Rate Of Progesterone Production Research Articles

Adrenomedullin in rat follicles and corpora lutea: expression, functions and interaction with endothelin-1

BackgroundAdrenomedullin (ADM), a novel vasorelaxant peptide, was found in human/rat ovaries. The present study investigated the interaction of ADM and endothelin-1 (ET-1) in follicles and newly formed corpora lutea (CL) and the actions of ADM on progesterone production in CL during pregnancy.MethodsThe peptide and gene expression level of adrenomedullin in small antral follicles, large antral follicles and CL was studied by real-time RT-PCR and EIA. The effect of ADM treatment on oestradiol production in 5-day follicular culture and on progesterone production from CL of different pregnant stages was measured by EIA. The interaction of ADM and ET-1 in follicles and CL at their gene expression level was studied by real-time RT-PCR.ResultsIn the rat ovary, the gene expression of Adm increased during development from small antral follicles to large antral follicles and CL. In vitro treatment of preantral follicular culture for 5 days with ADM increased oestradiol production but did not affect follicular growth or ovulation rate. The regulation of progesterone production by ADM in CL in culture was pregnancy-stage dependent, inhibitory at early and late pregnancy but stimulatory at mid-pregnancy, which might contribute to the high progesterone production rate of the CL at mid-pregnancy. Moreover, the interaction between ADM and ET-1 at both the production and functional levels indicates that these two vasoactive peptides may form an important local, fine-tuning regulatory system together with LH and prolactin for progesterone production in rat CL.ConclusionsAs the CL is the major source of progesterone production even after the formation of placenta in rats, ADM may be an important regulator in progesterone production to meet the requirement of pregnancy.

Localization and functional activity of cytochrome P450 side chain cleavage enzyme (CYP11A1) in the adult rat kidney

Cumulative evidence demonstrated effective downstream metabolism of pregnenolone in renal tissue. The aim of this study was to evaluate the expression and functional activity of cytochrome P450 side chain cleavage enzyme (CYP11A1), which converts cholesterol into pregnenolone, in adult rat kidney. Immunohistochemical labeling for CYP11A1 was observed in renal cortex and medulla, on structures identified as distal convoluted tubule and thick ascending limb of Henle's loop, respectively. Immunoblotting analysis corroborated the renal expression of the protein in inner mitochondrial membrane fractions. The incubation of isolated mitochondria with the membrane-permeant cholesterol analogue 22R-hydroxycholesterol resulted in efficient formation of pregnenolone, the immediate precursor for the synthesis of all the steroid hormones. The low progesterone production rate observed in these experiments suggested a poor activity of 3β-hydroxysteroid dehydrogenase enzyme in renal mitochondria. The steroidogenic acute regulatory protein (StAR), involved in the mitochondrial import of cholesterol, was detected in renal tissue at both mRNA and protein level. Immunostaining for StAR showed similar distribution to that observed for CYP11A1. The expression of StAR and CYP11A1 was found to be higher in medulla than in cortex. This enhanced expression of steroidogenesis-related proteins correlated with a greater pregnenolone synthesis rate and higher steroid hormones tissular content measured in medulla. In conclusion, we have established the expression and localization of StAR and CYP11A1 protein, the ability of synthesizing pregnenolone and a region-specific content of sex hormones in the adult rat kidney. These data clearly show that the kidney is a steroid hormones synthesizing organ. It is proposed that the existence in the kidney of complete steroidogenic machinery would respond to a physiological significance.

Cell Culture of Bovine Luteal Cells in a Continuous Bioreactor

ContentsFor long‐term culture of primary bovine luteal cells a continuous bioreactor using hollow‐fibre and fluidized‐bed modules was developed. Luteal cells were successfully cultured in continuous bioreactors over 21 days and their progesterone production in vitro was traced and quantified under stimulation by hCG and inhibition by PGF2α. Considerable progesterone production rates of about 102–103 molecules progesterone per cell and hour could be estimated.

The autonomy of the rabbit corpus luteum.

The rabbit corpus luteum possesses LH receptors that are coupled to adenylyl cyclase, but paradoxically it does not require LH as a luteotrophic factor for the maintenance of progesterone secretion. This suggests that rabbit luteal cells may not respond physiologically to LH. Therefore, the present study was undertaken to investigate the responsiveness of the rabbit corpus luteum of pseudopregnancy to human chorionic gonadotrophin (hCG) which acts on the same receptor as LH. Pseudopregnancy was induced by injection of 40 IU pregnant mare serum gonadotrophin followed 50 h later by an injection of 40 IU hCG (day 0). On days 7 and 11 of pseudopregnancy, corpora lutea were obtained and incubated for 2 or 5 h in the presence of either 0.1 or 1 microgram/ml hCG or 1 mM monobutyryl cyclic AMP (bcAMP). Neither hCG nor bcAMP stimulated progesterone production by the isolated corpus luteum, despite a sustained high rate of progesterone production by the tissue throughout the incubation period. By contrast, Graafian follicles removed from the same ovaries and incubated under the same conditions responded both to hCG and bcAMP with large increases in progesterone production. To determine whether the cyclic AMP content of the corpus luteum was altered by in vitro exposure to hCG, day 7 and day 11 corpora lutea were incubated for 5 or 15 min with various concentrations of hCG, and cyclic AMP in the tissue was then measured. Even at the highest concentration of hCG tested (10 micrograms/ml), the cyclic AMP content of the corpus luteum was unaltered.(ABSTRACT TRUNCATED AT 250 WORDS)

Mechanism of the HDL2 stimulation of progesterone secretion in cultured placental trophoblast.

Lipoprotein cholesterol (C) supports the high rate of progesterone production by the human placenta as endogenous cholesterol synthesis is low. To study underlying mechanisms whereby lipoproteins, including high density lipoprotein-2 (HDL2), stimulate progesterone secretion, trophoblast cells were isolated from human term placentas and maintained in primary tissue culture. Lipoproteins were added at several concentrations and medium progesterone secretion was determined. HDL2 (d 1.063-1.125 g/ml) as well as low density lipoproteins (LDL) (d 1.019-1.063 g/ml) but not HDL3 (d 1.125-1.21 g/ml) stimulated progesterone secretion in a dose-dependent manner, with HDL2 cholesterol entering the cell and serving as substrate for progesterone synthesis. Conversely, LDL and HDL2 produced a significant decrease in [2-14C]acetate incorporation into cell cholesterol. Cholesterol-depleted lipoproteins did not stimulate progesterone secretion. The stimulating effect of LDL was abolished by apolipoprotein modification by cyclohexanedione or reductive methylation and by the addition of anti-LDL receptor antibody or 10 microM chloroquine to the medium. [14C]acetate conversion into cholesterol was accelerated by these procedures. However, HDL2 stimulation of progesterone secretion and reduction of [14C]acetate incorporation into cholesterol was not blocked by chemical modification of apolipoproteins, anti-LDL receptor antibody, or chloroquine. Treatment of HDL2 with tetranitromethane or dimethylsuberimidate also did not block the stimulation of progesterone. To determine whether the capacity of HDL2 to deliver cholesterol to the trophoblast cells was restricted to subfractions differing in apoE content, HDL2 was chromatographed on heparin-Sepharose and three fractions (A, B, and C) were obtained. Fraction A was poorest in apoE and free cholesterol, fraction B contained the majority of cholesterol, and fraction C was the richest in apoE and free cholesterol. When added to trophoblast cells, fraction A stimulated little progesterone secretion, fraction B stimulated moderately, and fraction C did so greatly. Modification of these subfractions with cyclohexanedione or reductive methylation did not inhibit these effects. In conclusion, HDL2 stimulated progesterone secretion in human trophoblast cell culture. Contrary to LDL, the HDL effect was not mediated by apolipoproteins or the LDL receptor pathway. The ability of HDL2 to stimulate progesterone secretion is consistent with the passive transfer of free cholesterol to the cell membrane from a physicochemically specific subfraction of HDL. This mechanism may be an auxiliary source of cholesterol for human steroidogenic cells.

Luteinization of porcine thecal cells in vitro

The objective of this study was to determine the requirements for the functional luteinization of porcine thecal cells in vitro. In serum-free incubations with luteinizing hormone (LH) (250 ng/ml) androstenedione concentrations increased up to 14 h, after which time no further accumulation occurred; progesterone accumulation was low, and did not increase after 4 h. In the presence of 1% fetal bovine serum and LH, androstenedione production declined, but progesterone production per day increased over a 4-day period, while cellular protein remained constant. LH was required for both the induction and maintenance of elevated progesterone production. Insulin (maximal response at 500 ng/ml) in the presence of 1% serum enhanced the response to LH, causing a dramatic increase in progesterone production, an effect which became greater with time in culture. Dose-response curves for insulin and insulin-like growth factor I (IGF-I) were parallel, but IGF-I was approximately 23-fold more potent than insulin, suggesting that insulin was acting through IGF-I receptors. Our results show that porcine thecal cells, in the presence of LH, insulin or IGF-I, and 1% serum, undergo functional luteinization in vitro, such that androstenedione production declines, and the rate of progesterone production increases with time in culture.

Progesterone production and clearance in cyclic ewes passively imminized against progesterone

The effects of passive immunization of ewes against progesterone on plasma progesterone concentrations and on the metabolic clearance rate (MCR) and production rate (PR) of progesterone were investigated. Three treatment groups were studied: 1) nonimmunized controls, 2) ewes passively immunized with antiprogesterone serum, and 3) immunized progestagen-treated ewes, treated concomitantly with anti-serum and with a synthetic progestagen that is not bound by the antiserum. Progesterone levels in the immunized ewes reached a maximum of 27.7±4.8 nmol/l and were significantly higher (P<0.05) than in the nonimmunized controls (9.2±1.1 mol/l) or the immunized progestagen-treated ewes (15.6±1.6 nmol/l). Mean progesterone MCR in the immunized ewes was 1.6±0.5 and 2.1±0.3 liter/min on Days 7 and 13 of the estrous cycle, respectively, compared with 0.8±0.2 and 1.4±0.3 liter/min, respectively, in nonimmunized controls. The progesterone production rate in the immunized ewes was significantly higher than in nonimmunized controls, and reached 12.0±2.2 and 19.7±1.6 nmol/min on Days 7 and 13 of the estrous cycle, respectively, compared with 4.6±0.6 and 10.0±2.5 nmol/min in nonimmunized controls (P<0.03 for both comparisons). Treatment with progestagen had no significant effect on progesterone MCR or PR of immunized ewes. The LH pulse frequency on Days 10 to 11 of the cycle was 0.7±0.3, 1.8±0.3 and 0.0±0.0 pulses/6 h in the control, immunized and immunized progestagen-treated groups, respectively (P<0.05). It is concluded that the increased plasma progesterone levels in the immunized ewes are the result of an increased progesterone production rate, which may have been induced by an increase in gonadotrophin secretion or by a direct effect of the anti-progesterone serum on the ovary.

Sn-1,2-diacylglycerols and phorbol ester stimulate the production of progesterone from the human placenta.

Human term placental explants were used to investigate the possible role of phospholipid-sensitive and Ca2+ dependent protein kinase in the regulation of human placental progesterone production. Placental tissue was incubated with low density lipoprotein as a precursor of progesterone in the presence or the absence of phorbol 12-myristate-13-acetate, 1-oleoyl-2-acetyl-glycerol, and the calcium ionophore A23187. The rate of progesterone production by placental tissue was 21.7 +/- 4.6 ng. (mg wet wt)-1.(2 h)-1 (mean +/- SEM) with 500 mg low density lipoprotein/l (control). The rate of progesterone production was accelerated 2-fold by 1 nmol/l phorbol 12-myristate-13-acetate, 1.6-fold by 250 mumol/l 1-oleoyl-2-acetyl-glycerol and this increase was dose-related (25-250 mumol/l 1-oleoyl-2-acetyl-glycerol). A nonpromoting derivative, 4 alpha-phorbol-12,13-didecanoate had no effect. The phorbol 12-myristate-13-acetate or 1-oleoyl-2-acetyl-glycerol induced stimulation of progesterone production was not associated with a change in the intracellular cAMP level. Addition of 10 mumol/l A23187 further increased progesterone production with 125 mumol/l 1-oleoyl-2-acetyl-glycerol. The rate of progesterone production was accelerated 1.6-fold by 125 mumol/l 1-oleoyl-2-acetyl-glycerol and 10 mumol/l A23187 as compared with control. The effects of the phorbol ester and the diacyl glycerol were completely blocked by the addition of the protein synthesis inhibitor cycloheximide. We conclude that these phorbol regents are able to stimulate human placental progesterone production. The possible roles of intracellular Ca2+ and protein kinase C in placental steroidogenesis are discussed.

Changes in the blood concentrations of progesterone and 20 alpha-hydroxypregn-4-en-3-one during late pregnancy in the conscious rat: a specific role for metabolic clearance rate.

Near term in the rat, the blood concentration of progesterone falls while that of 20 alpha-hydroxypregn-4-en-3-one (20 alpha-DHP) increases. This is generally attributed to changes in ovarian secretion alone, but altered rates of hormone metabolism could also have a role. In the present study, therefore, metabolic clearance rate (MCR), production rate, and peripheral interconversion of progesterone and 20 alpha-DHP were measured on Day 16 of pregnancy, the time of maximal progesterone secretion, and on Day 22, one day prior to parturition. Conscious rats (n = 8 per group) were infused with either [3H]progesterone or [3H]20 alpha-DHP and the dynamics of progestin metabolism were calculated from the resultant isotopic and endogenous progesterone and 20 alpha-DHP concentrations. The blood concentration of progesterone declined by 69% between Day 16 (54 +/- 2 ng/ml) and Day 22 (17 +/- 2 ng/ml), and this was due to the combined effect of a 48% increase in the MCR and a 54% decrease in production rate of progesterone. In contrast, the production rate of 20 alpha-DHP was twofold greater on Day 22 compared to Day 16. As a result, the blood concentration of 20 alpha-DHP increased from 28 +/- 3 ng/ml on Day 16 to 40 +/- 6 ng/ml on Day 22, and this change would have been greater but for a concomitant increase (41%) in the MCR of 20 alpha-DHP. Although peripheral conversion of progesterone to 20 alpha-DHP was similar on Day 16 (transfer constant, 12.8 +/- 0.6%) and Day 22 (12.3 +/- 0.9%), the contribution of this conversion to total 20 alpha-DHP production fell from 32% to 7% between the two days.(ABSTRACT TRUNCATED AT 250 WORDS)

Mechanism of down regulation of luteinizing hormone receptors and steroidogenesis in corpora lutea

The mechanism of ‘down regulation’ of luteinizing hormone receptors was investigated in pseudopregnant rats using a modified radioimmunoassay capable of measuring endogenous tissue-bound hormone. Treatment of pseudopregnant animals with a desensitizing dose (desensitization treatment) of human chorionic gonadotropin resulted in a decrease in receptor concentration. This decrease was prevented if the animals were treated prior to the desensitization treatment with indomethacin, an inhibitor of prostaglandin biosynthesis, suggesting a role for prostaglandins in down regulation. The desensitization treatment resulted in a time-dependent decrease in subsequent responsiveness of the tissue to luteinizing hormone. Basal progesterone production rate was also decreased following desensitization. Total tissue cholesterol was found to be decreased following desensitization treatment, without any change in the ratio of free to esterified cholesterol. Mitochondrial cholesterol was significantly reduced and pregnenolone production by the mitochondria of desensitized corpora lutea was also markedly reduced. However, when cholesterol was added to the mitochondria of desensitized corpora lutea, pregnenolone production was increased, reaching values almost equal to that shown by the control mitochondria. These results show that decrease in the responsiveness following desensitization treatment is due to, besides receptor loss, decrease in tissue cholesterol, in particular mitochondrial cholesterol. The cholesterol side chain cleavage activity, although low, appears to be functionally intact; the low activity could be attributed to low levels of mitochondrial cholesterol.

Use of deuterium-labelled tracers to establish endogenous rates of production and clearance of progesterone during the peri-implantation period in gilts

Using a method based on the constant infusion of a deuterium-labelled tracer, production rates (PR) and metabolic clearance rates (MCR) of progesterone have been determined in gilts between Days 11 and 17 of gestation. This involved the development of a procedure to quantitate the tracer [(7,7,16- 2H 3)-progesterone] in plasma samples, and in the infusate, with the aid of gas chromatography-mass spectrometry. In a group of nine mated gilts, the average (± s.e.m.) progesterone PR was 274 (± 26) μmol/24 h, the average progesterone MCR being 3348 (± 312) 1 24 h . Declining peripheral plasma progesterone levels (PP) between Days 11 and 17 of gestation were associated with increasing progesterone MCR ( P < 0.05), and were not correlated with increasing PR. For comparison, progesterone PRs and MCRs were determined in five unmated gilts between Days 11 and 15 of oestrus, prior to the normal onset of luteolysis. The mean progesterone MCR in these animals (2735±275 1 24 h ) was similar to the respective pregnancy mean ( P > 0.1), but the PR (158±12 μmol/24 h) was lower ( P < 0.01). PP values, PR values and numbers of corpora lutea were not significantly correlated ( P > 0.1) in either mated or unmated groups of gilts. The results of this study support previous indications of luteotrophic effects of conceptus tissues after Day 10 of pregnancy in the sow, and provide quantitative bases for progesterone replacement in ovariectomized pigs between Days 11 and 17 after oestrus/coitus.

Oxytocin and vasopressin have no effect on progesterone production and cyclic AMP accumulation by rat luteal cells in vitro.

Enzymically dispersed luteal cells obtained from PMSG-hCG-treated immature pseudopregnant rats were incubated with oxytocin and vasopressin. In response to increasing doses of hCG the rat luteal cells produced progesterone and accumulated intracellular cAMP in a dose-dependent manner. A neuropeptide GnRH agonist (4 X 10(-6) M) produced a significant inhibition of hCG-stimulated progesterone production and of accumulation of intracellular cAMP. However, neither the basal nor the hCG-stimulated rate of progesterone production and level of intracellular cAMP was affected by the neurohypophysial peptides tested. Therefore, it is concluded that oxytocin and vasopressin do not have a direct action on steroidogenesis by rat luteal cells.

Ovarian production of progesterone and 20 alpha-dihydroprogesterone in vitro following prostaglandin F2 alpha induced luteolysis in the superluteinized rat.

Superluteinized rats were injected with the prostaglandin F2 alpha (PGF2 alpha) analogue cloprostenol to induce luteolysis. The treatment decreased progesterone production of ovarian homogenates from 8.9 +/- 0.5 to 4.0 +/- 0.7 nmol/ovary/10 min (mean +/- SEM) within 40 min. tochondrial fractions isolated from control and cloprostenol treated animals produced 4.7 +/- 0.4 and 2.8 +/- 0.3 nmol progesterone/ovary/10 min, respectively. Thus, the PGF2 alpha analogue treatment significantly reduced mitochondrial progesterone production. Addition of the 15 000 X g supernatant fraction did not influence the progesterone production rates of the mitochondrial fraction. The basal progesterone secretion from quartered ovaries decreased from 1.50 +/- 0.15 to 0.38 +/- 0.05 nmol/ovary during the initial 15 min of incubation following cloprostenol administration. hCG and N6,O2'-dibutyryladenosine 3':5'-cyclic monophosphate (DBC) stimulated the progesterone secretion from quartered ovaries, but the response was delayed in ovaries obtained from cloprostenol treated animals. Although the response was delayed, the progesterone secretion following cloprostenol treatment was re-activated with cAMP either directly or via hCG. The increment in progesterone secretion above unstimulated controls in response to DBC was not influenced by the cloprostenol treatment while the increment caused by hCG was decreased. Our data suggest that: 1) PGF2 alpha deactivates mitochondrial progesterone production, 2) this deactivation may be overcome by cAMP, and 3) PGF2 alpha decreases gonadotrophin responsive adenylyl cyclase.

Applications of heavy isotope tracers to clinical studies: progesterone urinary production rate determination in the menstrual cycle and pregnancy.

A method for the in vivo determination of progesterone production rate using progesterone labeled with deuterium as the tracer and gas chromatography-mass spectrometry for assessing isotope dilution in a urinary metabolite is described. By measuring the ratio of labeled to unlabeled free progesterone in a 24-h urine sample, the problem of identifying a unique metabolite appears to have been avoided. Median progesterone production rates on day 7 of the follicular phase and day 7 of the luteal phase were 3.5 mumol/24 h and 72.6 mumol/24 h, respectively. Where repeated determinations were performed through the luteal phase in two nonconceptual cycles, the familiar midluteal plateau of progesterone production was noted. The MCR of progesterone calculated from luteal phase data was 2051 1/24 h (SD, 275 1/24 h). When determined in pregnancy, progesterone production varied from 250 mumol/24 h at 6 weeks in a singleton pregnancy, to 1565 mumol/24 h at 35 weeks in a triplet pregnancy. Repeated determinations before term in a twin pregnancy detected no evidence of decreasing progesterone production before labor. The value of urinary pregnanediol and plasma progesterone to indirectly monitor progesterone production were confirmed.

Calcium ions in the steroidogenic action of HCG

Extensive studies have recently been conducted on the expression of hormone actions, especially on its mechanisms. Sutherland, et al. identified the function of C-AMP as an intracellular messenger of peptide hormones. Recent studies by several investigators including ours have concluded that the role of C-GMP and calcium are as important as that of C-AMP. In this report we present out findings on the role of Ca ions in the acceleration of steroid production in isolated porcine cells of the corpora lutea. (1) The incubation time needed to compare the production of progesterone and that of C-AMP is at least 120 mins. (2) Production rates of both C-AMP and progesterone in the presence of HCG were maximum at 10(-7) g/ml HCG. Inclusion of Ca ions in the medium increases this production rate. (3) When Ca ions are included in the medium, the accelerated rate of progesterone production takes on its highest value at 1.2mM Ca. (4) Verapamil and cycloheximide inhibit the production of progesterone. (5) The binding capacity of 125I-HCG combined with corpora lutea cells is independent of the Ca concentration in the medium. (6) Ca uptake into corpora lutea cells increases according to the concentration of HCG until it reaches a plateau at 10(-7) g/ml HCG. This acceleration by HCG is affected by Ca and is remarkably inhibited by verapamil. These results indicate the important role of Ca ions in the acceleration of progesterone production compared to that of C-AMP.

The dynamics of the steroidogenic response of perifused Leydig tumor cells to human chorionic gonadotropin, ovine luteinizing hormone, cholera toxin, and adenosine 3',5'-cyclic monophosphate.

A perifusion system has been developed in which a dose-dependent response of isolated Leydig tumor cells to steroidogenic stimuli, as assessed by the rates of steroid production, can be measured as a function of time. In response to a continuous perifusion for 340 min with a saturating concentration of hCG, ovine LH (oLH), cholera toxin, or 8-Br-cAMP, there is a rapid increase in the rate of progesterone production, which reaches a maximum about 100 min after the onset of stimulus in the medium and then declines to a rate somewhat higher than basal. Thus cholera toxin and 8-Br-cAMP as well as hCG and oLH are able to desensitize the Leydig tumor cells to further stimulation by the same agent. Although a 10-min pulse of a saturating concentration of hCG yields the same steroidogenic response as that elicited by continuous perifusion with saturating hCG, a pulse of a saturating concentration of oLH yields a steroidogenic response only when oLH is maintained in the perifusate. These data establish a substantial difference in the actions of hCG and oLH. The results could be explained by the higher apparent affinity of hCG for the gonadotropin receptor, such that, upon removal of hormone from the perifusate, oLH would be more readily eluted from the receptor. These findings support the hypothesis that oLH and hCG exert their stimulatory effects only while bound to the cell surface. (Endocrinology 108: 632, 1981)

Onset of synthesis of progesterone by ovine placenta.

The extra-ovarian contribution to progesterone levels in the circulation has been measured in ovariectomized ewes in which pregnancy was maintained by treatment with medroxyprogesterone acetate. Since adrenal production of progesterone is low this procedure allows the determination of placental secretion. Placental production of progesterone has been shown to rise initially between 50 and 70 days of gestation, with a second phase of increase between 90 and 120 days of gestation. Both periods of increased secretion of progesterone were reflected in rises in progesterone production by placental explants in organ culture and in the activity of 3 beta-hydroxysteroid dehydrogenase in the tissue. The activity of 3 beta-hydroxysteroid dehydrogenase exceeded the rate of progesterone production by approximately 30-fold, and it appears unlikely, therefore, that this enzyme is rate-limiting in the synthesis of progesterone. Surgical reduction of the number of cotyledons led to compensation by an increase in weight of individual cotyledons with no significant increase in specific 3 beta-hydroxysteroid dehydrogenase activity or rate of production of progesterone in organ culture. It was concluded that the rise in placental production of progesterone in the middle period of gestation is unlikely to result either from an increase in 3 beta-hydroxysteroid dehydrogenase activity or from exposure to factors stimulating placental growth.

Corpus luteum growth and plasma progesterone levels in unilaterally ovariectomized pregnant rats

Unilateral ovariectomy (ULO) was carried out on rats at Day 8 of gestation: term is Day 23. The effect on peripheral plasma progesterone levels at Day 16 and on growth and cellular changes in the remaining corporalutea (CL) at Day 17 was determined by comparison with results from control and sham-operated rats. ULO increased the volume of remaining CL by 18% at Day 17. At Day 16 this effect was only apparent in rats with three or fewer CL remaining. CL hypertrophy was due to an increase in the volume of individual luteal cells and not to cell hyperplasia. Luteal cell nuclear volume also increased as did the number of endothelial cells per corpus luteum. The proportion of the corpus luteum occupied by vascular space did not alter. ULO had little effect on mean plasma progesterone levels at Day 16 (92 +/- 7 ng/ml treated; 86 +/- 11 ng/ml controls). In rats with three or fewer CL remaining, however, progesterone levels were low (51 +/- 7 ng/ml). It was concluded that ULO can enhance the growth of corpora lutea and perhaps increase their rate of progesterone production.

Effects of Immunization with the β-Subunit of Ovine Luteinizing Hormone on Corpus Luteum Function in the Rhesus Monkey

Rhesus monkeys immunized with the beta-subunit of ovine luteinizing hormone (oLHbeta) developed circulating antibodies which cross-reacted strongly with rhesus monkey chorionic gonadotropin. Normal ovulatory cycles continued, but the fertility of immunized monkeys as compared with that of controls was significantly reduced. Thus, the rhesus monkey represented a useful animal model for the study of certain aspects of an "antifertility vaccine." We investigated the effects of circulating antibodies to oLHbeta on corpus luteum function by measuring production rates (PRs) and peripheral concentrations of progesterone during the luteal phase of the menstrual cycle. Both parameters were significantly lower in immunized animals than in control animals. The length of the menstrual cycle was also significantly reduced. Progesterone PRs were also determined on days 10 and 15 after mating to test the assumption that the antifertility vaccine prevents pregnancy by interfering with "corpus luteum rescue" (the increase in PRs of progesterone usually occurring on day 15 after mating in fertilized animals). PRs increased from days 10 to 15 in pregnant controls, were unchanged in nonpregnant controls, and were significantly lower on day 15 in immunized monkeys as compared with nonpregnant and pregnant controls. These results suggest that "corpus luteum rescue" is suppressed in immunized animals.

Metabolic Clearance Rates, Production Rates and Concentrations of Progesterone in Pregnant Rhesus Monkeys

It has been reported of rhesus monkeys that uterine vein levels of progesterone decrease by 75% during the 2nd half of pregnancy while maternal peripheral vein levels remain fairly constant. Whether this difference could be explained by declining placental and/or ovarian progesterone production rates (PRs) occurring along with declining metabolic clearance rates (MCRs) of progesterone was investigated in 8 rhesus monkeys (Macaca mulatta). Values for PR MCR and peripheral levels of progesterone on Day 151 of pregnancy were not markedly different from those on Day 72 of gestation. Others have reported a 22-fold increase in uterine blood flow in pregnant macaques over nonpregnant control values. Thus as PR and MCR did not change during late pregnancy it is concluded that declining uterine vein levels of progesterone near term reflect increased uterine blood flow which delivers to the peripheral blood an unchanged amount of progesterone in an increased amount of blood which accounts for declining concentrations.