Antiprogestin RU486 blunts the stimulatory effect of galanin on LH secretion from rat pituitaries in vitro in an estrous cycle stage-dependent manner

Galanin (GAL), a neuroactive peptide detected in the hypothalamus and anterior pituitary, stimulated in a dose (0.1 and 1 microM)-dependent manner luteinizing hormone (LH) secretion from metestrous and proestrous rat pituitaries incubated in culture medium devoid of progesterone (P). GAL had no effect on follicle-stimulating hormone (FSH). Antiprogestin RU486 (10 nM) decreased non-stimulated (basal) secretion of LH and FSH only in pituitaries from proestrous rats and blunted the stimulatory effects of GAL on LH secretion in both metestrous and proestrous pituitaries. These findings are consistent with the hypothesis that GAL-mediated signal transduction interacts with estrogen-dependent P receptor at the pituitary level to stimulate LH secretion.

The fate of corpora lutea in the cyclic golden hamster

Structural luteolysis shows striking interspecies differences. Morphological changes in the corpus luteum (CL) of the cyclic hamster have been studied alongside the potential involvement of known luteolytic hormones. Ovaries from intact Syrian golden hamsters killed at 1100 h on days 1 and 2 and at 1100 and 1700 h on days 3 and 4 of the estrous cycle were dissected for histological study. The day of ovulation, the day of estrus, was arbitrarily designated day 1 of the estrous cycle. Steroidogenic cells in the CL were scarcely luteinized on day 1 and reached full luteinization on day 2. On the morning of day 3, initial regressive changes (accumulation of lipid droplets, invasion by neutrophils, and accumulation of phagocytic cells) were observed. These regressive changes increased progressively and apoptotic cells as well as phagocytic cells containing phagocytized apoptotic cells were abundant on the evening of day 3. On the morning of day 4, apoptotic cells/bodies and phagocytic cells containing phagocytized material were extremely abundant throughout the CL. However, steroidogenic cells with intact nuclei and well-preserved blood vessels were also found. Surviving cells in the CL showed progressive morphological changes. These cells showed morphological features intermediate between luteal and interstitial cells in the evening of day 4 and were virtually indistinguishable from interstitial cells on day 1 of the following cycle. Additional animals were injected at 1100 h on day 2 with: (a) the dopaminergic agonist CB154 (0.4 mg) to block prolactin secretion, (b) the anti-estrogen LY117018 (1.6 mg) or the anti-androgen Flutamide (3 mg) to block estrogen or androgen receptors, respectively, and (c) progesterone (2 mg) to prevent the fall in serum progesterone concentrations. Ovaries from these animals were collected at 1700 h on day 3 and at 1000 h on day 4. The luteolytic process was not affected by any treatment. These data indicate that, in contrast to its close relatives (e.g., the rat), structural luteolysis in the hamster is independent of the apoptotic inducing luteolytic hormones. In addition, differences in the cellular mechanisms responsible for CL elimination were also present. In the hamster, part of the luteal cells do not undergo apoptosis and seemed to progress through another developmental path giving rise to interstitial-like cells.

The in vitro inhibitory action of antiprogestin RU486 on LH and FSH secretion in the absence of progesterone in rats is estrogen-dependent

Previous in vivo findings show that in the virtual absence of progesterone (P), the antiprogestin RU486 reduces LH and FSH secretion in proestrous rats, indicating that activation of P receptor (PR) can occur in the absence of the cognate ligand. The present study investigates, in vitro, whether or not the inhibitory effect of antiprogestin RU486 on gonadotropin secretion in the absence of P is estrous cycle dependent, and whether its specific expression in proestrus mirrors the high estrogen (E2) background. In the first experiment we investigated the effect of RU486 (10 nM) and/or LHRH (10 nM) on LH and FSH secretion in incubated pituitaries collected on each day of the estrous cycle of the rat. In the second experiment, we determined the effect of RU486 and/or LHRH on preovulatory LH and FSH release by pituitaries from female rats that were ovariectomized (OVX), treated with the antiestrogen LY117018-HCL (Eli Lilly & Co.), or injected with 20 micrograms of estradiol benzoate (EB). The third experiment investigated the effect of RU486 and/or LHRH on LH and FSH release by pituitaries collected from intact or EB-treated (0.1 mg/kg over three consecutive days) male rats. RU486 reduced both basal and LHRH-stimulated LH and FSH secretion in proestrous pituitaries from normal 4-day cyclic rats. By contrast, in diestrous pituitaries, RU486 increased both parameters of LH secretion but was without effect on FSH release. RU486 was also without effect in pituitaries collected from rats in estrus or metestrus, or from OVX or antiestrogen-treated rats. Moreover, EB injection or treatment induced the full inhibitory effect of RU486 in pituitaries from female and male rats, respectively. The above results suggested that P occupancy of the receptor is not required for the formation or function of the active receptor and hence for preovulatory LH and FSH secretion, and that this form of PR activation at pituitary level is E2-dependent and not genetically determined.

Different patterns of structural luteolysis in the human corpus luteum of menstruation

Structural luteolysis is a complex process responsible for the elimination of the corpus luteum (CL). The aim of this study was to analyse the luteolytic process of the CL of menstruation. For this, we have morphologically studied 654 ovaries from 340 cycling women. Apoptotic cells were observed almost exclusively during the perimenstrual period and were extremely scarce at advanced stages of involution. Steroidogenic luteal cells surviving to the perimenstrual apoptotic wave underwent characteristic degenerative changes, consisting of intense cytoplasmic vacuolation, expression of macrophage markers and accumulation of lipofuscin pigment, and they persisted for long periods of time. Accumulation of corpora albicantia (CA) was observed in only 25% of a subset of 168 women, whereas 28% showed involuting CL without hyalinization, consisting of clusters of pigment-filled cells, and 46.4% showed ovaries with a mixture of CA and involuting CL without hyalinization or involuting CL with intermediate features. Evolution of the CL towards CA seemed to be related to the presence of a large, blood-filled cavity. The data from this study suggested that different patterns of structural luteolysis exist during CL involution, and that the final fate of the involuting CL is dependent on the presence of a large, central, blood-filled cavity.

Luteinizing hormone secretion elicited in a ligand-independent activation of progesterone receptor manner at pituitary level in the rat: differential effect of two selective estrogen receptor modulators

In the absence of progesterone, RU486 reduced basal and luteinizing hormone-releasing hormone (LHRH)-stimulated LH secretion in pituitaries from proestrous rats, a fact which evidences a ligand-independent activation of progesterone receptors (LIAPR) at pituitary level. This was also observed in pituitaries from rats treated with tamoxifen, and absent in glands from either ovariectomized or raloxifene-treated animals. Both ovariectomy or raloxifene treatment reduced the stimulatory effect of LHRH on LH secretion, while tamoxifen induced an even higher response. Prolactin (PRL) secretion was unaffected by either RU486 or LHRH, nor it was influenced by ovariectomy or raloxifene treatment. However, treatment with tamoxifen elevated PRL in all groups. These findings indicate that LIAPR is an estrogen-dependent phenomenon at the anterior pituitary of the female rat, and that tamoxifen and raloxifene present agonist and antagonist estrogen activity, respectively, at this level.

Progesterone on an oestrogen background enhances prolactin-induced apoptosis in regressing corpora lutea in the cyclic rat: possible involvement of luteal endothelial cell progesterone receptors

Preovulatory surges of both prolactin (PRL) and progesterone have been suggested to be necessary for the induction of apoptosis in the regressing corpus luteum of the cyclic rat. The aim of these experiments was to study whether the administration of PRL and/or progesterone on the morning of pro-oestrus reproduces the regressive changes that happen in the cyclic corpus luteum (CL) during the transition from pro-oestrus to oestrus, and to analyse the temporal relationships between two characteristic features of structural luteolysis (luteal cell apoptosis and accumulation of macrophages). Cyclic rats (treated at 0900 h with an LHRH antagonist to block LH secretion) were injected at 1000 h with PRL and progesterone and killed at 0, 30, 60, 90 and 180 min after treatment. The number of apoptotic cells increased progressively from 60 min after treatment onward in hormone-treated rats, whereas the number of macrophages did not change throughout the period of time considered. Rats injected with PRL plus progesterone showed significantly greater numbers of apoptotic cells than those injected with PRL alone. The luteolytic effects of progesterone were in keeping with the presence of luteal endothelial cells showing progesterone receptor (PR) immunoreactivity in pro-oestrus. Treatment of rats during dioestrus and pro-oestrus with the specific antioestrogens LY117018 and RU58668 decreased the luteolytic effects of PRL and progesterone and the number of luteal endothelial cells immunostained for PR. These results strongly suggest that the preovulatory PRL surge and the preovulatory increase in progesterone together trigger structural regression of the corpus luteum. This seems to be dependent on oestrogen-driven cyclic changes in PRs in luteal endothelial cells.

Comparison of the effects of antiprogestins RU38486, ZK98299 and ORG31710 on periovulatory hypophysial, ovarian and adrenal hormone secretion in the rat

The antiprogestin (AP) RU38486 (RU) blocks progesterone (P) and glucocorticoid (G) actions. Administration of 4 mg RU on proestrous morning to cyclic rats dissociates LH and FSH secretion on proestrous afternoon, early estrus and on estrous afternoon. In order to ascertain which action blocked by RU is predominant in the control of periovulatory LH and FSH secretion, a study was made on the effects of: a) 1 or 4 mg of ZK98299 (ZK) (type I P antagonist; Schering), b) 2 or 8 mg of Org31710 (OR) (type II P antagonist lacking anti-G actions; Organon) or c) 1 or 4 mg of RU (type II P antagonist; Exelgyn) to 4-day cyclic rats on proestrous morning on serum concentrations of LH, FSH, inhibin-alpha (I), estradiol-17beta (E), progesterone (P) and corticosterone (B) at 18:30 h on proestrus and at 02:00 and 18:30 h on estrus. Controls, receiving 0.2 ml oil, had elevated serum concentrations of all six hormones on proestrous afternoon; at early estrus, only serum concentrations of FSH and P remained elevated, and, on estrous afternoon, all hormones but I and B, that peaked again, had reached their lowest serum levels. All AP treatments except 1 mg ZK had the same effects. On proestrous afternoon serum LH concentrations were reduced and serum FSH concentrations were suppressed whereas serum levels of I, E, P and B were unaffected. At early estrus, basal serum concentrations of LH and E increased while FSH secretion was abolished. Serum levels of I, P and B did not differ from controls. AP treatments increased basal LH concentration, hyperstimulated FSH secretion and reduced serum I concentration on the afternoon of estrus. E, P and B serum levels did not differ from controls at this stage. Treatment with 1 mg ZK was less effective in reducing serum FSH on proestrous afternoon and at early estrus, and had no effect on serum concentrations of any hormone on estrous afternoon. These results indicate that blockade of P receptor activation by P is, predominantly, the mechanism of AP action on periovulatory gonadotropin secretion in rats.

Antiprogestins RU486 and ZK299 suppress basal and LHRH-stimulated FSH and LH secretion at pituitary level in the rat in an oestrous cycle stage-dependent manner

We have previously shown that administration of antiprogestin (AP) type II RU486 to ovariectomized (OVX) rats on the morning of pro-oestrus decreases the magnitude of preovulatory gonadotrophin surge. This suggests that the effect of RU486 on LHRH-dependent gonadotrophin release may be independent of its ability to block progesterone actions. The aim of the present research was to study the possible site of RU486 action and to determine whether the gonadotrophin suppressive effect of APs RU486 and ZK299 is dependent on the oestrogen background. Intact or OVX rats in the morning of pro-oestrus were injected s.c. with 4 mg of RU486 or ZK299 (AP type I) at 0900 h on pro-oestrus. At 1830 h, serum concentration of FSH and LH and median eminence (ME) content of LHRH were determined. In the second experiment, the effect of RU486 and ZK299 on pituitary responsiveness to LHRH (100 ng, i.p.) and ME content of LHRH at 1830 h pentobarbital-blocked intact or OVX rats was evaluated. In the last study, the anterior pituitary release of FSH and LH from pro-oestrus or metoestrus donors incubated with or without LHRH (1, 10 or 100 nM) in the presence or absence of APs (20 nM) was evaluated. Both APs reduced serum FSH and LH levels at 1830 h on pro-oestrus in intact and OVX rats. The suppressive effect on gonadotrophin release brought about by AP treatment was also evidenced in PB-blocked intact and OVX rats. This suggested that the inhibitory effect of APs occurred, at least in part, at pituitary level. Furthermore, in the absence of the natural ligand, APs significantly reduced basal and LHRH-stimulated FSH and LH release from pro-oestrous but not from metoestrus pituitaries. In conclusion, these experiments have shown, both 'in vivo' and 'in vitro', that APs RU486 and ZK299 have suppressive effects at pituitary level on basal and LHRH-stimulated FSH and LH secretion, regardless of their antiprogestagenic activity, in pro-oestrus but not in metoestrus.

A quantitative study of changes in the human corpus luteum microvasculature during the menstrual cycle

Endothelial cells are the most abundant cell type in the corpus luteum (CL), and changes in blood vessels have been proposed to play a pivotal role in CL regression. We have studied quantitatively the changes in the human granulosa-luteal microvasculature in CL of various ages: young (Days 17-19 of the cycle), mature (Days 20-24), old (Days 25-27), early regressing (follicular phase of the following cycle), and late regressing (luteal phase of the following cycle). Blood vessels were identified by immunohistochemical staining for the endothelial cell marker CD34. Because of the anisotropy of blood vessels, both vertical and transverse sections of the granulosa-lutein layer (GLL) were used to estimate relative (volume, surface, and length densities) and absolute (mean cross-sectional area) vascular variables. Full luteinization from young to mature CL was accompanied by a 61% increase in the mean cross-sectional area of vascular profiles and a 52% increase in the mean volume of granulosa-lutein cells, as an estimator of changes in the volume of the GLL. In old and early regressing CL, there was a progressive increase in relative structural vascular variables, due to the shrinkage of the GLL, whereas the mean cross-sectional area of capillaries showed a 53% decrease from mature to old CL. Finally, in late regressing CL, there was a decrease in most relative structural variables, in spite of the increasingly shrunken GLL. The decrease in the capillary diameter found at the late luteal phase most likely leads to a decreased blood flow, and early changes in blood vessels could initiate and/or accelerate CL regression.

The antiprogestin RU486 dissociates LH and FSH secretion in male rats: evidence for direct action at the pituitary level

Administration of 4 mg of the antisteroid RU486 over 8 consecutive days to adult male rats dissociated in vivo and in vitro gonadotrophin secretion, increasing FSH and decreasing LH secretion. In subsequent experiments we evaluated the involvement of testicular or adrenal secretory products, as well as hypothalamic LHRH, in the effects of 4 consecutive days of RU486 treatment on the secretion of gonadotrophins. The first day of RU486 injection was designated day 1, subsequent days being numbered consecutively. Groups of rats injected with oil (0.2 ml) or RU486 (4 mg) were: (i) injected s.c. from day 1 to day 4 with the antiandrogen flutamide (10 mg/kg); (ii) bilateral orchidectomized (ORCH) on day 1; and (iii) bilateral adrenalectomized (ADX) on day 1. Controls were given flutamide vehicle or were sham operated. To ascertain whether the secretion of LHRH is involved in the effects of RU486 on gonadotrophin secretion, we measured the LHRH secretion into the pituitary stalk blood vessels at 1100 h on day 5 in oil- or RU486-treated rats. Additional oil- and RU486-treated rats were injected i.p. with 100 ng LHRH at 1000 h on day 5, or s.c. with 1 mg LHRH antagonist (LHRH-ANT) at 1000 h on days 2 and 4. Controls were given saline. All animals were decapitated at 1100 h on day 5, trunk blood collected and serum stored frozen until FSH, LH and testosterone assays.%While ADX had no effect on FSH and LH secretion in either oil- or RU486-treated rats, the removal of androgen negative feedback with flutamide treatment or by ORCH substantially increased serum levels of FSH and LH in both oil- and RU486-treated rats, and thus annulled the effects of RU486. No differences in pituitary stalk plasma LHRH concentrations were found between oil- and RU486-treated rats. Injection of LHRH increased serum FSH and LH concentrations in oil-treated rats but only, and to a lesser extent, LH concentrations in RU486-treated rats. Treatment with LHRH-ANT decreased serum concentrations of FSH and LH in both oil- and RU486-treated rats. These results suggest that RU486 inhibited LHRH-stimulated LH secretion at the pituitary level, and that FSH secretion increased in response to a reduction in the negative feedback of androgen.

Both prolactin and progesterone in proestrus are necessary for the induction of apoptosis in the regressing corpus luteum of the rat

This study was conducted to analyze the roles of prolactin (PRL) and progesterone in the induction of luteal cell apoptosis and accumulation of macrophages in the regressing corpus luteum. We studied the number of apoptotic cells and macrophages in regressing corpora lutea in estrus 1) in cycling rats or after blocking PRL secretion with the dopaminergic agonist CB154, and 2) after blocking progesterone actions with the progesterone receptor antagonists RU-486 or ZK98299. Cells showing the morphological features characteristic of apoptosis contained fragmented DNA as indicated by in situ 3' end labeling. In cycling rats, a 100-fold increase in the number of apoptotic cells and a 4-fold increase in the number of macrophages was found from the evening (1600 h) of proestrus to the morning (1100 h) of estrus. Both increases were blocked by PRL suppression with CB154. Furthermore, blocking progesterone actions with progesterone receptor antagonists RU-486 or ZK98299 without affecting PRL secretion inhibited apoptosis but did not affect the accumulation of macrophages, whether treatment was started on the morning of metestrus (blocking diestrous and proestrous progesterone) or on proestrus (blocking only proestrous progesterone). Otherwise, exogenous progesterone was not effective in inducing apoptosis in the absence of PRL. These results indicate that both PRL and progesterone in proestrus are necessary for the induction of apoptosis in the regressing corpora lutea, whereas the accumulation of macrophages seemed to be dependent exclusively on the PRL surge.

Macrophages, cell proliferation, and cell death in the human menstrual corpus luteum

We studied the presence and numbers of macrophages in the different compartments of the human menstrual corpus luteum (CL) in relation to the proliferative activity and apoptosis in luteal cells. Macrophages were recognized by immunohistochemical demonstration of the lysosome-associated glycoprotein CD68, and proliferating cells by immunohistochemical detection of the cell cycle-related protein Ki67 and by counting mitotic cells. In general, changes in the number of macrophages were parallel to the functional activity of the CL. Macrophage numbers increased up to the end of the early luteal phase, remained relatively unchanged during the midluteal phase, and decreased at the late luteal phase. Furthermore, macrophages showed prominent morphological changes during the cycle. They showed round or elongated cytoplasm during the early and late luteal phases, and dendritic features in the midluteal phase. Proliferating cells were very abundant on Days 15-16 and showed a significant decrease thereafter. Most proliferating cells corresponded to stromal (mainly vascular) cells. However, about 5% of granulosa-lutein cells and about 15% of theca-lutein cells were proliferating during the early and midluteal phases. Regression of the CL at the late luteal phase was associated with both a decrease in the number of proliferating cells and an increase in the number of apoptotic cells, which were highly increased on Days 25-27 of the cycle. The number of macrophages was not related to cell proliferation nor to cell death during the luteal phase. The observed changes in both macrophage number and morphology suggest the existence of a bidirectional communication between macrophages and steroidogenic cells in the human CL, or regulation of both cell populations by similar mechanisms.

A comparative study of mast cells and eosinophil leukocytes in the mammalian testis

The existence of a physiological integration between the immune and endocrine systems has long been recognized. In spite of the abundant literature data on the presence of cells of the immune system in the testis, mast cells and eosinophil leukocytes have received little attention. We have studied the presence, distribution and numbers of mast cells and eosinophils in the testes of 12 mammalian species. Mast cells were frequently found in equine (stallion, ass and mule) and human testis, whereas eosinophils were nearly absent. On the contrary, eosinophils were abundant in the hare testis, while mast cells were lacking. Both cells types were present in high numbers in swine (wild and domestic boar) testis. Otherwise, mast cells and eosinophils were absent from the testicular parenchyma of several species (rat, dog, cat, bull and deer), although they were present, in most cases, around blood vessels in the tunica albuginea. The presence of high numbers of mast cells and/or eosinophil leukocytes in the testicular parenchyma of some species suggest a role for these cells in local regulatory pathways.

Design and calibration of unicapillary pneumotachographs

This study presents a method for design and calibration of unicapillary pneumotachographs for small-animal experiments. The design, based on Poiseuille's law, defines a set of internal radius and length values that allows for laminar flow, measurable pressure differences, and minimal interference with animal's respiratory mechanics and gas exchange. A third-order polynomial calibration (Pol) of the pressure-flow relationship was employed and compared with linear calibration (Lin). Tests were done for conditions of ambient pressure (Pam) and positive pressure (Ppos) ventilation at different flow ranges. A physical model designed to match normal and low compliance in rats was used. At normal compliance, Pol provided lower errors than Lin for mixed (1-12 ml/s), mean (4-10 ml/s), and high (8-12 ml/s) flow rate calibrations for both Pam and Ppos inspiratory tests (P < 0.001 for all conditions) and expiratory tests (P < 0.001 for all conditions). At low compliance, they differed significantly with 8.6 +/- 4.1% underestimation when Lin at Pam was used in Ppos tests. Ppos calibration, preferably in combination with Pol, should be used in this case to minimize errors (Pol = 0.8 +/- 0.5%, Lin = 6.5 +/- 4.0%, P < 0.0005). Nonlinear calibration may be useful for improvement of flow and volume measurements in small animals during both Pam and Ppos ventilation.

Ovarian follicle macrophages: is follicular atresia in the immature rat a macrophage-mediated event?

Macrophages have recently been found to play roles in most ovarian events through cytokine release and/or cell-cell communication. We studied the presence of macrophages in the ovaries of neonatal (0-7 days of age), juvenile (10-20 days of age), and prepubertal (25-30 days of age) rats, as well as adult cycling rats, in relation to follicular development and atresia. Macrophages were extremely scarce in the ovarian stroma up to 30 days of age. However, at 10 days of age, about 13% of small growing healthy follicles contained macrophages among granulosa cells. The percentage of macrophage-containing follicles at 15 days of age was about 60%, and the vast majority of these follicles also had pyknotic granulosa cells, which increased in number from 15 to 20 days of age. This type of atresia showed distinctive morphological and functional features in comparison with the atretic process observed in adult cycling rats. At 25 and 30 days of age, atretic follicles in advanced stages of atresia, together with atretic follicles similar to those present in adult rats, were observed. In adult rats, only a small proportion of healthy growing follicles contained macrophages. These cells were absent from early atretic follicles, and invasion by macrophages occurred at advanced stages of atresia. These data indicate that a different type of atresia occurred during early postnatal development, probably related to the special endocrine environment in immature rats. The close association between the presence of macrophages inside the follicles and of apoptotic granulosa cells strongly supports the hypothesis that macrophages mediate follicular atresia in immature rats.

Proliferative activity of preovulatory follicles and newly formed corpora lutea in cycling rats from late prooestrus to early oestrus

Ovaries from adult cycling rats were studied from 1600 h on the day of prooestrus to 0700 h on the day of oestrus in order to relate the cyclic hormonal changes to the proliferative activity of preovulatory and postovulatory (i.e. newly-formed corpora lutea) follicles. Proliferative activity was studied by the immunohistochemical demonstration of DNA-incorporated 5-bromodeoxyuridine (BrdU). The proliferative activity of granulosa cells (GC) in large preovulatory follicles showed a centripetal pattern and decreased during prooestrus, reaching a minimum at 2100 h. However, a proliferative wave was found in the GC of preovulatory follicles at 0200 h on the day of oestrus and in those of newly-formed corpora lutea at 0700 h on the day of oestrus. These results suggest that the granulosa cells of preovulatory follicles show maturational changes that followed a different pattern, depending on their location within the follicle, and that the proliferative wave found from 0200 to 0700 h on oestrus is important for the establishment of the number of steroidogenic cells in the cyclic corpus luteum.

Effects of gonadotrophins on the proliferative activity of somatic testicular cells in neonatal and prepubertal rats

The proliferative activity of the different testicular somatic cell lineages was studied in neonatal and prepubertal rats after treatment with recombinant FSH (recFSH) and human chorionic gonadotrophin (hCG). Male rats were treated on days 5-9 or 15-19 with 1 or 3 IU/rat.day, respectively, of recFSH, 10 IU/rat.day of hCG or vehicle and sacrificed the day following the last injection. Proliferation was studied by the immunohistochemical demonstration of DNA-incorporated 5-bromodeoxyuridine (BrdU) in both paraffin- and Epon-embedded tissues. No differences existed for the labeling indices in paraffin- or Epon-embedded tissues, but the identification of some cell types were easier in these latter one. At 10 days of age, no significant differences were found for the proliferative activity of the different cell types, except for the labeling index of foetal Leydig cells that was increased in hCG-treated animals. At 20 days of age, treatment with recFSH increased the testicular weight and tubule diameter, as well as the size of adult type Leydig cells and the labeling index of macrophages. Treatment with hCG increased the testicular weight and the number and size of adult-type Leydig cells, as well as the labeling indices of mesenchymal, adult-type Leydig cells and macrophages. These results indicate that the effects of gonadotrophin treatment on the different somatic testicular cell types are dependent on both the type of cells and their developmental stage.

Role of the testis in the response of the pituitary-testicular axis to nitric oxide-related agents

Nitric oxide (NO) is generated from the guanidine group of L-arginine by NO synthases (NOS) in a wide variety of tissues, including endocrine organs. In order to discriminate between central and local effects of NO-related agents on the pituitary-testicular axis, adult rats were injected intraperitoneally with 1 g/kg body weight (bw) L-arginine methyl ester (L-AME, an exogenous substrate of NOS), 0.5 mg/kg bw sodium nitroprusside (SNP, an NO donor) or vehicle (0.9% NaCl) or intratesticularly with 2 mg/testis L-AME, 2 micrograms/testis SNP or 25 microliters vehicle, and killed at 60 or 120 min after treatment. Both intraperitoneal and intratesticular administration of L-AME had the same effects: a decrease in the serum concentrations of LH and testosterone and in those of testosterone in the testicular interstitial fluid. However, treatment with SNP was more effective when given intratesticularly, inducing a decrease in serum and interstitial fluid testosterone concentrations, without significant changes in LH concentrations. Furthermore, when rats were injected intraperitoneally with 4 mg L-AME (the same dose as that given intratesticularly), serum LH concentrations were not changed. In addition, L-AME administration was not effective in modifying serum LH concentrations in castrated rats. To test the possible role of Leydig cells, the effects of systemic administration of L-AME were studied in rats depleted of Leydig cells by treatment with ethylene dimethane sulphonate. In these animals L-AME significantly decreased serum LH concentrations. To study the role of macrophages in this system, rats depleted of testicular macrophages by the liposome-suicide approach were injected intraperitoneally (1 g/kg bw) or intratesticularly (2 mg/testis) with L-AME or vehicle, 10 days after macrophage depletion, and killed at 120 min after treatment. The effects of L-AME on serum LH concentrations were blocked when the drug was administered intratesticularly.

Role of prolactin in the regulation of macrophages and in the proliferative activity of vascular cells in newly formed and regressing rat corpora lutea

The proliferative activity of vascular cells and the number of macrophages were studied in corpora lutea of cycling and pregnant rats after prolactin (PRL) administration or depletion with the dopaminergic agonist CB154. Pregnant rats showed a higher proliferative activity of the vascular cells in newly formed corpora lutea than did cycling rats in metestrus. When cycling rats were treated with PRL, the proliferative activity was equivalent to that of pregnant rats. Treatment of pregnant rats with CB154 decreased the proliferative activity of vascular cells to the level in cycling rats. Otherwise, the proliferative activity was not modified in cycling rats after CB154 treatment. This indicates that the increase in the proliferative activity of vascular cells in the corpus luteum of pregnancy was due to the twice-daily PRL surges induced by mating. Treatment of cycling rats with CB154 decreased the number of macrophages in both newly formed and regressing corpora lutea, whereas PRL treatment increased the number of macrophages in regressing corpora lutea. In pregnant rats, treatment with CB154 decreased the number of macrophages in both newly formed and regressing corpora lutea. These results suggest that both the preovulatory and the twice-daily PRL surges regulate the macrophage population in newly formed and regressing corpora lutea.

Evidence for steroidogenic luteal cell hypertrophy and hyperplasia during pregnancy in the rat

The proliferative activity of the rat corpus luteum was studied on days 2, 3, 6, 9, 12, 15, 17, 19 and 21 of pregnancy. Proliferating cells were detected by the immunohistochemical demonstration of DNA-incorporated 5-bromodeoxyuridine (BrdU) and by the presence of mitoses. Steroidogenic luteal cells showed two proliferative waves on days 12-15 and on day 21, when relatively abundant BrdU-labeled and mitotic cells were observed. These cells were clearly distinguishable from non-steroidogenic cells by their round nuclei and large polygonal cytoplasm. The proliferative activity on days 12-15 was coincident with an increase in the size of the cells and in progesterone concentrations. On the other hand, the proliferative activity of non-steroidogenic luteal cells (especially endothelial cells of the blood and lymphatic vessels) followed a different pattern. These cells intensely proliferated on days 2-3 of pregnancy and this proliferative activity was significantly higher than that observed in non-pregnant rats on metestrus and diestrus. A new proliferative wave was observed on days 12-15, in association with the increase in the proliferative activity of steroidogenic cells. The presence of both BrdU-labeled and mitotic steroidogenic luteal cells provides evidence that these cells do proliferate and that both hypertrophy and hyperplasia are involved in the increase in the parenchyma of the corpus luteum during pregnancy. Also, the results suggest that different mechanisms are involved in the regulation of the proliferative activity in the corpus luteum at different times during pregnancy.

Follicular growth pattern in cyclic rats from late pro-oestrus to early oestrus

Adult cyclic rats were studied from 16:00 h on pro-oestrus to 07:00 h on oestrus to relate the cyclic hormonal changes to the proliferative activity and growth pattern of growing follicles. The proliferative activity was studied by 5-bromodeoxyuridine (BrdU) labelling and by the presence of mitoses. Small growing follicles (less than 275 microns in diameter) were divided into five classes: multilaminar classes a (Ma, up to 75 microns in diameter), b (Mb, 76-150 microns), c (Mc, 151-200 microns) and d (Md, 201-274 microns) and follicles measuring > or = 275 microns in diameter were considered as > or = class 1, following previous classifications. I.H concentrations were maximal at 18:30 h on pro-oestrus, and this was coincident with an increase in FSH, prolactin and progesterone concentrations, whereas oestradiol and testosterone concentrations were decreased. From 02:00 h on oestrus the concentrations of all hormones, except those of FSH, were decreased. The number of Ma, Mb and Mc follicles did not change during pro-oestrus-oestrus, whereas an increase in the number of follicles > or = class 1 was found at 07:00 h on oestrus. This appears to be a consequence of the increased proliferative activity of Md follicles, evidenced by the increase in the BrdU labelling and mitotic index of this follicle class, found from 02:00 to 07:00 h on oestrus, together with a decrease in the percentage of early atretic follicles > or = class 1 at 07:00 h on oestrus. This study provides an improved classification of small growing follicles into discrete classes and delineates a size class of follicles (Md follicles) that is responsive to the cyclic hormonal changes on early oestrus.

Response of the testis to gonadotrophin replacement in young hypophysectomized vs. gonadotrophin-releasing hormone antagonist-treated rats

We have studied the response of atrophic Leydig cells to gonadotrophin replacement in young hypophysectomized (HX) and GnRH antagonist (GnRH-ANT)-treated rats. Hypophysectomy was performed at 28 days of age. Age-matched rats were treated with GnRH-ANT from 28 to 51 days of age. From 45 to 51 days of age, animals were injected with 5 IU recFSH, 10 IU hCG or vehicle. Body and testicular weights, as well as the diameter of the seminiferous tubules were significantly higher in GnRH-ANT-treated than in HX rats. Both recombinant FSH and hCG treatments induced a similar increase in testicular weight and tubule diameter in HX and GnRH-ANT-treated rats. However, hCG treatment induced a significantly higher increase in Leydig cell size in HX (3.2-fold) than in GnRH-ANT-treated (1.4-fold) rats. These results suggest that the response of atrophic Leydig cells to gonadotrophin supplementation was partially inhibited in the presence of GnRH antagonist, whereas Sertoli cell-mediated responses seem not to be affected.

In vivo manipulation (depletion versus activation) of testicular macrophages: central and local effects

Testicular macrophages are a relevant cell type for the regulation of Leydig cell steroidogenesis. The availability of liposome technology allows in vivo manipulation of macrophages in order to analyze their role in the regulation of the hypothalamic-pituitary-testicular axis. In this study, adult (70 days of age) and prepubertal (22 days of age) rats were injected intratesticularly with liposomes containing either dichloromethylene diphosphonate (C12MDP) to deplete testicular macrophages or muramyl tripeptide (MTP-PE) to activate them. Control rats were injected with the corresponding volumes of 0.9% NaCl. Animals were killed 10 days after treatment. Adult rats injected bilaterally or unilaterally with C12MDP liposomes showed increased serum LH and testosterone concentrations, as well as increased testosterone concentrations in the testicular interstitial fluid. In unilaterally injected rats, testosterone concentrations in the interstitial fluid were higher in the macrophage-containing testes than in the contralateral, macrophage-depleted testes. Adult rats treated bilaterally with MTP-PE liposomes showed increased numbers of testicular macrophages, whereas the number of Leydig cells was unchanged. Serum LH concentrations were decreased, but no changes were found in testosterone concentrations. Prepubertal rats treated bilaterally with C12MDP liposomes showed decreased numbers of Leydig cells. However, serum LH and testosterone concentrations were increased. Otherwise, prepubertal rats treated bilaterally with MTP-PE liposomes showed increased numbers of macrophages and Leydig cells, as well as increased serum testosterone concentrations. These data suggest that testicular macrophage-derived factors act at two different levels in the pituitary-testicular axis: first, at a central level by inhibiting LH secretion, and secondly, at a local level by stimulating Leydig cell steroidogenesis.

Antiprogestagen RU486 prevents the LH-dependent decrease in the serum concentrations of inhibin in the rat

1. In the rat, the LH-dependent ovarian progesterone rise mediates several actions of the primary surge of LH on the ovary. This experiment was aimed at elucidating the effects of the antiprogestagen RU486 on the LH-dependent decrease in both the serum concentrations and the ovarian content of inhibin. 2. All rats in this experiment were treated with an antagonist of LHRH (1 mg/200 microliters saline at 0800 h in proestrus) to suppress the endogenous release of LH. One group of rats received 32 micrograms LH/250 microliters saline at 1200 h in proestrus. Other group was given 4 mg RU486/200 microliters oil at 0800 h in proestrus. The third group was injected with both RU486 and LH. Rats from the control group were injected with 250 microliters saline and 200 microliters oil. Animals were decapitated at 1700 h in proestrus and trunk blood and ovaries collected to determine the serum concentrations of LH, FSH, progesterone, 17 beta-estradiol and inhibin as well as the ovarian content of inhibin. 3. The ovulatory dose of LH in LHRHa-treated rats decreased both the serum concentrations and the ovarian content of inhibin and increased the serum concentrations of FSH. The administration of RU486 blocked the effect of LH on the serum concentrations of inhibin but not that on the ovarian content of inhibin. 4. Since the antiprogestagen RU486 blocked the effect of LH on the serum concentrations of inhibin, we conclude that ovarian progesterone, besides mediating the effects of the primary LH surge on the ovulatory process and luteinization, participates in the LH-dependent drop in the serum concentrations of inhibin in proestrous afternoon.

Ovary mediates the effects of RU486 given during proestrus on the diestrous secretion of luteinizing hormone in the rat

The aim of these experiments was to study the action of proestrous afternoon follicular progesterone secretion on the preovulatory secretion of gonadotropins in the rat. Four-day-cycling rats were given 4 mg of the antiprogestagen RU486 in the morning of proestrus (Day 1), and its effects on the pituitary function during diestrus were compared with those of RU486 given in the morning of estrus (Day 2). The pituitary function was assessed by measuring basal secretion of LH and FSH as well as the pituitary response to either estradiol benzoate (EB) (3 mug/100 g BW at 1300 h on Day 3) or LHRH (100 ng/rat at 1200 h on Day 4). In all experiments, trunk blood was taken at 1300 h on Day 4 to measure serum gonadotropin concentrations. In rats receiving an injection of RU486 on estrus, the absence of only the diestrous progesterone actions increased basal serum concentrations of LH and decreased those of FSH, and as in vehicle-treated controls, EB inhibited and LHRH stimulated LH secretion. In contrast, the absence of both proestrous afternoon and diestrous progesterone actions (as characterized rats treated with RU486 on proestrus) antagonized the inhibitory effect of EB and sensitized the pituitary to LHRH. These effects of RU486 on proestrus are ovary-dependent and eliminated by ovariectomy on metestrus. The increased ovarian secretion of testosterone and estradiol-17 beta during diestrus does not mediate the effects of proestrus-administered RU486 on pituitary function: no differences were found in the serum concentrations of estradiol-17 beta in diestrus between the groups of rats treated with RU486, and administration of the antiandrogen flutamide (2 mg/rat at 0900 h on Days 2 and 3) did not reverse the effects of RU486 on proestrus. In conclusion, the results suggest that in the absence of proestrous afternoon progesterone action, the ovaries of the 4-day-cyclic rat keep the pituitary gland in a state of low sensitivity to the inhibitory effects of estradiol and high sensitivity to the stimulatory effects of LHRH. Moreover, the results suggest that the putative ovarian factors involved are factors other than progesterone, androgens, or estradiol-17 beta.