL-5 following in vitro restimulation. Infection also induced production of mRNA for the beta2 chain of the IL-12 receptor in PP. We conclude that reovirus induces robust Th1 and weak Th2 cell responses in GALT.

Enteric reovirus infection as a probe to study immunotoxicity of the gastrointestinal tract.

The gastrointestinal (GI) tract contains a complex immune system that defends the host against a wide range of pathogens and toxins. The GI tract is also exposed to many environmental toxins that could adversely affect intestinal immunity, and few systems to study immunotoxicity of the GI tract have been described. We demonstrate that intestinal reovirus infection can be used as a system to assess the effects of toxins on intestinal and systemic immunity. Mice were given various doses of cyclophosphamide (CY) for 5 days at doses ranging from 100 to 500 mg/kg by the oral route or 200 mg/kg by the intraperitoneal route. On day 3 of dosing, mice were orally infected with reovirus serotype 1, strain Lang. The effects of CY on viral clearance, intestinal and systemic immune responses, and distribution of intestinal lymphocytes were assessed. Mice treated with CY failed to clear the virus in a dose-dependent manner, and serum anti-reovirus antibody titers were suppressed. Virus-specific IgA in cultures of intestinal tissue from CY-treated mice was significantly reduced compared to controls, although total IgA production was not affected. The virus-specific cytotoxic T-cell response in spleen was also suppressed in CY-treated animals. Cyclophosphamide treatment reduced the number and percentage of B-cells in Peyer's patches. Reovirus infection did not increase cellularity of Peyer's patches in CY-treated mice. Cyclophosphamide treatment also had little effect on the phenotype of intestinal intraepithelial lymphocytes. These data demonstrate that intestinal reovirus infection is useful in studying exposure of the GI tract to immunotoxic agents.

The effect of photoperiod and food intake on daily changes in plasma calcitonin in broiler breeder hens.

The roles of photoperiod, energy balance, and concentrations of plasma total calcium (CaT) on daily changes in plasma calcitonin (CT) were investigated in broiler breeder hens (84-100 weeks old). In the first study, broiler breeder hens (n = 24), reared on 14L:10D, were divided into two groups. One group was transferred from a restricted diet (DR) of 150 g/day to ad libitum (AL) for 14 days, while the other group remained on DR. After 2 weeks of ad libitum feeding, birds from each group (AL and DR) were bled every 2 hr for 24 hr for measurement of plasma CaT and CT. In a second study, the hens (n = 20) were transferred to continuous light (LL) for 30 days. After the 30 days, food was removed from one group for 48 hr prior to blood sampling for 24 hr at 3-hr intervals. In a third study, birds were transferred to an ahemeral light cycle (11L:10D) for 28 days. Food was removed from the birds (n = 11) for 48 hr prior to blood sampling every 3 hr for 24 hr. Four weeks later the same birds were bled again for 24 hr, but this time the birds were maintained on a restricted feeding schedule. Plasma CT was measured by a specific heterologous electrochemiluminescent (ECL) assay while plasma CaT was measured by atomic absorption. The results showed that plasma CT concentrations did not correlate with plasma CaT concentrations. Comparisons made between initial and final CaT and CT concentrations indicated an effect of stress due to repeated handling of the birds. Concentrations of plasma CT were significantly reduced in the fasted animals (P < 0.05) compared to diet-restricted controls. There was a significant increase in plasma CT during the dark period of fed animals which was abolished in animals maintained on LL or fasted. In conclusion, a surge in plasma CT requires that the hens be provided food and that they be exposed to a dark cycle.