Direct demonstration of intrinsic follicle-stimulating hormone receptor-binding activity in acid-treated equine luteinizing hormone

After dissociating equine gonadotropins as a function of time at pH 3, we examined them by radioligand assay and sodium dodecyl sulfate polyacrylamide gel electrophoresis under nondissociating conditions (low, 0.1% SDS). Equine follicle-stimulating hormone (FSH) rapidly lost its receptor-binding activity, and low SDS-polyacrylamide gels demonstrated dissociation into subunits. Maximum dissociation occurred after 20–30 min of pH 3 incubation. Equine luteinizing hormone (LH), however, retained most biologic activity and was largely intact after 72 h of pH 3 incubation. Dose-response curves of acid-treated equine LH and FSH and intact equine LH and FSH were compared in five types of radioligand receptor assays. LH and FSH receptor-binding activities of equine LH were unaffected by pH 3. Equine LH showed 19- and 32-times more activity in the rat testis FSH assay than it did in chicken or horse FSH assays, respectively, directly demonstrating the intrinsic FSH receptor-binding activity of equine LH and the relative lack of specificity for these hormone preparations of the rat FSH receptor. Acid-treated equine FSH lost 95% of its biologic activity in FSH assays. In LH assays, the slight (0.2%) activity of equine FSH was relatively unaffected by acid treatment, suggesting that contamination by equine LH accounts for this activity.     

Biological and immunological properties of zebra pituitary gonadotropins: comparison with horse and donkey gonadotropins

Previous studies from this laboratory have described the properties of purified luteinizing hormone (LH) and follicle-stimulating hormone (FSH) from horse and donkey anterior pituitary glands. The present study afforded the opportunity to further characterize these previously purified hormone preparations and to compare them with enriched gonadotropin fractions from zebra pituitary glands. Although a single LH and FSH fraction was usually obtained for each pool of pituitaries, two separate zebra LH and two donkey FSH preparations were generated. Purified hormone preparations from the horse were designated eLH and eFSH. Preparations zLH-A, zLH-B, and zFSH were obtained from zebra pituitaries, and fractions dLH, dFSH-A, and dFSH-B were prepared from donkey pituitary glands. These preparations were analyzed by LH and FSH radioimmunoassays (RIAs), radioreceptor assays (RRAs), LH bioassay, and chromatofocusing. Clear immunological differences were observed between equid gonadotropins. Homologous RIAs for eLH and eFSH did not cross-react similarly, or in a parallel fashion, with gonadotropins from the donkey and zebra. In contrast, RIAs capable of assessing LH or FSH in a wide number of species showed all equid gonadotropin preparations to have considerable activity and to produce parallel dilution curves. Relative to eLH (1.00), zLH-A was found to have higher LH bioactivity:LH RIA (2.50), LH RRA:LH RIA (1.42), and LH bioactivity: LH RRA (2.21) activity ratios. The dLH and zLH-B fractions only differed from eLH in LH RRA:LH RIA activity (0.69 and 0.62, respectively). Only LH from the horse possessed clear intrinsic FSH-receptor-binding activity.(ABSTRACT TRUNCATED AT 250 WORDS)     

Generation of hypophysiotropic activity in hypothalamic extracts in vitro.

The luteinizing hormone (LH) and follicle stimulating hormone (FSH) releasing activity, as well as the prolactin (PRL) release-inhibiting activity were measured in both neutral aqueous, and acid ethanolic extracts of rat hypothalami. LH and FSH-releasing activities were detectable only in the latter type of extract, whereas PRL release-inhibiting activity appeared in both. Neutral ultrafiltrates of the neutral extracts contained no gonadotropin releasing activity, however, acidification of the filtration medium induced its appearance. PRL release was inhibited by both neutral and acid filtrates. These results suggest that LH and FSH releasing factor(s) may be stored in the hypothalamus in an inactive form from which the active peptide is generated in vitro under acid conditions; however, this does not appear to be true for the component(s) responsible for the inhibition of PRL release.     

Chemical, biological and immunological properties of pituitary gonadotropins from the donkey (Equus asinus): comparison with the horse (Equus caballus)

Donkey gonadotropins (donkey luteinizing hormone, dLH; donkey follicle-stimulating hormone, dFSH) have been isolated in purified form from 191 donkey pituitaries using essentially the same procedures previously employed for the purification of equine gonadotropins. Chemically, dLH and dFSH were observed to be similar to equine LH (eLH) and FSH (eFSH) in fractionation behavior and glycoprotein nature. Two forms of the dFSH molecule were observed, as is the case for eFSH. Donkey LH had significantly less total carbohydrate (13.5%) and sialic acid (1.9%) than eLH (26.7% and 5.8%, respectively). Carbohydrate (17-21%) and sialic acid (2.4%) content of the two dFSH preparations closely resembled that of eFSH. A slightly higher tyrosine content in the donkey gonadotropins was noted in a comparison of amino acid compositions. Immunologically, in a heterologous FSH radioimmunoassay (RIA), dFSH preparations were equal to or twice as active as eFSH preparations. However, in homologous RIAs for equine chorionic gonadotropin (eCG), eFSH and eLH, both the dLH and dFSH preparations were considerably less active than the equine gonadotropins, and their inhibition curves were all nonparallel. Biologically, in the Steelman-Pohley assay both dFSH preparations were equipotent and as potent as eFSH (approximately 40 times NIH-FSH-S12). In the Sertoli cell assay for cAMP (FSH assay) and the Leydig cell assay for testosterone (LH assay), both dFSH and dLH were 2- or 6-fold more active than eFSH and eLH, respectively. In rat and equine testis FSH homologous radioreceptor assays, dFSH preparations were as active and up to 6-fold more active than eFSH. In contrast, dLH was 10-fold less active than eLH in the equine LH homologous radioreceptor assay. Unlike eLH, dLH was found to possess little intrinsic FSH activity or FSH inhibitory activity, and the small amount of FSH activity observed was most likely due to FSH contamination. Therefore, eLH behaves much like eCG (pregnant mare's serum gonadotropin, PMSG) which also possesses both LH and FSH activity. In contrast, dLH behaves more like donkey chorionic gonadotropin (dCG) which possesses only a low degree of FSH activity.     

Dependence of secretory responses to gonadotropin-releasing hormone on diacylglycerol metabolism. Studies with a diacylglycerol lipase inhibitor, RHC 80267

The role of diacylglycerol (DG) as a source of arachidonic acid during gonadotropin-releasing hormone (GnRH) stimulation of gonadotropin secretion was analyzed in primary cultures of rat anterior pituitary cells. An inhibitor of DG lipase (RHC 80267, RHC) caused dose-dependent blockade of GnRH-stimulated luteinizing hormone (LH) and follicle-stimulating hormone (FSH) secretion. The DG lipase inhibitor did not alter gonadotropin responses to arachidonic acid, and addition of arachidonic acid reversed its inhibition of GnRH-stimulated LH and FSH release. In [3H]arachidonic acid-prelabeled cells, incubation with RHC increased the accumulation of [3H]DG. These results suggest that DG lipase participates in GnRH action and that arachidonic acid mobilization from DG is involved in the mechanism of gonadotropin release. Gonadotropin responses to tetradecanoyl phorbol acetate and dioctanoyl glycerol were not altered by RHC, and the addition of these activators of protein kinase C (Ca2+- and phospholipid-dependent enzyme) did not prevent the inhibition of GnRH-induced gonadotropin release by RHC. Activation of phospholipase A2 by melittin increased LH and FSH secretion, whereas blockade of this enzyme by quinacrine reduced GnRH-stimulated hormone release. However, RHC did not diminish the gonadotropin response to melittin. The inhibitory actions of RHC and quinacrine were additive and were reversed by concomitant treatment with arachidonic acid. Ionomycin also increased LH and FSH release, and the gonadotropin responses to the ionophore were unaltered by RHC but were reduced by quinacrine. Incubation of cells in Ca2+-depleted (+/- [ethylenebis(oxyethylenenitrilo)]tetraacetic acid) medium reduced but did not abolish the LH and FSH releasing activity of GnRH. Treatment with RHC also reduced the gonadotropin responses to GnRH under Ca2+-depleted conditions. These observations indicate that RHC inhibition of GnRH action is not due to nonspecific actions on Ca2+ entry, protein kinase C activation and actions, nor phospholipase A2 enzyme activity. The results of this study provide further evidence for an extracellular Ca2+-independent mechanism of GnRH action, and suggest that GnRH causes mobilization of arachidonic acid by two distinct lipases, namely, phospholipase A2 and DG lipase, during stimulation of gonadotropin secretion.     

Steroidal modulation of in vitro gonadotropin secretion in prepubertal and adult male Siberian hamsters

The effects of exogenous gonadal steroids, testosterone (T), and 17beta-estradiol (E(2)) upon the hypothalamo-pituitary-gonadal axis were reported to be different between prepubertal and adult Siberian hamsters. Utilizing an in vitro static culture system, we investigated if age-related differences in steroid responsiveness occurs at the pituitary. Prepubertal (20 days old) or adult (140 days old) male Siberian hamsters were implanted with 1 mm silastic capsules containing undiluted T, E(2) or cholesterol (Ch, control). After 15 days, pituitaries were removed, incubated in vitro, and subjected to the following treatments: two baseline measurements, one challenge with 10ng/ml of D-Lys(6)-gonadotropin-releasing hormone (GnRH), and three post-challenge washes. Fractions were collected every 30 minutes and measured for follicle-stimulating hormone (FSH) and luteinizing hormone (LH). T and E(2 )reduced basal secretion of LH and FSH in juveniles but not adults. In juveniles, E(2) increased GnRH-induced FSH and LH secretion, while T augmented GnRH-induced FSH secretion but attenuated GnRH-induced LH secretion. Steroid treatment had no effect on GnRH-stimulated LH or FSH release in adults. The only effect of steroid hormones upon adult pituitaries was the more rapid return of gonadotropin secretion to baseline levels following a GnRH challenge. These data suggest both basal and GnRH-induced gonadotropin secretion are more sensitive to steroid treatment in juvenile hamsters than adults. Further, differential steroidal regulation of FSH and LH at the level of the pituitary in juveniles might be a mechanism for the change in sensitivity to the negative effects of steroid hormones that occurs during the pubertal transition.     

Purification of equine gonadotropins and comparative study of their acid-dissociation and receptor-binding specificity

A method for the simultaneous purification of luteinizing hormone (LH) and follicle-stimulating hormone (FSH) from equine pituitaries is briefly described. Different forms of each hormone were obtained. The total yield of LH was 24.2 mg·kg^?1 with a recovery of 22% and the yield of FSH was 26 mg·kg^?1 with a recovery of 34%. The specific activities of both hormones, measured in homologous equine radio-receptor assays are equal to or higher than those of the preparations described so far. In all species studied so far the acid-dissociation curves of LH and FSH are similar; this is an agreement with the view that the binding of the common α-subunit and the specific β-subunits involves polypeptide regions which are identical in both hormones. In contrast, the acid-dissociation pK_a of equine LH was found to be considerably lower (3.9) than that of equine FSH (5.8). The equine gonadotropins exhibit a much lower specificity with receptors of a porcine testicular fraction compared with an equine fraction. Equine LH exhibited a binding activity on FSH receptors from a porcine testicular fraction equal to 20% that of equine FSH instead of only 1% for an equine binding fraction. Similarly, all the equine FSH preparations tested exhibited a five-fold higher binding-activity on porcine LH receptors than on equine LH receptors. In the porcine system, pregnant mare serum gonadotropin behaved like equine LH towards LH and FSH receptors. In contrast, on equine binding fraction, pregnant mare serum gonadotropin was only 4% as active as equine LH and was devoid of FSH activity. All the data we have obtained are consistent with the ‘negative specificity’ model we proposed recently.     

Equine follicle-stimulating hormone. Purification, acid dissociation, and binding to equine testicular tissue

A simple method of purification of equine follicle-stimulating hormone is described by which two forms of the hormone are obtained. The acid dissociation of the most active preparation was studied and a pKa of 5.8 was determined at 37 degrees C. This value is 2 pH units higher than that observed for pregnant mare serum gonadotropin suggesting that the binding areas between subunits are not identical in the two hormones. We also describe an homologous radioreceptor assay of equine follicle-stimulating hormone which is highly specific for this hormone in contrast to the heterologous systems described so far. The analysis of the properties of equine gonadotropins in homologous and heterologous radioreceptor assays suggests that all glycoprotein hormones share a common high affinity binding site and that specificity of binding is due to binding prohibition sites preventing fixation of each hormone to the receptors of the other glycoprotein hormones. This specific hindering is defined as "negative specificity."     

Similar effects of inhibin and cycloheximide on gonadotropin release in superfused pituitary cell cultures

The actions of two inhibin preparations and cycloheximide on gonadotropin release were investigated in superfused pituitary cell cultures. Pituitary cells isolated from 18-day-old male rats were grown in Matrigel-coated superfusion chambers in chemically defined medium. After stationary culture for 4 days, the cell monolayers were superfused at a constant speed (0.25 ml/min) and were intermittently stimulated (6 min/h) with 10 nM gonadotropin-releasing hormone (GnRH). Groups of cultures were exposed to the test substances for varying time periods during stationary culture and/or during superfusion. Inhibitory effects of both inhibin preparations on the secretion of follicle-stimulating hormone (FSH) and luteinizing hormone (LH) in response to GnRH pulses were observed after 2 h of exposure and became maximal after about 6 h. Basal secretion of FSH between GnRH pulses was also suppressed, whereas the basal interpulse secretion of LH was not changed. When exposure to inhibin was discontinued, the secretion of both FSH and LH progressively increased and returned to control values by approximately 6 h. Cycloheximide (500 ng/ml) affected gonadotropin release with dynamics similar to those observed for the inhibin preparation. These data support the hypothesis that inhibition of gonadotropin synthesis may be an important step in the molecular mechanism of action by which inhibin regulates gonadotropin release.     

Differential actions of GnRH and rat hypothalamic extracts in release of hypophysial FSH and LH in vitro.

A study was made of the separate patterns of luteinizing hormone (LH) and follicle stimulating hormone (FSH) release from isolated rat pituitary tissue evoked by synthetic gonadotropin releasing hormone (GnRH) or female hypothalamic extracts (HE), respectively, in a continuous perifusion system. Under defined conditions, gonadotropin release from hemipituitaries was relatively stable and reproducible. Absolute levels of LH and FSH release evoked by HE in terms of their GnRH content were always greater than those following exposure to synthetic GnRH at varying doses. Synthetic GnRH released more FSH than LH. In contrast, the HE released slightly higher levels of LH than FSH. The data suggest that the female rat hypothalamus contains substances other than GnRH, capable of releasing both LH and FSH. It is possible that such unidentified components can modify the hypophysial action of GnRH, resulting in particular circumstances in a differential release of LH and FSH.     

Effect of tyrosine modification on the biological and immunological properties of equine chorionic gonadotropin

The tyrosine residues of equine chorionic gonadotropin have been nitrated with tetranitromethane and the resulting effects on the biological and immunological activities of the hormone studied. All of the tyrosine residues in equine chorionic gonadotropin were found to react with tetranitromethane when a 100-fold molar excess of reagent was used or with an 8.6 molar excess in the presence of 5 M guanidine hydrochloride. Complete nitration abolished the biological activities and decreased the immunological activity of the hormone. The nitration of one tyrosine residue resulted in the loss of 70% of the LH activity of equine chorionic gonadotropin; the FSH activity declined in a similar fashion. Maximal nitration resulted in the loss of about 50% of the immunological activity of the native hormone. Nitrated derivatives of equine chorionic gonadotropin were unable to compete with the native hormone in the rat Leydig cell assay for LH. The results indicate that the tyrosine residues of equine chorionic gonadotropin play an important role in the manifestation of both the FSH and LH activity of the hormone.     

Excitatory amino acid regulation of gonadotropin secretion: modulation by steroid hormones

Excitatory amino acids (EAAs) can potently modulate gonadotropin secretion in the male rat and monkey. In the present study we examined of EAAs on luteinizing hormone (LH) and follicle-stimulating hormone (FSH) in the female rat under low estrogen (ovariectomized) and high estrogen (proestrus) backgrounds. In ovariectomized immature female rats (NMDA) inhibited LH but not FSH secretion at 30 min post-injection. In contrast, NMDA potently stimulated LH but not FSH secretion when administered on proestrus to adult female rats. Both glutamate and kainate were also found to stimulate LH but not FSH secretion in estrogen-treated ovariectomized immature rats. This study suggests that EAA neurotransmission may be an important component in the expression of gonadotropin surges and that EAA effects appear to be subject to gonadal steroid regulation.     

Influence of gonadectomy on isoelectrofocusing profiles of pituitary gonadotropins in rhesus monkeys

Isoelectrofocusing (IEF) profiles of bioactive and immunoreactive follicle-stimulating hormone (FSH) and luteinizing hormone (LH) were studied in saline extracts of pituitary glands from rhesus monkeys. No sex differences were found in the IEF profiles of FSH and LH in intact or gonadectomized animals. Gonadectomy in both sexes resulted in a marked increase in the formation of relatively more acidic molecular species of FSH and LH in parallel with the production of an unusual strongly alkaline FSH species.     

Dissociation of copulation from ovulation in pregnant rabbits

Experiments were designed to determine why copulation in the pregnant rabbit does not terminate pregnancy while treatment with ovulatory doses of luteinizing hormone (LH) human chorionic gonadotropin (hCG) or luteinizing hormone-releasing hormone (LHRH) is known to do so. Pregnant rabbits (Day 8) were mated or were injected with hCG (25 IU/doe) or LHRH (1, 10 micrograms/kg). Serial blood samples were collected over the next 72 h and analyzed for content of LH, follicle-stimulating hormone (FSH) and progesterone. At sacrifice, uteri and ovaries from these animals were examined for viability of the embryos and for signs of recent ovulation. Injection of hCG or LHRH into pregnant animals led to ovulation and to patterns of LH, FSH and progesterone secretion like those which precede ovulation in estrous rabbits. However, mating the pregnant does did not lead to ovulation or to any changes in the circulating hormones. To investigate whether the elevated levels of progesterone during pregnancy were responsible for the dissociation of coitus from ovulation, nonpregnant rabbits were injected with progesterone (2 mg/kg) and then mated or injected with hCG or LHRH. In virtually every respect, the numbers of ovulations and the patterns of hormone secretion in the progesterone-treated, nonpregnant rabbits mimicked those observed in the 8-day pregnant animals; injection of hCG or LHRH caused ovulation and hormonal surges while hCG caused ovulation only. Mating did not lead to ovulation or any change in blood levels of LH, FSH or progesterone. Taken together, the results show that the elevated circulating levels of progesterone, characteristic of pregnancy, are probably responsible for the dissociation of copulation from gonadotropin release in pregnant rabbits.     

Quenching of the intrinsic fluorescence of liver alcohol dehydrogenase by the alkaline transition and by coenzyme binding

The fluorescence of alcohol dehydrogenase is quenched by the acid dissociation of some group on the protein having an apparent pKa of 9.6 at 25 degrees C. The pKa of this alkaline quenching transition is unchanged by the binding of trifluoroethanol or pyrazole to the enzyme or by the selective removal of the active site of Zn2+ ion. This indicates that the ionization of a zinc-bound water molecule is not responsible for the quenching. The binding of NAD+ to the enzyme causes a drop in protein fluorescence and an apparent shift in the alkaline quenching transition to lower pH. In the ternary complex formed with NAD+ and trifluoroethanol the alkaline transition is difficult to discern between pH 6 and pH 11. In the NAD+-pyrazole ternary complex, however, a small but noticeable fluorescence transition is observed with a pKa(app) approximately 9.5. We propose that the alkaline transition centered at pH 9.6 is not shifted to lower pH upon binding NAD+. Instead, the amplitude of the alkaline quenching effect is decreased to the point that it is difficult to detect when NAD+ is bound. We present a model that describes the dependence of the fluorescence of the protein on pH and NAD+ concentration in terms of two independently operating, dynamic quenching mechanisms. Our data and model cast serious doubt on the identification, made previously in the literature, between the alkaline quenching pKa and the pKa of the group whose ionization is coupled to NAD+ binding.(ABSTRACT TRUNCATED AT 250 WORDS)     

Channel Catfish Follicle-Stimulating Hormone and Luteinizing Hormone: Complementary DNA Cloning and Expression During Ovulation

Gonadotropins are important regulators of reproduction. To develop molecular resources for production of recombinant gonadotropins, we have cloned and sequenced complementary DNA encoding the channel catfish (Ictalurus punctatus) follicle-stimulating hormone (FSH) and luteinizing hormone (LH), which encode 132 and 140 amino acid proteins, respectively. The deduced amino acid sequences of the catfish FSH and LH are highly conserved with those cloned from other teleosts. Both the FSH and the LH were highly induced during ovulation after injection of carp pituitary extract. Taken together with our previous findings of enhanced expression of growth hormone and other pituitary hormones, this research suggests that a hormonal cocktail may be needed for more efficient manipulation of catfish reproduction. The availability of the catfish FSH and LH cDNAs provides the opportunity for production of immunologically or biologically active recombinant gonadotropins for the study of catfish reproductive physiology and the manipulation of artificial spawning for aquaculture. Received March 12, 2001; accepted June 27, 2001     

Cloning and sequence analysis of FSH and LH in the giant panda (Ailuropoda melanoleuca)

The giant panda (Ailuropoda melanoleuca) is an endangered species and indigenous to China. It has been proposed that it has a highly specialized reproductive pattern with low fecundity, but little is known about its basic reproductive biology at the molecular level. In this report the genes encoding gonadotropin subunits alpha, follicle-stimulating hormone (FSH) beta and luteinizing hormone (LH) beta of the giant panda were amplified for the first time by RT-PCR from pituitary total RNA, and were cloned, sequenced and analyzed. The results revealed that the open reading region (ORF) of gonadotropin subunits alpha, FSH beta and LH beta are 363, 390 and 426 bp long, respectively. They displayed a reasonably high degree (74-94, 85-93, 75-91%, for alpha, FSH beta and LH beta subunits, respectively) of identity when deduced amino acids were compared with homologous sequences from partial available mammals including human, cattle, sheep, pig, rat, mouse. Three distinct differences were found at the site of 59 aa of the alpha subunit and 55 aa, 68 aa of FSH beta subunit. Our results provide an insight into understanding the mechanism of reproduction regulation and genetic characteristics of giant panda which will make an actual contribution to its conservation. In addition they lay a foundation for a further study towards producing recombinant panda FSH and LH which can be used in artificial breeding aimed to increase its captive reproductive efficiency.     

Regulation of the pulsatile releases of luteinizing and follicle-stimulating hormones in ovariectomized hamsters

We have combined for modifications of common radioimmunoassay (RIA) techniques to increase the sensitivity of the gonadotropin assays by an order of magnitude compared with those generated according to the instructions provided by the National Pituitary Agency. The four modifications are: a) enzymatic radioiodination, b) purification of radiolabeled hormones by Sephadex and concanavalin A chromatography, c) reduced first antibody concentration, and d) a prolonged incubation time. These methods increase the sensitivities of the RIAs and allow for the quantitation of luteinizing hormone (LH) and follicle-stimulating hormone (FSH) levels in small volumes of plasma. We have used these methods to measure the changes in pulse frequency and amplitude of LH and FSH in ovariectomized hamsters after a variety of neuroendocrine manipulations. Alterations in catecholaminergic neurotransmission affect the frequency and amplitude of LH but not FSH release, and suggest that the hypothalamic mechanisms responsible for LH releasing hormone (LHRH)-mediated LH release are distinct from those that regulate FSH secretion. Further, alterations in LHRH-pituitary interactions (elicited by injections of LHRH antisera or a potent LHRH agonist), suggest the existence of separate control mechanisms responsible for LH and FSH release at the level of the adenohypophysis. Combined, these studies provide further evidence for complex and separate neuroendocrine regulatory control over the secretion of each gonadotropin.     

Gonadotropin regulation of rat ovarian lysosomes: Existence of a hormone specific dual control mechanism

Gonadotropic hormones PMSG (15 IU/rat), FSH (3 g/rat), LH (9 g/rat) and hCG (3 g/rat) were shown to decrease the free cytosolic lysosomal enzymes during the acute phase of hormone action in rat ovaries. When isolated cells from such rats were analyzed for the cathepsin-D activity, the granulosa cells of the ovary showed a reduction in the free as well as in the total lysosomal enzyme activities in response to FSH/PMSG; the stromal and thecal compartment of the ovary showed a reduction only in the free activity in response to hCG/PMSG. The results suggest the presence of two distinct, target cell specific, mechanisms by which the lysosmal activity of the ovary is regulated by gonadotropins.Abbreviations PMSG pregnant mare serum gonadotropin - FSH follicle stimulating hormone - LH luteinizing hormone - hCG human chorionic gonadotropin - GC granulosa cells - S/T stromal and thecal cells     

Plasma gonadotropin patterns characterizing the development of polycystic ovaries in the estradiol valerate treated rat

Polycystic ovaries (PCO) develop in female rats within 4 weeks of an injection of estradiol valerate (EV). The final morphological transition from a noncystic to a cystic state occurs in the presence of estrous (control) mean serum gonadotropin concentrations, suggesting that gonadotropin patterns rather than mean concentrations are causal to PCO. We have examined plasma luteinizing hormone (LH) and follicle-stimulating hormone (FSH) patterns in female rats at estrus and on days 5, 11, 16, and 21 following EV treatment. Estrous animals displayed large amplitude LH pulses of short duration, interspersed among frequent, low amplitude pulses of similar duration, and infrequent, broad-based LH episodes. Following EV treatment, there was a progressive decline in the frequency and magnitude of the large amplitude LH pulses, such that by day 16, they ceased altogether. Conversely, the frequency of the low amplitude pulses increased such that the total pulse frequency remained constant. The onset of this pattern coincides with the wave of atresia that precedes the emergence of cystic follicles. The pulsatile plasma pattern of FSH seen at estrus remained unaltered at all time intervals examined after EV treatment. We conclude that there is a specific LH pattern responsible for the generation and maintenance of the PCO condition.