Daniel R. Deaver

Effects of resistance training on neuromuscular junction morphology

The aim of this study was to determine the impact of resistance exercise on neuromuscular junction (NMJ) architecture. Eighteen Sprague‐Dawley rats either participated in a 7‐week resistance training program or served as untrained controls. Following the experimental period, the NMJs of soleus muscles were visualized with immunofluorescent techniques, and muscle fibers were stained histochemically. Results indicate that resistance training significantly (P < 0.05) increased endplate perimeter length (15%) and area (16%), and significantly enhanced the dispersion of acetylcholine receptors within the endplate region. Pre‐ and post‐synaptic modifications to resistance exercise were well‐coupled. No significant alterations in muscle fiber size or fiber type were detected. The data presented here indicate that the stimulus of resistance training was sufficiently potent to remodel NMJ structure, and that this effect cannot be attributed to muscle fiber hypertrophy or fiber type conversion.

Triiodothyronine Reduces Growth Hormone Secretion and Pituitary Growth Hormone mRNA in the Chicken, in Vivo and in Vitro

Abstract The influence of triiodothyronine (T3) on growth hormone (GH) mRNA and GH secretion has been examined in the chicken. Initially T3 treatment in the diet for three days did not alter plasma concentrations of GH. Plasma concentrations of GH were depressed with seven and 14 days of T3 treatment (1 or 5 ppm in the diet). There was a concomitant decline in pituitary GH mRNA with T3 treatment. Pituitary GH content was reduced with 14 but not seven days of T3 treatment. No effect of T3 was observed on the percentage by somatotroph cells in the anterior pituitary gland by fluorescence flow cytometry analysis. While exposure of pituitary cells in vitro from young chickens to GHRF for 2 hr increased GH mRNA, no effect was observed with T3. The presence of T3, for 48 hr in vitro, tended to reduce GH mRNA in adenohypophyseal cells from young chickens and decreased GH mRNA with anterior pituitary cells from adult chicks. It is concluded that T3 chronic administration of T3 depresses circulating concentrations of GH, at least in part, by decreasing GH mRNA and hence GH synthesis.

Metabolic rate and thyroxine monodeiodinase activity in iron-deficient female Sprague-Dawley rats: Effects of the ovarian steroids☆

Abstract Iron deficiency results in altered thyroid hormone metabolism throughout the estrous cycle. To assess the interactions of the ovarian steroids, thyroid hormones, and iron deficiency, we examined indices of thyroid function in ovariectomized iron-deficient animals and control animals treated with estradiol (mean plasma concentration, 260 pmol/L), progesterone (mean plasma concentration, 45 nmol/L), estradiol and progesterone, or no steroid (sham-treated). Neither steroid affected plasma triiodothyronine (T 3 ) concentrations relative to sham-treated animals, but estradiol treatment (either alone or with progesterone) elevated plasma thyroxine (T 4 ) concentrations ( P ⩽ 0.001). Plasma T 3 and T 4 concentrations were lower in iron-deficient ovariectomized rats ( T 3 = 0.38 ± 0.08 nmol/L; T 4 = 22.0 ± 9.7 nmol/L) relative to ovariectomized controls ( T 3 = 0.44 ± 0.11 nmol/L; T 4 = 27.4 ± 8.4 nmol/L; P ⩽ 0.05 and 0.01, respectively. Hepatic thyroxine monodeiodinase activity was lower in iron-deficient rats (422 ± 241 versus 565 ± 251 pmoles I · mg protein −1 · 20 minutes −1 ; P ⩽ 0.03). Brown adipose tissue deiodinase activity decreased in estradiol-treated groups relative to sham-treated animals ( P ⩽ 0.03); however, the brown adipose tissue thyroxine monodeiodinase was unaffected by iron deficiency. Metabolic rates were elevated in iron-deficient rats ( P ⩽ 0.003) and were lower in estradiol-treated rats. Iron-deficient rats exhibit an altered thyroid response to exogenous ovarian steroids. In conclusion, plasma parameters of thyroid function are altered in iron-deficient rats, and these appear to be affected by the ovarian steroids. Tissue deiodinase activities are lower and metabolic rates are higher in iron-deficient rats.

Metabolic rate and thyroxine 5′-deiodinase in iron deficiency: Effects of the estrous cycle

Abstract Thyroid function is severely compromised in male iron-deficient (ID) rats. Similar effects in female rats are undocumented. Therefore, we examined thyroid hormone metabolism in female iron-deficient and control (CN) rats throughout the estrous cycle. Overall, iron-deficient rats had significantly lower plasma concentrations of thyroxine than controls (25.1 ± 8.4 nmol/L in ID; 31.5 ± 9.3 nmol/L in CN, mean ± SD, p≤0.001), while plasma triiodothyronine concentrations were similar to those of controls (0.44 ± 0.19 nmol/L vs. 0.48 ± 0.16 nmol/L, p≥0.05). Oxygen consumption was unaffected by either iron deficiency or the estrous cycle. Control animals had higher liver thyroxine 5′-deiodinase activity at estrus (567 ± 260 pmoles I − produced • mg protein −1 • 20 min −1 ) while iron-deficient animals had lower activity (310 ± 145 pmoles I − • mg protein −1 • 20 min −1 ) relative to other stages of the estrous cycle. In contrast, the lower interscapular brown adipose tissue 5′-deiodinase activity in iron-deficiency rats (p≤0.02) was not affected by the estrous cycle (p≥0.05). In conclusion, iron deficiency alters the normal estrous cycle variation in hepatic triiodothyronine production and plasma thyroid hormone concentrations

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.