Influence of Short-Term Fasting on the Pituitary-Testicular Axis in Normal Men

Röjdmark, Sven

doi:10.1159/000180645

Cited by 46 publications

(13 citation statements)

References 14 publications

(15 reference statements)

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“…Consequently, GnRH dose, sex, and age are factors which should be taken into account when evaluating the gonadotropin responsiveness to GnRH in hyperthyroid patients. Previous studies from this and other clinics have shown that human thyrotrophs are dependent on glucose to function normally [24,25], This may also hold true for human gonadotrophs [9]. However, similar blood glu cose concentrations were recorded in this investigation when blood glucose measurements were carried out in the thyrotoxic and euthyroid states.…”

Section: Discussionsupporting

confidence: 83%

“…In normal men short-term fasting increases the sensi tivity of the pituitary gonadotrophs to exogenous GnRH [8,9], This is of interest in this context since thyrotoxic patients and starving individuals have several factors in common such as catabolic metabolism, weight loss, and decreased stress tolerance. Furthermore, hyperthyroid patients, like normal fasting subjects, display decreased thyroid-stimulating hormone (TSH) responsiveness to exogenous thyrotropin-releasing hormone (TRH) [4,[10][11][12][13].…”

Section: Introductionmentioning

confidence: 99%

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Hypothalamic-Pituitary-Testicular Axis in Patients with Hyperthyroidism

Röjdmark¹,

Berg

Källner³

1988

Horm Res

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To test whether chronic thyroid hormone excess influences the hypothalamic-pituitary-testicular axis, 8 hyperthyroid men were given two identical intravenous GnRH tests. The first test was performed before any treatment had been instituted, the second 6–13 months later, when medical treatment had made the patients euthyroid. Although basal serum luteinizing hormone (LH), follicle-stimulating hormone (FSH) and testosterone (T) levels were of similar magnitudes before and after the medical treatment, LH and FSH responsiveness to gonadotropin-releasing hormone (GnRH), as reflected by the hormone incremental areas (U/l × min), were significantly larger in the thyrotoxic state compared with the euthyroid state (LH incremental areas: 3,999 ± 665 vs. 2,640 ± 430, p < 0.02; FSH incremental areas: 825 ± 193 vs. 542 ± 98, p < 0.05). Furthermore, serum T increased significantly in response to GnRH when the patients were hyperthyroid (T incremental area: 162 ± 51 p < 0.02), but failed to do so when they were euthyroid (T incremental area: 92 ± 53, NS). These results imply that chronic thyroid hormone excess makes the pituitary gonadotrophs ‘hypersensitive’ to exogenous GnRH. This may in turn explain why human Ley dig cells respond more powerful to exogenous GnRH in thyrotoxic patients than in euthyroid subjects.

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Section: Discussionsupporting

confidence: 83%

Section: Introductionmentioning

confidence: 99%

Hypothalamic-Pituitary-Testicular Axis in Patients with Hyperthyroidism

Röjdmark¹,

Berg

Källner³

1988

Horm Res

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“…the same blood sampling procedure without 48 h of fasting) there was no decrease in repro ductive hormone secretion. These results confirm and extend the report by Rojdmark [25] that normal men fasted for 56 h have a significant decrease in mean LH and testosterone concentrations. These findings, thus, further support the hypothesis that signal(s) which even tually cause complete suppression of reproductive axis activity during chronic undernutrition are present in the early stages of undernutrition and are beginning to slow the central drive to the reproductive axis.…”

Section: Effects Of Mild Undernutrition On Reproductive Functionsupporting

confidence: 92%

Metabolic Cues for the Onset of Puberty

Cameron¹

1991

Horm Res

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The hypothesis that the timing of puberty is at least in part stimulated by some ‘metabolic signal’ that tells the central control system of the reproductive axis that the body is becoming large enough, and that there are enough metabolic fuel stores, to support reproductive function has received considerable attention over the past several decades. However, direct experimental support for the hypothesis that mild metabolic changes, such as those that occur slowly during development, are actually capable of modulating reproductive function has been lacking. Our recent studies have shown that very brief periods of fasting in both male rhesus monkeys and men can modify the pulsatile release of LH and testosterone. In monkeys, missing a single meal is associated with a suppression of mean plasma LH, FSH and testosterone concentrations, and with a slowing of the frequency of pulsatile LH secretion. Current studies are aimed at identifying the specific metabolic signals which cause these changes. It is hoped that the results of these studies will eventually help to answer the question of whether normal metabolic changes occurring during development play a role in timing puberty onset.

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“…The observation that LH secretion was suppressed by short‐term fasting in male macaques but not in females during the follicular phase of the menstrual cycle was similar, although less dramatic, compared to the changes observed in humans (4–7, 19, 20). These studies suggest that, in both human and rhesus monkey females, LH secretion is protected against the inhibitory effect of short‐term food deprivation.…”

Section: Discussionmentioning

confidence: 66%

“…In both men (4–6) and male macaques (2, 3), the fasting induced suppression of LH and testosterone release is exerted at the hypothalamic level (7). The response is more rapid and profound in macaques than in humans (2, 3).…”

mentioning

confidence: 99%

Sex Differences in the Neuroendocrine Response to Short‐Term Fasting in Rhesus Macaques

Lado-Abeal

Robert-McComb

Qian

et al. 2005

J Neuroendocrinology

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When energy intake is restricted in mammals, there are neuroendocrine adjustments in the secretion of reproductive and metabolic hormones to reallocate energy for vital functions. In the present study, we investigated whether there were differences in the luteinising hormone (LH), growth hormone (GH) and cortisol responses to a 48-h fast in adult gonad-intact male and female rhesus macaques. In both male and female macaques, blood glucose levels were significantly lower in fasted than in control studies, and levels were higher in males than in females. Male rhesus monkeys had significantly lower (P < 0.01) mean serum LH levels after a 48-h fast than under fed conditions and this was attributable primarily to a decrease in the amount of LH released during each secretory episode. In fasted females, serum LH levels were significantly greater (P < 0.05) than during the fed conditions but no differences were found in pulse amplitude or in the number of pulses. Almost twice as many GH pulses were observed in both males and females during fasting but there was no difference in either mean serum GH levels or pulse amplitude between control and fasted studies. A typical diurnal profile in cortisol levels was observed in both sexes and both experimental conditions. Under control conditions, male macaques released less cortisol than females, and although fasting increased mean cortisol levels in both males and females, only the males shown a significant rise over levels observed in control studies. The changes in plasma LH and cortisol levels in fasted rhesus macaques are similar to those observed in humans and suggest that gonadotrophin and corticotrophin secretion are more resistant to short-term energy deprivation in female than in male primates.

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Influence of Short-Term Fasting on the Pituitary-Testicular Axis in Normal Men

Cited by 46 publications

References 14 publications

Hypothalamic-Pituitary-Testicular Axis in Patients with Hyperthyroidism

Hypothalamic-Pituitary-Testicular Axis in Patients with Hyperthyroidism

Metabolic Cues for the Onset of Puberty

Sex Differences in the Neuroendocrine Response to Short‐Term Fasting in Rhesus Macaques

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