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Biomedical subjects

G D Niswender

Publications and source records attributed to G D Niswender.

At least 37 records · Page 2Linked to original sources
PubMed1995

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)

Animals↗
PubMed1994

Regulation of cytochrome P450scc synthesis and activity in the ovine corpus luteum.

The rate-limiting step in luteal biosynthesis of progesterone consists of cleavage of the side chain of cholesterol by mitochondrial cytochrome P450 side-chain cleavage enzyme (P450scc) to form pregnenolone. Luteal mRNA encoding P450scc, quantitated on selected days of the 16-day ovine estrous cycle, was similar on days 3 and 6, increased by 2-fold on day 9 (P < 0.05) and remained elevated on day 15. Levels of P450scc mRNA on day 15 of pregnancy were not different from those found on any day of the cycle (P < 0.05). To determine whether levels of mRNA encoding P450scc are hormonally regulated, ewes on day 10 of the estrous cycle were injected with hCG or prostaglandin F2 alpha (PGF2 alpha). P450scc mRNA was not increased for up to 36 h after injection of hCG, nor decreased within 8 h after injection of PGF2 alpha (P < 0.05). An assay for P450scc activity was developed which utilized ovine small and large luteal cells in the presence of 22R-hydroxycholesterol and ovine high density lipoprotein. Enzyme activity was quantitated by measurement of progesterone production. In small luteal cells activation of the protein kinase A (PKA) second-messenger system by treatment with LH resulted in 910% increase in progesterone production without altering activity of P450scc. Activation of the protein kinase C (PKC) second-messenger system with phorbol 12-myristate 13-acetate caused a 51% reduction in progesterone secretion from large luteal cells but did not alter activity of P450scc. These findings suggest that in mature luteal tissue steady state levels of mRNA encoding P450scc, and enzyme activity are independent of acute regulation by activation of PKA or PKC second-messenger systems.

Animals↗
PubMed1994

Luteal function: the estrous cycle and early pregnancy.

A number of morphological and biochemical changes occur as the cells of the recently ovulated follicle luteinize and develop into a functional CL. There are two distinct steroidogenic luteal cell types that appear to differentiate from thecal and granulosal cells in the follicle. The control of progesterone secretion is quite different in the two cell types. Prostaglandin F2 alpha (PGF2 alpha) is the primary luteolytic hormone in most mammals. PGF2 alpha appears to exert its antisteroidogenic actions via activation of the protein kinase C system, while its cytotoxic effects appear to be mediated via a dramatic increase in intracellular levels of free calcium. The mechanisms involved in maternal recognition of pregnancy are very diverse between species and may involve direct luteotropic stimulation of the CL, reduced uterine secretion of PGF2 alpha, and/or inhibition of actions of PGF2 alpha at the level of the CL.

Animals↗
PubMed1994

Steady-state concentrations of messenger ribonucleic acid encoding cytochrome P450 side-chain cleavage and 3 beta-hydroxysteroid dehydrogenase/delta 5,delta 4 isomerase in ovine corpora lutea during the estrous cycle.

The objective of these experiments was to determine the pattern of mRNA expression for cytochrome P450 side-chain cleavage (P450scc) and 3 beta-hydroxysteroid dehydrogenase/delta 5,delta 4 isomerase (3 beta-HSD) during luteinization of the follicle and in ovine luteal tissue on Days 3, 6, 9, 12, and 15 of the estrous cycle. Mean concentration of mRNA for P450scc was not different in follicles collected 4 or 24 h after the onset of estrus but increased (p < 0.05) 3-fold by 48 h (corpus hemorrhagicum). With the methods used, mRNA for 3 beta-HSD was not detected until after ovulation and formation of the corpus hemorrhagicum (48 h after onset of estrus). In luteal tissue, mean concentration of mRNA for P450scc increased from Days 3 to 9 (p < 0.05) and had decreased (p < 0.05) by Day 15. Mean concentration of mRNA for P450scc was higher (p < 0.05) in small luteal cells on Day 9 than on Day 15, with values on Days 6 and 12 being intermediate. In large luteal cells, mean concentrations of P450scc mRNA increased (p < 0.05) between Days 6 and 12 and then decreased (p < 0.05) on Day 15. Mean concentration of mRNA for 3 beta-HSD was not different (p = 0.33) in luteal tissue on any day examined. In small luteal cells, mean concentrations of mRNA for 3 beta-HSD decreased between Days 6 and 15 (p < 0.05) while in large luteal cells, mean concentrations decreased (p < 0.05) between Days 12 and 15.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1994

Protein kinase C second messenger system mediates the antisteroidogenic effects of prostaglandin F2 alpha in the ovine corpus luteum in vivo.

Experiment I was designed to determine the optimal dose of phorbol 12-myristate 13-acetate (PMA) that inhibited progesterone production when infused into the ovarian artery. The most efficacious dose of PMA was 2 mumol. Experiment II was designed to determine whether activation of protein kinase C (PKC) inhibited progesterone production without initiating luteolysis. Ewes received ovarian arterial infusions of 4 alpha-phorbol (2 mumol, n = 4), PMA (2 mumol, n = 8), or prostaglandin F2 alpha (PGF2 alpha; 1 mumol, n = 5). Concentrations of progesterone in serum decreased by 3 h in PMA-treated ewes and by 5 h in PGF2 alpha treated ewes (p < 0.05). By 48 h, serum levels of progesterone in PMA-treated ewes had returned to control values; but in PGF2 alpha-treated ewes they remained low for the duration of the experiment. Luteal weights and progesterone contents at 48 h were similar in 4 alpha-phorbol- and PMA-treated ewes but were decreased in PGF2 alpha-treated ewes (p < 0.05). Experiment III was designed to determine whether PGF2 alpha or PKC activation induced oligonucleosome formation or influenced mRNA levels for cytochrome P450sec or 3 beta-hydroxysteroid dehydrogenase/delta 5-delta 4 isomerase (3 beta-HSD). Ewes received treatments as in experiment II, and CL were collected at 3, 12, or 24 h (n = 3-4 per group). Luteal weights were decreased (p < 0.05) and oligonucleosome formation was increased (p < 0.05) in PGF2 alpha-treated ewes compared to controls or to PMA-treated ewes by 12 h.(ABSTRACT TRUNCATED AT 250 WORDS)

3-Hydroxysteroid Dehydrogenases↗
PubMed1993

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.

Animals↗
PubMed1993

Steroidogenic enzyme activity after acute activation of protein kinase (PK) A and PKC in ovine small and large luteal cells.

Intracellular effector systems which utilize PKA and PKC can be pharmacologically activated by forskolin and phorbol 12-myristate 13-acetate (PMA) and appear to be important for regulation of steroidogenesis by cells of the corpus luteum. In this study the effect of pharmacologic activation of PKA (forskolin) or PKC (PMA) on the activity of adenylate cyclase, cholesterol esterase, P450 cholesterol side chain cleavage (P450scc) and 3 beta-hydroxysteroid dehydrogenase/delta 5, delta 4 isomerase (3 beta HSD) was determined. Basal adenylate cyclase activity (as measured by intracellular and secreted cAMP) was extremely low in both large and small luteal cells. Forskolin stimulated adenylate cyclase activity in both large and small luteal cells but progesterone production was increased only in small cells. PMA inhibited progesterone production by large and forskolin-stimulated small cells without altering adenylate cyclase activity. Basal cholesterol esterase activity was greater in small than in large cells and was stimulated by forskolin only in small cells. PMA did not significantly alter cholesterol esterase activity in either cell type. Activity of P450scc or 3 beta HSD was measured by conversion of hydroxylated cholesterol derivatives (P450scc) or pregnenolone (3 beta HSD) to progesterone. Although basal progesterone production was 47 times greater in large than small cells, there was only 5.1 (P450scc) and 6.4 (3 beta HSD) times greater enzyme activity in large than in small luteal cells. Activation of PKA and/or PKC did not alter the activity of P450scc or 3 beta HSD in either cell type.(ABSTRACT TRUNCATED AT 250 WORDS)

3-Hydroxysteroid Dehydrogenases↗
PubMed1993

Regulation of messenger ribonucleic acid encoding 3 beta-hydroxysteroid dehydrogenase/delta 5-delta 4 isomerase in the ovine corpus luteum.

Three experiments were conducted to determine how steady-state levels of mRNA encoding 3 beta-hydroxysteroid dehydrogenase/delta 5-delta 4 isomerase (3 beta-HSD) in the ovine corpus luteum vary 1) between the two steroidogenic luteal cell types, 2) during the estrous cycle, and 3) during prostaglandin F2 alpha (PGF2 alpha)-induced luteolysis. In the first experiment, RNA (10 micrograms) was isolated from purified preparations (n = 4) of large or small steroidogenic luteal cells. Large luteal cells contained 42% more (p < 0.05) message for 3 beta-HSD per microgram RNA than did small luteal cells, while the amount of mRNA for tubulin did not differ between the two types of luteal cells. To determine whether luteal levels of mRNA for 3 beta-HSD differ during the estrous cycle, corpora lutea were collected from cycling ewes (n = 3/day) on Days 3, 6, 9, 12, and 15 postestrus. Levels of mRNA for 3 beta-HSD were similar on Days 3, 6, 9, and 12 but were lower (p < 0.05) on Day 15 postestrus, while levels of mRNA for tubulin were unchanged. In the final experiment, ewes were treated on Day 10 postestrus with two injections of PGF2 alpha (5 mg each) or saline (control) at a 4-h interval. Corpora lutea were collected from ewes (n = 4/treatment) 1 h or 8 h after the second injection of PGF2 alpha or 8 h after the second saline injection.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1992

Proteins secreted from the early ovine conceptus block the action of prostaglandin F2 alpha on large luteal cells.

In this study we evaluated whether the early conceptus secretes a factor that blocks the action of prostaglandin (PG) F2 alpha on cultured ovine large luteal cells. PGF2 alpha inhibited progesterone production by lipoprotein-stimulated large luteal cells and this anti-steroidogenic action was blocked in a dose-dependent manner by conceptus proteins secreted from Day 15 embryos. Purified ovine trophoblast protein-1 (oTP-1) did not exhibit the anti-PGF2 alpha activity, but secreted conceptus proteins devoid of oTP-1 did prevent the anti-steroidogenic effects of PGF2 alpha. This activity does not appear to be a nonspecific effect of protein since neither serum albumin nor thyroglobulin, gamma globulin, insulin, LH, secreted ovine endometrial proteins, or heat-inactivated secreted conceptus proteins had this action. After molecular-sizing chromatography we found a high- and a low-molecular weight fraction with luteal protective activity. Neither of the secreted conceptus protein fractions blocked the binding of 3H-PGF2 alpha to large luteal cells. However, conceptus proteins did block the anti-steroidogenic action of phorbol ester and calcium ionophore on large luteal cells, suggesting that secreted conceptus proteins act after activation of the free calcium/protein kinase C intracellular effector pathways. Thus, the early ovine conceptus secretes a luteal protective protein(s) that may be important for maintaining the corpus luteum during early pregnancy; however, the physiologic significance of this luteal protective protein(s) cannot be stated without further investigation.

Animals↗
PubMed1992

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)

Animals↗
PubMed1991

Differential actions of second messenger systems in the corpus luteum.

Our current working hypothesis for the intracellular mechanism of action for LH and PGF-2 alpha is shown in Fig. 8. Luteinizing hormone appears to act primarily on the small luteal cell through the cAMP/protein kinase A effector system and thereby stimulates secretion of progesterone. Activation of the protein kinase C effector pathway is inhibitory to progesterone secretion from stimulated small luteal cells but it is not clear which hormones, if any, activate this effector system. Results from studies in whole animals suggest that LH may also stimulate differentiation of small luteal cells into large luteal cells (Donaldson & Hansel, 1965; Farin et al., 1988). Although there are LH receptors on large luteal cells, LH treatment does not stimulate progesterone secretion and does not appear to activate any of the second messenger pathways which we have examined. Prostaglandin F-2 alpha appears to act on the large luteal cell through free intracellular calcium and protein kinase C effector systems. Apparently, PGF-2 alpha-induced activation of protein kinase C results in the acute inhibition of progesterone production seen in the first 8 h after PGF-2 alpha treatment. The cytotoxic effects of PGF-2 alpha on the large luteal cell (Fitz et al., 1984; Braden et al., 1988) may be caused by a sustained elevation in free intracellular calcium concentrations. No direct effects of PGF-2 alpha on small luteal cells have been detected (no inhibition of progesterone production, no activation of protein kinase C, no increase in free intracellular calcium), which is consistent with an absence of high affinity PGF-2 alpha receptors on this cell type. The cytotoxic effects of PGF-2 alpha on small luteal cells and endothelial cells (Braden et al., 1988) may be caused by decreases in luteal blood flow (Niswender et al., 1975; Wiltbank et al., 1990b), actions of cytotoxic agents released by large luteal cells, or increases in cytotoxic white blood cells (Murdoch, 1987; Bagavandoss et al., 1988).

Animals↗
PubMed1990

Nuclear changes in ovine luteal cells in response to PGF2 alpha.

Percentages of normal and apoptotic parenchymal cells, fibroblasts and endothelial cells in ovine corpora lutea at 12, 24 and 36 hr following administration of a luteolytic dose of PGF2 alpha were determined and compared to percentages for identical cell types in corpora lutea removed from control ewes on days 10 (n = 5) and 12 (n = 6) postestrus. In corpora lutea obtained from control ewes greater than or equal to 95% of nuclei examined were scored normal for each of the respective cell types with no difference (P greater than .05) observed between luteal tissue obtained on days 10 and 12 postestrus. Following treatment with PGF2 alpha there were significant (P less than .05) reductions in the percentages of nuclei scored normal. Compared to controls the percentage of endothelial cell nuclei scored normal was reduced at 12 hr following PGF2 alpha-treatment; however significant reductions in percentages of parenchymal and fibroblast nuclei scored normal were not evident until 24 and 36 hr, respectively. Consistent with the concept of apoptosis, nuclear condensation and/or margination indicative of apoptosis did not occur synchronously within a given cell type: i.e., irrespective of the time point examined some cells appeared normal, whereas others had undergone nuclear condensation and/or margination. A sequence of events to explain structural and functional changes that occur during luteolysis following the interaction of PGF2 alpha with specific receptors in large steroidogenic luteal cells is discussed.

Animals↗
PubMed1990

Regulation of the corpus luteum by protein kinase C. II. Inhibition of lipoprotein-stimulated steroidogenesis by prostaglandin F2 alpha.

This study was designed to examine the antisteroidogenic action of prostaglandin (PG) F2 alpha on ovine luteal cells in vitro. Purified populations of large and small steroidogenic luteal cells were treated with lipoproteins, luteinizing hormone (LH), and/or PGF2 alpha. To investigate the involvement of the protein kinase C (PKC) pathway in hormone action, luteal cells were made PKC-deficient by treatment for 12 h with 1 microM phorbol-12-myristate-13-acetate. Progesterone production by nonstimulated large and LH-stimulated small luteal cells was significantly increased by treatment with high- and low-density lipoprotein (HDL, 5-fold increase; LDL, 2-fold increase). PGF2 alpha inhibited (p less than 0.0001) progesterone production by HDL-stimulated large luteal cells in a dose-dependent manner, with 60 nM causing maximal inhibition. No effect of PGF2 alpha (20nM-20 microM) was found on production of progesterone by HDL-stimulated, PKC-deficient large cells or by LH- and HDL-stimulated small luteal cells. These results suggest that PGF2 alpha has a direct antisteroidogenic effect on the large luteal cell that is mediated through the PKC second messenger pathway.

Animals↗
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↗
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

Characterization of endometrial receptors for ovine trophoblast protein-1 during the estrous cycle and early pregnancy in sheep.

Scatchard analysis was used to determine the distribution, number, and affinity of unoccupied receptors for ovine trophoblast protein-1 (oTP-1) in endometrium of sheep throughout the estrous cycle and early pregnancy. In Experiment I, oTP-1 receptor characteristics were determined in membrane preparations of caruncular and intercaruncular regions of endometrium collected from uterine horns ipsilateral and contralateral to the ovary bearing the corpus luteum. Receptor concentrations and affinity constants for oTP-1 were not different (p greater than 0.1) between the four endometrial regions examined, suggesting that the expression of receptors for oTP-1 occurs uniformly throughout the endometrium. Endometrial receptor characteristics for oTP-1, luteal wet weights, and progesterone contents were determined throughout the estrous cycle and early pregnancy in Experiment II. Concentration of receptors and affinity constants for oTP-1 varied throughout the estrous cycle and early pregnancy (p less than 0.01), with the pattern of change differing between cyclic and pregnant ewes (p less than 0.01). Numbers of receptors for oTP-1 were maximal on Day 4 of the estrous cycle and declined progressively to Day 12 (p less than 0.05) in both cyclic and pregnant ewes. After Day 12, the quantity of unoccupied receptors for oTP-1 increased (p less than 0.05) gradually to Day 16 in cyclic ewes, but declined (p less than 0.05) further in the endometrium of pregnant ewes. The affinity constants of endometrial receptors for oTP-1 were similar in cyclic and pregnant ewes prior to Day 12, increasing threefold from Days 4 to 12 (p less than 0.05).(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗