02515naa a2200217 a 450000100080000000500110000800800410001910000170006024501030007726000090018052019320018965000130212165000140213465000100214865000110215865300180216970000160218770000170220370000170222077300600223715288062002-11-06       1999    bl uuuu     u00u1 u    #d1 aDALEY, C. A.  aEffect of stress-like concentrations of cortisol on gonadotroph function in orchidectomized sheep.  c1999  aThe effect of stress-like concentrations of cortisol (C) on the feedback potency of estradiol (E,) was assessed using 32 orchidectomized sheep (wethers) assigned at random to 1 of 4 treatment groups in a 2 x 2 factorial design. Wethers received C (3.6 mg/50 kg per hour; groups 2 and 4) or a comparable volume of C delivery vehicle (groups 1 and 3) as a continuous infusion for 7 days. During the final 48 h of infusion, wethers received E2 (0.3 ug/50 kg/h; groups 3 and 4) or E2 delivery vehicle (groups 1 and 2). The pattern of LH secretion was assessed during a 4 h period of intensive blood collection beginning 44 h after initiation of E2 infusion. Gonadotroph responsiveness (LH secretion induced by GnRH challenge [500 ng, i.v.]) was determined 48 h after E2 delivery was begun. Although lhe frequency of secretory episodes of LH was not affected (p &gt 0.05) by infusion of C or E2 alone, LH pulse frequency was significantly decreased in wethers receiving C and E2 in combination. In contrast, neither the magnitude of basal gonadotroph responsiveness nor the extent of E2-dependent augmentation of responsiveness was significantly affected by stress-like concentrations of C. In a second experiment, the effect of C on the magnitude of E2-induced in- crease in pituitary concentration of GnRH receptor and GnRH receptor mRNA was assessed using 32 additional wethers. Continuous infusion of E2 for 48 h increased (p &lt 0.05) tissue concentrations of GnRH receptor and GnRH receptor mRNA. Con- current delivery of C did not affect (p &gt 0.05) E2-induced in- crease in GnRH receptor mRNA but significantly reduced the magnitude of the E2-dependent increase in pituitary concentration of GnRH receptor. Collectively, these data indicate that stress-like concentrations of C enhance the negative feedback potency of E2 and reduce estrogen-dependent augmentation of the concentration of GnRH receptor in pituitary tissue.  acortisol  aHormônio  aOvino  aStress  aGonadotropina1 aSAKURAI, H.1 aADAMS, B. M.1 aADAMS, T. E.  tBiology of Reproductiongv. 60, n. 1, p. 158-163, 1999.