Abstract
Diabetes mellitus or hypoinsulinemia was induced successfully in the male dwarf goats aged be-tween 2 - 3 years with 2 consecutive administrations of streptozotocin. A comparable group of intact control goats was also maintained. In ruminants including goats unlike non-ruminants, insulin generally displays ineffectiveness or resistance in their biochemical setup to facilitate gluco-neogenesis, the only source of glucose in these animals. In present study almost in the absence of insulin through induced hypoinsulinemia the effects of thyrotropin releasing hormone (TRH) (30 μg/kg body weight) and thyroid stimulating hormone (TSH) (2.5 μg/kg body weight) on circulatory glucose and different fatty acid fractions were studied in insulin resistant ruminant model. Fatty acid fractions were estimated by gas chromatography. Both TRH and TSH administration lowered glycemia in insulin deficient goats compared to the controls but significantly with TSH dose only. In intact goats the detectable circulating long chain fatty acids (LCFAs) fractions of lauric, myristic, palmitic, stearic, oleic and linoleic acid were undetected except linoleic acid in the hypoinsulinemic state, however were found restored following TRH and TSH administrations and some of LCFAs; stearic (6417%), oleic (1676%) and linoleic acid (1225%) increased exceptionally with TSH dose. In Intact goats however the hormones variedly increased the fractions. The volatile fatty acid fractions (VFAs) of formic, acetic, propionic, iso-butyric, n-butyric, iso-valeric, n-valeric, iso-caproic, n-caproic and heptanoic acid were detected in the goats. The most VFAs fractions markedly increased in hypoinsulinemic goats compared to the control goats following TRH and TSH infusion. These results have indicated that endogenously stimulated thyroid hormones with TRH and TSH in insulin deficient state inhibit the mechanisms of utilizing the fatty acids in glucose production. Therefore the study reveals thyroid hormones inhibitory effects on gluconeogenesis in insulin resistance and hyperglycemia.
Highlights
There is a close relationship between the hypothalamus, the anterior pituitary and the thyroid gland
In intact goats the detectable circulating long chain fatty acids (LCFAs) fractions of lauric, myristic, palmitic, stearic, oleic and linoleic acid were undetected except linoleic acid in the hypoinsulinemic state, were found restored following thyrotropin releasing hormone (TRH) and thyroid stimulating hormone (TSH) administrations and some of LCFAs; stearic (6417%), oleic (1676%) and linoleic acid (1225%) increased exceptionally with TSH dose
These results have indicated that endogenously stimulated thyroid hormones with TRH and TSH in insulin deficient state inhibit the mechanisms of utilizing the fatty acids in glucose production
Summary
There is a close relationship between the hypothalamus, the anterior pituitary and the thyroid gland. Hypothalamus is the source of the TRH that regulates TSH secretion from anterior pituitary. TSH is the major regulator of the morphologic and functional states of the thyroid and the secretion of T4 and T3 from the gland [1]. The administration of TRH and TSH elicits physiological stimulation of thyroid hormones compared to pharmacological administration of thyroid hormones and is preferred approach to studying the sensitive biochemical targets for thyroid hormones’ actions. Physiological mechanisms of insulin have been studied while destroying its source of beta cell of endocrine pancreas. Hypoinsulinemic state is obtained for investigating the physiological responses in extreme insulin deficiency. Hypoinsulinemia for decades has been induced by beta cell destruction with cytotoxic streptozotocin [2]
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