Astressin B, a nonselective corticotropin-releasing hormone receptor antagonist, prevents the inhibitory effect of ghrelin on luteinizing hormone pulse frequency in the ovariectomized rhesus monkey

Abstract

Administration of ghrelin, a key peptide in the regulation of energy homeostasis, has been shown to decrease LH pulse frequency while concomitantly elevating cortisol levels. Because increased endogenous CRH release in stress is associated with an inhibition of reproductive function, we have tested here whether the pulsatile LH decrease after ghrelin may reflect an activated hypothalamic-pituitary-adrenal axis and be prevented by a CRH antagonist. After a 3-h baseline LH pulse frequency monitoring, five adult ovariectomized rhesus monkeys received a 5-h saline (protocol 1) or ghrelin (100-microg bolus followed by 100 microg/h, protocol 2) infusion. In protocols 3 and 4, animals were given astressin B, a nonspecific CRH receptor antagonist (0.45 mg/kg im) 90 min before ghrelin or saline infusion. Blood samples were taken every 15 min for LH measurements, whereas cortisol and GH were measured every 45 min. Mean LH pulse frequency during the 5-h ghrelin infusion was significantly lower than in all other treatments (P < 0.05) and when compared with the baseline period (P < 0.05). Pretreatment with astressin B prevented the decrease. Ghrelin stimulated cortisol and GH secretion, whereas astressin B pretreatment prevented the cortisol, but not the GH, release. Our data indicate that CRH release mediates the inhibitory effect of ghrelin on LH pulse frequency and suggest that the inhibitory impact of an insufficient energy balance on reproductive function may in part be mediated by the hypothalamic-pituitary-adrenal axis.

Figure 1

The decrease in LH pulse frequency induced by a 5-h ghrelin infusion (100-μg bolus followed by 100 μg/h) is prevented by astressin B (a CRH receptor antagonist) pretreatment. LH pulse frequency during ghrelin treatment was significantly lower (*, P < 0.05) than during all other treatments and during the 3-h baseline.

Figure 2

Upper graph, The increase in cortisol (percent over baseline) during ghrelin infusion is prevented by astressin B (*, P < 0.05). Overall mean baseline cortisol (100%) was 26.8 ± 1.0 μg/dl. Lower graph, The GH increase after ghrelin is not prevented by astressin B; responses in the two groups are not statistically different but are significantly higher than in the saline alone or saline plus astressin groups (*, P < 0.05). Overall mean baseline GH (100%) was 2.6 ± 0.71 ng/ml.

Figure 3

Increase in total ghrelin levels during ghrelin infusion.

Figure 4

Pulsatile LH release and cortisol concentrations in response to infusions of saline, ghrelin, ghrelin plus astressin B, and saline plus astressin B in an individual monkey (no. 89D361). The experiment was divided into two periods, a 3-h baseline period (i.e.13 samples) and a 5-h treatment period. A dotted vertical line denotes the time of the ghrelin bolus and the start of the 5-h ghrelin or saline infusions. Arrows indicate the time of injection of astressin B. Note the reversal of the decrease in LH pulse frequency that occurs during ghrelin infusion by the CRH receptor antagonist. *, Identified LH pulse.