Yen-Jui Chang

Effects of Subacute Hypothyroidism on Metabolism and Growth-Related Molecules

Thyroid hormones are crucial hormones that primarily regulate the metabolism of entire body cells. In this study, Sprague-Dawley rats were grouped into sham thyroidectomy (Sham Tx), thyroidectomy (Tx), Tx with thyroxine replacement (Tx + T4), and PTU injection (PTU) groups. Metabolic parameters were measured by means of metabolic cages for 14 days. After 14 days, the rats were sacrificed while the levels of plasma or serum TSH and growth-related molecules, such as active and total ghrelin, GH, and IGF-1, were assayed. The results revealed that hypothyroid rats tended to eat less food and experienced substantial body weight gain, whereas the rats with T4 replacement tended to eat more food while continuing to lose weight. In hypothyroid rats, the growth-related molecules, such as active ghrelin and total ghrelin secretion, were enhanced, and the ghrelin receptors were also up-regulated. However, circulating GH levels were not elevated and IGF-1 secretion was inhibited in hypothyroid rats. In the Tx + T4 group, the changes of active ghrelin, total ghrelin, GHS-R expression, and IGF-1 were reversed, whereas the GH secretion was higher than that of the Sham Tx group and hypothyroid groups. This study resulted in the novel finding that the ghrelin/GHS-R axis and GH/IGF-1 axis are interrupted in hypothyroid rats.

A radioimmunoassay for rat ghrelin: evaluation of method and effects of nonylphenol on ghrelin secretion in force-fed young rats.

Antiserum YJC 13-31 against the rat ghrelin conjugated to bovine serum albumin (BSA) was produced in the rabbit and a double antibody radioimmunoassay (RIA) for ghrelin has been developed. Characterization results of this antiserum revealed no cross-reaction with human growth hormone and somatostatin. Weak cross-reactions with insulin (0.1%), rat growth hormone (0.1%) and glucagon (0.3%) were observed, which scarcely interfered the assay system. The sensitivity of this RIA was 5 pg per assay tube. With the rat serum samples, the within-assay precision was 7.1% and the between-assay precision was 12.3%. The RIA was also available to detect the ghrelin in rat tissue extracts with good parallelism to the rat ghrelin standard. In application, the serum ghrelin and corticosterone levels in weaned rats were measured by RIA. Gavage of saline was sufficient to raise serum ghrelin from 2.6 +/- 0.18 to 6.7 +/- 0.7 ng/ml (P < 0.01). Gavage with nonylphenol (NP) suppressed the elevation of serum ghrelin levels in a dose-dependent manner. Besides, gavages of saline elevated the serum levels of corticosterone from 108.8 +/- 13.5 to 188.7 +/- 23.5 ng/ml (P < 0.01) but the elevation effects of corticosterone from gavages were overcome by NP in the low dose of 50 mg/kg. It can be speculated that ingestion of NP is harmful to young animals during growth and environmental adaptation.

Radioimmunoassay for Ghrelin: Evaluation of Method and the Effect of Fasting in Rats

A double antibody radioimmunoassay (RIA) for ghrelin has been developed and characterized. Antisera against the human ghrelin conjugated to bovine serum albumin (BSA) were produced in the rabbit. Since the ghrelin of human and rat are close homologies, this antiserum (No. YJC 7-36) is cross-reacted (100%) to rat ghrelin. Therefore, it can be applied to both human and rat RIA of ghrelin for measurement of ghrelin in serum. No cross-reactivities with human insulin, rat growth hormone, somatostatin, and glucagon were detected in this RIA system. Very weak cross-reactivity with human growth hormone was found (0.65%). Sensitivity of the RIA was 300 pg per assay tube. The within-assay precision of serum samples were 4.8% in the human being and 8.7% in the rat. The between-assay precision was 9.4% in human being and 9.0% in rats. The serum ghrelin levels of 12 rats were 1.87±0.29 ng/ml in non-fasting status, but 4.28±0.58 ng/ml in fasted rats.

Effects of Liquid Formula on Plasma Glucose, Insulin, and Ghrelin Levels in Healthy Humans with Mixed Meal Tests

Diet modulation is an important component of the treatment of type 2 diabetes. Glucerna SR is a complete nutritional product containing carbohydrates of low glycemic response with monounsaturated fats composing 24% of the total energy. The aim of this study was to examine the postprandial responses of plasma glucose, insulin, and ghrelin in a mixed meal test (MMT) of Glucerna SR and an ordinary meal (sandwich) in healthy human subjects. Twenty-one healthy human subjects, with a mean age of 24.0 ± 0.9 years were recruited. Anti-human ghrelin antibodies, YJC 1-19, were produced in rabbits by means of keyhole limpet hemocyanin conjugation. Steamed buns, sandwiches, and Glucerna SR were ingested over 3 separate days after fasting overnight. Blood was drawn either at 30 min or serially at 10, 20, 30, 60, 90, 120, and 180 min after meals as part of the MMT, and plasma glucose, insulin, and ghrelin were assayed. The results revealed that anti-serum YJC 1-19 was highly sensitive and specific to human ghrelin, and plasma ghrelin concentration was a proper indicator of hunger or satiety. At the 30 min point, sandwich ingestion resulted in the highest elevation of glucose and insulin, while steamed bun ingestion resulted in the least suppression of ghrelin. The MMT revealed that Glucerna SR ingestion resulted in lower glucose and insulin responses but similar ghrelin responses as compared to sandwich ingestion. In conclusion, the liquid formula of Glucerna SR induces a lower elevation of plasma glucose and insulin levels. The ingestion of Glucerna SR induces a similar decrease of plasma ghrelin levels, thus it does not trigger hunger sensations for 3 h.