David B. King

Serum triiodothyronine levels in the embryonic and post-hatching chicken, with particular reference to feeding-induced changes.

Abstract Serum triiodothyronine (T 3 ) levels were ascertained in late embryonic and early post-hatching chicks by radioimmunoassay, with particular reference to feeding-induced changes. The average T 3 concentration was 11 ng% for 17-day embryos, and increased to 31 and 47 ng% for 2 different hatches at 19 days of incubation. The average serum T 3 level on the day of hatching had risen to approximately 330 ng%, but the levels for 1-day-old chicks were less than one-half the values observed closer to hatching. Two-day-old chicks fed for 24 hr consumed little food, and had serum T 3 levels which were the same as for day-old fasted chicks, but 3 times the value for 2-day-old fasted chicks. At 3 days post-hatching and 48 hr after initiating feeding, food consumption had increased and serum T 3 levels had risen 2.5 times that in day-old chicks. Food consumption and T 3 levels remained high in 4- to 6-day-old chicks, but the T 3 concentration had decreased by 10 days of age to an average value of 225 ng%, which was close to that observed at 33–44 days of age. Goitrogen treatments or changes in iodine intake did not prevent a rise in serum T 3 in response to feeding fasted 2-day-old chicks. Serum T 3 levels for 7-day-old cockerels treated with propylthiouracil (PTU) or methimazole from hatching were approximately 60% of control values, whereas the T 3 levels for older cockerels treated with PTU for 25–36 days were only 10% of control values.

Effect of Mammalian Growth Hormone and Prolactin on the Growth of Hypophysectomized Chickens

Body weight gain and shank-toe growth during a 26-day treatment period following hypophysectomy were 55 and 46%, respectively, of control values, but the body weight gain was unaffected and bone growth only slightly reduced when the hypophysectomized chickens were fed a low dose of corticosterone (5 ppm). Bovine growth hormone (0.5 mg GH/kg body wt/day for 18 days) enhanced body weight gain and shank-toe length increase (an estimate of bone growth) by 46 and 33%, respectively, compared to the growth of hypophysectomized chickens receiving only corticosterone. These same endpoints were increased approximately 24% after ovine growth hormone treatment in hypophysectomized chickens not receiving corticosterone. Body weight gain during 18 days of treatment with bovine prolactin (0.5 mg PRL/kg/day) was 27% greater than the value for corticosterone-treated hypophysectomized chickens, but bone growth was unaffected. The mammalian GH preparations increased heart weight of the hypophysectomized chickens (25-29%), but pectoralis muscle weight was unaffected. GH treatment enhanced thymal weights by 71% in corticosterone-treated hypophysectomized chickens, and by 93% in hypophysectomized animals not receiving corticosterone. GH had no significant effect on bursal weights, and PRL had no effect on either of these lymphoid organ weights in corticosterone-treated hypophysectomized chickens. GH increased liver and adipose tissue weights considerably more than the large increases that followed treatment of hypophysectomized chickens with corticosterone alone (69 and 126% greater, respectively), but had no effect on these endpoints in hypophysectomized chickens not receiving corticosterone. PRL also greatly increased liver and adipose tissue weights in corticosterone-treated hypophysectomized chickens (79 and 75%, respectively). These results provide evidence that mammalian GH enhances body weight gain, bone growth, and the growth of several organs in the hypophysectomized chicken. Mammalian PRL increased body weight gain, liver weight, and adipose tissue weight in corticosterone-treated hypophysectomized chickens, but did not influence bone growth or the weights of the heart, pectoralis, thymi, or bursa.

Effect of hypophysectomy of young cockerels, with particular reference to body growth, liver weight, and liver glycogen level

Abstract Several end-points were examined after hypophysectomy of cockerels at approximately 3 weeks of age. The final body weight and combined length of the shank and middle toe of hypophysectomized cockerels in preliminary experiments (Series 1) were 58 to 88% and 70 to 82%, respectively, of the control values at 3 to 8 weeks after pituitary removal. In later experiments (Series 2), the increases in body weight and shank-toe length of hypophysectomized cockerels were about 75 and 50%, respectively, of the control values during a 12-day period after operation when hypophysectomized cockerels consumed 22–23% less food ad libitum . When hypophysectomized cockerels were force-fed enough food to cause the same or greater body weight gains as controls fed ad libitum , there was still a considerable reduction in bone growth. Growth was observed in one experiment during two consecutive 12-day periods after removal of the pituitary. Hypophysectomy resulted in a 17% lesser body weight gain and a 32% lesser shank-toe increase than controls during the first 12-day period but the bone growth of hypophysectomized cockerels during the 13–24-day period was considerably less than during the 1–12-day period. Thyroxine stimulated bone growth of hypophysectomized cockerels during the first 12-day period to such a degree that the shank-toe increase was not different from intact controls but had a much lesser effect during the second 12-day period. The liver weights (as percentage of the body weight) of controls and hypophysectomized cockerels fed ad libitum were the same at 12 days after hypophysectomy, while the liver glycogen levels were more than doubled in the pituitaryless birds. Hypophysectomized cockerels force-fed enough food to cause the same or greater body weight gains as controls fed ad libitum had liver weights 55–56% greater than ad libitum controls and liver glycogen levels as much as 4.5 times the controls. Gonad weight, thyroid weight, and comb growth were all drastically less for hypophysectomized cockerels than for controls.

Effect of hypophysectomy and growth hormone on immune development in the domestic fowl

The effect of hypophysectomy and recombinant growth hormone (rcGH) treatment on the growth and development of the immune system was investigated in young chickens. Flow cytometric analysis of cell surface markers revealed no changes in the proportion of thymocytes expressing CT-1a, CD4, and/or CD8 among any of the treatment groups. In contrast, the proportion of both single positive CD4 and CD8 peripheral blood lymphocytes (PBL) was altered in hypox birds treated with rcGH compared to the vehicle-treated group. Specifically, rcGH treatment produced a decrease in the proportion of CD8+ cells and an increase in the percentage of CD4+ PBL. There was little change in the labeling intensity of PBL or thymocytes associated with any treatment; however, double positive (CD4+CD8+) thymocytes from hypophysectomized chicks that were not given rcGH had increased fluorescence relative to rcGH supplemented hypox chicks. As expected, hypophysectomy reduced body, skeletal, and thymic growth. Treatment of hypox chicks with rcGH enhanced body weight while thymic weights were somewhat increased. Skeletal growth was not significantly altered by rcGH. Bursal growth appeared refractory to either treatment. These studies support the conclusion that growth hormone influences thymic growth and the maturation of thymus-derived lymphocytes. These results also demonstrate a biological activity for chicken growth hormone derived through recombinant technology.

Thyroidal influence on gastrocnemius and sartorius muscle growth in young white leghorn cockerels.

Abstract The fresh weights and total amounts of DNA, crude fibrillar protein (CFP), and actin for gastrocnemius muscles from severely hypothyroid white Leghorn cockerels were 48, 48, 45, and 53%, respectively, of control values following 8 weeks of propylthiouracil (PTU) injections which started at 2 days of age. Hypothyroidism had approximately 20% less effect on sartorius muscle growth compared to the gastrocnemius. The results are compared with those of an earlier study using identical treatments and the same strain of chickens during a 4-week growth period following hatching. There was apparently no further proliferation of nuclei between 4 and 8 weeks of age in the muscles of the hypothyroid cockerels, whereas total DNA continued to increase in controls. By the end of 8 weeks of PTU treatment, there had been sufficient reduction in the accumulation of CFP and actin so that CFP:DNA and actin:DNA ratios were normal. This suggests some regulation of the amounts of CFP and actin relative to DNA content.

Effect of triiodothyronine on the expression of T cell markers and immune function in thyroidectomized white leghorn chickens

Abstract Hypothyroid K-strain chickens were produced by neonatal thyroidectomy and treatment with 6-propyl-2-thiouracil. Thyroidectomized birds were given 0, 1.5, 4.5, 15, or 45 μg/kg body wt of triiodothyronine (T3) by daily injection. At 5 weeks of age, thymocytes were prepared for flow cytometric analysis of CT-1a, CD3, CD4, and CD8 expression. Sham-operated birds had the smallest proportion of CT-1a+ cells and the brightest CT-1a+ cells. Unsupplemented thyroidectomized birds presented an inverse picture, while T3-Vtreated thyroidectomized birds were intermediate. Fewer and less brightly labeled CD3+, CD4+, and CD8+ cells were associated with sham-operated birds or with higher levels of T3 replacement. Low levels (1.5 μg/kg body wt) or no T3 treatment produced a greater proportion of positive, highly fluorescent cells. The ratios of CD4+ to CD8+ thymocytes were increased (P ≤ 0.05) by T3 supplementation. Functionally, thyroidectomy produced a decrease in mitogen-stimulated proliferation of peripheral blood lymphocytes. This effect was ameliorated by T3 supplementation. Further, thyroidectomy produced an elevation of plasma growth hormone concentrations. These results suggest that thyroid factors and alterations of thymic status significantly affect the generation of specific thymus-derived lymphocyte populations and their functional capabilities, perhaps due to changes in the thymic microenvironment. These alterations may have important consequences for the development of immunocompetence and disease resistance in chickens.

Avian muscular dystrophy: thyroidal influence on pectoralis muscle growth and glucose-6-phosphate dehydrogenase activity.

Abstract The pectoralis muscles of dystrophic chickens (line 413) were hypertrophic on the basis of fresh weight and fat-free dry weight. They also had greater DNA content and greater glucose-6-phosphate dehydrogenase (G6PD) and 6-phosphogluconate dehydrogenase (6PGD) activities. Of the parameters measured, the largest differences between pectoralis muscles from dystrophic and normal (line 412) chickens were for DNA content and G6PD activity. These parameters were 4.3- and 6.7-fold, respectively, the values for control pectoralis at 5 wk of age. The average number of nuclei per unit length of isolated muscle fiber was also greater (approximately 3-fold) for the dystrophic pectoralis. Body weight and pectoralis fresh weight, fat-free dry weight, DNA content, G6PD activity and 6PGD activity were reduced significantly in propylthiouracil (PTU)-treated normal and dystrophic chickens. Moreover, the effects of PTU were more pronounced in the dystrophic strain. Thyroid deprivation significantly improved the righting ability of the dystrophic chickens, in addition to its influence on muscle hypertrophy and body growth. Thyroxine (T 4 ) replacement reversed the PTU effects in both strains. Of all the variables measured, total G6PD activity was the most affected by PTU treatment of dystrophic chickens and was only 16% of the control dystrophic value. In addition to the effects of thyroid deprivation on the expression of avian muscular dystrophy, we observed significant differences in thyroid-related variables in the two strains. The average thyroid weight at 4 wk and serum triiodothyronine level at 5 wk for dystrophic chickens were 65 and 76%, respectively, of the normal values. The results that we report here indicate that altered thyroid function affects the expression of avian muscular dystrophy.

Effect of the goitrogen methimazole on skeletal muscle growth of chick embryos.

Abstract The effect of methimazole (MMI) treatment on the body growth of chick embryos, with particular reference to skeletal muscle growth, was ascertained during the second half of embryogenesis. MMI-induced hypothyroidism is easily achieved and the optimum effective dose appears to be 2.5 mg/100 g body wt/day. When this dose is administered from 10 through 19 days of incubation, the following parameters at 20 days of incubation are reduced below control levels by the percentages indicated in parentheses: body wt (38%), shank-toe length (20%a), gastrocnemius muscle weight (50%), gastrocnemius total actin (75%), gastrocnemius total crude fibrillar protein (60%), sartorius muscle weight (48%), sartorius total actin (65%), and sartorius total crude fibrillar protein (50%). Muscle DNA levels were not appreciably altered by the MMI treatment. Most of the effect of hypothyroidism on body weight and muscle growth becomes apparent between 17 and 20 days of incubation when there are normally large increases in these parameters. The effects of MMI were counteracted, in part, by thyroxine replacement from 16 through 19 days of incubation. The effect of MMI administration from 10 through 19 days of incubation was compared to the effectiveness when administered from 10 through 14 or 15 through 19 days. At 20 days of incubation, body weight and gastrocnemius muscle weight and actin content were affected nearly the same following either 5-day treatment as following 10-day MMI treatment. Apparently, early hypothyroidism effects a change in body and gastrocnemius muscle growth which persists after withdrawal of MMI. Also, this early influence of thyroid deprivation does not seem to be required for a nearly full effect of MMI-induced hypothyroidism on these parameters from 15 to 20 days of incubation.

Thyroidal involvement in the expression of avian muscular dystrophy.

We showed previously that propylthiouracil (PTU), a thyroid inhibitor, could alleviate several major signs of hereditary muscular dystrophy in chickens. The goals of the present investigation were to: (1) determine whether a nearly athyroid condition (achieved within two days after hatching by surgical thyroidectomy plus PTU) during an 11-day period beneficially affects the dystrophic condition when followed by triiodothyronine (T3) replacement to 33 days of age; (2) determine the beneficial effects on the expression of avian dystrophy when the thyroidectomized-PTU-treated chickens received a wide range of moderate to low T3 replacement doses beginning by two days after thyroidectomy; and (3) examine the thyroid hormone receptor system in dystrophic muscle for a possible abnormality. Thyroid deprivation increased muscle function (righting ability) and reduced plasma creatine kinase activity in dystrophic chickens. The major thyroid-related abnormality in dystrophic pectoralis muscles was an increased maximum binding capacity of solubilized nuclear T3 receptors.

Muscle growth and development in chick embryos—thyroidal influence on ribosomal RNA metabolism☆

Thyroidal influence on muscle ribosomal RNA (rRNA) metabolism was examined during late embryogenesis of the chick, when there is normally considerable growth. RNA polymerase I activity of leg muscle nuclei was 52% of the control value at 20 days of incubation, following 1 week of methimazole (MMI) treatment (P < 0.01). The enzyme activity for nuclei isolated from muscle of 19-day, MMI-treated embryos at 48 hr after the administraton of 300 ng of thyroxine (T4) was 31% greater than for embryos receiving MMI alone (P < 0.01). At 24 hr after the administration of [14C]orotic acid, and 23.5 hr after the administration of 300 ng of T4, the amount of 14C incorporated into the RNA from leg muscles of 18-day, MMI-treated embryos was 29% higher than for MMI-treated embryos receiving Ringers solution at the time of hormone injection (P < 0.02); T4 did not influence incorporation into total RNA at 3, 6, or 12 hr after administration of labeled precursor. The average specific activity of the cytoplasmic ribosomal-polysomal RNA fraction was increased approximately 43% in the T4-treated embryos at 24 hr after administration of [14C]orotic acid, and 23.5 hr after hormone, compared to that of MMI controls (P < 0.01), and the specific activity of the combined 18-S and 28-S rRNA, isolated from the ribosomal-polysomal RNA fraction, was increased 39% in the T4-treated embryos (P < 0.01). Data on the 24-hr, cumulative incorporation of [14C]orotic acid into perchloric acid-soluble components of leg muscle indicate that the increased incorporation of labeled precursor into RNA was not due to greater uptake of [14C]orotic acid into muscle or a higher specific activity of uridine nucleotide precursors. The present report of thyroidal influence on muscle rRNA metabolism supports earlier observations which indicated that thyroid function is important to muscle growth during late embryogenesis in the chick.