Abstract
Total sleep deprivation (TSD) exerts strong modulatory effects on the secretory activity of endocrine systems that might be related to TSD-induced challenges of cerebral glucose metabolism. Here, we investigate whether TSD affects the course of male pituitary-gonadal and pituitary-thyroid axis related hormones during a subsequent 240-min hypoglycemic clamp. Ten healthy men were tested on 2 different conditions, TSD and 7-hour regular sleep. Circulating concentrations of total testosterone, prolactin (PRL), thyroid stimulating hormone (TSH), free triiodothyronine (fT3), and free thyroxin (fT4) were measured during baseline and a subsequent hypoglycemic clamp taking place in the morning. Basal, i.e. at 07∶00 am measured, concentrations of total testosterone (P = 0.05) and PRL (P<0.01) were lower while the values of TSH (P = 0.02), fT3 (P = 0.08), and fT4 (P = 0.04) were higher after TSD as compared to regular sleep. During the subsequent hypoglycemic clamp (all measurements from baseline to the end of the clamp analyzed) total testosterone concentrations in the regular sleep (P<0.01) but not in the TSD condition (P = 0.61) decreased, while PRL levels increased (P = 0.05) irrespectively of the experimental condition (P = 0.31). TSH concentrations decreased during hypoglycemia (P<0.01), with this decrease being more pronounced after TSD (P = 0.04). However, at the end of the hypoglycemic clamp concentrations all of the above mentioned hormones did not differ between the two sleep conditions. Our data indicate a profound influence of TSD on male pituitary-gonadal and pituitary-thyroid axis hormones characterized by reduced basal testosterone and PRL levels and increased TSH levels. However, since concentrations of these hormones measured at the end of the 240-min hypoglycemic clamp were not affected by TSD it can be speculated that the influence of TSD on the two endocrine axes is rather short lived or does not interact in an additive manner with their responses to hypoglycemia.
Highlights
The pituitary-thyroid and pituitary-gonadal axis are important parts of the human endocrine system
At 07:00 am, serum testosterone concentrations were significantly lower after Total sleep deprivation (TSD) than regular sleep (17.363.85 vs. 22.264.84 nmol/l; t(7) = 22.22, P = 0.05), while there were no significant differences in luteinizing hormone (LH) levels (3.2361.82 vs. 4.4962.50 IU/l; t(8) = 21.10, P = 0.30)
As previously observed [24,25], we found a reduction in circulating testosterone and thyroid stimulating hormone (TSH) levels during a 240-min hypoglycemic clamp starting in the morning which may reflect an inhibitory influence of hypoglycemia on the secretory activity of both of the two endocrine axes
Summary
The pituitary-thyroid and pituitary-gonadal axis are important parts of the human endocrine system Both of these two endocrine axes are crucially involved in the regulation of metabolism, body composition, growth, reproduction, immunity, and psychological well-being [1,2,3,4,5]. I.e. unbound and biological active, T3 and T4 (free T3 and free T4, i.e. fT3 and fT4, respectively) inhibit TSH secretion from the anterior pituitary gland directly or via inhibition of hypothalamic TSH-releasing hormone (TRH) release thereby establishing a negative feedback loop [6]. Within the pituitary-gonadal axis, hypothalamic secretion of the gonadotropin-releasing hormone (GnRH) stimulates the release of luteinizing hormone (LH) and follicle-stimulating hormone (FSH) from the pituitary to the blood stream. According to a negative feedback loop testosterone, in turn, inhibits the release of GnRH from the hypothalamus as well as of LH and FSH from the pituitary [7]. High concentrations of SHGB reduce of free fraction of circulating testosterone thereby reducing the biological activity of the hormone [8]
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