Sub-chronic exposure to dibromoacetic acid, a water disinfection by-product, does not affect gametogenic potential in mice.

Water disinfection by-products, such as dibromoacetic acid (DBA), are formed when drinking water is treated with chlorination, bromination, or ozonation. Epidemiological studies have linked these byproducts to adverse effects in humans such as cancer, developmental defects, and reproductive toxicities. DBA has been shown to produce reproductive toxicity in rodents at relatively high doses. The present study used a mouse model to determine the developmental and reproductive effects of sub-chronic, low-dose exposure to DBA. Pregnant mice (10/dose group) were exposed with DBA in drinking water at 0, 5, or 50 mg/kg/day from gestation day 15 though nursing. Upon weaning at 3 weeks, one group of pups (pre-pubertal group: 7-10 pups of each gender/treatment group) were euthanized and weights of liver, paired kidneys, testes, and ovaries were measured. In the 50 mg dose group, weights of testes and liver in males and weights of liver and kidneys in females were significantly higher (p < 0.05). The remaining pups (15-17 of each gender/dose group) continued to be dosed similarly through adulthood. At 7 weeks of age (neo-pubertal group), animals were euthanized and tissues weighed and processed for evaluation of reproductive organs and gametogenic potential. Except for decreased (p < 0.05) testes and kidney weights in 50 mg dose group males, there were no differences in organ weights. No significant differences were noted between control and dosed animals in daily sperm production, testicular sperm counts, epididymal sperm reserves, morphology of seminiferous epithelium, or ovarian follicle counts.

Physiology of GDF9 and BMP15 signalling molecules.

Two related oocyte-derived members of the transforming growth factor-beta (TGF-beta) superfamily, namely growth differentiation factor 9 (GDF9) and bone morphogenetic protein 15 (BMP15, also known as GDF9B), have recently been shown to be essential for ovarian follicular growth. In addition, both proteins have been shown to regulate ovulation rate in sheep, and although it is evident that these growth factors interact both with one another and with other intra- and extra-ovarian factors, the precise mechanisms by which they influence follicular growth and ovulation rate have not been thoroughly elucidated.

Chronic exposure to dibromoacetic acid, a water disinfection byproduct, diminishes primordial follicle populations in the rabbit.

To determine if dibromoacetic acid (DBA) affects ovarian folliculogenesis, four groups of female Dutch-belted rabbits were exposed daily to 0, 1, 5, or 50 mg DBA/kg body weight in drinking water beginning in utero from gestation day 15 throughout life. Functionality of the endocrine axis was assessed by measuring serum concentrations of gonadotropins following an im injection of 10 microg GnRH at 12 (prepubertal; n = 6/dose group) and 24 (postpubertal; n = 10/dose group) weeks of age. A day after GnRH challenge, number of ovulation sites and ovarian weights were determined at necropsy. Left ovaries were processed for histopathology, serially sectioned at 6 microm, and every twelfth section stained with hematoxylin and eosin was evaluated. All healthy follicles were categorized as primordial, primary, small preantral, large preantral, or small antral follicles. The area of each section evaluated was measured and the number of follicles in each category expressed per mm2 unit area. In prepubertal animals, DBA caused a reduction in number of primordial follicles (p < 0.05) and total healthy follicles (p < 0.05) at 50 mg/kg dose level. In adult animals, there were fewer primordial follicles in both the 5 (p < 0.01) and 50 (p = 0.1) mg/kg dose groups. No profound changes in gonadotropin profiles were observed. Although chronic exposure to DBA did not appear to have an effect on late follicular development or ovulation, DBA did reduce the population of primordial follicles. The long-term health consequences of diminished primordial follicles are unknown, but it is very likely that reproductive senescence would occur earlier.

Oocyte-derived growth factors and ovulation rate in sheep.

The physiological mechanisms controlling ovulation rate in mammals involve a complex exchange of endocrine signals between the pituitary gland and the ovary, and a localized exchange of intraovarian hormones between the oocyte and its adjacent somatic cells. The discoveries in sheep of mutations in bone morphogenetic protein 15 (BMP15) and bone morphogenetic protein receptor type IB (BMPR-IB) together with recent findings on the physiological effects of growth differentiation factor 9 (GDF9) and BMP15 on follicular development and ovulation rate highlight some important differences in the way in which the oocyte may function in mammals with different ovulation rate phenotypes. In sheep, BMP15 and GDF9 have each been shown to be essential for the early and later stages of follicular development. In addition, ovulation rate is sensitive to changes in the dose of either of these two oocyte-derived growth factors. These findings are in contrast to those reported for mice in which GDF9, but not BMP15, is essential for follicular development. The evidence to date is consistent with the hypothesis that the oocyte plays a central role in regulating key events in the process of follicular development and hence, is important in determining ovulation rate. Moreover, it appears that the mechanisms that the oocyte uses to control these processes differ between species with low and high ovulation rate phenotypes.

Expression of growth and differentiation factor-9 in the ovaries of fetal sheep homozygous or heterozygous for the inverdale prolificacy gene (FecX(I)).

Abnormal follicular and oocyte growth in ovaries of sheep homozygous (II) for the Inverdale gene, FecX(I), suggest that this gene may influence a fundamental event in initiation of folliculogenesis, with two copies of the gene inhibiting growth at the primordial/primary stage. In addition, striking similarities in ovarian morphology between mice deficient in growth and differentiation factor-9 (GDF-9) and II sheep suggest a relationship between the FecX(I) gene and GDF-9 function in the ovary. Therefore, it was hypothesized that GDF-9 mRNA expression would be inhibited in ovaries of II fetal sheep. To test this hypothesis, in situ hybridization was used to characterize GDF-9 mRNA expression in ovaries of homozygous (II), heterozygous (I+), and control (++) fetal sheep at Day 135 of gestation. GDF-9 mRNA expression was localized exclusively to oocytes from the type 1 follicle stage onward in all genotypes and is the first demonstration of GDF-9 mRNA expression in ovaries of fetal sheep. In addition, GDF-9 mRNA expression was detected in oocytes of abnormal type 2 follicles in the ovaries of II sheep. Thus, it does not appear that inhibition of GDF-9 gene expression is the mechanism of action whereby the FecX(I) gene exerts its influence. However, the possibility of translation at specific stages of follicular development cannot presently be ruled out. In addition, the FecX(I) gene may be involved, either directly or indirectly, in regulating expression of receptors for GDF-9. At present, however, neither the FecX(I) gene product nor the GDF-9 receptor has been isolated or characterized.

Effect of dose of prostaglandin F(2alpha) on steroidogenic components and oligonucleosomes in ovine luteal tissue.

To determine whether prostaglandin (PG) F(2alpha) had a dose-dependent effect upon secretion of progesterone, oligonucleosome formation, or loss of luteal weight, ewes on Day 9 or 10 of the estrous cycle were administered 0, 3, 10, or 30 mg PGF(2alpha) per 60 kg BW (i.v.), and luteal tissue was collected 9 and 24 h after injection. All doses of PGF(2alpha) decreased (P < 0. 05) concentrations of progesterone in sera by 9 h; however, in ewes treated with 3 mg PGF(2alpha), concentrations of progesterone were similar to control values at 24 h and higher (P < 0.05) than those in the 10- or 30-mg groups. Concentrations of progesterone in sera over all dose levels were highly correlated to luteal concentrations of mRNA encoding steroidogenic acute regulatory protein (P < 0.001), cytochrome P450 side-chain cleavage (P < 0.02), and 3beta-hydroxysteroid dehydrogenase (P < 0.01). Corpora lutea collected at 24 h from ewes treated with the 10- and 30-mg doses of PGF(2alpha) weighed less (P < 0.05) than those from controls. Oligonucleosomes were not present in luteal tissues from control ewes. Surprisingly, all doses of PGF(2alpha)-induced oligonucleosomes in a majority of animals at 9 h and in a majority of ewes treated with 10 and 30 mg of PGF(2alpha) at 24 h. In conclusion, 3 mg of PGF(2alpha) per 60 kg BW transiently decreased serum concentrations of progesterone and induced oligonucleosome formation, but did not result in reduced luteal weight. The 10- and 30-mg doses of PGF(2alpha) decreased secretion of progesterone and induced oligonucleosome formation and luteolysis.

Molecular cloning of the ovine Growth/Differentiation factor-9 gene and expression of growth/differentiation factor-9 in ovine and bovine ovaries.

Recently a novel member of the transforming growth factor beta (TGFbeta) superfamily termed growth/differentiation factor-9 (GDF-9) was shown to be expressed in ovaries of mice and humans, and to be essential for normal follicular development beyond the primary (type 2) follicle stage in mice. In the present study, the gene for ovine GDF-9 was isolated and characterized, and expression of GDF-9 mRNA in ovaries of domestic ruminants was examined. The predicted amino acid sequence of ovine GDF-9 is 77% and 66% homologous to human and mouse GDF-9, respectively. Specific hybridization using homologous 35S-antisense probes was restricted to oocytes. In contrast to similar studies in mice in which GDF-9 was first detected beginning at the primary (type 2) follicle stage, in ovine and bovine ovaries GDF-9 mRNA was expressed beginning at the primordial (type 1) follicle stage. The observed timing and pattern of GDF-9 expression in oocytes of domestic ruminants is consistent with a role for GDF-9 in the initiation and maintenance of folliculogenesis in these species, and supports the general concept that early stages of follicular growth and development are regulated by intraovarian factors.

Carcinoma in situ and seminoma in equine testis.

The presence of atypical germ cells resembling carcinoma in situ of human testis is reported for the first time in an unilaterally cryptorchid stallion. These cells were found in association with developing intratubular seminoma indicating they represented carcinoma in situ.

Localization and quantification of binding sites for follicle-stimulating hormone, luteinizing hormone, growth hormone, and insulin-like growth factor I in sheep ovarian follicles.

In sheep, growth and development of ovarian follicles beyond 2 mm in diameter is acutely dependent on gonadotropin support. As a consequence, following hypophysectomy (HPX) or hypothalamic-pituitary stalk disconnection (HPD), growth of follicles beyond 2 mm is arrested and all follicles > 2 mm undergo atresia. Although administration of exogenous gonadotropins stimulates follicular growth and ovulation in HPD ewes, follicles in HPX ewes remain unresponsive unless growth hormone (GH) is also given. To determine whether the difference in follicular sensitivity to gonadotropins after HPD (gonadotropin sensitive) or HPX (gonadotropin insensitive) is related to the distribution and quantity of binding sites for FSH, LH, and/or insulin-like growth factor I (IGF-I), binding sites for these hormones were localized and quantified using topical autoradiography in healthy follicles from control (pituitary-intact), HPD, and HPX ewes. In addition, in situ hybridization was performed to localize mRNA for GH and FSH receptors. Irrespective of treatment, binding of FSH and mRNA for FSH receptor were greatest (p < 0.05) in the membrana granulosa; LH binding was greatest (p < 0.05) in the theca interna; and IGF-I binding was greatest (p < 0.05) in the theca externa. Although the relative number of binding sites for LH did not differ among treatments, those for FSH and IGF-I were lower (p < 0.05) in HPD and HPX ewes compared to controls. Attempts to quantify binding sites for GH were unsuccessful due to high nonspecific binding. However, mRNA for GH receptor was most abundant (p < 0.05) in the membrana granulosa and oocytes of small antral and preantral follicles. Compared to levels in controls and HPD ewes, the level of GH receptor mRNA was lower (p < 0.05) in follicles obtained from HPX ewes. On the basis of these data, failure of small antral follicles in HPX ewes to respond to exogenous gonadotropins is not due to a reduction in receptors for FSH, LH, or IGF-I. The observed reduction of mRNA for GH receptor in the membrana granulosa of follicles from HPX ewes provides evidence that GH may play an important role in early stages of folliculogenesis and that it is involved in the maintenance of sensitivity to gonadotropins.

Steady-state luteinizing hormone receptor messenger ribonucleic acid levels and endothelial cell composition in bovine normal- and short-lived corpora lutea.

The short-lived corpus luteum (CL) contributes to reproductive inefficiency during the postpartum period in beef cows. The cause for the early demise of the short-lived CL is not fully understood but is believed to involve a premature release of prostaglandin F2 alpha. The objectives of this study were to evaluate norgestomet-hCG-induced normal-lived CL and hCG-induced short-lived CL in postpartum cows with respect to serum progesterone (P4) and 13,14-dihydro-15-keto, prostaglandin F2 alpha (PGFM) concentrations and luteal LH receptor (LH-R) concentrations, LH-R mRNA levels, and vascularity. Although serum P4 profiles from the time of hCG administration (Day 0) until luteectomy (Day 6, 7, or 8) were similar between CL life span groups, PGFM concentrations were elevated (p < 0.05) on Day 8 in cows expected to have short-lived CL compared to normal-lived CL. The LH-R concentrations were similar between normal- and short-lived CL on all days measured. Irrespective of luteal life span and day of luteectomy, all CL possessed a 4.4-kb LH-R transcript. Actin-normalized LH-R mRNA levels were similar between normal- and short-lived CL on Days 6 and 7; however, Day 8 short-lived CL contained less (p < 0.05) LH-R mRNA than Day 8 normal-lived CL. Although the area of luteal tissue occupied by capillaries in normal- and short-lived CL was similar on Days 6 and 7, the area occupied by capillaries in short-lived CL was lower (p < 0.05) than that for normal-lived CL on Day 8. Collectively, these results indicate that there is a decrease in steady-state LH-R mRNA and a reduction in luteal vascularity in CL expected to be short-lived. These changes occur concomitantly with a rise in serum PGFM, but prior to a decline in serum P4.

Use of semen as biopsy material for assessment of health status of the stallion reproductive tract.

Conventional light microscopic evaluation does not fully utilize potential indicators in seminal ejaculates for diagnosis of disorders of the reproductive tract. The technique of evaluation of all cellular components of semen, as described in this article, utilizing both light and transmission electron microscopy is a valuable diagnostic tool. Compare with other common biopsy procedures, use of semen as biopsy material is noninvasive, more representative than excisional biopsy, less expensive, and helps in the longitudinal evaluation after a therapeutic regimen.

Immunolocalization of tissue inhibitor of metalloproteinases-1 within ovine periovulatory follicular and luteal tissues.

In previous studies, tissue inhibitor of metalloproteinases (TIMP)-1 mRNA increased in follicular tissue after the preovulatory gonadotropin surge and was expressed in luteal tissue. However, the localization of TIMP-1 protein within ovine periovulatory follicular and luteal tissues is unknown. The objectives of the present study were to 1) localize TIMP-1 within follicles collected before and after a preovulatory gonadotropin surge and within Day 3 and Day 10 corpora lutea (CL), 2) determine whether TIMP-1 was colocalized to Day 10 luteal cells with oxytocin or TIMP-2, and 3) determine whether TIMP-1 was present within secretory granules of large luteal cells. Ovaries were removed from ewes before (presurge; n = 4) or 12-14 h after (postsurge; n = 5) an LHRH-induced gonadotropin surge (36 h following PGF2 alpha-induced luteolysis; objective 1). Additionally, ovaries containing CL were collected on Days 3 (n = 5; objective 1) and 10 (n = 4, 3, and 2 for objectives 1, 2, and 3, respectively). TIMP-1 immunoreactivity was observed within the granulosa cells of postsurge but not presurge follicles. On Days 3 and 10, TIMP-1 was localized within luteal tissue in a cell-specific manner. On Day 10, many of the cells that were immunopositive for TIMP-1 were judged to be large luteal cells on the basis of morphology (diameter > 22 microns; round nucleus) and colocalization with oxytocin and TIMP-2. Electron microscopy demonstrated that TIMP-1 was localized to secretory granules undergoing exocytosis from Day 10 large luteal cells. These data indicate that TIMP-1 is produced by granulosa cells following a gonadotropin surge and is packaged in secretory granules by large steroidogenic cells of the ovine CL.

An increase in serum lipids increases luteal lipid content and alters the disappearance rate of progesterone in cows.

To determine whether an increase in serum lipids alters the area occupied by lipid droplets in steroidogenic luteal cells and(or) clearance rates of progesterone from serum, pregnant beef heifers received control (n = 6) or treatment (n = 5) diets. To increase serum lipids, the treatment diet contained calcium soaps of fatty acids. Control and treatment diets were formulated to be isocaloric and isonitrogenous. Feeding of diets was initiated approximately 100 d before parturition and continued through the third postpartum estrous cycle. On d 12 or 13 of the third postpartum cycle, corpora lutea were collected by ovariectomy and a center slice was processed for electron microscopy. Eight samples from each slice were sectioned, stained, and examined at a magnification of 2,500x. Five micrographs per sample were analyzed for area occupied by small (SLC) and large (LLC) luteal cells, percentage of the area of each steroidogenic cell type occupied by lipid, and total steroidogenic area (SLC + LLC) occupied by lipid. Jugular blood was collected before and after ovariectomy, and progesterone, cholesterol, high-density lipoprotein (HDL), and low-density lipoprotein (LDL) were quantified. Cows consuming treatment diets had approximately twice (P < .05) the concentration of cholesterol, HDL, and progesterone in serum that controls had. The percentage of the area of SLC, LLC, and total area occupied by lipid was greater (P < .05) in treated than in control cows. The average time required for serum concentrations of progesterone to decrease by 50% after ovariectomy was greater (P < .05) in treated than in control cows (170 +/- 16 vs 113 +/- 15 min).(ABSTRACT TRUNCATED AT 250 WORDS)

Structural and functional properties of the corpus luteum of pregnancy.

In domestic ruminants the parenchyma of the corpus luteum consists of two subpopulations of steroidogenic cells commonly referred to as small and large luteal cells. These cells differ not only in size and structural characteristics, but also in functional properties. During the mid-luteal phase of the oestrous cycle approximately 60% of the corpus luteum is occupied by steroidogenic cells. Although the steroidogenic capacity of these cells declines as pregnancy advances, the cells persist as distinct populations throughout pregnancy and for several days following parturition. In general, structural changes typically observed at the end of the oestrous cycle also occur after parturition, but over a more extended period. These include deletion of endothelial cells and occlusion of capillary lumina with cellular debris and apoptotic bodies, an infiltration of eosinophils and macrophages, and fragmentation and lysis of parenchymal cells. However, not all parenchymal cells undergo lysis, nor are they rapidly phagocytosed by macrophages. Instead, many fuse to form what appear to be large syncytia that contain numerous lipid droplets, tightly packed mitochondria and multiple nuclei with condensed chromatin. Fusion of parenchymal cells to form syncytial profiles begins 2-3 days after parturition and the syncytia persist for at least 22 days post partum. By day 35 post partum transformation of the corpus luteum into a corpus albicans is essentially complete.

Effects of luteinizing hormone and growth hormone on luteal development in hypophysectomized ewes.

To test the hypothesis that growth hormone (GH) as well as luteinizing hormone (LH) is required for normal luteal growth and function, 16 western range ewes were hypophysectomized (HPX) on day 5 of the estrous cycle. Ewes were randomly assigned to receive saline (S), LH, GH, or LH + GH (n=4 per group) from the time of HPX until collection of corpora lutea 7 days after HPX (day 12). Corpora lutea were also collected from pituitary-intact ewes on days 5 (day 5 control,n=4) and 12 (day 12 control,n=4) of the estrous cycle. To assess luteal function, concentrations of progesterone in sera, luteal weights and luteal concentrations of mRNA encoding cytochrome P450 side-chain cleavage enzyme (P450(scc)) and 3ß-hydroxysteroid dehydrogenase/Δ5,Δ4 isomerase (3ß-HSD) were determined. Concentrations of progesterone in sera and luteal weights increased between days 5 and 12 of the estrous cycle in control ewes, but not in HPX + S ewes. In HPX ewes treated with LH, concentrations of progesterone in sera and luteal mRNA for P450(scc) and 3ß-HSD increased but luteal weights were unaffected. Treatment with GH increased luteal weight and luteal concentrations of mRNA encoding P450(scc) but did not increase concentrations of mRNA encoding 3ß-HSD compared to HPX + S ewes. Concentrations of progesterone in sera of GH-treated, HPX ewes were similar to those of day 12 control ewes but not significantly different from those in HPX + S ewes. Treatment of HPX ewes with LH + GH increased all parameters of luteal function measured to values similar to those in day 12 controls. In conclusion, both GH and LH are necessary for normal luteal development in the ewe.

Recombinant bovine somatotropin does not improve superovulatory response in sheep.

Although treatment of heifers and ewes with recombinant bovine somatotropin (rbST) does not increase ovulation rate, data for heifers indicate that the number of small antral follicles is approximately doubled. Accordingly, the objectives of this study were to determine whether 1) treatment of ewes with rbST would increase the number of small antral follicles, thereby increasing the number of follicles that could potentially respond to superovulation treatment, and 2) superovulatory responses could be improved in ewes with "synchronized" populations of follicles. Twenty-four ewes were divided into four groups: control, control+rbST, hypothalamic-pituitary stalk disconnected (HPD), and HPD+rbST. Beginning on d 5 of the estrous cycle, ewes were injected once daily for 13 d with either rbST (3 mg) or saline. The superovulatory regimen consisted of a single dose of PMSG followed by twice-daily injections of FSH for four consecutive days. After ovariectomy, ovulation sites and follicles were counted. Twice-daily blood samples were assayed for somatotropin (ST) and IGF-I. The concentrations of ST in rbST-treated ewes were greater (P < .05) than those in controls. Treatment with rbST increased (P < .05) the mean serum concentration of IGF-I in control but not in HPD ewes. There was no increase in ovulation rate or number of small antral follicles in response to rbST. Synchronizing follicle populations also failed to increase ovulation rate or reduce variability of response. We conclude that supplementation with rbST and synchronization of follicles does not increase the superovulatory response in sheep.

PGE2 attenuates PGF2 alpha-induced increases in free intracellular calcium in ovine large luteal cells.

When ovine large luteal cells are placed in culture and exposed to PGF2 alpha, there is a rapid and sustained increase in the concentration of free intracellular calcium which is believed to play a major role in the luteolytic and cytotoxic effects of PGF2 alpha. Since administration of exogenous PGE2 can prevent spontaneous and PGF2 alpha-induced luteolysis in vivo, and the cytotoxic effects of PGF2 alpha on large luteal cells in vitro, the objective of this study was to determine if one mechanism by which PGE2 acts is to attenuate increases in free intracellular calcium induced by PGF2 alpha. At concentrations of 10 nM or greater, PGF2 alpha caused a significant and sustained increase in free intracellular calcium in large luteal cells. Similarly, PGE2 also induced increases in free intracellular calcium but required doses 20-fold greater than PGF2 alpha. When PGE2 (1, 10 or 100 nM) was incubated with PGF2 alpha (100 nM) increases in free intracellular calcium induced by PGF2 alpha were attenuated (P < 0.05) when measured 5 min, but not at 30 min, after initiation of treatment. The observed decrease in the concentration of free intracellular calcium at 5 min in response to PGF2 alpha was the result of fewer cells responding to PGF2 alpha. In addition, the concentrations of free intracellular calcium attained in the cells that did respond was reduced 25% compared to cells treated with PGF2 alpha alone. Thus, part of the luteal protective actions of PGE2 appears to involve an inhibition of the early (5 min) increase in free intracellular calcium induced by PGF2 alpha.

Receptors for prostaglandins F2 alpha and E2 in ovine corpora lutea during maternal recognition of pregnancy.

Plasma membrane receptors for prostaglandins (PG) F2 alpha and E2 were quantified in ovine corpora lutea obtained from nonpregnant and pregnant ewes on Days 10, 13, and 15 post-estrus, and from additional ewes on Days 25 and 40 of pregnancy. Regardless of reproductive status or day post-estrus, concentrations of luteal receptors for PGF2 alpha were 7- to 10-fold greater than those for PGE2. In pregnant ewes the concentration of receptors for PGF2 alpha was highest on Day 10 (35.4 +/- 2.8 fmol/mg) and lowest on Day 25 (22.3 +/- 2.5 fmol/mg). A difference in the concentration of luteal receptors for PGF2 alpha between pregnant and nonpregnant ewes was apparent only on Day 15 post-estrus, at which time the concentration of receptors for PGF2 alpha was higher in pregnant ewes than in nonpregnant ewes (27.1 +/- 2.7 vs. 17.7 +/- 2.7 fmol/mg). Concentrations of receptors for PGE2 in pregnant ewes were similar (p > 0.05; 2.8 +/- 0.3 to 3.7 +/- 0.2 fmol/mg) between Days 13 and 40 but were higher (p < 0.05) than in corpora lutea obtained from nonpregnant ewes on Days 10 (5.0 +/- 0.4 vs. 4.1 +/- 0.2 fmol/mg) and 15 (3.7 +/- 0.2 vs. 2.0 +/- 0.4 fmol/mg) post-estrus. Although concentrations of receptors for both PGF2 alpha and PGE2 were lowest in corpora lutea obtained from nonpregnant ewes on Day 15, this was not due to luteal regression since the weights and concentrations of progesterone in corpora lutea on Day 15 were not lower than those for corpora lutea obtained on Days 10 and 13.(ABSTRACT TRUNCATED AT 250 WORDS)

Gonadotrope- and thyrotrope-specific expression of the human and bovine glycoprotein hormone alpha-subunit genes is regulated by distinct cis-acting elements.

The proximal 5'-flanking region of the alpha-subunit gene from humans and cattle confers pituitary-specific expression to heterologous reporter genes in transgenic mice. To investigate whether these promoter regions also contain the necessary regulatory elements for cell-specific expression and hormonal regulation, we used three independent lines of transgenic mice. Two lines of transgenic mice contained chimeric genes consisting of either 1.6 kilobasepairs (kbp) of human or 3 15 basepairs of bovine alpha-subunit proximal 5'-flanking sequence linked to the bacterial gene encoding chloramphenicol acetyltransferase (CAT). A third line of transgenic mice contained the proximal 1.6 kbp of 5'-flanking sequence of the human alpha-subunit gene linked to the bacterial lacZ gene encoding beta-galactosidase (beta gal; H alpha beta gal transgenic mice). Hormonal replacement paradigms indicate that both human and bovine alpha CAT transgenes are regulated by GnRH, suggesting that their expression occurs in gonadotropes. Thus, the proximal 5'-flanking regions of both the human and bovine alpha-subunit genes must contain regulatory elements that confer both gonadotrope-specific expression and responsiveness to GnRH. In contrast to the human alpha-subunit promoter, the bovine alpha-subunit promoter lacks a functional cAMP response element, suggesting that transduction of both cell-specific and GnRH transcriptional signals occurs through cAMP response element-independent pathways. Thyrotropes also express the glycoprotein hormone alpha-subunit gene. Yet, hormone replacement paradigms with propylthiouracil and T3 were ineffective in altering CAT activity in the pituitary of human or bovine alpha CAT transgenic mice. Because a thyroid hormone response element has been localized to the proximal 5'-flanking region of the human alpha-subunit gene, these data suggest that the alpha CAT transgenes lack sufficient information to direct expression to thyrotropes. Direct evidence for this possibility was obtained through immunocytochemical studies performed on pituitaries from H alpha beta gal transgenic mice. beta-Galactosidase activity appeared in gonadotropes, but not thyrotropes. We conclude, therefore, that distinct and separable regulatory elements mediate the expression of the alpha-subunit gene in gonadotropes and thyrotropes.

Proliferation of jejunal mucosal cells in rats flown in space.

To examine the effects of spaceflight on the proliferation and turnover of jejunal mucosal cells, we compared the percentages of mitotic cells present in the crypts of Lieberkühn in the proximal, middle, and distal jejunum in each of five rats flown on the COSMOS 2044 mission and in rats included in the vivarium, synchronous, and caudal-elevated groups. On the basis of the data obtained, there was no difference in mitotic indexes between animals in the flight and vivarium (ground control) groups. Thus it appears that the ability of jejunal mucosal cells to proliferate is not affected by microgravity conditions associated with spaceflight. Although the length of villi and depth of crypts were reduced in flight animals compared with those in the vivarium group, the observed reduction is probably attributable to changes in the connective tissue core of villi and is not likely due to an impairment of the proliferation and migration of jejunal mucosal cells.