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.     

Dystocia in cattle a review and implications

The economic importance of dystocia in terms of calf losses and subsequent impaired reproductive performance has been well documented (1, 2, 3, 4, 5). The incidence of dystocia must be minimized to improve reproductive performance and maximize profits.The occurrence of dystocia in primiparous heifers is primarily a function of two factors: size of the calf and pelvic area of the dam (6, 7, 8, 9). There are medical (ie- late abortion, hydrops, monsters) and hormonal reasons for dystocia these will not be reviewed in this paper. Primarily, the relationship of calf size and pelvic area and the factors which affect them will be reviewed.     

Effect of monensin, energy level, and cow body condition on pregnancy rate in nonlactating beef cows

One hundred eighty-two nonlactating cycling Brahman crossbred and Angus cows were used to study the effects of monensin, cow body condition and supplemental energy level on pregnancy rate. The cows were classified as being in either moderate or poor body condition at the start of the experiment and were fed either 9 or 18 Mcal of supplemental metabolizable energy/head/day with or without 125 mg of monensin in the ration. Feeding commenced 21 days prior to and throughout a 45-day breeding season. In the monensin treated group ruminal propionic acid levels (molar %) were increased (P<.01) while acetic and butyric acid levels were lowered (P<.05) regardless of supplemental energy intake. Pregnancy rate, pregnancy rate at first service, and the percentage of conceptions per estrus were increased (P<.05) when cows were fed 18 Mcal of supplemental energy per head per day. Neither cow body condition nor addition of monensin to the diet had an effect on the preceding reproductive endpoints. Cows in poor body condition and receiving 18 Mcal of supplemental energy per head per day had increased (P<.05) reproductive performance as evidenced by an increase in the pregnancy rate, pregnancy rate at first service, and percentage of conceptions per estrus when compared to the other groups.     

The flat-plate plant-microbial fuel cell: the effect of a new design on internal resistances

Due to a growing world population and increasing welfare, energy demand worldwide is increasing. To meet the increasing energy demand in a sustainable way, new technologies are needed. The Plant-Microbial Fuel Cell (P-MFC) is a technology that could produce sustainable bio-electricity and help meeting the increasing energy demand. Power output of the P-MFC, however, needs to be increased to make it attractive as a renewable and sustainable energy source. To increase power output of the P-MFC internal resistances need to be reduced. With a flat-plate P-MFC design we tried to minimize internal resistances compared to the previously used tubular P-MFC design. With the flat-plate design current and power density per geometric planting area were increased (from 0.15 A/m² to 1.6 A/m² and from 0.22 W/m² to and 0.44 W/m²)as were current and power output per volume (from 7.5 A/m³ to 122 A/m³ and from 1.3 W/m³ to 5.8 W/m³). Internal resistances times volume were decreased, even though internal resistances times membrane surface area were not. Since the membrane in the flat-plate design is placed vertically, membrane surface area per geometric planting area is increased, which allows for lower internal resistances times volume while not decreasing internal resistances times membrane surface area. Anode was split into three different sections on different depths of the system, allowing to calculate internal resistances on different depths. Most electricity was produced where internal resistances were lowest and where most roots were present; in the top section of the system. By measuring electricity production on different depths in the system, electricity production could be linked to root growth. This link offers opportunities for material-reduction in new designs. Concurrent reduction in material use and increase in power output brings the P-MFC a step closer to usable energy density and economic feasibility.     

Physiological and immunocytochemical evidence for a new concept of blood flow regulation in the corpus luteum

To explain the high rate of blood flow in the corpus luteum, we hypothesize that luteal blood vessels offer minimal resistance to flow and are incapable of vasomotion. This hypothesis was tested in rabbits at mid-pseudopregnancy by measuring blood flow in the corpus luteum and ovarian stroma with tracer-labeled microspheres at three levels of arterial blood pressure, which was manipulated by constricting the aorta above the ovarian artery. In addition, the distribution of vascular smooth muscle in the ovary was evaluated with morphological and immunocytochemical techniques. Decreases in arterial pressure were paralleled by reductions in blood flow in the corpus luteum, whereas ovarian stromal blood flow was unchanged. Consistent with our hypothesis, there was no change in the low level of vascular resistance offered by blood vessels in the corpus luteum, supporting the view that they are maximally dilated and incapable of autoregulation. Morphologically, the vessels within the corpus luteum appeared as large sinusoidal capillaries without smooth muscle, providing an anatomical explanation for the lack of vasomotor control demonstrated physiologically. The absence of vascular smooth muscle was confirmed with immunocytochemistry using an antibody against the muscle-specific intermediate filament, desmin. The fluorescein-labeled antibody decorated arteries and arterioles within the ovarian stroma and near the capsule of the corpus luteum, but did not decorate vessels in the corpus luteum of pseudopregnancy, providing additional evidence that the vessels of the corpus luteum lack the smooth muscle investment necessary to change vascular caliber. From these findings, we have proposed a novel scheme to explain intraovarian blood flow regulation. Vascular resistance in the ovarian stroma, as in most tissues, is acutely regulated by dilation or constriction of intratissue arterioles. In contrast, vascular resistance within the corpus luteum is modeled as a relatively invariable parameter, fixed at a low level by the morphological characteristics of the luteal vasculature. Therefore, the corpus luteum operates on a linear (maximally "vasodilated") pressure-flow curve, does not actively regulate intratissue blood flow, and is subject to acute regulation of perfusion only through changes in extra-luteal vessels.     

An alteration in the hypothalamic action of estradiol due to lack of progesterone exposure can cause follicular cysts in cattle

Many mammals, including cattle, can develop ovarian follicular cysts, but the physiological mechanisms leading to this condition remain undefined. We hypothesized that follicular cysts can develop because estradiol will induce a GnRH/LH surge on one occasion but progesterone exposure is required before another GnRH/LH surge can be induced by estradiol. In experiment 1, 14 cows were synchronized with an intravaginal progesterone insert (IPI) for 7 days, and prostaglandin F(2alpha) was given on the day of IPI removal. Estradiol benzoate (EB; 5 mg i.m.) was given 3 days before IPI removal to induce atresia of follicles. Cows were given a second EB treatment 1 day after IPI removal to induce a GnRH/LH surge in the absence of an ovulatory follicle. All cows had an LH surge following the second EB treatment, and 10 of 14 cows developed a large-follicle anovulatory condition (LFAC) that resembled follicular cysts. These LFAC cows were given a third EB treatment 15 days later, and none of the cows had an LH surge or ovulation. Cows were then either not treated (control, n = 5) or treated for 7 days with an IPI (n = 5) starting 7 days after the third EB injection. Cows were treated for a fourth time with 5 mg of EB 12 h after IPI removal. All IPI-treated, but no control, cows had an LH surge and ovulated in response to the estradiol challenge. In experiment 2, cows were induced to LFAC as in experiment 1 and were then randomly assigned to one of four treatments 1) IPI + EB, 2) IPI + GnRH (100 microg), 3) control + EB, and 4) control + GnRH. Control and IPI-treated cows had a similar LH surge and ovulation when treated with GnRH. In contrast, only IPI-treated cows had an LH surge following EB treatment. Thus, an initial GnRH/LH surge can be induced with high estradiol, but estradiol induction of a subsequent GnRH/LH surge requires exposure to progesterone. This effect is mediated by the hypothalamus, as evidenced by similar LH release in response to exogenous GnRH. This may represent the physiological condition that underlies ovarian follicular cysts.     

Alterations in follicular estradiol and gonadotropin receptors during development of bovine antral follicles

It was hypothesized that growth divergence of dominant and subordinate follicles during Wave 1 and growth termination of the dominant follicle would be associated with changes in the number of gonadotropin receptors on granulosa cells and estradiol in follicular fluid. To test this hypothesis, follicular development of 16 Holstein heifers was monitored by ultrasound, and follicles were collected on Days 2,4,6 and 10 (Day 0 = ovulation). Dominant follicles were compared across days, whereas dominant and largest subordinate follicles were compared on Days 2 and 4 only. The numbers of LH and FSH receptors on the granulosa cells of dominant follicles did not differ significantly over Days 2, 4, 6 and 10. In contrast, concentrations of estradiol in follicular fluid decreased (P < 0.05) from Days 2 to 10 (373 +/- 150 to 42 +/- 12 ng/ml) and concentrations of progesterone in follicular fluid increased (P < 0.05) from Days 2 to 10 (12.2 +/- 2.3 to 24.4 +/- 4.8 ng/ml). Correspondingly, the ratio of estradiol:progesterone in the dominant follicles decreased (P < 0.05) from Days 2 to 10. Comparisons between dominant and subordinate follicles indicated greater (P < 0.05) estradiol concentrations in the dominant follicle on Day 2, but the number of gonadotropin receptors was not different until Day 4. Thus, differences in concentrations of follicular fluid estradiol, but not numbers of granulosa cell gonadotropin receptors, were associated with the early growth divergence of dominant and subordinate follicles (Day 2) and the eventual growth termination of the dominant follicle (Day 10). Late divergence (Day 4) was associated with higher gonadotropin receptor numbers and follicular estradiol concentrations in the dominant than in the subordinate follicles. These results indicate that an increase in estradiol productivity of the selected dominant follicle occurred before an increase in the number of gonadotropin receptors.     

Transvaginal, ultrasound-guided biopsy of the corpus luteum in cattle

An ultrasound-guided transvaginal technique for corpus luteum biopsy was developed and tested in cattle. The biopsy needle set consisted of an inner needle (o.d. 1 mm) with a 20-mm long specimen notch, an outer cannula (o.d. 1.2 mm) with a cutting edge, and an automated spring-loaded handle with trigger. The biopsy needle set was inserted into the channel guide of the handle of a convex-array transvaginal ultrasound probe. The transducer was positioned in the vaginal fornix, and the ovary was manipulated transrectally against the vaginal wall and transducer face. During monitoring on the ultrasound screen, the inner needle was pushed through the vaginal wall into the corpus luteum, and the cutting cannula was fired, cutting and trapping luteal tissue in the specimen notch. Three luteal biopsies at each of Hours 0 and 4 were taken 10 d after ovulation in 6 heifers; 6 other heifers served as controls. A biopsy core was obtained in 36 of 39 attempts (92%). The tissue specimens seemed normal based on gross evaluation. The effect of biopsy on luteal function was assessed by daily ultrasound monitoring of luteal area, by assay of progesterone concentrations in blood samples obtained daily, and by the length of the interval from biopsy to ovulation. No significant differences were found for post-biopsy function for any of the 3 end points. The results indicated repeated transvaginal, ultrasound-guided biopsy of the corpus luteum in cattle is a practical procedure and may be useful for experimental and diagnostic purposes.     

Effect of dietary phosphorus concentration on estrous behavior of lactating dairy cows

The objective of this study was to determine the effect of dietary phosphorus (P) concentrations of 0.38 (adequate) or 0.48% (excess) of the total mixed ration (TMR) (dry matter basis) on estrous behavior of lactating cows as measured by a radiotelemetric system (HeatWatch; De Forest, WI, USA). At calving, 42 Holstein cows (n=21 per treatment) were randomly assigned to one of two dietary P treatments. Cows were milked twice daily and milk weights were recorded. Cows were housed in a free-stall barn and were fitted with a radiotelemetric transmitter 40 days postpartum to record estrous mounting activity. The total number of estruses recorded for the 42 cows were 72 (37 and 35 for cows in the adequate and excess P groups, respectively). The mean duration of estrous cycles was 22 +/- 0.6 days and 21 +/- 0.4 days for cows fed the adequate and excess P diets, respectively (P=0.14). The mean duration of estrus was 8.9 +/- 1.1 h and 8.6 +/- 1.2 h (P=0.86), the average number of mounts during estrus was 7.0 +/- 1.2 and 8.2 +/- 1.7 (P=0.57), and the total mounting time was 27.1 +/- 4.3 s and 30.8 +/- 6.5 s (P=0.64) for cows fed the adequate and excess P diets, respectively. Phosphorus treatment had no significant effect on intensity or duration of estrus.     

A new presynchronization system (Double-Ovsynch) increases fertility at first postpartum timed AI in lactating dairy cows

This study evaluated a novel presynchronization method, using Ovsynch prior to the Ovsynch-timed AI protocol (Double-Ovsynch) compared to Presynch-Ovsynch. Lactating Holstein (n=337) cows, were assigned to two treatment groups: (1) Presynch (n=180), two injections of PGF 14 d apart, followed by the Ovsynch-timed AI protocol 12 d later; (2) Double-Ovsynch (n=157), received GnRH, PGF 7 d later, and GnRH 3 d later, followed by the Ovsynch-timed AI protocol 7 d later. All cows received the same Ovsynch-timed AI protocol: GnRH (G1) at 68+/-3 DIM (mean+/-SEM), PGF 7 d later, GnRH (G2) 56h after PGF, and AI 16 to 20h later. Pregnancy was diagnosed 39-45 d after timed AI. Double-Ovsynch increased the pregnancies per AI (P/AI) compared to Presynch-Ovsynch (49.7% vs 41.7%, P=0.03). Surprisingly, Double-Ovsynch increased P/AI only in primiparous (65.2% vs 45.2%; P=0.02) and not multiparous (37.5% vs 39.3%) cows. In a subset of 87 cows, ovarian ultrasonography and progesterone (P4) measurements were performed at G1 and 7 d later. Double-Ovsynch decreased the percentage of cows with low P4 (<1ng/mL) at G1 (9.4% vs 33.3%) and increased the percentage of cows with high P4 (> or =3ng/mL) at PGF (78.1% vs 52.3%). Thus, presynchronization of cows with Double-Ovsynch increased fertility in primiparous cows compared to a standard Presynch protocol, perhaps due to induction of ovulation in non-cycling cows and improved synchronization of cycling cows. Future studies are needed, with a larger number of cows, to further test the hypothesis of higher fertility with Double-Ovsynch, and to elucidate the physiological mechanisms that underlie apparent changes in fertility with this protocol.