Distribution of luteinizing hormone-releasing hormone receptors in the rat ovary

The distribution of luteinizing hormone-releasing hormone (LHRH) receptors was studied in the adult rat ovary using autoradiography after injection of the stable LHRH agonist ¹²⁵I-labelled [D-Ser(TBU)⁶,des-Gly-NH₂¹⁰]LHRH ethylamide (Buserelin) and by radioreceptor assay using the same tracer. In intact cycling female rats, no differences in ovarian LHRH receptor levels could be observed between day diestrus I and day proestrus. Moreover, similar levels are observed in total ovarian homogenate, corpora lutea and the remaining ovarian tissue in adult animals treated with PMSG (pregnant mare's serum gonadotropins) and hCG (human chorionic gonadotropin). Radioautographic data show a comparable distribution of grains over theca interna and externa, granulosa and luteal cells. The present findings indicate the presence of LHRH receptors in both the interstitial and follicular cells throughout all stages of cellular differentiation.     

Activity of alkaline phosphatase in uterine flushings of dairy cows affected with ovarian cysts or endometritis

Both uterine horns of 14 dairy cows with ovarian follicular cysts, and four animals affected with purulent endometritis were flushed via catheter using 30 ml phosphate buffered saline, following evisceration at a local abattori. Activity in the flushing media of alkaline phosphatase (ALP) and aspartate aminotransferase (GOT) were examined. Ovaries were prepared for light microscopy. Amount and morphological integrity of luteinized tissue found on the ovaries were reflected by correspondent levels in ALP activity, which was higher in the media taken from the ipsilateral to the luteal tissue situated uterine horns (651 +/- 228 vs 244 +/- 62 u/l, n = 3). Only cows having relatively large amounts of luteal tissue on the cystic ovaries (as in luteinized follicular cysts) exhibited very high ALP activity in uterine flushings (2693 +/- 1348 u/l, n = 2). Results suggest the existence of local relationships between luteal tissue in the ovary and the ipsilateral uterine horn in cows with ovarian follicular cysts.     

Absence of specific luteinizing hormone-releasing hormone (LHRH) receptors in the ovaries of Djungarian hamsters (Phodopus sungorus)

High affinity binding sites for luteinizing hormone-releasing hormone (LHRH) were characterized in Djungarian hamsters. Scatchard analysis was used to demonstrate specific LHRH-binding in hamster and, serving as controls, rat pituitaries (dissociation constant, KD = 0.6 nM, binding capacity, BM = 2.5 +/- 0.7 fmol/mg tissue; KD = 0.6 nM, BM = 6.9 +/- 1.9 fmol/mg tissue, respectively). In contrast to results obtained with rat ovaries (KD = 0.9 nM, BM = 3.0 +/- 0.9 fmol/mg tissue), no specific LHRH-binding was detected in hamster ovaries. Thus, it seems that direct gonadal action of LHRH in the Djungarian hamster is not involved in ovarian regulation.     

Gonadotropin-releasing hormone binding inhibitors in the ovary

A protein present in ovaries and other tissues of many species competitively and reversibly inhibits high affinity binding of gonadotropin-releasing hormone (GnRH) to rat ovarian membranes, but this protein is not GnRH. This protein has been partially purified and characterized from bovine ovaries. The absence of GnRH binding inhibitory (GBI) activity in plasma and follicular fluid indicates that this protein may act in a localized manner within or near its site of production or release. The bovine ovarian GBI protein evokes antigonadotropic activity in ovarian cells from both the rat and the bovine. The biological effect of GBI may occur independently of interaction with high affinity binding sites for GnRH, since these are absent from the bovine ovary. Thus, the GBI protein may abrogate gonadotropin-dependent responses in ovarian cells by mechanisms separate from interaction with GnRH receptors. A complete characterization of the GBI protein and evaluation of its mechanism of action in ovarian and pituitary cells will dictate conclusions on the physiological importance of this protein.     

Follicle stimulating hormone secretion and compensatory ovarian hypertrophy in prepubertal ewes

A study was conducted to determine the effect of unilateral ovariectomy (ULO) on follicle stimulating hormone (FSH) secretion and compensatory ovarian hypertrophy in prepubertal ewes. Thirty-three ewe lambs were allotted according to age and weight to a control (C) or ULO group. In the C group, a sham ovariectomy was performed on day 0 and both ovaries were removed on day 7. In the ULO group, one ovary was removed on day 0 and the remaining ovary was removed on day 7. Blood samples were collected from the jugular vein via venipuncture at 0, 6, 12 and 24 hours after the time of sham surgery or ULO (day 0). Subsequent samples were collected daily until day 7, and all samples were assayed for FSH and LH. Unilateral ovariectomy increased (P<0.01) ovarian weight and follicular fluid weight; however, lyophilized ovarian weight was similar for both groups. Within the ULO group, removal of the ovary having the largest follicle(s) did not prevent an increase in ovarian weight or follicular fluid weight of the remaining ovary. Unilateral ovariectomy had no effect on the total number of follicles (1 to 6 mm) per ovary; however, the number of large (5 to 6 mm) follicles per ovary was increased (P<0.05) following ULO. By 12 hours after ULO there was a transient increase (P<0.05) in the circulating concentrations of FSH. Circulating concentrations of luteinizing hormone (LH) were either low or undetectable in these prepubertal ewes and no LH response was observed following ULO. These results indicate that compensatory ovarian hypertrophy in ULO prepubertal ewes is accompanied by a transient rise in circulating FSH concentrations.     

Receptors for luteinizing hormone and follicle-stimulating hormone in largest follicles of postpartum beef cows

Follicles collected from cows destined to enter relatively normal or short luteal phases if induced to ovulate were compared for numbers of receptors for luteinizing hormone (LH) in granulosal and thecal cells and for follicle-stimulating hormone (FSH) in granulosal cells. Eleven suckled beef cows received ear implants of 6 mg norgestomet for 9 days (expected normal luteal phase) and 11 served as controls (expected short luteal phase). At 48 h after implants were removed (average 34 days postpartum), the ovary containing the largest follicle was identified by transrectal ultrasound and removed. The largest follicle was dissected free of surrounding ovarian stroma and frozen in liquid nitrogen. Thecal and granulosal cells were isolated, and numbers of receptors for LH and FSH in granulosal cells and for LH in thecal cells were quantified. Concentrations of estradiol were measured in follicular fluid. Both granulosal and thecal cells from norgestomet-treated cows had greater numbers of receptors for LH than did those from control cows (p less than 0.01). Numbers of receptors for FSH in granulosal cells did not differ between treated and control cows. Follicles from norgestomet-treated cows were heavier (p less than 0.01) than follicles from control cows, mostly due to greater amounts of follicular fluid (p less than 0.01). Concentrations of estradiol were higher in follicular fluid from the treated cows (p less than 0.05). It is suggested that increases in numbers of follicular receptors for LH and secretion of estradiol are integral components of a sequence of events by which norgestomet prepares follicles to become fully functional corpora lutea.     

Proteolytic inactivation of luteinizing hormone-releasing hormone (LHRH) by the whole rat ovary in vitro

Using 3H-labeled luteinizing hormone-releasing hormone (LHRH) at low concentrations, the in vitro proteolytic inactivation of the peptide hormone by whole rat ovaries was studied and compared with that by the soluble and particulate rat ovarian fraction. Whole rat ovaries were found to express the three proteolytic activities that were, according to their properties, also observed in rat ovarian homogenates: (1) soluble intracellular activity which was released into the medium, (2) released activity of membrane-bound origin, and (3) firmly membrane-bound activity. It is suggested that in vivo LHRH is largely inactivated extracellularly at least by enzymes that are located in the plasma membrane although the membrane-bound activity comprises only about 1% of the whole LHRH-inactivating capacity of the ovary.     

Rat ovarian angiotensin II receptors. Characterization and coupling to estrogen secretion

Angiotensin II receptor agonist (125I-angiotensin II) and antagonist (125I-[Sar1,Ile8]angiotensin II) bind in a specific and saturable manner to rat ovarian membranes. Agonist and antagonist binding affinity (KD approximately 0.5 nM) and the number of sites estimated (Bmax approximately 60 fmol/mg of protein) were similar. Dissociation of receptor-bound agonist was more rapid than the dissociation of receptor-bound antagonist, and agonist, but not antagonist, dissociation from the receptor was accelerated by GTP gamma S. A 0-150 mM increase in Na+ produced a 27% increase in the KD of agonist binding. Antagonist binding was not modified by Na+. These studies suggest that both agonist and antagonist identify putative angiotensin II receptors in the ovary but that the properties of agonist and antagonist binding are distinct. Angiotensin II antagonist binding sites are present on the granulosa cell layer of rat ovarian follicles (Speth, R. C., Bumpus, F. M., and Husain, A. (1986) Eur. J. Pharmacol. 130, 351-352). To determine the role of angiotensin II in ovarian function, we examined angiotensin II receptors and function during the onset of puberty. High affinity and low capacity angiotensin II receptors were present in ovaries from immature rats. After pregnant mare's serum gonadotropin induced ovulation in immature rats, antagonist binding to total ovarian membranes increased over 3-fold. In vitro incubation of peripubertal ovaries with 1 microM angiotensin II produced a stimulation of estrogen, but not progesterone, secretion. This steroidogenic effect of angiotensin II was most pronounced in the luteal phase of the estrus cycle. These studies point toward the involvement of angiotensin II in the regulation of ovarian function, possibly through modulation of follicular estrogen levels.     

Pituitary and ovarian responses to luteinizing hormone releasing hormone in a rat with polycystic ovaries

Female rats injected with a single dose of 2 mg estradiol valerate (EV) develop anovulatory acyclicity characterized by persistent vaginal cornification and the formation of multiple large cystic follicles on the ovaries. In order to determine if these effects of EV are accompanied by changes in ovarian and/or pituitary function, the following studies were conducted. Ovarian androgen production was determined by the measurement at 4, 5 and 6 weeks after EV treatment of circulating dehydroepiandrosterone, androstenedione and testosterone. The capacity of the polycystic ovary to ovulate in response to luteinizing hormone releasing hormone (LHRH) stimulus was assessed. Ovarian histology was examined at the termination of the study (9 weeks after EV treatment). Pituitary function was assessed 9 weeks after the EV treatment by examining the acute changes in plasma luteinizing hormone (LH) concentration in response to a double pulse of LHRH. Plasma concentrations of the androgens were unchanged over the 3-week sampling period and were similar to those found in sesame-oil-treated normal cycling control rats. The ovaries from EV-treated animals were smaller than those of controls and the cystic follicles exhibited marked thecal hypertrophy and attenuation of the granulosa cell layer. The basal plasma LH concentration at 9 weeks after EV treatment were significantly lower than in proestrus controls and plasma concentrations of LH elicited by LHRH pulses was significantly lower than in controls. The relative increase in plasma LH following the LHRH stimulus was, however, greater in the EV-treated animals than in controls. In spite of the diminished LH surge elicited in response to LHRH, the EV-treated animals ovulated as indicated by the presence of fresh corpora lutea on the ovaries. These results indicate that androgens are not responsible for the polycystic ovarian condition in this system and that the polycystic ovary is capable of ovulatory function when appropriately stimulated.     

Localization of the renin-angiotensin system in the bovine ovary: cyclic variation of the angiotensin II receptor expression.

Angiotensin (Ang) II may modulate reproductive function in the bovine ovary. Therefore, expression and localization of a local ovarian renin-angiotensin system (RAS) were investigated by elucidating the influence of the estrus cycle, pregnancy, and the presence of follicular cysts. Receptor analysis and autoradiography were used to characterize and localize Ang II receptors. Cyclic variations in the density of ovarian Ang II receptors were found with a higher value in estrus than in diestrus. The density in ovaries with follicular cysts was in the same order of magnitude as in estrus. The Ang II receptor type 2 (AT(2)) dominated in all three groups. Autoradiography showed that the majority of antral follicles and follicular cysts had intense AT(2) receptor binding in the theca externa. Binding was less intense in the theca interna, whereas there was no binding in the granulosa layer. In the corpora lutea, the AT(2) receptor was dominant in the capsule and in connective tissue infoldings, whereas no binding was observed in the luteal tissue. The type 1 Ang II receptor (AT(1)) was dominant in the stroma and showed no cyclic changes. Angiotensin-converting enzyme (ACE) activity was detected in all aspirated follicular fluids and homogenates of ovarian tissue. Autoradiography showed that most of the ACE was localized on endothelial cells. Renin immunoreactivity was found in granulosa and thecal cells of antral follicles and in luteal cells. Furthermore, solitary cells in the stroma, presumably macrophages, displayed intense staining. Our finding of cyclic changes support the concept of an active and regulated RAS in the bovine ovary.     

Follicular development, steroidogenesis and ovulation within ovaries exposed in vitro to hormone levels which mimic those of the rat estrous cycle

In order to more clearly define the hormonal factors responsible for follicular growth, ovulation and steroidogenesis, a perifusion culture system was developed. This culture system was capable of exposing the ovaries to hormonal levels which mimic the 4-day estrous cycle of the rat. Using this culture system, ovaries were exposed to the in vivo levels of luteinizing hormone (LH), follicle-stimulating hormone (FSH), estradiol-17 beta and progesterone to within the mean +/- one standard deviation of the values reported by Butcher et al. (1974a). During the 4-day culture period, the diameter of the follicles gradually increased in a manner similar to that of cycling rats. After 4 days in vitro, the ovaries ovulated 4.3 +/- 0.6 oocytes/ovary as assessed by the presence of ruptured-partially luteinized follicles. This in vitro ovulation rate was not significantly different from the in vivo ovulation rate of 5.0 +/- 0.8 oocytes/ovary (P greater than 0.05). The pattern of follicular growth within cultured ovaries was similar to that of the cycling rat, although the number of small follicles recruited to grow was reduced. The steroid secretory patterns also were slightly different in the cultured ovaries. These data indicate that physiological ovarian responses which are similar to those of cycling rats can be induced within cultured ovaries. With further utilization of this culture technique, the precise role of gonadotropins, ovarian steroids and other hormonal agents can be examined in order to define specific ovarian functions which are controlled by each hormonal agent.     

Down-regulation of mt1 melatonin receptors in rat ovary following estrogen exposure.

In this study, we have demonstrated that 2-[125I]-iodomelatonin binds specifically to rat ovarian granulosa cell (GC) membranes with high affinity (KD=83 pM; Bmax=3.28 fmol/mg protein). Using immunoblot analysis and an anti-mt1 melatonin receptor antibody, we have also detected mt1 melatonin receptors in rat ovary. Because melatonin has been reported to alter the steroidogenic responses of ovarian tissues to gonadotropins, a physiological role for intra-ovarian melatonin may exist. Thus, in order to investigate a possible intra-ovarian role for melatonin, we have used both an in vivo and in vitro model of follicular development. Treatment of immature (day 21) female rats with estradiol (E; 0.2 mg/d x 3 d; subcutaneous) was used to induce follicular growth. Membranes from both untreated (U) and E-treated animals' ovaries contained high-affinity 2-[125I]-iodomelatonin (I-MEL) binding sites (Kd=83 and 23 pM, respectively). Estradiol treatment in vivo caused a significant decrease (P<0.05) in binding of 2-[125I]-iodomelatonin to ovarian membranes with untreated animals' ovaries having a Bmax=3.28 fmol/mg protein vs. estradiol-treated animals' ovaries having a Bmax=0.92 fmol/mg protein. In addition, following Estradiol treatment, mt1 melatonin receptors in rat ovary were down-regulated (approximately 95%) using immunoblot analysis. Granulosa cells isolated from E-treated rats were further matured in vitro with testosterone (T) and the pituitary gonadotropin follicle-stimulating hormone (FSH). Granulosa cells were cultured with either T (10 ng/ml) or FSH (5.71 ng ovine FSH-20/ml) alone, or both FSH and T for 48 h. There was no statistically significant specific binding of 2-[125I]-iodomelatonin to GC membranes cultured with T or FSH alone. However, following a 48-h exposure to FSH and T in vitro specific 2-[125I]-iodomelatonin binding occurred with total 2-[125I]-iodomelatonin binding =3.15 [corrected] fmol/mg protein. Therefore, the existence of hormonally-regulated expression of high-affinity melatonin binding sites suggests that melatonin may have an important intra-ovarian physiological role.     

Relationship between concentrations of immunoreactive insulin-like growth factor-I in follicular fluid and various biochemical markers of differentiation in bovine antral follicles

Three experiments were conducted to determine the relationship between concentrations of insulin-like growth factor-I (IGF-I) in ovarian follicular fluid and various biochemical markers of follicular differentiation in bovine follicles. In Experiment I, ovaries were removed on Days 7, 14, 28, 42, or 56 after parturition from a total of 21 cows. In Experiment II, ovaries of 31 cows were removed between Days 20 and 30 postpartum after 48 or 96 h of either saline (0.9% NaCl, 5 ml) or luteinizing hormone-releasing hormone (LHRH, 500 ng/5 ml saline) injections given every 2 h via jugular cannulae. In Experiment III, ovaries of six cows were removed 48-50 h after a 35-mg injection of prostaglandin F2 alpha during the midluteal phase of an estrous cycle. In Experiments I and II, all follicles greater than or equal to 8.0 mm in diameter were removed from each ovary (n = 33 and 46, respectively). In Experiment III, fluid from all follicles greater than 4 mm in diameter were removed individually (n = 10), and fluid from follicles 1-4 mm in diameter were pooled for each cow. Follicles for each experiment were further categorized as either estrogen-active (E-A, concentration of estradiol greater than progesterone in follicular fluid) or estrogen-inactive (E-I, concentration of progesterone greater than estradiol in follicular fluid). Measurements of immunoreactive IGF-I (i-IGF-I) were made after separating IGFs from their binding proteins with an acid-ethanol extraction.(ABSTRACT TRUNCATED AT 250 WORDS)     

Growth hormone receptors in ovary and liver during gametogenesis in female rainbow trout (Oncorhynchus mykiss).

Changes of growth hormone receptivity in the ovary during the reproductive cycle were studied in rainbow trout (Oncorhynchus mykiss). A method for characterizing growth hormone receptors in crude ovary homogenate was required for this. Binding of radiolabelled recombinant rainbow trout growth hormone (125I-labelled rtGH) to crude ovary preparation was dependent on ovarian tissue concentration. The sites were specific to growth hormone, with no affinity for prolactins and gonadotrophins. Similar high affinities for 125I-labelled rtGH were obtained with crude ovary (4.2 x 10(9) +/- 0.3 mol l-1) and crude liver preparations (4.9 x 10(9) +/- 0.1 mol l-1) at all stages of ovogenesis, and with ovarian membrane preparations (8.2 x 10(9) mol l-1) tested at the beginning of vitellogenesis. Ovarian growth hormone receptor concentration was highest during the early phases of follicular development (endogenous vitellogenesis: 315-310 fmol g-1 ovary) and decreased regularly during oocyte and follicular growth (exogenous vitellogenesis) to reach a minimal value at oocyte maturation (42 fmol g-1 ovary). In postovulated fish, binding was at a similar level (297 fmol g-1 ovary) to that found in endogenous vitellogenesis. Conversely, the absolute binding capacity of the whole ovary was low from immaturity to early exogenous vitellogenesis (0.1-0.6 pmol per pair of gonads), increased slowly during vitellogenesis and more markedly during rapid oocyte growth and at the time of final maturation (10.8 pmol per pair of gonads). In postovulated fish, the absolute binding capacity decreased partially (4.4 pmol per pair of gonads). Mean hepatic growth hormone receptor concentration did not vary with the reproductive stage for most of the cycle (3.0-4.5 pmol g-1 liver) except in endogenous vitellogenesis where significantly higher concentrations were observed (6.7 pmol g-1 liver). Individual ovarian growth hormone receptor concentrations were correlated with hepatic growth hormone receptor concentrations, indicating that they are regulated in a similar way. We conclude that growth hormone receptors are present in the ovary during the entire ovarian cycle in rainbow trout, probably mainly in somatic cells as indicated by the same concentration of binding sites in immature and in postovulated fish. Growth hormone is potentially important during oocyte recruitment in vitellogenesis and initiation of growth and during final follicular maturation.     

Effects of recombinant bovine somatotropin on luteinizing hormone and ovarian function in lactating dairy cows

Thirty-two lactating Holstein cows were assigned to 1 of 4 groups in a randomized block design using a 2 X 2 factorial arrangement of treatments. Recombinant bovine growth hormone (rbSt; 25 mg/day) or placebo was administered beginning at Day 35 or 70 postpartum. All cows began treatment approximately 3 days post-estrus. Blood samples were collected at least once daily for a 70-day period to determine the concentration of progesterone and the duration of the luteal and follicular phases. During estrous cycles 1 and 3, frequent blood samples were taken (every 10 min for 8 h) 24 and 60 h after the onset of luteal regression. These samples were assayed for luteinizing hormone (LH), and samples coincident with the second LH pulse detected were assayed for estradiol. Ultrasonography was used to determine the size of the largest ovarian follicle from Day 17 until ovulation in estrous cycles 1 and 3. Luteal life span, length of the follicular phase, and diameter of the largest follicle were not affected by treatment with rbSt. Administration of rbSt increased the concentration of progesterone in plasma during the first two luteal phases (p less than 0.01). Progesterone was elevated during the mid-luteal phase of cycle 3 in rbSt-treated cows that began treatment about Day 35 postpartum but not in cows that began treatment on Day 70 postpartum (Treatment X Stage X Day, p less than 0.01). During the first follicular phase studied, LH pulse frequency was higher (p = 0.06) in rbSt-treated cows than in cows receiving the placebo.(ABSTRACT TRUNCATED AT 250 WORDS)     

Hormonal regulation of LH receptor mRNA and expression in the rat ovary.

Agonist-induced changes in expression and mRNA levels of luteinizing hormone (LH) receptors were compared during stimulation of ovarian follicular maturation and luteinization by gonadotropic hormones. Three major species of LH receptor mRNA, 5.8, 2.6 and 2.3 kb, were present throughout differentiation and changed similarly, the 5.8 kb species being consistently more abundant than the smaller forms. The increased expression of plasma-membrane LH receptors in preovulatory follicles and luteinized ovaries and their homologous down-regulation during follicular and luteal desensitization were closely correlated with the steady-state receptor mRNA levels. The reappearance of LH receptors following desensitization during the luteal stage was preceded by an increase in mRNA levels. These studies have demonstrated that the expression of LH receptors during follicular maturation, ovulation and desensitization is related to the prevailing levels of receptor mRNA in the ovary.     

Some biological properties of human chorionic follicle stimulating hormone.

The biological properties of human chorionic FSH (hCFSH) for rat ovaries were investigated. Highly purified hCFSH had similar response to the ovarian augmentation test as bovine FSH and significantly enhanced 3H-thymidine uptake by granulosa cells and theca cells in the ovary of hypophysectomized rat. In contrast, highly purified hCG little responded to the ovarian augmentation test and had no effect on 3H-thymidine uptake by the ovary. These results indicate that hCFSH may promote the follicular growth of ovary resulting from granulosa cell proliferation and its enlargement. In addition, freshly harvested porcine granulosa cells were employed in an in vitro system to investigate specific binding of hCFSH to ovarian receptor. Radioiodinated hCFSH (125I-hCFSH) and hCG (125I-hCG) were respectively incubated with cell suspensions. Binding of these hormone preparations was proportional to the cell number and increased with the time of incubation through 120 minutes. The binding ability of 125I-hCFSH to the cells was greater than that of 125I-hCG. Increasing concentrations of unlabeled hCFSH in the incubation mixture progressively inhibited the uptake of 125I-hCFSH by granulosa cells. Unlabeled hCG was not able to compete with 125I-HCFSH binding. The similar phenomenon to inhibit the binding of 125I-hCG to the cells was also recognized in the presence of unlabeled hCG. These findings suggest that granulosa cell has at least two different types of receptor sites: one for hCFSH and the other for hCG.     

Expression of follicle stimulating hormone and luteinizing hormone receptors during follicular growth in the domestic cat ovary

In order to better understand the pituitary regulation of follicular growth in the domestic cat, follicle stimulating hormone (FSH) and luteinizing hormone (LH) receptors (R) were localized and quantified in relation to follicle diameter and atresia using in situ ligand binding on ovarian sections. Expression of FSHR was homogeneous and restricted to follicle granulosa cells from the early antral stage onwards, whereas expression of LHR was heterogeneous on theca cells of all follicles from the early antral stage onward, and homogeneous on granulosa cells of healthy follicles larger than 800 microm in diameter and in corpora lutea. LHR were also widely expressed as heterogeneous aggregates in the ovarian interstitial tissue. Atretic follicles exhibited significantly reduced levels of both FSHR and LHR on granulosa cells, compared with healthy follicles whatever the follicular diameter, whereas levels of LHR on theca cells were lower only for atretic follicles larger than 1,600 microm in diameter. In healthy follicles, levels of FSHR and LHR in all follicular compartments increased significantly with diameter. Although generally comparable to that observed in other mammals, the expression pattern of gonadotropin receptors in the cat ovary is characterized by an early acquisition of LHR on granulosa cells of growing follicles and islets of LH binding sites in the ovarian interstitial tissue.     

Gonadotropin-releasing hormone binding sites in ovaries of normal cycling and persistent-estrus rats

The gonadotropin-releasing hormone (GnRH) binding capacity in ovaries and pituitaries of normal cycling rats at different stages of the estrous cycle and in ovaries of persistent-estrus rats was measured using radioligand-receptor assay (RRA). Persistent estrus was induced either by neonatal administration of testosterone propionate (1.25 mg s.c.) on the second day of life or by a hypothalamic suprachiasmatic frontal cut made with Halász' knife. All animals were killed during the critical period (1400-1600 h), and GnRH receptor was assayed. GnRH receptor levels in both ovaries and pituitaries changed during the estrous cycle. The total number of ovarian GnRH binding sites was significantly higher in proestrus than in diestrus 1, the stage in which the lowest level was found. When binding sites were expressed in fmol/mg ovary, the highest level was observed in diestrus 2; however, no changes were observed during the estrous cycle when GnRH binding sites were expressed as fmol/mg protein. Changes noted were very similar to those demonstrated in pituitary GnRH receptors in our present and previous experiments. Higher levels of pituitary binding sites were found in diestrus 2 and proestrus than in estrus and diestrus 1. The changes in the GnRH receptor levels were more striking in the pituitary than in the ovaries. It appears that the total number of ovarian GnRH binding sites was not altered in either of the two persistent-estrus groups, but that their concentration was significantly higher (expressed in fmol/mg ovary or fmol/mg protein) than on any day during the estrous cycle.(ABSTRACT TRUNCATED AT 250 WORDS)     

Pituitary and ovarian luteinizing hormone releasing hormone receptors during the estrous cycle, pregnancy and lactation in the rat

Female Sprague-Dawley rats were decapitated at various stages of the estrous cycle, pregnancy, lactation and following ovariectomy. Anterior pituitary and ovarian tissues were collected and assayed to quantify luteinizing hormone releasing hormone (LHRH) receptors. No changes were noted in receptor affinity either between tissues or physiological stages studied. Pituitary LHRH receptor concentrations and content were greater (P less than 0.05) during diestrus II and proestrus than during estrus. Pituitary LHRH receptor concentrations and content during pregnancy were not different from those during estrus, however, a significant decrease was noted in pituitary LHRH receptor content and concentrations during lactation compared to estrus. Ovarian LHRH receptor content did not change with stage of reproduction (P less than 0.05). There was, however, a decrease (P less than 0.05) in ovarian LHRH receptor concentrations at Week 3 of pregnancy and Week 1 of lactation which was possibly due to the increase ovarian weight noted at both these physiological stages. There was no correlation (P less than 0.1) between ovarian and pituitary LHRH receptor numbers (r = 0.096). These findings suggest that the internal mechanisms which control changes in pituitary LHRH receptor numbers do not control ovarian LHRH receptor numbers.