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C E Farin

Publications and source records attributed to C E Farin.

36 records · Page 2Linked to original sources
PubMed1994

Identification of cDNAs encoding bovine cyclin B and Cdk1/Cdc2.

cDNA sequences encoding homologs of cyclin B and Cdk1/Cdc2 were isolated from bovine blastocyst-stage embryos produced in vitro. The bovine CycB sequence is 1548 nucleotides (nt) in length and contains the conserved motif 'FLRRXSK', characteristic for known cyclin B proteins. The deduced protein contains 427 amino acids (aa) and has an estimated mass of 47,653 Da. The bovine cdk1/cdc2 sequence is 1275 nt in length and contains the highly conserved motif 'EGVPSTAIREISLLKE'. The deduced protein contains 297 aa (33,931 Da).

Amino Acid Sequence↗
PubMed1994

Inhibition of germinal vesicle breakdown in bovine oocytes by 5,6-dichloro-1-beta-D-ribofuranosylbenzimidazole (DRB).

5,6-Dichloro-1-beta-D-ribofuranosyl-benzimidazole (DRB) is an analog of the nucleoside adenosine that has been used to inhibit transcription in a variety of cell types. The present studies were designed to evaluate the ability of DRB to block germinal vesicle breakdown (GVBD) in bovine oocytes matured in vitro and to characterize culture conditions required for DRB-mediated arrest of meiosis. Administration of DRB (60-90 microM) at 2-3 h intervals during culture of COC blocked GVBD in approximately 70 percent of oocytes. The inhibitory effect of DRB was reversible and required the presence of cumulus cells. Treatment with DRB was associated with a 57% decrease in 3H-uridine incorporation into total COC RNA and a 90.8% decrease into mRNA but did not affect the incorporation of 3H-leucine into COC proteins. The ability of DRB to arrest meiosis was significantly compromised if supplemental gonadotropin preparations were absent from the maturation media. Gonadotropin-induced GVBD as well as cumulus cell expansion was blocked by treatment with DRB but not with adenosine. GVBD in cultured bovine COC was initially inhibited and then stimulated when supplemental gonadotropin preparations were included in the culture media. DRB treatment in the presence of gonadotropin supplementation blocked the stimulatory effect of gonadotropins on GVBD. In conclusion, DRB can be used to arrest GVBD in bovine COC in a specific and reversible manner. The data support the hypothesis that gene transcription is required for the stimulatory phase of gonadotropin-mediated GVBD in cultured bovine COC.

Animals↗
PubMed1991

Induction of trophoblastic interferon expression in ovine blastocysts after treatment with double-stranded RNA.

Ovine trophoblast protein-1 (oTP-1) is an interferon (IFN) related to the IFN-omega. The objectives of this research were: (i) to attempt to induce oTP-1 mRNA in day-11 ovine conceptuses with polyinosinic-polycytidylic acid (poly(I).poly(C], and (ii) to determine if IFN-omega mRNA is also produced on day 11 of gestation. In experiment I, conceptuses were cultured in presence of 100 micrograms/ml poly(I).poly(C) (n = 5) or medium alone (control, n = 3) for up to 8 h. In situ hybridization was used to assess effects of treatment on mRNA concentrations for oTP-1 and actin (positive hybridization control). Poly(I).poly(C) increased oTP-1 mRNA concentrations approximately 2.5-fold (p less than 0.01), but had no effect on actin mRNA. In experiment II, the presence of mRNA for oTP-1 and ovine IFN-omega was determined by using reverse transcription-polymerase chain reaction (RT-PCR) analysis of conceptus total RNA coupled with Southern blot hybridization of the PCR reaction products with specific cDNA probes. oTP-1 mRNA was detectable in all poly(I).poly(C)-treated (n = 7) and control (n = 6) conceptuses, whereas IFN-omega mRNA was detected in only three of seven poly(I).poly(C)-treated conceptuses and not in any controls. Together these results demonstrate that expression of oTP-1 mRNA can be enhanced by treatment with poly(I).poly(C) and that oTP-1 is the primary but not the only type I-IFN inducible in conceptuses on day 11 of gestation.

Animals↗
PubMed1991

Slowed transcription and rapid messenger RNA turnover contribute to a decline in synthesis of ovine trophoblast protein-1 during in vitro culture.

Ovine trophoblast protein-1 (oTP-1) is produced in massive amounts by conceptuses during the Day-12-20-period of early pregnancy. The rate of production of oTP-1 declines during culture of conceptuses, however, suggesting a role for critical intrauterine factors for continued production. The present study was conducted to define the mechanism responsible for the in vitro decline in oTP-1 synthesis. Over 24 h culture, synthesis of oTP-1 was initially rapid but then declined such that there was little increase in either the protein or its antiviral activity after 12 h. By contrast, the release of total protein into the medium continued at an approximately linear rate for the entire 24-h period of culture. By using in situ hybridization to tissue sections and dot-blot analysis of tissue extracts with labeled cDNA probes, it was shown that the quantity of oTP-1 mRNA fell 3- to 5-fold during culture, whereas the amount of actin mRNA remained relatively constant. To determine whether this selective fall in levels of oTP-1 mRNA resulted from decreased transcription rate and/or high turnover rate of existing mRNA, conceptuses were either provided continuously with [3H]uridine for 24 h or labeled for 9 h and then exposed to medium enriched in unlabeled uridine and cytidine for a further 15 h. Specific incorporation of 3H into oTP-1 mRNA was assessed by hybridization to excess oTP-1 cDNA immobilized on nitrocellulose membranes. In the continuous labeling study, 3H in total RNA increased at an approximately linear rate for at least 18 h, whereas the content of 3H in oTP-1 mRNA peaked at 9 h and declined about 10-fold by 24 h.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1991

The polypeptides and genes for ovine and bovine trophoblast protein-1.

Ovine and bovine trophoblast protein-1 (oTP-1 and bTP-1) have been strongly implicated as antiluteolytic agents and responsible for maternal recognition of pregnancy in sheep and cattle, respectively. Both are interferons (IFN) belonging to the IFN-alpha family, but their length (172 residues versus 166 for most IFN-alpha) places them in an unusual subclass (the IFN-alpha II). The various isoforms of oTP-1 and bTP-1 produced by trophoblast tissue appear to arise in part from translation of multiple mRNAs which are themselves the products of distinct genes. These genes, like those for other IFN-alpha, are without introns. However, the genes for oTP-1 and bTP-1 form a distinct subgroup within the IFN-alpha II on the basis of their overall primary sequences and the high conservation of the 3'-untranslated ends of their transcription units. The bTP-1 genes also differ from the bovine IFN-alpha II in the organization of the promoter regions upstream from the transcription start site. Nevertheless, computer-aided analysis of the primary polypeptide sequences of oTP-1 and bTP-1 indicates that the molecules are likely to have approximately the same shapes and dimensions as all other IFN-alpha molecules. It remains to be determined whether they have unique biological properties which distinguish them from other IFN-alpha molecules.

Amino Acid Sequence↗
PubMed1990

Characterization of the antiviral activity constitutively produced by murine conceptuses: absence of placental mRNAs for interferon alpha and beta.

Antiviral activity has been found in conceptus and placental tissues in numerous species, including mice, pigs, sheep, cattle and humans. In sheep and cattle, the antiviral activity is due to an interferon alpha (IFN-alpha), but in other species the nature of the protein(s) responsible for placental activity is unknown. The objectives of this study were to determine if the constitutive antiviral activity associated with the mouse conceptus is produced as early as the peri-implantation period, and to determine if the activity is due to an IFN-alpha or -beta. Conceptus and placental tissue explants released antiviral activity from Day 4 through at least Day 16 of gestation as measured in an agar overlay bioassay employing CHO cells challenged with vesicular stomatitis virus. This activity was neutralized by antiserum against MuIFN-alpha/beta. The same antiserum failed, however, to immunoprecipitate radiolabeled proteins from medium collected from Day 4 blastocysts cultured in the presence of L-[35S]-methionine. S1 nuclease analysis of placental RNA and screening of ectoplacental cone and extraembryonic ectoderm cDNA libraries with MuIFN-alpha and -beta probes failed to detect IFN related mRNAs, even under relatively non-stringent conditions of hybridization. Thus, while antiviral activity is produced by peri-implantation conceptuses in several diverse mammalian species, it does not appear to be due to a conserved type of IFN in all these species.

Agar↗
PubMed1990

Expression of trophoblastic interferon genes in sheep and cattle.

The trophoblastic interferons ovine and bovine trophoblast protein-1 (oTP-1 and bTP-1, respectively) have been implicated as mediators of maternal recognition of pregnancy in sheep and cattle. The objective of this study was to describe the onset and duration of gene expression for oTP-1 and bTP-1 in preimplantation ovine and bovine conceptuses by in situ hybridization and Northern analysis. Sections from paraffin-embedded ovine conceptuses, collected on Days 10, 11, 12, 13, and 15 of gestation (n = 1, 3, 3, 2, 2), and bovine conceptuses, collected on Days 12/13, 15/16, and 19 (n = 2, 4, 5), were hybridized to specific [35S]-labeled cDNA probes. Two different probes, one encompassing bases 442-918 and representing both coding and 3'-untranslated regions, and a second 3'-specific probe (bases 650-912) were used to detect oTP-1 mRNA. At all stages examined, oTP-1 mRNA was confined to trophectoderm of ovine conceptuses. Consistent with earlier studies, expression increased markedly at Day 13. oTP-1 mRNA was detected at low levels in seven of seven ovine conceptuses prior to Day 13 when the longer probe was employed. With the 3'-specific probe, however, oTP-1 mRNA was detected in only one of the seven ovine conceptuses prior to Day 13. Thus, although low amounts of oTP-1 mRNA may be present in ovine conceptuses prior to Day 13, massive induction of this mRNA occurs on Day 13 coincident with the initiation of maternal recognition of pregnancy.(ABSTRACT TRUNCATED AT 250 WORDS)

Actins↗
PubMed1990

Effects of luteinizing hormone on luteal cell populations in hypophysectomized ewes.

To examine the effect of purified LH on development and function of luteal cells, 27 ewes were assigned to: (1) hypophysectomy plus 2 micrograms ovine LH given i.v. at 4-h intervals from Days 5 to 12 of the oestrous cycle (oestrus = Day 0; Group H + LH; N = 7); (2) hypophysectomy with no LH replacement (Group N-LH; N = 6); (3) control (no hypophysectomy) plus LH replacement as in Group H + LH (Group S + LH; N = 7); (4) control with no LH treatment (Group S-LH; N = 7). Blood samples were collected at 4-h intervals throughout the experiment to monitor circulating concentrations of LH, cortisol and progesterone. On Day 12 of the oestrous cycle corpora lutea were collected and luteal progesterone concentrations, unoccupied receptors for LH and number and sizes of steroidogenic and non-steroidogenic luteal cell types were determined. Corpora lutea from ewes in Group H-LH were significantly smaller (P less than 0.05), had lower concentrations of progesterone, fewer LH receptors, fewer small luteal cells and fewer non-steroidogenic cells than did corpora lutea from ewes in Group S-LH. The number of large luteal cells was unaffected by hypophysectomy, but the sizes of large luteal cells, small luteal cells and fibroblasts were reduced. LH replacement in hypophysectomized ewes maintained luteal weight and the numbers of small steroidogenic and non-steroidogenic luteal cells at levels intermediate between those observed in ewes in Groups L-LH and S-LH. In Group H + LH ewes, luteal and serum concentrations of progesterone, numbers of luteal receptors for LH, and the sizes of all types of luteal cells were maintained. Numbers of small steroidogenic and non-steroidogenic cells were also increased by LH in hypophysectomized ewes. In Exp. II, 14 ewes were assigned to: (1) sham hypophysectomy with no LH replacement therapy (Group S-LH; N = 5); (2) sham hypophysectomy with 40 micrograms ovine LH given i.v. at 4-h intervals from Day 5 to Day 12 of the oestrous cycle (Group S + LH; N = 5); and (3) hypophysectomy plus LH replacement therapy (Group H + LH; N = 4). Experimental procedures were similar to those described for Exp. I. Treatment of hypophysectomized ewes with a larger dose of LH maintained luteal weight, serum and luteal progesterone concentrations and the numbers of steroidogenic and non-steroidogenic luteal cells at control levels.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗
PubMed1990

Numbers of steroidogenic luteal cells in Booroola Merino ewes.

In Exp. 1 ovulation rates, plasma concentrations of progesterone, mean individual and total CL weights were determined on Days 4, 10 and 12 after oestrus of Booroola Merino ++ ewes and FF ewes. Mean ovulation rates ranged from 1.5 to 1.8 in ++ ewes and from 5.3 to 6.2 in FF ewes (P less than 0.01). There were no differences in plasma concentrations of progesterone or total luteal weight between the two groups on any of the days studied. Individual CL were smaller (P less than 0.01) in FF ewes than in ++ ewes. In Exp. 2 the numbers of luteal cells in CL collected from 5 ++ and 5 FF ewes on Day 10 of the oestrous cycle were morphometrically determined. The CL from FF ewes were smaller (P less than 0.01) and had fewer total steroidogenic cells (P less than 0.01), fibroblasts (P less than 0.01), and capillary endothelial cells and pericytes (P less than 0.05). However, the luteal cell volume density, number of cells/g tissue, average cell diameter or average cell volume was not different between the two groups of ewes for any cell type studied. It is concluded that the 5-6 CL in FF ewes function in an identical fashion to the 1-2 CL in ++ ewes.

Animals↗
PubMed1990

Trophoblast proteins and maternal recognition of pregnancy.

IFNs are produced by conceptus and/or placental tissues in several mammalian species. Of these IFNs, the trophoblast interferons, oTP-1 and bTP-1, are clearly the most well characterized and have been found to be members of an unusual 172-amino-acid-long IFN-alpha subfamily. Although classified as IFN-alpha IIs, they are unique in two respects. First, the 3' non-coding regions of their mRNAs differ from those of other IFN-alpha s and, secondly, oTP-1 and bTP-1 are expressed in extraordinarily large amounts during a defined period of early pregnancy. oTP-1 and bTP-1 have physiological actions which are clearly anti-luteolytic, although it is suspected that they are not the only conceptus products required to maintain the corpus luteum of pregnancy. A role for trophoblast interferons in local regulation of the uterine immune system is also anticipated. Because IFNs are known to exhibit other activities, including effects on cell proliferation, cell differentiation, and the induction of specific gene transcription in target cells, the trophoblast and/or placental interferons may also be influencing uterine function by such mechanisms. However, this question remains largely unexplored. Finally, the regulation of expression of the trophoblast interferons represents an important area of research that has the potential to lead to significant reductions in the incidence of embryonic loss in mammals.

Amino Acid Sequence↗
PubMed1990

Interferons at the placental interface.

The antiluteolytic factors secreted by sheep and cattle conceptuses are closely related structurally to alpha-interferons (IFN-alpha s). They are known as ovine and bovine trophoblast protein-1 (oTP-1 and bTP-1), respectively. The mRNAs for oTP-1 and bTP-1 are transcribed from multiple genes and are the major translatable messages of Day 13-17 sheep conceptuses and Day 15-20 cattle conceptuses. The proteins belong to the 172-amino acid IFN-alpha II (or IFN-omega) subfamily and have the typical antiviral and antiproliferative properties of the 166-residue IFN-alpha Is. These embryonic interferons also bind to the IFN-alpha receptor, which is present in uterine endometrium in high concentrations, and can influence the production of prostaglandin F-2 alpha and the pattern of protein secretion in that tissue. Through use of in-situ hybridization procedures on tissue sections and Northern and dot blot analyses of extracted conceptus RNA, ovine oTP-1 mRNA has been shown to increase markedly around Day 13 and to decrease after about Day 15 of pregnancy. The mRNA is confined entirely to cells of the trophectoderm. Significant induction of mRNA that hybridizes to an oTP-1 cDNA occurs in response to exposure to polyI:polyC in Day 11 sheep blastocysts which normally have low levels of oTP-1 expression. However, the basis for induction in the normal progression of embryonic development remains unclear. The fact that preimplantation conceptuses of other species, e.g. pig, release substances with antiviral activity suggests that IFNs may have an important role in pregnancy that extends beyond the domestic ruminants.

Amino Acid Sequence↗
PubMed1989

Morphometric quantification of mitochondria in the two steroidogenic ovine luteal cell types.

Progesterone secretion is regulated by different mechanisms in large and small steroidogenic ovine luteal cells. Large cells secrete approximately 7-fold more progesterone in an unstimulated state than small cells. Since cholesterol side-chain cleavage, which is catalyzed by an inner mitochondrial membrane enzyme complex, is a major rate-limiting step in progesterone synthesis, mitochondrial components were quantified in the two steroidogenic cell types throughout the estrous cycle. Corpora lutea collected on Days 4 (n = 4), 8 (n = 4), 12 (n = 5), and 16 (n = 6) of the estrous cycle were prepared for electron microscopy. Volume densities of cell types within corpora lutea and mitochondrial densities within cell types were estimated by point-counting; nuclear and cytoplasmic volume densities were estimated by planimetric analysis. A total of 570 micrographs (magnification 5300 X) were analyzed. Large cell volume density was unchanged during the cycle (35 +/- 1%) while small cell volume density increased (p less than 0.05) from 13 +/- 1% on Day 4 to 20 +/- 3% on Day 12. Large cell mitochondrial volume density increased (p less than 0.05) from 13 +/- 1% on Day 4 to 23 +/- 1% on Day 16 accompanied by an increase in cytoplasmic volume density such that nuclear to cytoplasmic ratio increased (p less than 0.05) from 1:14 to 1:34 between Days 4 and 16. Small cell mitochondrial volume density increased from 11 +/- 1% on Day 4 to 14 +/- 1% (p less than 0.05) for the rest of the cycle while the nuclear to cytoplasmic ratio remained at 1:14.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1989

In situ localization of mRNA for the interferon, ovine trophoblast protein-1, during early embryonic development of the sheep.

The embryonic interferon, ovine trophoblast protein-1 (oTP-1), is considered to be the major protein signal by which the developing ovine conceptus communicates its presence to the mother in order to provide extension of luteal progesterone secretion critical for the establishment of pregnancy. The objective of the present study was to examine the distribution of mRNA for oTP-1 in developing ovine embryos by using in situ hybridization. A total of 11 ovine embryos were collected on days 11, 13, 15, 17, and 23 of gestation (n = 1, 2, 3, 3, and 2, respectively) and were subjected to either immediate paraformaldehyde fixation or culture for 24 h followed by fixation. Fixed embryos were embedded in paraffin and oTP-1 mRNA levels determined by in situ hybridization with a 35S-labeled cDNA probe specific for the 3'-untranslated region of the oTP-1 mRNA. Controls included parallel hybridizations with a 35S-labeled gamma-actin cDNA to detect actin mRNA (positive control) and with 35S-labeled plasmid cDNA (negative control). Hybridization signals were detected by autoradiography and quantified by computer-assisted video image analysis. Ovine TP-1 mRNA levels in tissue were low but detectable on day 11, rose 6.5-fold to peak concentrations on day 13, and declined in a linear fashion through day 23. A low, detectable signal was present in portions of chorionic tissue on day 23. Messenger RNA was localized solely to the trophectoderm and did not appear in the extraembryonic endoderm, yolk sac, and embryonic disc. The relative hybridization signal for actin mRNA was approximately 12-fold lower than that for oTP-1 mRNA on day 13. However, by day 17 oTP-1 and actin mRNA hybridization signals were similar. In conclusion, oTP-1 mRNA is localized in the trophectoderm of the developing embryo, being produced between days 11 and 23 of gestation with peak amounts produced per cell at approximately day 13 of gestation.

Animals↗
PubMed1989

Analysis of cell types in the corpus luteum of the sheep.

The parenchyma of the corpus luteum of the ewe consists of two distinct steroidogenic cell types: small luteal cells and large luteal cells. Although both cell types produce and secrete progesterone, they differ with respect to morphological and biochemical characteristics. During the oestrous cycle, and continuing into pregnancy, the cellular composition of the corpus luteum is altered. As the oestrous cycle progresses small luteal cells increase in number but not size whereas large luteal cells remain constant in number but increase in size. Changes in the cellular composition of the ovine corpus luteum appear to be regulated by LH. Moreover, small luteal cells obtained from pregnant ewes were larger and lacked responsiveness to LH compared to those from non-pregnant animals. The basis of this loss of responsiveness is not clear as there is no concomitant loss of receptors for LH. The corpus luteum is a dynamic gland which changes in cellular composition and hormonal responsiveness with alterations in the reproductive state of the animal.

Animals↗
PubMed1988

Effect of luteinizing hormone and human chorionic gonadotropin on cell populations in the ovine corpus luteum.

Two experiments were conducted to examine the effect of treatment with human chorionic gonadotropin (hCG) or ovine luteinizing hormone (LH) on the number and size distribution of steroidogenic luteal cells. In Experiment I, 27 ewes were assigned to one of three groups: 1) hCG (300 IU, i.v.) administered on Days 5 and 7.5 of the estrous cycle (Day 0 = Estrus); 2) LH (120 micrograms, i.v.) administered at 6-h intervals from Days 5 to 10 of the cycle; 3) saline (i.v.) administered as in the LH treatment group. Blood samples were drawn daily from the jugular vein for quantification of progesterone. On Day 10, corpora lutea were collected, decapsulated, weighed, and dissociated into single cell suspensions. Cells were fixed, stained for 3 beta-hydroxysteroid dehydrogenase (3 beta HSD) activity, and the size distribution of 3 beta HSD-positive cells was determined. Treatment with hCG, but not LH, increased (p less than 0.05) concentrations of progesterone in serum and the weight of corpora lutea. Treatment with either hCG of LH increased the proportion of cells greater than 22 micron in diameter and decreased the proportion of cells less than or equal to 22 micron (p less than 0.01). The ratio of small to large luteal cells decreased after treatment with either hCG or LH (p less than 0.05). In Experiment II, 9 ewes were assigned to one of two groups: 1) LH (120 micrograms, i.v.) administered at 6-h intervals from Days 5 to 10 of the estrous cycle, and 2) saline (i.v.) administered as in the LH treatment group.(ABSTRACT TRUNCATED AT 250 WORDS)

3-Hydroxysteroid Dehydrogenases↗
PubMed1986

Role of luteinizing hormone in regulating luteal function in ruminants.

The technique of hypothalamic-pituitary stalk-disconnection was used to reinvestigate the roles of luteinizing hormone (LH) and prolactin in the regulation of luteal function in ewes. Stalk-disconnection was performed on d 5 of the estrous cycle and ewes were administered either saline (control), LH at 40 micrograms at 4-h intervals, 2 mg of alpha-ergocryptine at 12-h intervals or both LH and ergocryptine. The treatment regimen for LH was designed to mimic luteal phase concentrations of this hormone. Blood samples were collected from all stalk-disconnected and 6 sham-disconnected ewes at 4-h intervals beginning at 0600 h on the day of surgery for determination of serum concentrations of prolactin, cortisol and progesterone. Corpora lutea were collected from control ewes on d 5 of the estrous cycle and from the stalk-disconnected and sham-disconnected ewes on d 12 of the cycle. The luteal tissue was weighed, a slice taken for morphometric analysis of cell numbers, sizes and types and luteal progesterone content was determined. The weight and progesterone content of corpora lutea collected from stalk-disconnected ewes were similar to those observed in control ewes on d 5 of the cycle but less (P less than .05) than those in control ewes on d 12 of the cycle. However, serum concentrations of progesterone were unaffected by stalk-disconnection. Luteinizing hormone replacement therapy increased both the weight and progesterone content of corpora lutea in stalk-disconnected ewes to values similar to those observed in control ewes on d 12. Treatment of stalk-disconnected ewes with alpha-ergocryptine reduced serum concentrations of prolactin by greater than 95% but was without effect on the parameters of luteal function measured. The number of small steroidogenic luteal cells in any of the stalk-disconnected ewes was not different from that observed in control ewes. However, treatment of stalk-disconnected ewes with LH was followed by an increase (P less than .05) in the diameter of small luteal cells. The number of large luteal cells was greater (P less than .05) in LH-treated, stalk-disconnected ewes than in intact control ewes on d 12 of the estrous cycle. The mean diameter of large luteal cells was not affected by treatment with LH.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗
PubMed1986

Morphometric analysis of cell types in the ovine corpus luteum throughout the estrous cycle.

The cellular composition of ovine corpora lutea obtained during the early (Day 4), mid (Days 8 and 12), and late (Day 16) stages of the estrous cycle was determined by morphometric analysis. Individual corpora lutea were collected via midventral laparotomy from a total of 19 ewes. A center slice from each corpus luteum was processed for electron microscopy and subsequent morphometric analysis of the numbers and sizes of steroidogenic and nonsteroidogenic cells. Luteal weight progressively increased throughout the estrous cycle (p less than 0.05). Corpora lutea collected on Day 16 were assigned to one of two subgroups on the basis of gross appearance and weight: nonregressed (NR, 542 +/- 25 mg) or regressed (R, 260 +/- 2 mg). There were no significant changes in the proportion of the corpus luteum occupied by small luteal cells (19 +/- 2%) or large luteal cells (36 +/- 1%) throughout the estrous cycle. The total number of steroidogenic cells per corpus luteum increased from 21.8 +/- 3.7 (X 10(6)) on Day 4 to 61.7 +/- 5.4 (X 10(6)) on Day 8 (p less than 0.05) and remained elevated thereafter. The number of small luteal cells was 10.0 +/- 2.7 (X 10(6)), 39.7 +/- 1.4 (X 10(6)), 46.1 +/- 5.8 (X 10(6)), 49.0 +/- 13.7 (X 10(6)), and 29.9 +/- 8.6 (X 10(6)) on Days 4, 8, 12, 16 (NR), and 16 (R), respectively (p less than 0.05, Day 4 vs. Days 8, 12, 16 NR). In contrast, the number of large luteal cells was 11.8 +/- 1.5 (X 10(6)) on Day 4 and did not vary significantly during the remainder of the estrous cycle. The numbers of nonsteroidogenic cell types increased (p less than 0.05) from Day 4 to Day 16 (NR) but were decreased in regressed corpora lutea (Day 16 R). Regression was characterized by a 50% decrease (p less than 0.05) in the total number of cells per corpus luteum from 243 +/- 57 ( X 10(6)) on Day 16 (NR) to 125 +/- 14 ( X 10(6)) on Day 16 (R) (p less than 0.05). Small luteal cells remained constant in volume throughout the entire estrous cycle (2520 +/- 270 microns 3), whereas large luteal cells increased in size from 5300 +/- 800 microns 3 on Day 4 to 16,900 +/- 3300 microns 3 on Day 16 (NR) (p less than 0.05). In summary, small luteal cells increased in number but not size throughout the estrous cycle, whereas large luteal cells increased in size but not number.

Animals↗