GnRH agonist versus GnRH antagonist in assisted reproduction cycles: oocyte morphology

BACKGROUND

The selection of developmentally competent human gametes may increase the efficiency of assisted reproduction. Spermatozoa and oocytes are usually assessed according to morphological criteria. Oocyte morphology can be affected by the age, genetic characteristics, and factors related to controlled ovarian stimulation. However, there is a lack of evidence in the literature concerning the effect of gonadotropin-releasing hormone (GnRH) analogues, either agonists or antagonists, on oocyte morphology. The aim of this randomized study was to investigate whether the prevalence of oocyte dysmorphism is influenced by the type of pituitary suppression used in ovarian stimulation.

METHODS

A total of 64 patients in the first intracytoplasmic sperm injection (ICSI) cycle were prospectively randomized to receive treatment with either a GnRH agonist with a long-term protocol (n: 32) or a GnRH antagonist with a multi-dose protocol (n: 32). Before being subjected to ICSI, the oocytes at metaphase II from both groups were morphologically analyzed under an inverted light microscope at 400x magnification. The oocytes were classified as follows: normal or with cytoplasmic dysmorphism, extracytoplasmic dysmorphism, or both. The number of dysmorphic oocytes per total number of oocytes was analyzed.

RESULTS

Out of a total of 681 oocytes, 189 (27.8%) were morphologically normal, 220 (32.3%) showed cytoplasmic dysmorphism, 124 (18.2%) showed extracytoplasmic alterations, and 148 (21.7%) exhibited both types of dysmorphism. No significant difference in oocyte dysmorphism was observed between the agonist- and antagonist-treated groups (P>0.05). Analysis for each dysmorphism revealed that the most common conditions were alterations in polar body shape (31.3%) and the presence of diffuse cytoplasmic granulations (22.8%), refractile bodies (18.5%) and central cytoplasmic granulations (13.6%). There was no significant difference among individual oocyte dysmorphisms in the agonist- and antagonist-treated groups (P>0.05).

CONCLUSIONS

Our randomized data indicate that in terms of the quality of oocyte morphology, there is no difference between the antagonist multi-dose protocol and the long-term agonist protocol. If a GnRH analogue used for pituitary suppression in IVF cycles influences the prevalence of oocyte dysmorphisms, there does not appear to be a difference between the use of an agonist as opposed to an antagonist.

Leydig cells express follicle-stimulating hormone receptors in African catfish

This report aimed to establish, using African catfish, Clarias gariepinus, as model species, a basis for understanding a well-known, although not yet clarified, feature of male fish reproductive physiology: the strong steroidogenic activity of FSHs. Assays with gonadotropin receptor-expressing cell lines showed that FSH activated its cognate receptor (FSHR) with an at least 1000-fold lower EC50 than when challenging the LH receptor (LHR), whereas LH stimulated both receptors with similar EC50s. In androgen release bioassays, FSH elicited a significant response at lower concentrations than those required to cross-activate of the LHR, indicating that FSH stimulated steroid release via FSHR-dependent mechanisms. LHR/FSHR-mediated stimulation of androgen release was completely abolished by H-89, a specific protein kinase A inhibitor, pointing to the cAMP/protein kinase A pathway as the main route for both LH- and FSH-stimulated steroid release. Localization studies showed that intratubular Sertoli cells express FSHR mRNA, whereas, as reported for the first time in a vertebrate, catfish Leydig cells express both LHR and FSHR mRNA. Testicular FSHR and LHR mRNA expression increased gradually during pubertal development. FSHR, but not LHR, transcript levels continued to rise between completion of the first wave of spermatogenesis at about 7 months and full maturity at about 12 months of age, which was associated with a previously recorded approximately 3-fold increase in the steroid production capacity per unit testis weight. Taken together, our data strongly suggest that the steroidogenic potency of FSH can be explained by its direct trophic action on FSHR-expressing Leydig cells.

Intracellular calcium mobilization in response to the activation of human wild-type and chimeric gonadotropin receptors

It is well established that LH action is mediated primarily by adenylate cyclase/cAMP. However, the role of inositol phosphate/calcium in LH signaling is less well established. We examined the effects of gonadotropins in primary culture human granulosa-lutein cells and in HEK293 cells transiently transfected with human wild-type or chimeric gonadotropin receptors. The intracellular free calcium concentration was measured using fura-2 microspectrofluorometric techniques. Human (h) LH (2-4 microg/ml) and CG (10 IU/ml) consistently evoked oscillatory calcium signals in HEK293 cells transfected with hLH receptor, whereas hFSH (2-4 microg/ml) failed to elicit any response. Conversely, both hLH and hFSH failed to elicit a calcium response from HEK293 cells transfected with hFSHR, indicating the specificity of the response to the LH receptor. Pretreatment of transfected HEK293 cells with pertussis toxin (100 ng/ml) attenuated all gonadotropin-evoked calcium mobilization. Studies with chimeric LH receptor showed that the sequence of the long extracellular portion of the receptor was not critical for stimulation of PLC activity, but maintained agonist binding specificity. The C-terminal sequence of the receptor was clearly important for the generation of the basal calcium oscillations, but the precise extent of the critical sequence has yet to be identified. Although various subdivisions of this region were capable of stimulating calcium transients, an intact carboxyl-terminal third of the receptor was required for normal and sustained intracellular calcium signaling. Our study unequivocally shows that the hLH receptor is coupled to the inositol phosphate/calcium signaling pathway via a pertussis toxin-sensitive G protein-coupled receptor.

Endocrine and reproductive responses of male and female cattle to agonists of gonadotrophin-releasing hormone

The pituitary response in cattle to treatment with GnRH agonist has two phases. In the acute phase secretion of LH is increased, while the chronic phase is characterized by a downregulation of GnRH receptors and insensitivity of gonadotrophs to natural sequence GnRH. After long-term treatment with GnRH agonist, cattle do not have pulsatile secretion of LH but maintain basal LH. This is associated with reduced pituitary contents of LH, LH mRNA, FSH and FSH mRNA. Long-term treatment of bulls with GnRH agonist results in an increase in testicular LH receptors and high plasma testosterone. Heifers treated with a GnRH agonist from early in the oestrous cycle develop a larger corpus luteum and secrete more progesterone. Increased steroidogenesis is reflected in increased steroid acute regulatory (StAR) protein and steroidogenic enzymes in the testes and corpus luteum. GnRH agonists have potential as novel strategies for reproductive management in cattle. A GnRH agonist bioimplant was recently used to block the LH surge after FSH stimulation of follicle growth in heifers. Ovulation was induced by injection of LH, and heifers were inseminated relative to the LH injection. This GnRH agonist-LH protocol provides a model for studying the gonadotrophin requirements for follicular growth and oocyte maturation in cattle, and will enable controlled in vivo maturation of oocytes before recovery for in vitro procedures.

Effect of estradiol and progesterone on myometrial LH/hCG receptors in pigs

High affinity luteinizing hormone/human chorionic gonadotropin (LH/hCG) receptors have been identified in porcine, rabbit and rat uteri and immunocytochemically demonstrated in the human uterus. We have now assessed the effect of estradiol and progesterone on the capacity and affinity of LH/hCG binding sites in crude membrane fractions of porcine myometria. Nineteen cross-bred gilts were ovariectomized at 6-7 months of age. Five weeks later, the experiment was conducted and gilts were given estradiol benzoate 2 mg (N = 5), progesterone 50 mg (N = 4) and 2 mg of estradiol benzoate plus 50 mg of progesterone in 2 ml of corn oil (N = 6), im for five consecutive days. Controls (N = 4) received 2 ml of the vehicle. Gilts were hysterectomized 24 h after the last injection. Blood samples for assays of LH, estradiol and progesterone were collected 1 h before hysterectomy. The numbers and affinities of unoccupied LH/hCG binding sites were characterized in all samples of myometrium. The results indicate that treatment with estradiol benzoate increases (p less than 0.01) the number of LH/hCG binding sites compared with gilts receiving corn oil. Progesterone treatment caused elevation in the number of LH/hCG receptors (p less than 0.05), when compared with estradiol alone (2.9 +/- 0.3 vs 1.2 +/- 0.1 fmol/mg protein, respectively). Combined administration of estradiol and progesterone increased receptor capacity to 2.7 +/- 0.4. Steroid treatment did not alter the affinity (Ka) of [125I]hCG binding to receptors and it varied from 1.8 +/- 0.8 to 2.9 +/- 0.2 x 10(11) l/mol.(ABSTRACT TRUNCATED AT 250 WORDS)

Effect of 80 kDa protein of porcine follicular fluid on gonadotropin stimulated progesterone production in rat granulosa cells in vitro

We reported the presence of a 80 kDa polypeptide in porcine follicular fluid that inhibited the binding of 125I-radiolabelled hFSH as well as hCG to the rat ovarian gonadotropin receptors. In the present study, the biological activity of the receptor binding inhibitor is determined using an in vitro bioassay procedure. Granulosa cells isolated from PMSG primed immature rat ovaries respond to exogenously added gonadotropins in terms of progesterone production. Addition of fractions containing the gonadotropin receptor binding inhibitory activity inhibited progesterone production stimulated by the gonadotropins in a dose-dependent fashion. The receptor binding inhibitory activity was also capable of inhibiting progesterone production stimulated by PMSG, which has both FSH- and LH-like activities in rats. In contrast, progesterone production stimulated by dbcAMP was not inhibited by the receptor binding inhibitor. This result indicates that the site of action of the inhibitor is proximal to the formation of the cAMP. The above observations point out to a possible role for this factor in modulating gonadotropin activity at the ovarian level.

Different binding of stimulatory-type and blocking-type TSH receptor antibody with guinea-pig testis membrane

A receptor assay using [125I]bTSH-binding to guinea-pig testis membrane was developed. Unlabelled hCG and FSH inhibited [125I]bTSH binding. In patients with Graves' disease and in untreated hyperthyroid patients, almost all long-acting thyroid stimulators and thyroid-stimulating antibodies, respectively did not inhibit [125I]bTSH binding, which on the other hand was inhibited by thyroid stimulation blocking antibodies in patients with primary hypothyroidism. When the inhibitory effect on the binding of [125I]hCG and 125I-synthetic alpha-subunit peptide (alpha 26-46) of hCG to testis membrane was examined, bTSH resulted in a significant inhibition. However, all three kinds of TSH receptor antibodies had no inhibitory effect. This study demonstrated 1. interaction of alpha-subunit of TSH and hCG with the testicular receptor; 2. binding of thyroid stimulation-blocking antibody and lack of binding of thyroid-stimulating antibody to the testicular TSH receptor in spite of binding of these TSH receptor antibodies to the thyroidal TSH receptor, and 3. lack of binding of thyroid-stimulating antibody and thyroid stimulation-blocking antibody to the testicular gonadotropin receptor.

Follicular arrest during the midfollicular phase of the menstrual cycle: a gonadotropin-releasing hormone antagonist imposed follicular-follicular transition

The functional dependency of the dominant follicle on pulsatile gonadotropin inputs was evaluated by using a GnRH antagonist as a probe. Hormonal dynamics, particularly the relationship of FSH, estradiol, and inhibin, during and after the withdrawal of GnRH receptor blockade achieved by treatment with Nal-Glu GnRH antagonist (50 micrograms/kg, im) for 3 days in the midfollicular phase of the cycle (days 7-9) were ascertained. Daily blood samples were obtained for LH, FSH, estradiol (E2), progesterone, and immunoreactive inhibin (i-INH) measurements by RIA during 2 consecutive (control and treatment) cycles in 12 women. In 5 women, LH pulsatility was assessed by 10-min blood sampling for 12 h before, during, and after Nal-Glu treatment. The administration of Nal-Glu prolonged both follicular phase (14.0 +/- 0.5 vs. 19.7 +/- 0.8 days; P less than 0.0001) and total cycle length (28.1 +/- 0.5 vs. 34.1 +/- 1.2 days; P less than 0.0001). Gonadotropin suppression (50-60%) was achieved, as reflected by a marked decrease in mean LH levels (14.3 +/- 1.9 to 5.4 +/- 0.5; P less than 0.01) and LH pulse amplitude (5.5 +/- 0.7 to 2.4 +/- 0.3 IU/L; P less than 0.01) in response to Nal-Glu antagonist. The number of LH pulses was reduced (36%), but pulses remained discernible. Concentrations of FSH (10.8 +/- 1.4 to 5.9 +/- 0.4 IU/L; P less than 0.05), E2 (322.7 +/- 71.9 to 84.8 +/- 7.7 pmol/L; P less than 0.01) and i-INH (284.0 +/- 25.9 to 164.4 +/- 7.5 U/L; P less than 0.01) decreased concomitantly. Within 24-48 h of the last injection of Nal-Glu, all hormones had returned to pretreatment levels. This was followed by normal functional expression of follicular growth and maturation, as reflected by an increase in E2 and i-INH levels, timely ovulation, and normal luteal function. These findings indicate that an approximately 50% decline in gonadotropin support to the dominant follicle leads to functional arrest, but not demise, of the developing follicle(s) without triggering new folliculogenesis. The follicular apparatus retained its ability to reinitiate its original functionality once appropriate gonadotropin inputs were reinstated.

Effects of human chorionic gonadotrophin on contractile activity of steroid-primed pig myometrium in vitro

We examined the effects of (a) oestrogen and progesterone on concentrations of luteinizing hormone/human chorionic gonadotrophin (LH/hCG) receptors in uterine smooth muscle in vivo and (b) hCG on spontaneous myometrial contractions in vitro. Ovariectomized gilts received 2 ml corn oil (control; n = 5), 2 mg oestradiol benzoate (n = 6) or 20 mg progesterone (n = 5) for 5 days. Gilts were hysterectomized 8 h after the last injection and longitudinal sections of myometrium were incubated in modified Krebs' solution with 0 or 10 i.u. of hCG (n = 10/gilt) for 4 h at 37 degrees C in 95% O2:5% CO2. After incubation, myometrial sections were placed in a tissue chamber perfused with Krebs' solution and mechanical activity was recorded for 30 min. Cell membrane fractions were prepared from myometrial tissue not used for in-vitro studies and analysed for LH/hCG receptors. Treatment with oestradiol benzoate increased (P less than 0.01) the number of LH/hCG-binding sites compared with gilts receiving corn oil or progesterone. Incubation of myometrium with hCG reduced (P less than 0.01) the frequency and amplitude of spontaneous uterine contractions in gilts treated with oestradiol benzoate. In contrast, hCG had no effect (P greater than 0.05) on the pattern of myometrial contractions in gilts given corn oil or progesterone. These results indicate that oestradiol promotes the synthesis of LH/hCG receptors in pig myometrium and incubation of oestrogen-primed tissue with hCG has a quiescent effect on myometrial contractility.

Extracellular domain chimeras of the TSH and LH/CG receptors reveal the mid-region (amino acids 171-260) to play a vital role in high affinity TSH binding

We constructed a series of TSH-LH/CG receptor chimeras by homologous substitution of relatively small regions of the TSH receptor extracellular domain for the corresponding region of the extracellular domain of the LH/CG receptor. Constructs were stably expressed in Chinese hamster ovary cells. Of the five chimeric receptors, only TSH-LHR-14, which contains mid-region domain C (amino acid residues 171-260) of the extracellular component of the TSH receptor, exhibited TSH binding of relatively high affinity. Consistent with this TSH binding, chimera TSH-LHR-14 was the only one that demonstrated a functional response to TSH stimulation in terms of intracellular cAMP generation. These data indicate that domain C plays a vital role in TSH receptor function.

Effects of chronic ethanol diet on pituitary-testicular function of the rat

We studied the effects of a 6% ethanol liquid diet administered for 5 wk on the pituitary-gonadal function of adult male rats. Because ethanol is known to reduce body weight, we used sucrose-fed animals as controls. No significant differences in body, testis, or prostate weights were found between the rats exposed to ethanol and their sucrose-fed controls at the end of the 5-week treatment. Seminal vesicle weights decreased significantly (p less than 0.05) in the ethanol-treated group. Serum and testicular testosterone concentrations were significantly reduced in the ethanol-treated group, to 43.6% and 48.3% of levels in the sucrose-fed controls, respectively (p less than 0.05). Serum luteinizing hormone (LH) and follicle-stimulating hormone (FSH) levels of the ethanol-treated rats were 37.9% and 41.3%, respectively, of those of the sucrose-fed controls (p less than 0.01-0.05). The pituitary levels of these hormones were similar to those of controls, but the ratios of pituitary LH and FSH to their serum levels were clearly increased after ethanol exposure, to 492% and 206.1%, respectively (p less than 0.05). In contrast, pituitary prolactin (PRL) of the ethanol-treated rats was decreased to 40.2% (p less than 0.01) of sucrose-fed controls. Testicular content of LH receptors was significantly reduced (to 77.0% of controls; p less than 0.01), but content of FSH receptors was slightly increased by the ethanol diet (to 121.5% of sucrose-fed controls; p less than 0.05). No ethanol-associated changes were apparent in testicular PRL and gonadotropin-releasing hormone (GnRH) receptors or in pituitary GnRH receptors.(ABSTRACT TRUNCATED AT 250 WORDS)

Chloride channels mediate the response to gonadotropin-releasing hormone (GnRH) in Xenopus oocytes injected with rat anterior pituitary mRNA

Functional expression of receptors for GnRH was studied using Xenopus laevis oocytes injected with poly(A)+ mRNA extracted from rat anterior pituitary glands. Whole-cell currents were monitored using two-electrode voltage-clamp techniques. In oocytes which responded to both GnRH and TRH, the GnRH response showed a longer latency and time-to-peak than the TRH response. The response to GnRH or an agonist of GnRH receptors, buserelin (1 nM-1 microM) consisted of current fluctuations and occurred in a dose-dependent manner. This GnRH response was blocked by the Cl- channel blockers 9-AC (9-anthracene carboxylic acid; 1 mM), 4,4'-diisothiocyanastilbene-2,2'-disulfonic acid (0.1 mM), and diphenylamine-2-carboxylic acid (0.1 mM). The reversal potential for the GnRH-induced current fluctuations was -25 mV, comparable with the reported Cl- equilibrium potential in Xenopus oocytes, and its shift, when the external concentration of Cl- was changed, was reasonably described by the Nernst equation. These results indicate that the GnRH-induced response was dependent on the activity of Cl- channels. Ca2+ also plays a role, as the GnRH-induced response was reversibly suppressed by a calmodulin inhibitor, chlordiazepoxide (0.2 microM), and by a blocker of intracellular Ca2+ release, TMB-8 (8-(N.N-diethylamino) octyl-3,4,5-trimethoxybenzoate; 0.1-0.2 mM). It is concluded that GnRH (and TRH) receptors, expressed in Xenopus oocytes by injecting exogenous mRNA from rat anterior pituitary glands, operate via activation of Ca2+-dependent Cl- channels.

Incompletely processed LH molecules synthesized by rat gonadotrophs treated with inhibitors of oligosaccharide processing

Inhibitors of N-linked oligosaccharide processing are useful tools for studies on the biological function of the oligosaccharide structures in glycoprotein hormones. We have synthesized molecules of lutropin (LH) containing high-mannose- and hybrid-type oligosaccharides using rat gonadotroph-enriched primary cultures in the presence of castanospermine (a glucosidase I inhibitor) or swainsonine (a mannosidase II inhibitor), in order to compare the actions of these molecules with that of the hormone containing complex-type oligosaccharides in the activation of the receptor-adenylate cyclase system. Treatment of gonadotrophs with the above inhibitors caused an increase in the synthesis of highly basic LH molecules (pI 9.6-10.0), because addition of charged carbohydrate moieties to these molecules was prevented. Characterization of the oligosaccharide structure performed by enzymatic treatment (endoglycosidase H and neuraminidase) and the use of immobilized lectins (wheat germ agglutinin and Ricinus communis agglutinin-120) showed that these inhibitor-synthesized LH molecules contained high-mannose- and hybrid-type (asialo and sialylated) oligosaccharides. Their immunological properties were similar to that of complex-type oligosaccharide LH, but they had significantly higher receptor-binding ability in comparison with a sialylated complex-type oligosaccharide LH (about 12-fold) and an asialo complex-type oligosaccharide LH (about 3-fold). It was noted that the incompletely processed molecules were less potent than complex-type oligosaccharide LH in the activation of adenylate cyclase of Leydig cells, showing about 40-60% of the activity induced by the sialylated complex-type oligosaccharide molecule. The present data indicate that the inhibition of terminal processing of N-linked oligosaccharides by castanospermine and swainsonine impairs the full hormonal function of rat LH.

Tumor necrosis factor-alpha inhibits follicle-stimulating hormone-induced differentiation in cultured rat granulosa cells

We have investigated the effects of TNF-alpha on FSH-induced LH receptor expression, cAMP and progesterone production in cultured rat granulosa cells. TNF-alpha (0.5-100 ng/ml) inhibits the stimulating action of FSH on LH receptor formation in a dose-dependent manner with an IC50 of 1 ng/ml and an almost complete suppression of LH receptor induction for 50-100 ng/ml TNF-alpha. The inhibitory effect of TNF-alpha is not due to variations in cell number or viability but rather to a reduction of the LH receptor content per cell with no change in binding affinity (KD = 0.8 x 10(-10)M). TNF-alpha also inhibits the FSH-induced cAMP production but at a lower extent, with a maximum reduction of 60% for 100 ng/ml TNF-alpha. Moreover, TNF-alpha impairs the LH receptor formation induced by forskolin, cholera toxin or 8-Bromo-cAMP, indicating that the cytokine also acts at a step distal to FSH receptor and to cAMP formation. Finally, TNF-alpha decreases dramatically the progesterone synthesis that is stimulated by FSH, with a reduction to undetectable levels on and after 10 ng/ml TNF-alpha. These results suggest that TNF-alpha may drastically reduce the capacity of granulosa cells to differentiate upon FSH stimulation and to respond to LH during the physiological ovarian follicular maturation. Such anti-gonadotropic action of TNF-alpha on granulosa cell differentiation may be also relevant to the alteration of ovarian function during physiopathological processes like inflammatory or infection diseases.

Specific and weight loss-associated effects of one-week exposure to ethanol on pituitary-gonadal function of male rats

We studied the effects of one-week ethanol exposure (2.2 g/kg twice daily) on pituitary-gonadal functions of male rats. Because ethanol decreases the food-intake of the animals, diet-restricted rats were used as controls. Testicular LH and PRL receptors of ethanol-treated rats were significantly (P less than 0.05-0.01) reduced in comparison with weight-matched controls. In contrast, testicular GnRH receptors of the ethanol group were increased (P less than 0.05). Testicular FSH binding, pituitary GnRH-receptors, and serum gonadotropins and testosterone were not affected by ethanol. The present results demonstrate a specific effect of ethanol on testicular LH and PRL receptors which, unlike some other endocrine changes during ethanol exposure, is not due to a concomitant weight loss. In addition, the results suggest a concurrent change in the putative testicular GnRH receptor associated paracrine regulation, as implied by increased testicular GnRH binding upon ethanol exposure.

Effect of prenatal and neonatal exposure to lead on gonadotropin receptors and steroidogenesis in rat ovaries

Sprague-Dawley rats were treated with lead chloride (20 or 200 ppm) or sodium chloride (controls) in their drinking water, either prior to pregnancy or during pregnancy and lactation, and female offspring were examined at weaning (21 d) or at 150 d. Other female rats were treated from d 21 to 35. Tissue (blood, kidney, bone) lead levels, body, ovary, and uterus weights, ovarian steroidogenesis, and gonadotropin (luteinizing hormone and follicle-stimulating hormone) levels, and gonadotropin-receptor binding were determined. Prenatal and/or postnatal exposure to lead at these levels (20 and 200 ppm) did not affect tissue weights but did cause a significant decrease in gonadotropin-receptor binding in the prepubertal, pubertal and adult females. Conversion of progesterone to androstenedione and dihydrotestosterone was significantly decreased in 21-d-old rats; in 150-d-old females, the prenatal and/or postnatal exposure to lead resulted in significantly increased conversion to the 5-alpha-reduced steroids, normally high during puberty. The results demonstrate that lead exposure prior to mating may affect gonadotropin-receptor binding in the offspring and that lead exposure (in utero, via mother's milk, or post weaning) may significantly alter steroid production and gonadotropin binding in ovaries of the prepubertal, pubertal, and adult female.

Characteristics of prolactin-modulated LH induction of LH/hCG receptors. Transient inhibition of receptor induction following prolactin exposure

The temporal relationship between exposure to prolactin (PRL) and luteinizing hormone (LH) induction of LH receptors was investigated in hypophysectomized adult male rats. Testicular homogenate membrane preparations were incubated with [125I]hCG for analysis of LH/hCG binding. Seven days after hypophysectomy, the rats were injected with 100 micrograms/day of PRL for another 7 days and then given a single 10-micrograms dose of LH at 2, 4, 6, 12, 24, or 36 hours after the last PRL injection. The priming effect of PRL on LH induction of receptors was not observed if LH was administered 2 to 12 hours from the last PRL injection. However, after this inhibitory period, injections of LH to PRL-primed rats resulted in induction of LH receptors and the effect persisted for 36 hours. This study supports previous reports demonstrating a unique dependence upon PRL for LH up-regulation of the LH receptor and characterizes the brief refractory period following exposure to PRL.

Effects of cycloheximide during the periovulatory period on ovarian follicular FSH, hCG, and prolactin receptors and on follicular maturation in the hamster

Hamsters were injected sc at 1400 hr on proestrus with either 4 mg cycloheximide (which blocks ovulation but only transiently affects ovarian protein synthesis) or saline and killed at 2-hr intervals until 0400 hr on estrus. After cycloheximide, the first surge of FSH (at 1600 hr) was half the normal value and the second surge of FSH (beginning at 2200 hr) was eliminated. Control follicles at 1400 hr had approximately the same number of FSH and hCG receptors with about one-third as many PRL receptors. Down regulation of FSH and hCG receptors for control follicles occurred by 2400 hr while PRL receptors dropped abruptly 4 hr earlier. Compared to the 1400-hr control values, the maximal loss of FSH, LH, and PRL receptors was 40, 45, and 85%, respectively. Although cycloheximide tended to slightly delay the loss of FSH receptors at 2000-2200 hr it did not prevent the ultimate fall in FSH and hCG receptors; the loss of PRL receptors was accelerated by 4 hr. Cycloheximide prevented or delayed follicular growth, resumption of meiosis, and cumulus expansion. The altered proestrous profile of steroids after cycloheximide (prolonged follicular estradiol and reduced progesterone) is therefore not associated with drastic alterations in the number of FSH and hCG binding sites. On the other hand, PRL receptors represent fast turnover protein(s).

Antibody binding to the beta-subunit of deglycosylated chorionic gonadotropin converts the antagonist to an agonist

The murine Leydig tumor cell line, MLTC-1, has a gonadotropin-responsive adenylate cyclase system. Binding of human chorionic gonadotropin (hCG) stimulates the accumulation of cyclic AMP in these cells. Chemically deglycosylated hCG (DG-hCG) is an antagonist that binds with high affinity to the gonadotropin receptor, but fails to stimulate adenylate cyclase. This antagonism can be reversed if the binding of DG-hCG is followed by treatment of the DG-hCG-receptor complex with antibodies against hCG. Polyclonal antibodies against DG-hCG were raised in rabbits. These antibodies were strongly cross-reactive with hCG, bound to both the alpha- and beta-subunits of hCG and DG-hCG, and reversed the antagonism of DG-hCG. The antiserum was divided into two fractions by affinity chromatography on hCG-Sepharose. The fraction that was not retained reacted only with DG-hCG (DG-hCG antibodies) and, on Western blots, bound to both the alpha- and beta-subunits of DG-hCG. DG-hCG antibodies did not reverse the antagonism of DG-hCG. However, using 125I-protein A, we were able to detect binding of these antibodies to the cell surface DG-hCG-receptor complex. The fraction of antibodies retained by the affinity column reacted with both DG-hCG and hCG (DG-hCG/hCG antibodies). On Western blots, DG-hCG/hCG antibodies bound to the beta-subunit, but only weakly to the alpha-subunit of both hCG and DG-hCG. These antibodies also bound to the cell surface DG-hCG-receptor complex. In addition, DG-hCG/hCG antibodies were able reverse the antagonism of DG-hCG. Reversal of DG-hCG antagonism by the whole antiserum was blocked by the beta- but not the alpha-subunit of hCG. Polyclonal antiserum against the beta- but not the alpha-subunit of hCG reversed the antagonism of DG-hCG. From these results, we conclude that antibody binding to specific determinants common to both native and deglycosylated beta-subunit reverses the antagonism of DG-hCG. In addition, antibodies directed against unique determinants on the deglycosylated beta-subunit are not capable of reversing the antagonism of DG-hCG.

Effects of N-ethylmaleimide on gonadotropin and beta-adrenergic receptor function coupled to rabbit luteal adenylyl cyclase

The effects of the sulfhydryl-reactive alkylating agent N-ethylmaleimide (NEM) on the rabbit luteal adenylyl cyclase system were studied. Treatment of luteal membranes with NEM revealed three activities with differing sensitivities to NEM treatment. When luteal membranes were treated with NEM on ice for 30 min, it was found that NaF-stimulated adenylyl cyclase activity in cholate extracts of these membranes was most sensitive to this treatment. Half-maximal inhibition was obtained at 0.09 mM NEM. The activity of the stimulatory guanine nucleotide- and Mg-binding regulatory component (Ns), as assessed by functional reconstitution of NaF-stimulated adenylyl cyclase activity into membranes from the cyc-variant of the S49 mouse lymphoma, was less sensitive to this treatment, with half-maximal inhibition occurring at 0.69 mM NEM. In contrast, high affinity gonadotropin and beta-adrenergic binding, as assessed by competitive displacement of [125I]iodo-hCG by bovine LH and (-)3-[125I]iodocyanopindolol by isoproterenol, was unaffected by NEM concentrations up to 50 mM when membranes were treated on ice. However, when membranes were treated with NEM at 25 C for 30 min, high affinity gonadotropin and beta-adrenergic binding demonstrated similar sensitivities to NEM treatment, such that 50 mM NEM completely inhibited high affinity binding to both receptors. Under either of the conditions described above, neither the number of receptors nor the affinities of the labeled probes for their receptors were altered by NEM treatment. Thus, there appears to be at least three NEM-sensitive sites necessary for the functioning of the rabbit luteal adenylyl cyclase system, one associated with the catalytic component, one on Ns which interacts with the catalytic component, and one involved in high affinity agonist binding. Furthermore, it appears that formation of the high affinity binding state is regulated similarly for gonadotropin and beta-adrenergic receptors.