Weight-bearing alters the expression of collagen types I and II, BMP 2/4 and osteocalcin in the early stages of distraction osteogenesis.

This study was performed to investigate the effect of loading on the biology of newly forming bone during limb lengthening. Unilateral 2.0 mm femoral lengthenings were performed in 20 male Sprague Dawley rats. Half (n = 10) of the animals were allowed to bear weight freely, while the other half were prevented from weight-bearing via an ipsilateral through-knee amputation. The animals in each group were sacrificed after one (n = 5) or four (n = 5) days of consolidation (post-operative days seven and 10, respectively). In situ hybridization for osteocalcin and collagen I, and antibody staining for collagen II and BMP 2/4 were used to evaluate the molecular influence of loading. There was more new bone in the distraction gap of the weight-bearing animals than there was in the non-weight-bearing animals. BMP 2/4 expression, and the messages for collagen I and osteocalcin, were more abundant in tissue from the weight-bearing animals; collagen II was higher in the non-weight-bearing animals. This suggests that early regenerate tissue is capable of responding to loading, and that weight-bearing appears to stimulate intramembranous ossification. These findings support the concept of early weight-bearing after limb lengthening.

Developmental changes in mullerian inhibiting substance in the cynomolgus monkey, Macaca fascicularis.

Mullerian inhibiting substance (MIS) is a glycoprotein hormone produced in Sertoli cells of the fetal and postnatal testis, and granulosa cells of the pubertal ovary. We examined MIS expression in a nonhuman primate, the cynomolgus macaque monkey (Macaca fascicularis), to define an animal model for studying MIS gene regulation. Changes in testicular MIS mRNA with age were assessed by in situ hybridization of prepubertal to adult testes, Northern analysis of pubertal and adult specimens, and determination of serum MIS concentrations from infancy to adulthood. We found that MIS expression was highest in the youngest animals and decreased progressively with increasing age. Serum MIS concentrations correlated inversely with increasing age (r = -0.74), body weight (r = -0.79), and testicular volume (r = -0.73), but not with testosterone levels (r = -0.35). The mean MIS concentrations +/- SEM for the four developmental age groups were 270.6 +/- 23.8 (infants), 195.5 +/- 18.5 (juveniles), 102.7 +/- 28.4 (peripubertals), and 51.6 +/- 7.1 (adults). This study confirms that nonhuman primate and human MIS are highly homologous and have similar developmental patterns. The normative data for serum MIS concentrations in cynomolgus monkeys at different ages and developmental stages will be invaluable for further work examining MIS regulation.

Interrelationship between the actions of testosterone and primate Sertoli cell inhibin in the control of gonadotropin secretion by cultured pituitary cells.

There is accumulating evidence that the differential regulation of LH and FSH secretion in the male is partly accomplished by the direct actions of testosterone (T) and inhibin on the pituitary. The present study was designed to examine the interaction between T and inhibin, in the presence and absence of GnRH, using dispersed pituitary cells in monolayer culture and cells perifused with pulses of GnRH from intact, 2-week castrated, and castrated T-replaced young adult male rats. The effect of partially purified inhibin from primate Sertoli cell culture medium (pSCI) to suppress basal FSH secretion was similar with pituitary cells from intact and castrated rats. T increased basal FSH secretion in the presence or absence of pSCI but did not alter the dose-dependent suppression of FSH by pSCI with cells from either intact or castrate rats. Castration increased basal FSH and LH secretion, whereas only basal FSH release was increased with cells from T-replaced castrates. T pretreatment increased the action of pSCI to suppress GnRH-stimulated FSH and LH release from perifused pituitary cells. These data indicate that T and inhibin exert opposite but independent effects on basal FSH release. The action of inhibin to suppress basal FSH secretion is not impaired by the absence of T and inhibin subsequent to castration. By contrast, the actions of T and inhibin to suppress GnRH-stimulated gonadotropin secretion are coordinated and interrelated.

Comparison of the effects of cycloheximide and inhibin on the gonadotropin subunit messenger ribonucleic acids.

Cycloheximide (CHX) has been shown to mimic the action of inhibin on gonadotropin secretion by pituitary cell cultures. We showed previously that suppression of FSH secretion by inhibin is associated with a rapid and profound suppression of FSH beta mRNA levels. The present study was designed to examine the mechanism of action of CHX and to determine whether inhibin's actions involve new proteins synthesis. Pituitary cell cultures were treated with control medium or medium containing inhibin, CHX, or inhibin plus CHX for 2 or 6 h. At 6 h, secretion of FSH was decreased by inhibin (72% of control), CHX (58% of control), and the combined inhibitors (56% of control). LH secretion was not significantly changed, while that of free alpha-subunit was reduced only by CHX (68% of control). Levels of FSH beta, LH beta, and alpha-subunit mRNAs were measured by Northern analysis. At 2 h inhibin decreased FSH beta mRNA to 49% of the control value. CHX alone had no effect, while CHX plus inhibin produced intermediate levels (77% of control). By 6 h, however, inhibin and CHX each decreased FSH beta mRNA to very low levels (12% and 15% of control, respectively), and in cultures treated with both inhibin and CHX, this RNA was barely detectable. To determine the reversibility of the effects of these inhibitors, cells were incubated with fresh control medium after 6 h. Secretion of FSH and free alpha-subunit remained suppressed 4 h later; recovery was complete by 16 h in inhibin treated cultures. FSH beta mRNA returned to control levels by 4 h in inhibin-treated and by 16 h in CHX-treated cultures. Levels of LH beta and alpha-subunit mRNA were comparable to control values at all times. In conclusion, 1) CHX, like inhibin, suppresses FSH beta mRNA levels, although its actions are less rapid and less rapidly reversible; 2) inhibin requires ongoing protein synthesis for full expression of its inhibitory effects; 3) the synthesis and secretion of LH are much less sensitive to inhibition by either inhibin or CHX than are the synthesis and secretion of FSH; and 4) secretion of free alpha-subunit involves a labile protein(s).

Developmental changes in testicular inhibin and androgen-binding protein during sexual maturation in the cynomolgus monkey, Macaca fascicularis.

Inhibin was measured by RIA in testicular extracts and plasma of cynomolgus monkeys during four stages of sexual maturation. Immunoactive inhibin levels were compared to those of another Sertoli cell secreted protein, androgen-binding protein (ABP). ABP steroid-binding (bioactive) activity was measured in testes and epididymal segments using the radiolabeled ligand [3H]dihydrotestosterone (DHT). Testicular immunoreactive inhibin concentrations were maximal in late prepubertal monkeys, 2.5-3.5 yr old, while the total testicular content of inhibin progressively increased with age into adulthood. Bioactive testicular ABP concentrations were maximal during the pubertal period of the cynomolgus monkey (3.5-4.0 yr old), while the total ABP content of the testes also increased with sexual maturation. Mean (+/- SE) plasma concentrations of inhibin and testosterone (T) in adults, 6-8 yr old (17.72 +/- 3.5 microliters inhibin equivalents/ml and 7.07 +/- 2.45 ng/ml T, respectively), were significantly higher (P less than 0.05 and P less than 0.001, respectively) than those in early prepubertal, juvenile monkeys, aged 1.5-2.5 yr (5.85 +/- 2.1 microliters inhibin equivalents/ml and 0.27 +/- 0.02 ng/ml T). The increased plasma levels of inhibin and T in adults were associated, respectively, with the increased inhibin and androgen contents of the testes in these same animals. The developmental changes in testicular steady state mRNA concentrations for the inhibin alpha-, beta A-, and beta B-subunits as well as ABP were examined during sexual maturation by Northern blot analysis using heterologous human cDNA probes. Densitometric analysis of the autoradiograms revealed that the inhibin alpha-subunit mRNA concentrations were higher than those of inhibin-beta A and -beta B and ABP mRNA during all stages of pubertal development. Although the relative concentrations of each inhibin subunit mRNA were decreased in the adult animals relative to those in the juvenile monkeys, the total amount of steady state mRNA for the subunits was greater than that in the immature animals. A similar situation existed for the ABP mRNA.(ABSTRACT TRUNCATED AT 400 WORDS)

Serum immunoreactive inhibin levels before and after luteectomy in the cynomolgus monkey (Macaca fascicularis).

Whereas studies in women have demonstrated that serum immunoreactive inhibin concentrations peak during the luteal phase of the menstrual cycle and that the corpus luteum (CL) encodes mRNA for the inhibin subunits, a clear link between the presence of the CL and circulating inhibin has not been established in primates. Therefore, we measured serum immunoreactive inhibin levels in monkeys before and after luteectomy as well as immunoreactive inhibin concentrations and mRNA encoding the alpha-inhibin subunit in luteal tissue. Monkeys were assigned to one of four groups depending on which day of the luteal phase luteectomy was performed: group A, days 4-5; group B, days 7-8; group C, days 9-10; and group D, days 11-12 (the day after the estrogen surge = day 1 of the luteal phase). Daily blood samples were obtained for 3 days before luteectomy, immediately before surgery, and for 2 days after luteectomy. Immunoreactive inhibin concentrations were measured with a double antibody RIA using an antiserum to bovine 31-kDa inhibin, bovine 31-kDa inhibin for iodination, and a human follicular fluid inhibin preparation as standard. Total RNA was isolated from luteal tissue and transferred by Northern blot onto a Zeta-probe membrane. The probe used for hybridization was the PstI/NcoI restriction enzyme fragment (381 basepairs) of alpha-inhibin DNA generated from a human ovarian cDNA library. Serum inhibin concentrations decreased (P less than 0.05) 24 h after removal of the corpus luteum in each of the four groups studied.(ABSTRACT TRUNCATED AT 250 WORDS)

Effect of inhibin from primate Sertoli cells and GnRH on gonadotropin subunit mRNA in rat pituitary cell cultures.

Partially purified inhibin from primate Sertoli cell culture medium (pSCl) suppresses both LH and FSH secretion from cultured rat pituitary cells stimulated with GnRH. To examine the mechanism of action of pSCl, we have measured steady state levels of mRNAs for the gonadotropin subunits in pituitary cell cultures exposed to 10 nM GnRH for 6 h in control or pSCl-containing medium (short term) and after 72-h pretreatment with pSCl or control medium (long term). Messenger RNA levels were determined by Northern analysis using specific cDNA probes for rat FSH beta, LH beta, and the common alpha-subunit. In the long term experiments, pSCl inhibited GnRH-stimulated release of FSH (47.4 +/- 3.3% of control), LH (69.2 +/- 2.3%), and free glycoprotein alpha-subunit (74.2 +/- 4.5%), and intracellular FSH declined to 88.4 +/- 3.5% of control. Concentrations of the subunit mRNAs were all decreased: FSH beta to 54.4 +/- 5.0%, LH beta to 79.6 +/- 9.4%, and alpha to 70.8 +/- 8.7% of control. In the short-term experiments, pSCl also suppressed FSH, LH, and alpha-subunit secretion to 75.9 +/- 3.6%, 79.5 +/- 2.1%, and 90.9 +/- 1.8% of control, respectively. Intracellular LH and alpha-subunit levels were significantly increased in cells treated for 6 h with GnRH and pSCl (155 +/- 18%, 145 +/- 14% of control), while FSH was comparable to control. After 6 h, pSCl selectively reduced the level of mRNA for FSH beta (56.5 +/- 5.8% of control).(ABSTRACT TRUNCATED AT 250 WORDS)

Rapid and profound suppression of messenger ribonucleic acid encoding follicle-stimulating hormone beta by inhibin from primate Sertoli cells.

We showed previously that inhibin, partially purified from cynomolgus monkey Sertoli cell culture medium (primate Sertoli cell inhibin referred to as pSCI), selectively suppressed basal FSH secretion from dispersed rat pituitary cells and decreased total cellular FSH, but not LH content, suggesting a decrease in FSH biosynthesis. In order to investigate the mechanism of action of inhibin at the molecular level, we have now examined the effects of pSCI on steady state levels of the subunit mRNAs encoding LH and FSH and correlated these with release and intracellular content of LH, FSH, and glycoprotein alpha-subunit. Dispersed pituitary cells from 7- to 8-week-old adult male rats were cultured in the presence of pSCI or control medium for 2-72 h. FSH secretion was reduced significantly by 6 h (P less than 0.05) and reached a nadir (38% of control) by 48 h. LH secretion was unchanged, while release of the alpha-subunit was decreased to 89% of control at 72 h (P less than 0.05). Also by 72 h, cell content of both FSH (73% of control) and alpha-subunit (81% of control) were significantly suppressed (P less than 0.001, P less than 0.01), while LH was slightly affected. Total RNA was extracted from the pituitary cell cultures, electrophoresed in 1.2% agarose-formaldehyde gels, transferred to nylon membranes, and hybridized with 32P-labeled cDNA probes for the rat alpha-, LH beta-, and FSH beta-subunits.(ABSTRACT TRUNCATED AT 250 WORDS)

Effects of gonadal steroids on gonadotropin secretion in males: studies with perifused rat pituitary cells.

The feedback effects of testosterone (T) and estradiol (E2) on FSH and LH secretion were compared in dispersed pituitary cells from adult male rats perifused with pulses of GnRH. Cells were stimulated with 10 nM GnRH for 2 min every 1 h. T (10 nM) pretreatment for 24 h reduced the amplitude of FSH and LH pulses to 77 +/- 4% (mean +/- SE) and 47 +/- 3% of control values, respectively (P less than 0.01), whereas 6-h T treatment was without effect. By contrast, interpulse secretion of FSH was increased after 24 h T to 184 +/- 7% of the control value (P less than 0.01), but interpulse LH release was unchanged (104 +/- 5%). E2 (0.075 nM) treatment of pituitary cells reduced GnRH-stimulated FSH and LH release within 2 h to 75 +/- 2% and 73 +/- 3% of control values, respectively (P less than 0.01). E2 pretreatment for 24 h stimulated (P less than 0.025) GnRH-induced FSH (136 +/- 10%) and LH (145 +/- 8%) release and also increased (P less than 0.01) interpulse FSH (127 +/- 5%) and LH (145 +/- 8%) secretion. These data indicate that the suppression of FSH and LH secretion by T in males is due in part to a direct effect on the pituitary. The findings that T suppresses GnRH-stimulated FSH less than LH, and that T stimulates interpulse FSH, but not LH, provide evidence for differential regulation of FSH and LH secretion by T. The dissimilar actions of T on GnRH-stimulated pulses and interpulse gonadotropin secretion suggest that interpulse secretion is unrelated to stimulation by GnRH, although its physiological significance is unknown. Since E2, in physiological levels for males, increased pituitary FSH and LH secretion, the suppression of gonadotropin secretion by E2 in vivo in males may result from an effect on the hypothalamic pulse generator; however, additional studies are needed before extending these conclusions to higher mammals and men.

Effects of inhibin from primate Sertoli cells on follicle-stimulating hormone and luteinizing hormone release by perifused rat pituitary cells.

We used a pituitary cell perifusion system to investigate the time course and selectivity of the inhibin effect on pulsatile GnRH-stimulated LH and FSH release. Dispersed pituitary cells from 7- to 8-week-old male rats were perifused on a Cytodex bead matrix and stimulated with 10 nM GnRH for 2 min every hour for 8-11 h. The addition of a preparation of inhibin partially purified from primate Sertoli cells reduced pulsatile FSH release within 2 h. After removal of inhibin from the perifusion medium, the effect was reversed within 3 h. GnRH-stimulated LH release was also influenced by inhibin, although the decline in LH was less than that in FSH (80 +/- 3% vs. 68 +/- 4% of control; P less than 0.025). Smaller doses of inhibin suppressed GnRH-induced FSH secretion, but had no effect on LH release. Further, prolonged incubation of pituitary cells with inhibin at the higher dose reduced its FSH inhibitory effect and eliminated the effect on LH. These results indicate that inhibin can reduce both LH and FSH secretion in vitro, although the specificity and magnitude of the effect are a function of both the dose and duration of inhibin treatment. Further, the actions of inhibin and GnRH on the pituitary may be interrelated.

Identification of inhibin secreted by cynomolgus monkey Sertoli cell cultures.

An inhibin was identified in the media of primary Sertoli cell-enriched cultures from the cynomolgus monkey, Macaca fascicularis, and some of its biochemical properties were studied. Conditioned monkey Sertoli cell culture medium (m-SCCM), when added to pituitary cells from 6-week-old male rats, inhibited the basal secretion of FSH but not that of LH. This specificity was lost after the addition of GnRH; mSCCM inhibited not only FSH but also LH release, determined by both RIA and mouse interstitial cell bioassay, from pituitary cells exposed for 6 h to 10 nM GnRH. FSH-inhibiting activity persisted when m-SCCM was boiled for 30 min, but activity was lost after incubation for 1 h at 37 C with 0.1% trypsin. m-SCCM inhibin activity was completely retained by Concanavalin A-Sepharose and could be eluted with 0.2 M alpha-methyl-D-glucoside. Gel filtration high pressure liquid chromatography with a Superose-12 column revealed inhibin activity between 20-60K, with the greatest activity at 40K. Our results indicate that primate Sertoli cells produce an inhibin-like factor which could play a role in controlling gonadotropin secretion in males.

Testicular control of prostaglandin E2 production in rat vas deferens.

Orchidectomy decreased and testosterone (T) replacement restored prostaglandin E2 (PGE2) concentrations in adult rat vas deferens. To explain this finding, phospholipase A (PLase-A) and PG synthetic activity were studied in vas tissue from 9-week-old rats orchidectomized with or without T replacement as well as in rats in which the cauda epididymidis was ligated. PG synthetic activity fell to 3% of intact levels in 14-day castrate rats and was restored to normal by T replacement. Although vas PLase-A activity was also significantly (P less than 0.01) reduced to 38% of the control level in 14-day castrate rats, this change appears in part to reflect a castration-related increase in endogenous phospholipid concentrations. Further, T replacement only partially restored PLase-A activity to 59% of intact levels. Ligation of the cauda epididymidis in intact rats reduced vas PLase-A activity to castrate levels without altering vas T concentration. These results demonstrate both a direct effect of T on the biosynthesis of PGs in rat vas deferens as well as a paracrine effect, which appears to be mediated by a factor(s) other than T. These data suggest the existence of a new mechanism through which testicular products contribute to the function of the vas deferens.

Assay of primate seminiferous tubule androgen receptors using [3H]mibolerone.

The synthetic radiolabelled androgen mibolerone (7 alpha, 17 alpha-dimethyl-19-nortestosterone) was used to characterize androgen receptor binding in the seminiferous tubules from Cynomolgus monkey testis. Mibolerone binding was of high affinity (Kd = 0.6-5.4 nM) and limited capacity (37-50 fmol/mg protein), and was androgen specific. Sucrose density gradient centrifugation using a vertical tube rotor permitted the identification of a 9S molybdate-stabilized receptor under low salt conditions. The receptor bound to DEAE-cellulose. Methyltrienolone, but not mibolerone, also bound to a low affinity high capacity binding site in tubule cytosol, which probably represents glucocorticoid receptor binding, since it could be displaced by excess dexamethasone. However, occupancy of this low-affinity binding site by dexamethasone in an androgen receptor assay with [3H]methyltrienolone lead to a 33% underestimation of receptor binding, which appeared to relate to radioactive decomposition. Mibolerone, as well as methyltrienolone, bound to a progestin-binding protein in seminiferous tubule cytosol. These studies provide methods for the study of seminiferous tubule androgen receptors in subhuman primates and indicate that, due to its greater stability and lack of binding to glucocorticoid receptor, mibolerone is a useful new ligand in the study of androgen receptors in testis and its constituent cells.

Identification of androgen-binding protein from testis cytosol and sertoli cell culture medium of the cynomolgus monkey, Macaca fascicularis.

The biochemical and immunological properties of monkey androgen-binding protein (mABP) from the cynomolgus monkey, Macaca fascicularis, have been examined in testis cytosol and medium of primary Sertoli cell-enriched cultures. mABP in testis tissue was separated from the serum protein testosterone-estradiol-binding globulin (mTeBG) by affinity chromatography on Concanavalin A-Sepharose (Con A). mTeBG from serum extracts was completely retained by the lectin and could be displaced with buffer containing alpha-methyl-D-glucoside. In contrast, mABP from testis extracts either did not interact with the Con A and appeared in the void volume or was partially retained by the column and could be eluted with buffer alone. A third component retained by the Con A may represent mTeBG contamination, a form of mABP which binds to Con A, or both. The specific 5 alpha-dihydrotestosterone (DHT)-binding activity in the void volume of the Con A column was designated mABP and was further studied. [3H]DHT binding to mABP was saturable and of limited capacity (0.163 +/- 19 pmol/mg protein). Scatchard analysis of the data was consistent with a single class of binding sites with an apparent dissociation constant (Kd) at 4 C of 2.6 +/- 0.2 X 10(-9) M. DHT was the most effective competitor of [3H]DHT binding to mABP, followed by 2-methoxyestradiol, testosterone, estradiol, and cyproterone acetate. Concentrated Sertoli cell culture medium subjected to steady state polyacrylamide gel electrophoresis produced a single peak of specifically bound [3H]DHT with a mobility similar to that of other androgen-binding proteins. [35S]Methionine-labeled medium proteins were immunoprecipitated with a rabbit anti-human TeBG antiserum. Two bands, corresponding to mol wt of approximately 46,000 and 48,000, were observed by fluorography, with the lighter component being more intense. After androgen affinity chromatography of radiolabeled medium proteins, these two bands were again observed on sodium dodecyl sulfate-urea-containing polyacrylamide gels. These results demonstrate that 1) mABP may be separated from mTeBG by lectin affinity chromatography, as in humans; 2) hTeBG and mABP are antigenically related; and 3) mABP consists of subunits of different mol wt in unequal ratios.

Comparison of media proteins from ovariectomized rat uteri following estrogen treatment.

Ovariectomized rats were treated with estradiol for 3 days after which their uteri were incubated in vitro and radioactive media proteins were analyzed by sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE). Media were also chromatographed on G-25 Sephadex Blue Sepharose columns to isolate subsets of proteins. The results demonstrate that two proteins are consistently increased following estrogen treatment. These proteins have molecular weights of 104,000 and 65,000. Neither protein binds to Blue Sepharose to a great extent. The use of the protein synthesis inhibitors, emetine and actinomycin D, demonstrates that the proteins are synthesized de novo. These two proteins may serve as markers for genomic response to estradiol in the rat uterus.

Monoclonal antibody to rat uterine peroxidase and its use in identification of the peroxidase as being of eosinophil origin.

Peroxidase was purified from uteri of estrogen-treated rats by calcium chloride extraction, affinity chromatography on concanavalin A-Sepharose and hydrophobic interaction chromatography on phenyl-Sepharose. An overall purification of greater than 1700-fold was achieved with a final recovery of 27%. Monoclonal antibodies to peroxidase were subsequently prepared by immunization of male C57BL/10J mice with the highly purified peroxidase from rat uterus. Spleen and lymph node cells from the mice were fused with Sp2/0-Ag 14 mouse myeloma cells. The resultant hybrid cells were screened for production of antibody using a solid-phase, double antibody radioimmunoassay. The mature rat spleen, shown previously to be abundant in eosinophils, contains high peroxidase activity. Spleen peroxidase purified by the same procedure as the uterine enzyme cross-reacted with a monoclonal antibody, designated IgG-107B, used in all subsequent studies. Peroxidase extracted from isolated rat eosinophils also cross-reacted with the antibody and yielded identical titers as the spleen and uterine peroxidases. Spleen, uterine and horse eosinophil peroxidase had the same apparent molecular weight, 57000, as determined by sodium dodecyl sulfate-urea polyacrylamide gel electrophoresis. Following electrophoretic transfer to nitrocellulose, spleen, uterine and eosinophil peroxidase reacted with monoclonal antibody, using an immunoblotting technique. These results provide biochemical and immunological evidence that the majority of the calcium chloride-extractable peroxidase activity from the uteri of estrogen-treated rats is derived from infiltrating eosinophils.

Modulation of estrogen-induced peroxidase activity in the rat uterus by thyroid hormones.

The effect of thyroid hormones, iodide, propylthiouracil and other thyroid-active agents on estrogen receptor concentration and on the induction of peroxidase in the immature rat uterus by estradiol (E2) was examined T3 (0.5 mg/Kg) given daily for 6 days produced a large decrease in E2-induced uterine peroxidase but lowered only slightly the concentration of cytosolic or nuclear receptors in this organ. T4 also decreased the effect of E2 on uterine peroxidase induction and the inhibitory action of T3 was observed in thyroidectomized rats. The administration of iodide (10 mM) in the drinking water for 6 days caused a 2-fold increase in estrogen-induced peroxidase in both normal and thyroidectomized immature animals without influencing the estrogen receptor concentration in the uterus. The effect of other thyroid-active agents on serum T3 and T4 levels was also determined. Treatment for 6 days with propylthiouracil (6 mM) increased the concentration of estrogen receptors in the uterus and decreased serum T3 and T4 levels without any effect on uterine peroxidase activity while bromide and perchlorate did not influence these parameters. Possible mechanisms for the inhibitory effects of thyroid hormones on uterine peroxidase induction by E2 are discussed.

Distribution of oestrogen-induced peroxidase in the rat uterus.

The activity of oestrogen-induced peroxidase in sections along the uterus of normal and mammary tumour-bearing adult rats was measured. Oestradiol increased the activity of this enzyme in the cervix as well as in other parts of the uterus in ovariectomized or immature rats. Peroxidase activity per mg protein was twice as high in the cervix as in the rest of the uterus where it was evenly distributed along both horns. The concentrations of oestrogen receptors in the cytosol and nucleus in each uterine horn and in the cervix was also determined and found to be lower in the cervix than in other sections of the uterus.