Variations in the number of pituitary LHRH receptors correlated with altered responsiveness to LHRH

Meidan, Rina; Aroya, Nurit Ben; Koch, Yitzhak

doi:10.1016/0024-3205(82)90266-1

Cited by 13 publications

(6 citation statements)

References 21 publications

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“…The fact that this difference in the direction of the response was limited to the effect of ovariectomy only, while in all other models pituitary gonadoliberin receptors changed in the same direction regardless of the tissue preparation used, suggested that this apparent discrepancy might be of biological interest. This conclusion was supported by the finding that replacement treatment with estradiol benzoate could reverse the decrease in pituitary gonadoliberin receptor levels caused by ovariectomy [5], indicating that this change is steroid-dependent.…”

supporting

confidence: 74%

“…Following ovariectomy pituitary responsiveness to gonadoliberin was reported to decrease [I 51 whereas gonadoliberin receptor density, as measured in pituitary homogenates, was reported to increase [10,11]. In contrast, we have recently reported that gonadoliberin binding activity measured in cells derived from ovariectomized rats is about half that found in metestrus-derived cells; this decline in the levels of gonadoliberin receptors was paralleled by a much lower responsiveness to gonadoliberin exhibited by the cells [5]. Thus the response of pituitary gonadoliberin receptors to ovariectomy appeared to differ qualitatively depending on the tissue preparation utilized for the receptor density measurement.…”

mentioning

confidence: 71%

“…Since the cell dispersion procedure which was utilized in our previous study [ 5 ] involved the use of three enzymes (collagenase, hyaluronidase and trypsin), the possibility that any one (or more) of them may selectively affect gonadoliberin receptor binding in ovariectomized rats was considered. As an initial test of this possibility, pituitary glands derived from metestrous and ovariectomized rats were dispersed by em- ,n gonadoliberin receptor binding activity in cells derived ,from metestrous and ovariectomized rats.…”

Section: Eifect Of Trypsin On Gonadoliberin Receptor Binding In Dispementioning

confidence: 99%

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A differential effect of trypsin on pituitary gonadotropin‐releasing hormone receptors from intact and ovariectomized rats

Liscovitch¹,

Ben-Aroya²,

Meidan³

et al. 1984

European Journal of Biochemistry

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The present report demonstrates that pituitary receptors for gonadotropin-releasing hormone generated following ovariectomy are susceptible to the action of trypsin while those present in intact metestrous females are not. The action of trypsin of gonadotropin-releasing hormone receptors in pituitary cells derived from ovariectomized rats was dependent on time and dose. Trypsin exerted a maximal effect of 40 -50 % reduction without causing full abolition of the binding activity, indicating that two populations of gonadotropin-releasing hormone receptors can be differentiated in pituitaries derived from ovariectomized rats : one which is sensitive to limited proteolysis by trypsin and another which is resistant to it. Scatchard analysis of gonadotropin-releasing hormone antagonist binding to homogenate of trypsin-treated hemipituitaries derived from ovariectomized rats, revealed that trypsin reduced receptor density while slightly increasing binding affinity. The in vitro responsiveness of hemipituitaries from ovariectomized rats to gonadotropin-releasing hormone and to K+-induced depolarization was reduced following trypsin treatment, while that of hemipituitaries derived from metestrous females was not affected or increased. Trypsin reduced the maximal response level by 30 -50 but did not modify the median effective dose of gonadotropin-releasing hormone (1 nM). The reduced gonadotropin-releasing hormone receptor density and the lower responsiveness caused by trypsin in pituitary tissue from ovariectomized rats are not due to a selective loss of gonadotrophs, as trypsin treatment did not affect the lutropin content of the glands. These findings indicate that two populations of gonadotropin-releasing hormone receptors can be distinguished on the basis of their susceptibility or resistance to limited proteolysis by trypsin and suggest that these two gonadotropin-releasing hormone receptor populations are reciprocally affected by ovariectomy.

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supporting

confidence: 74%

mentioning

confidence: 71%

Section: Eifect Of Trypsin On Gonadoliberin Receptor Binding In Dispementioning

confidence: 99%

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A differential effect of trypsin on pituitary gonadotropin‐releasing hormone receptors from intact and ovariectomized rats

Liscovitch¹,

Ben-Aroya²,

Meidan³

et al. 1984

European Journal of Biochemistry

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“…Similarly, other investigators (Meidan, Ben Aroya & Koch, 1982;Tang, Martellock & Horiuchi, 1982) have demonstrated a direct pitu¬ itary induction of GnRH receptors by oestradiol in dispersed pituitary cells either treated with oestradiol in vitro or obtained from ovariectomized rats shortly after oestradiol injection. Thus, in contrast to the effects of oestradiol on GnRH-induced gonado¬ trophin secretion, a rise in GnRH receptors requires the actual presence of circulating oestradiol in ad¬ dition to pituitary exposure to GnRH (Duncan et al 1986).…”

Section: Discussionmentioning

confidence: 93%

Regulation by oestradiol of serum levels of LH and FSH and pituitary levels of gonadotrophin-releasing hormone receptors after ovariectomy in the rat

Rosen

Jameel

Dee

et al. 1989

Journal of Endocrinology

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We studied cyclic and ovariectomized, oestradiol treated rats to investigate whether oestradiol concentrations before ovariectomy determine the dynamics of the rises in serum levels of LH and FSH, and in pituitary gonadotrophin-releasing hormone (GnRH) receptors after ovariectomy. In cyclic rats, ovariectomy on metoestrus (oestradiol = 44 pmol/l), but not at midnight of dioestrus (oestradiol = 254 pmol/l) was followed by a rise in GnRH receptors 40 h later. Randomly cyclic females were ovariectomized under ether anaesthesia and treated with s.c. oestradiol implants for 2 days to provide serum levels spanning the physiological range. Exposure to lower oestradiol concentrations (48 or 74 pmol/l) resulted in significant rises in levels of LH and FSH, and in GnRH receptors earlier than exposure to higher (148 or 309 pmol/l) oestradiol levels (2 compared with 4 days). GnRH given for 24 h after removal of the implant was unable to induce a rise in GnRH receptors in any group, while LH and FSH responses to GnRH were proportional to the pretreatment levels of oestradiol. This suggests that the concentration of oestradiol before ovariectomy determines the subsequent dynamics of LH and FSH and of GnRH receptors through actions at the hypothalamic and pituitary level.

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“…Binding of LHRH to specific plasma membrane receptors on the pituitary gonadotropes is the first step leading to gonadotropin secretion (Corm et al 1981). Radioligand receptor assays with pituitary homogenates (Pedroza et al 1977;Clayton et al 1980), membrane fractions (Spona 1973;Marian et al 1981), and cells in culture (Naor et al 1980;Meidan et al 1982;Loumaye et al 1982;Andries and Denef 1986;Koiter et al 1986), have been used extensively to characterize the LHRHreceptor interaction. Most of these studies were carried out with superactive analogs of LHRH modified at position 6 and 10.…”

Section: Introductionmentioning

confidence: 99%

Characterization of the receptor for gonadotropin-releasing hormone in the pituitary of the African catfish,Clarias gariepinus

et al. 1988

Fish Physiol Biochem

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Receptors for gonadotropin-releasing hormone (GnRH) were characterized using a radioligand prepared from a superactive analog of salmon GnRH (sGnRH), D-Arg(6)-Pro(9)-sGnRH-NEt (sGnRHa). Binding of(125)I-sGnRHa to catfish pituitary membrane fractions reached equilibrium after 2 h incubation at 4°C. Displacement experiments with several GnRH analogs as well as other peptides, demonstrated the specificity of(125)I-sGnRHa binding. Specific binding was enhanced in the presence of the cation chelator ethylene bis (oxyethylenenitrilo) tetra-acetic acid (EGTA), indicating an inhibitory effect of cations on GnRH-receptor binding. The binding of(125)I-sGnRHa to pituitary membranes was found to be saturable at radioligand concentrations of 5 nM and above. A Scatchard analysis of the saturation data suggested the presence of a single class of high-affinity binding sites (Ka=0.901±0.06×10(9)M(-1), Bmax=1678±150 fmol/mg protein). A comparative study on(125)I-sGnRHa binding to pituitary membrane fractions of male and female catfish, indicated that there were no differences in binding affinity and binding capacity between both sexes. The results demonstrate the presence of specific, saturable GnRH receptors in the African catfish pituitary.

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Variations in the number of pituitary LHRH receptors correlated with altered responsiveness to LHRH

Cited by 13 publications

References 21 publications

A differential effect of trypsin on pituitary gonadotropin‐releasing hormone receptors from intact and ovariectomized rats

A differential effect of trypsin on pituitary gonadotropin‐releasing hormone receptors from intact and ovariectomized rats

Regulation by oestradiol of serum levels of LH and FSH and pituitary levels of gonadotrophin-releasing hormone receptors after ovariectomy in the rat

Characterization of the receptor for gonadotropin-releasing hormone in the pituitary of the African catfish,Clarias gariepinus

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