Effects of hypothyroidism on the growth hormone axis in sheep

Fletcher, Timothy David; Clarke, I. J.

doi:10.1677/joe.0.1400495

Cited by 13 publications

(6 citation statements)

References 28 publications

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“…In contrast to observations in other mammals, in dogs both basal and integrated GH levels were significantly higher in hypothyroidism than in euthyroidism. In some mammals, such as sheep and steers, primary hypothyroidism does not seem to affect GH secretion (Elsasser et al 1992, Fletcher & Clarke 1994, whereas in rats (Varela et al 1991, Santini et al 1993, Mizobuchi et al 1996, Tam et al 1996, Osorio et al 1998) and pigs (Morovat & Dauncey 1998) primary hypothyroidism is associated with low circulating GH levels.…”

Section: Discussionmentioning

confidence: 99%

“…Low circulating GH levels have been reported in hypothyroid pigs (Morovat & Dauncey 1998). In contrast, hypothyroidism did not affect spontaneous GH secretion in sheep and steers, although the response to stimulation with GHRH was reduced in hypothyroid sheep (Elsasser et al 1992, Fletcher & Clarke 1994.…”

Section: Introductionmentioning

confidence: 86%

“…This may be explained by a blunted response of the pituitary somatotrophs to GHRH. Indeed, administration of GHRH results in a markedly reduced GH response in hypothyroid humans (Root et al 1985, Williams et al 1985, Damjanovic et al 1996, Pimentel-Filho et al 1997, hypothyroid rats (Williams et al 1985, Tam et al 1996 and hypothyroid sheep (Fletcher & Clarke 1994). Moreover, in hypothyroid rats a reduced pituitary content of GHRH receptor mRNA has been reported (Tam et al 1996, Korytko & Cuttler 1997.…”

Section: Dogmentioning

confidence: 96%

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Primary hypothyroidism in dogs is associated with elevated GH release

Diaz-Espineira²,

Mol³

et al. 2001

Journal of Endocrinology

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The pulsatile secretion patterns of GH were investigated in seven beagle bitches by collecting blood samples every 10 min for 6 h during euthyroidism and 1·5 years after induction of primary hypothyroidism. Hypothyroidism was induced by surgical removal of the thyroid gland and subsequent destruction of any remnant thyroid tissue by oral administration of sodium [131 I]iodide. Some of the physical changes observed in the dogs with primary hypothyroidism mimicked those of acromegaly. During both euthyroidism and hypothyroidism GH was secreted in a pulsatile fashion. The mean ( ...) basal plasma GH concentration was significantly higher (P=0·003) in the hypothyroid state (4·1 1·6 µg/l) than in the euthyroid state (1·2 0·4 µg/l). Likewise, the mean area under the curve (AUC) for GH above the zero-level during hypothyroidism (27·0 10·0 µg/l 6 h) was significantly higher (P=0·004) than that during euthyroidism (11·7 2·0 µg/l 6 h). The mean AUC for GH above the baseline was significantly lower (P=0·008) during hypothyroidism (2·4 0·8 µg/l 6 h) than during euthyroidism (4·5 1·8 µg/l 6 h), whereas there was no significant difference in GH pulse frequency. The mean plasma IGF-I level was significantly higher (P<0·01) in the hypothyroid state (169 45 µg/l) than in the euthyroid (97 15 µg/l). The results of this study demonstrate that primary hypothyroidism in dogs is associated with elevated basal GH secretion and less GH secreted in pulses. This elevated GH secretion has endocrine significance as illustrated by elevated plasma IGF-I levels and some physical changes mimicking acromegaly. It is discussed that the increased GH release in hypothyroid dogs may be the result of the absence of a response element for thyroid hormone within the canine pituitary GH gene and alterations in supra-pituitary regulation.

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Section: Discussionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 86%

Section: Dogmentioning

confidence: 96%

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Primary hypothyroidism in dogs is associated with elevated GH release

Diaz-Espineira²,

Mol³

et al. 2001

Journal of Endocrinology

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“…LH pulses were defined as previously described (33). The within-assay CV and assay sensitivity were also taken into consideration, as defined by Fletcher and Clarke (34) in the following quadratic equation: y ϭ 24.4 (log x)2 Ϫ 42.7 log x ϩ 24.1. This program enables the selection of both high narrow peaks and smaller broad peaks based on the G parameters.…”

Section: Discussionmentioning

confidence: 99%

Central Administration of Leptin to Ovariectomized Ewes Inhibits Food Intake without Affecting the Secretion of Hormones from the Pituitary Gland: Evidence for a Dissociation of Effects on Appetite and Neuroendocrine Function*

Henry¹,

et al. 1999

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We have studied the effect of leptin on food intake and neuroendocrine function in ovariectomized ewes. Groups (n = 5) received intracerebroventricular infusions of either vehicle or leptin (20 microg/h) for 3 days and were blood sampled over 6 h on days -1, 2, and for 3 h on day 3 relative to the onset of the infusion. The animals were then killed to measure hypothalamic neuropeptide Y expression by in situ hybridization. Plasma samples were assayed for metabolic parameters and pituitary hormones. Food intake was reduced by leptin, but did not change in controls. Leptin treatment elevated plasma lactate and nonesterified fatty acids, but did not affect glucose or insulin levels, indicating a state of negative energy balance that was met by the mobilization of body stores. Pulse analysis showed that the secretion of LH and GH was not affected by leptin treatment, nor were the mean plasma concentrations of FSH, PRL, or cortisol. Expression of messenger RNA for neuropeptide Y in the arcuate nucleus was reduced by the infusion of leptin, primarily due to reduced expression per cell rather than a reduction in the number of cells observed. Thus, the action of leptin to inhibit food intake is dissociated from neuroendocrine function. These results suggest that the metabolic effects of leptin are mediated via neuronal systems that possess leptin receptors rather than via endocrine effects.

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“…TRH seems to be equipotent to GHRH 109 in the case of chickens 110 but not in fowl 110–113 . In mammals, TRH has been demonstrated to stimulate GH release in cattle 114 and in sheep 73,115,116 . In humans, the ability of TRH to induce GH release is maintained in tumor somatotropinoma cells, while this effect is less evident in normal subjects, thereby suggesting that, as for PACAP, TRH has lost, at least in part, its capacity to act as a primary stimulus for the somatotrope axis 117–120 …”

Section: Regulation Of Gh Secretionmentioning

confidence: 99%

Understanding the Multifactorial Control of Growth Hormone Release by Somatotropes

Gahete

Durán-Prado

Luque

et al. 2009

Annals of the New York Academy of Sciences

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Control of postnatal growth is the main, but not the only, role for growth hormone (GH) as this hormone also contributes to regulating metabolism, reproduction, immunity, development, and osmoregulation in different species. Likely owing to this variety of group-specific functions, GH production is differentially regulated across vertebrates, with an apparent evolutionary trend to simplification, especially in the number of stimulatory factors governing substantially GH release. Thus, teleosts exhibit a multifactorial regulation of GH secretion, with a number of factors, from the newly discovered fish GH-releasing hormone (GHRH) to pituitary adenylate cyclase-activating peptide (PACAP) but also gonadotropin-releasing hormone, dopamine, corticotropin-releasing hormone, and somatostatin(s) directly controlling somatotropes. In amphibians and reptiles, GH secretion is primarily stimulated by the major hypothalamic peptides GHRH and PACAP and inhibited by somatostatin(s), while other factors (ghrelin, thyrotropin-releasing hormone) also influence GH release. Finally, in birds and mammals, primary control of GH secretion is exerted by a dual interplay between GHRH and somatostatin. In addition, somatotrope function is modulated by additional hypothalamic and peripheral factors (e.g., ghrelin, leptin, insulin-like growth factor-I), which together enable a balanced integration of feedback signals related to processes in which GH plays a relevant regulatory role, such as metabolic and energy status, reproductive, and immune function. Interestingly, in contrast to the high number of stimulatory factors impinging upon somatotropes, somatostatin(s) stand(s) as the main primary inhibitory regulator(s) for this cell type.

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Effects of hypothyroidism on the growth hormone axis in sheep

Cited by 13 publications

References 28 publications

Primary hypothyroidism in dogs is associated with elevated GH release

Primary hypothyroidism in dogs is associated with elevated GH release

Central Administration of Leptin to Ovariectomized Ewes Inhibits Food Intake without Affecting the Secretion of Hormones from the Pituitary Gland: Evidence for a Dissociation of Effects on Appetite and Neuroendocrine Function*

Understanding the Multifactorial Control of Growth Hormone Release by Somatotropes

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