Dose Of Prostaglandin F2 Alpha Research Articles

Endometrial and luteal responses to a prostaglandin F2alpha pulse: a comparison between heifers and mares†.

In heifers and mares, multiple pulses of prostaglandin F2alpha (PGF) are generally associated with complete luteal regression. Although PGF pulses occur before and during luteolysis, little is known about the role of minor PGF pulses during preluteolysis on subsequent luteal and endometrial PGF production that may initiate luteolysis. Heifers (n = 7/group) and mares (n = 6/group) were treated with a single minor dose of PGF (3.0 and 0.5mg, respectively) during mid-luteal phase (12 and 10days postovulation respectively). After treatment, a transient decrease in progesterone (P4) concentrations occurred in heifers between Hours 0 and 2 but at Hour 4 P4 was not different from pretreatment. In mares, P4 was unaltered between Hours 0 and 4. Concentrations of P4 decreased in both species by Hour 24 and complete luteolysis occurred in mares by Hour 48. Luteal and endometrial gene expression were evaluated 4h posttreatment. In heifers, luteal mRNA abundance of PGF receptor and PGF dehydrogenase was decreased, while PTGS2, PGF transporter, and oxytocin receptor were increased. In the heifer endometrium, receptors for oxytocin, P4, and estradiol were upregulated. In mares, luteal expression of PGF receptor was decreased, while PGF transporter and oxytocin receptor were increased. The decrease in P4 between Hours 4 and 24 and changes in gene expression were consistent with upregulation of endogenous synthesis of PGF. The hypotheses were supported that a single minor PGF treatment upregulates endogenous machinery for PGF synthesis in heifers and mares stimulating endogenous PGF synthesis through distinct regulatory mechanisms in heifers and mares.

Effect of additional PGF2? dose on pregnancy rate in Nellore females subjected to FTAI

This study examined the effect of administering an additional dose of prostaglandin F2 alpha (PGF2?), in a fixed-time artificial insemination protocol (FTAI), on the fertility of female Nellore cattle. Two experiments were carried out: the first (Experiment I) took place in the state of Tocantins and the second (Experiment II) in the state of Pará, Brazil. In Experiment I (E1), 80 cows were used in three treatments (T1, T2 and T3) in which all received the same FTAI protocol. In T1 (n = 29), the cows received 12.5 mg of Dinoprost on day 9; in T2 (n = 28), they received the additional dose on day 10; and in T3 (n = 23; control group), the animals did not receive the additional PGF2? dose. Experiment II consisted of 147 bovine females distributed into two treatment groups, namely, T1 - 72 animals receiving the same protocol as T1 of E1; and T2 - 75 animals receiving the same protocol as T3 of E1. Statistical analysis was performed using SAS software, applying the PROC NPARWAY procedure for E1, and means were compared by the Wilcoxon test at the 5% significance level. In Experiment II, the data were subjected to analysis of variance by PROC GLIMMIX and means were compared by the T test at the 5% significance level. The following pregnancy rates were obtained in Experiment I: T1 - 62.06% (18/29); T2 - 57.14% (16/28); and T3 - 52.17% (12/23), with no significant difference observed between treatments. In Experiment II, pregnancy rate in T1 was 66.67% (48/72), whereas in T2 it was 41.33% (31/75), with a significant difference detected (P < 0.05). An additional dose of PGF2? provides an increase in pregnancy rate in Nellore females.

Hormonal protocols for early resynchronization of ovulation in ewes: The use of progestagens, eCG, and inclusion of early pregnancy diagnosis with color Doppler ultrasound

This study aimed to evaluate 1) the effect of inserting an intravaginal sponge containing medroxyprogesterone during the late luteal phase on the corpus luteum (CL) function and endogenous production of P4; 2) the effectiveness of two different equine chorionic gonadotrophin (eCG) doses on synchronization of ovulations for a resynchronization treatment; and 3) the inclusion of an early pregnancy diagnosis in an early resynchronization protocol for ovulation in ewes. For all studies, the synchronization protocol was based on a short-term protocol of six days of progestogen treatment plus one dose of prostaglandin F2alpha, one dose of eCG, and gonadorelin acetate after sponge withdrawal. For the first study, the ewes were mated with fertile rams; a second sponge was inserted in half of these ewes 12 days later, and blood samples were collected daily for six days, until sponge withdrawal. For the second study, the ewes were not mated, and received a second sponge during the same period, after which they were divided into three groups according to eCG dose (0, 200, or 300 IU). In the third study, all ewes were artificially inseminated and received the second sponge during the same period. At sponge withdrawal, pregnancy was diagnosed by color Doppler ultrasonography (DUS) of the CL, and only non-pregnant ewes were re-inseminated two days later. In the first study, serum progesterone values were similar regardless of whether an intravaginal sponge had been inserted. In the second study, the ovulation time was more concentrated in those ewes which received 200 IU of eCG. In the third study, there was no difference between the experimental groups (with or without a previous pregnancy diagnosis) in pregnancy rate at the first insemination, accumulated pregnancy rate, and pregnancy loss. The insertion of an intravaginal sponge impregnated with medroxyprogesterone acetate did not affect the endogenous production of P4. The application of 200 IU of eCG provided the best result with regard to the synchronization of ovulations in the resynchronization treatment. Also, the inclusion of an early pregnancy diagnosis with DUS is useful and improves the general results of resynchronization programs, shortening the total working period.

Effects of Different Estrous Synchronization Methods on the Composition of Simmental Cow’s Milk

Background: Estrous synchronization is one of the primary applications performed to improve the fertility and to consolidate the parturition times in dairy cattle farms. Since the primary objective is to increase fertility regardless of the method of synchronization used, the effect of this process on the udder health and the quality of milk is generally ignored. Therefore, in the present study, the aim was to investigate the effect of different estrous synchronization methods t on the milk quality in a dairy cattle farm.Materials, Methods & Results: In this study, a total of 100 Simmental cows the same farm under good management practices were used. The animals were randomly divided into 4 groups of 25 cows each. The animals in the 1st group were used as a control group without any treatment. Progesterone-releasing intravaginal device (PRID) was inserted to the animals in the 2nd group, double dose of prostaglandin F2 alpha (PGF2-alpha) with 11 days apart was applied to the animals in the 3rd group, and the Ovsynch protocol was applied to the animals in the 4th group. Starting from the first day of the applications, milk samples from each milk tank belonging to the groups were taken, kept frozen for 3 months and analyzed for the levels of fat, nonfat solids, density, protein, lactose and minerals over the course of one month. According to the results, the minimum milk fat content was found in the PRID group as 2.47 ± 0.354%, and the highest value was in the PGF2-alpha group as 3.58 ± 0.207%. The difference in milk fat ratio between the groups was found to be significant (P < .05). However, the differences between the groups for other parameters were not significant (P > .05).Discussion: Among the reasons for the low values of the milk fat rates obtained in the present study than the mean values of all lactation milk fat rates of the Simmental breed, the effect of the lactation period in which the milk samples were collected comes to mind. Because, as we know, the first 45-60 day period following the start of lactation after parturition in cattle is accepted as the period in which daily milk yield reaches to the maximum level of the lactation period. This period lasts for a certain period of time, and then starts to decrease gradually. Among the non-hereditary factors, the most important factor causing changes in the composition of the milk and its amount is the lactation period. In this study, the significant difference in the milk fat rates between the control and the application groups is quite remarkable compared to the low level of milk fat rates in the milk in all groups. According to the multiple comparison test results to determine which groups these differences arise from, the difference was found to be particularly between the PGF2-alpha group and PRID group. In this study, no significant effects of different synchronization methods on all components of the milk except the milk fat and the density values were determined. But results indicate that Ovsynch group was the synchronization group that caused the minimum change in milk fat compared to the other groups.

Plasma Clearance and Half-Life of Prostaglandin F2alpha: A Comparison Between Mares and Heifers1

Horses are about five times more sensitive to the luteolytic effect of prostaglandin F2alpha (PGF) than cattle, as indicated by a recommended clinical dose of 5 mg in horses and 25 mg in cattle. Novel evaluations of the PGF plasma disappearance curves were made in mares and in heifers, and the two species were compared. Mares and heifers (n = 5) of similar body weight were injected (Min 0) intravenously with PGF (5 mg per animal). Blood was sampled every 10 sec until Min 3, every 30 sec until Min 5, every 10 min until Min 60, and every 30 min until Min 240. The mean PGF concentration was greater (P < 0.05) in mares than in heifers at Min 1 through Min 60 and at Mins 180 and 240. The mean time to maximum PGF concentration was not different between mares (42.0 ± 8.6 sec) and heifers (35.0 ± 2.9 sec). The apparent plasma clearance, distribution half-life, elimination half-life, and maximum plasma PGF concentration were 3.3 ± 0.5 L h(-1) kg(-1), 94.2 ± 15.9 sec, 25.9 ± 5.0 min, and 249.1 ± 36.8 ng/ml, respectively, in mares and 15.4 ± 2.3 L h(-1) kg(-1), 29.2 ± 3.9 sec, 9.0 ± 0.9 min, and 51.4 ± 22.6 ng/ml, respectively, in heifers. Plasma clearance was about five times less (P < 0.0005), maximum plasma PGF concentration was five times greater (P < 0.002), and the distribution half-life and elimination half-life were about three times longer (P < 0.005) in mares than in heifers. The fivefold greater plasma clearance of PGF in heifers than in mares corresponds to the recommended fivefold greater clinical dose of PGF in cattle and supported the hypothesis that the metabolic clearance of PGF is slower in mares than heifers.

Effects of one versus two doses of prostaglandin F2alpha on AI pregnancy rates in a 5-day, progesterone-based, CO-Synch protocol in crossbred beef heifers

The present study determined whether a 5-d progesterone-based CO-Synch protocol with a single dose of prostaglandin F 2α (PGF) at progesterone withdrawal on Day 5, would yield a timed AI pregnancy rate similar to two doses of PGF given 6 h apart on Day 5. Angus cross beef heifers (N = 562) at six locations were used. All heifers received 100 µg of gonadorelin hydrochloride (GnRH) and a controlled internal drug release (CIDR) insert on Day 0. Within farm, heifers were randomly allocated to receive one dose of 25 mg dinoprost (PGF) at CIDR removal on Day 5 (1 PGF; N = 264), or two doses of 25 mg PGF, with the first dose given on Day 5 at CIDR removal, and the second dose 6 h later (2 PGF; N = 298). Most heifers (N = 415) received a heat detector patch at CIDR removal. After CIDR removal, heifers were observed twice daily through Day 7 for estrus and heat detector aid status was recorded. On Day 8, heifers were given 100 µg of GnRH, heat detector aid status was recorded, and heifers were inseminated approximately 72 h after CIDR removal. Accounting for significant variables such as location (P < 0.01), heifers in estrus at or prior to AI (P < 0.001), and a treatment by location interaction (P < 0.01), two doses of PGF on Day 5 tended to have higher pregnancy rates to timed AI compared to those that received one dose of PGF (P = 0.06). In conclusion, heifers given two doses of PGF at CIDR removal on Day 5, in a 5-d CIDR-CO-Synch protocol, tended to have a higher pregnancy rate than those that received only one dose of PGF.

Comparison among Different Doses of Prostaglandin F2alpha (PGF) on Luteal Function of the Day 5 Corpus Luteum (CL) in Nonlactating Holstein Cows.

Comparison among Different Doses of Prostaglandin F2alpha (PGF) on Luteal Function of the Day 5 Corpus Luteum (CL) in Nonlactating Holstein Cows.

Comparison of the Timing of the Second Dose of Prostaglandin F2 Alpha in a Five-Day Progesterone-based Timed AI Synchronization Protocol in Angus Cross Beef Cows

Artificial insemination (AI) is a highly effective reproductive technology for promoting genetic improvement in beef cattle. The most commonly used timed-AI program in beef cattle is the CO-Synch program. Pregnancy rates achieved through this program have ranged from 31 to 66% across a series of published reports, a rate that is acceptable to many beef producers. It has been shown that reducing the interval from the initial GnRH treatment to PGF2a (and withdrawal of a progestin) improves the outcome of timed-AI. With this protocol, termed the 5-day Co-Synch+ CIDR protocol, cows are given GnRH and have a CIDR device placed intravaginally, have the device removed after five days, and are given PGF2a, and then are time inseminated at 72 hours. However, this protocol requires the injection of two doses of PGF2a with an inconvenient 12-hour wait between the two doses. Reducing the interval between the two doses of PGF2a will allow cows to be handled twice with only a single penning and sorting to remove calves. The objective of this study was to compare reproductive performance of Angus cross beef cows synchronized with 5-day Co-Synch+ CIDR protocol and two doses of dinoprost tromethamine (PGF) given at CIDR removal and either at 2 h or 8 h following CIDR withdrawal.

Comparison of one versus two doses of prostaglandin F2 alpha in a 5-day, progesterone-based synchronization protocol in Angus-cross beef cows

Comparison of one versus two doses of prostaglandin F2 alpha in a 5-day, progesterone-based synchronization protocol in Angus-cross beef cows

Reproductive performance of lactating dairy cows following oestrus synchronisation with progesterone, oestradiol and prostaglandin

The ability to synchronise onset of oestrus, and hence the time of breeding and calving, offers potential economic and management benefits to dairy farmers, especially in herds with seasonally concentrated calving patterns. A trial involving 2681 cows in 11 seasonal herds was conducted to evaluate the reproductive performance of lactating dairy cows following oestrus synchronisation with a combination of progesterone, oestradiol and prostaglandin. Cows were randomly assigned within herds to synchronised and control groups, balanced for age, date of calving, body condition and breed. Cows in the synchronised group were treated with an intravaginal progesterone-releasing device containing 1.9 g of progesterone and a gelatin capsule containing 10 mg of oestradiol benzoate 10 days prior to the planned start of the breeding season (Day 0). The device was removed 8 days later on Day -2 and a luteolytic dose of prostaglandin F2alpha was administered 2 days prior to removal of the progesterone-releasing device. Returns to service for cows in the synchronised group were synchronised by inserting a previously used intravaginal device during Days 16-21 after the start of the breeding season. Cows in the control group were left untreated. The percentage of cows being inseminated during the first 5 days was 89.0% for the synchronised group compared to 29.7% for the control group. Compared to cows in the control group, those in the synchronised group had a lower conception rate to the first insemination (52.9% v. 64.3%, p<0.001), a lower conception rate to the second insemination (51.8% v. 62.5%, p<0.001), a higher percentage of empty cows at the end of the breeding season (7.3% v. 5.1%, p<0.05), and more insemination services per pregnancy to artificial insemination (2.0 v. 1.6, p<0.001). There was no difference between the synchronised and control groups in the percentage of cows pregnant to artificial insemination (81.8% v. 85.5%, p>0.10). The mean day of conception from the start of the breeding season was advanced (p>0.0 1) by 1.3 days in synchronised cows (19.9 +/- 0.7 days; mean +/- SEM) compared to control cows (21.2 +/- 0.5 days). It is concluded that the oestrus synchronisation regime used in the present study caused a reduction in fertility, which reduced the potential gains from using such a programme to increase reproductive efficiency in dairy cows.

Steroidogenic Activity, Insulin-Like Growth Factor-I Production, and Proliferation of Granulosa and Theca Cells Obtained from Dominant Preovulatory and Nonovulatory Follicles during the Bovine Estrous Cycle: Effects of Low-Density and High-Density Lipoproteins1

The role of high- and low-density lipoproteins (HDL and LDL) in regulating steroidogenic activity, cellular viability and proliferation, and insulin-like growth factor-I (IGF-I) production was examined in granulosa and theca cells from dominant preovulatory (DO) and nonovulatory (DNO) bovine follicles. Follicles were obtained from pluriparous nonlactating beef cows at ovariectomy 24 h after administration of a luteolytic dose of prostaglandin F2 alpha (DO) or during the first follicular wave on Days 5-8 of the estrous cycle (DNO). Lipoprotein effects on hormone production (ng/1.5 x 10(5) viable cells) and cell viability were studied in serum-free, defined medium containing LH and FSH (granulosa) or LH only (theca). During late stages (96-144 h) of culture, HDL in the presence of gonadotropins increased (p < 0.001) the production of progesterone by granulosa and theca cells and the production of IGF-I by granulosa cells. LDL did not stimulate granulosa or thecal progesterone synthesis and attenuated HDL-stimulated progesterone production by both cell types. Gonadotropin stimulation of terminal synthetic pathways was either attenuated (granulosa estradiol production) by addition of lipoproteins or maximally stimulated (theca cell androstenedione production) by a combination of LDL and HDL. Both lipoproteins increased (p < 0.05) granulosa cell viability in both follicle types, and a marked proliferation (p < 0.001) of steroidogenically inactive theca cells was observed from DO but not DNO follicles. Proliferation potential appeared to be switched off during the late stages of maturation of DNO follicles and switched on after induced luteal regression and rescue of DO follicles.

Differentiation of bovine preovulatory follicles during the follicular phase is associated with increases in messenger ribonucleic acid for cytochrome P450 side-chain cleavage, 3 beta-hydroxysteroid dehydrogenase, and P450 17 alpha-hydroxylase, but not P450 aromatase.

In cattle, a dramatic increase in plasma estradiol occurs during the short 2- to 3-day follicular phase. The objective of this study was to investigate the molecular mechanisms that mediate this critical change, specifically whether increases in the steroidogenic ability of granulosa and thecal cells of the preovulatory follicle are associated with increases in the levels of messenger RNA (mRNA) for steroidogenic enzymes. Luteolysis and a follicular phase were induced cycling Holstein heifers (n=15) by injection of a luteolytic dose of prostaglandin F2 alpha (PGF 2 alpha) on day 6 or 7 of the estrous cycle (day 0 = estrus), and preovulatory follicles were obtained at three stages of differentiation (0, 12, or 24 h post-PGF2 alpha treatment). To assess developmental changes in steroidogenesis in vivo, estradiol and androstenedione were measured in follicular fluid and in culture medium after a 3-h incubation of granulosa and thecal cells in defined medium with or without gonadotropins. To determine whether changes in mRNA for steroidogenic enzymes are associated with changes in follicular steroidogenesis, levels of mRNA for cytochrome P450 side-chain cleavage (P450scc), 3 beta-hydroxysteroid dehydrogenase (3 beta HSD), cytochrome P450 17 alpha-hydroxylase, and cytochrome P450 aromatase (P450arom) were measured in thecal and granulosa cells using ribonuclease protection assays. Concentrations of estradiol in follicular fluid were relatively high at time zero, increased significantly by 12 h, and increased further by 24 h post-PGF2 alpha treatment. However, the aromatizing activity of granulosa cells was high at the time of PGF2 alpha injection and did not increase significantly during the first 24 h after the initiation of luteolysis. The aromatizing activity of granulosa cells was reflected in levels of mRNA for P450arom, which was relatively abundant in granulosa cells obtained before luteolysis and did not increase further during the first 24 h of the follicular phase. Concentrations of androstenedione were virtually undetectable in follicular fluid at time zero and had increased dramatically by 12 and 24 h post-PGF2 alpha treatment. Similarly, thecal cells isolated at 24 h secreted 3-fold more androstenedione than cells isolated at the time of PGF2 alpha injection. Androstenedione production by thecal cells in response to LH was also markedly higher at 12 and 24 h than at the time of PGF2 alpha injection. Likewise; levels of mRNA for P450 17 alpha-hydroxylase increased significantly by 12 h post-PGF2 alpha treatment.(ABSTRACT TRUNCATED AT 400 WORDS)

Estrus and pregnancy rate of dairy cows given one or two doses of prostaglandin F2 alpha 8 or 24 hours apart

A total of 329 cows was used in 2 experiments to study the effect of PGF2a given 8 or 24 h apart on the number of cows observed in estrus within 7 d and the pregnancy rate to a single insemination at this time. In Experiment 1, 233 cows were divided into 2 groups. Cows in Group 1 (n = 117) were treated twice with 25 mg, im of PGF2a (0 and 8 h) while cows in Group 2 (n = 116) were treated only once (0 h). In Experiment 2, 96 cows were divided into 2 groups. Cows in Group 1 (n = 49) were treated twice with 25 mg, im of PGF2a (0 and 24 h) while cows in Group 2 (n = 47) were treated only once (0 h). In Experiment 1, blood samples were obtained from cows in both groups on Days 0 and 2. However, in Experiment 2, blood samples were obtained from cows in both groups only on Day 0. Plasma progesterone concentration was determined using radioimmunoassay. Cows in both experiments were observed for estrus within 7 d of treatment and were inseminated within 12 h of the observed estrus. In Experiment 1, more cows in Group 1 were observed in estrus within 7 d than in Group 2 (P <0.03). In Experiment 2, there was no significant difference in the number of cows in both groups that were observed in estrus within 7 d. However, the interval from treatment to the first observed estrus for cows not observed in estrus within 7 d was significantly longer in cows treated at 0 and 24 h compared with the cows treated once at 0 h. In both experiments, the pregnancy rate for cows inseminated within 7 d was similar for cows in all groups. From the results of this study, it is concluded that treatment of dairy cows with 2 luteolytic dosages of PGF2a at an 8-h interval resulted in more cows being observed in estrus than at a 24-h interval.

Effect of progesterone on ovarian follicles, emergence of follicular waves and circulating follicle-stimulating hormone in heifers.

The hypothesis was tested that greater growth of the dominant follicle of wave 1 (first follicular wave of an interovulatory interval), compared with that of subsequent anovulatory waves, is due to lower circulating concentrations of progesterone during the growing phase of the follicle. Control heifers (n = 6) were compared with heifers (n = 6) treated with a decreasing dose of progesterone from day 0 to day 5 (ovulation = day 0). Maximum diameter (12.7 +/- 0.9 versus 15.3 +/- 0.7 mm) and mean diameter of the dominant follicle of wave 1, averaged over days, were smaller (P < 0.05) in the progesterone-treated than in the control group. Progesterone treatment did not suppress circulating follicle-stimulating hormone (FSH); but the second FSH surge was earlier, resulting in earlier emergence of wave 2 as indicated by a tendency (P < or = 0.1) for group x day interactions attributed to earlier detection of the dominant follicle and an earlier rise in the total number of follicles detected. The stated hypothesis was supported. We also tested the hypothesis that exposure to low circulating concentrations of progesterone at the end of the growing phase of the anovulatory dominant follicle of wave 1 results in continued growth and prolonged maintenance of the dominant follicle. Heifers (n = 6 per group) were given a luteolytic dose of prostaglandin F2 alpha (PGF2 alpha) on day 6 and treated with a low (30 mg day-1), physiological (150 mg day-1), or high (300 mg day-1) dose of progesterone on days 6 to 20. Continued periodic emergence of anovulatory follicular waves occurred (2.1 +/- 0.0 waves, 2.8 +/- 0.2 waves, 3.8 +/- 0.3 waves, respectively; P < 0.05) until treatment was stopped (interovulatory intervals: 26.2 +/- 1.0, 30.8 +/- 0.6 and 40.3 +/- 1.7 days, respectively; P < 0.05). Compared with the physiological dose group, the growth of the dominant follicle was inhibited to a lesser degree in the low-dose group since it grew for longer (P < 0.05) and to a larger diameter (P < 0.05), and persisted for longer (P < 0.05). Prolonged dominance of this oversized (> 20 mm) follicle was associated with delayed emergence of wave 2. The hypothesis was supported. Results also showed that the high dose of progesterone suppressed the dominant follicle more than the physiological dose when given during the growing phase, but not when given after the growing phase.(ABSTRACT TRUNCATED AT 400 WORDS)

Evaluation of prostaglandin F2 alpha and prostacyclin interactions in the isolated perfused rat lung.

To characterize the interactions between prostaglandin F2 alpha and prostacyclin in controlling tone in the pulmonary circulation, isolated rat lungs were ventilated, perfused with blood, and subjected to challenge by prostaglandin F2 alpha in increasing doses. The pulmonary resistance was evaluated using occlusion techniques that separate the resistance into segments of large and small arteries and veins. The total vascular compliance was evaluated using outflow occlusion. Resistance increased after prostaglandin F2 alpha, and this resistance change was primarily in the small artery segment. The maximum resistance increase by prostaglandin F2 alpha (Rmax,PGF2 alpha), calculated from the Michaelis-Menton equation, was 16.6 +/- 3.6 cmH2O.l-1.min.100 g-1 for total vascular resistance with a concentration required to produce 50% Rmax (K0.5) of 5.26 +/- 3.57 nM. The Rmax,PGF2 alpha for small artery resistance was 13.5 +/- 2.4 cmH2O.l-1.min.100 g-1 with a K0.5 of 2.35 +/- 1.57 nM. The vascular compliance decreased during vasoconstriction by prostaglandin F2 alpha, and the maximum decrease in compliance (Cmin,PGF2 alpha) was -0.43 +/- 0.12 ml/cmH2O with a K0.5 of 2.84 +/- 2.99 nM. At each dose of prostaglandin F2 alpha, prostacyclin was administered in increasing doses to reverse the vasoconstriction caused by prostaglandin F2 alpha. For each concentration of prostaglandin F2 alpha, prostacyclin almost completely reversed the resistance increases and approximately one-half the compliance decrease. The maximum change in vascular resistance or compliance produced by prostacyclin was dependent on the dose of prostaglandin F2 alpha; yet the K0.5 for prostacyclin was within the picomolar range for all doses of prostaglandin F2 alpha.(ABSTRACT TRUNCATED AT 250 WORDS)

Effects of an Agonist of Gonadotropin-Releasing Hormone on Ovarian Follicles in Cattle1

Three experiments were conducted to examine effects of Buserelin, a potent agonist of gonadotropin-releasing hormone, on characteristics of ovarian follicles in cycling cows and heifers. In experiment 1, heifers were injected once with 10 micrograms Buserelin on Day 11, 12, or 13 of the estrous cycle (estrus = Day 0), or once with 20 micrograms of Buserelin on Day 12. Additionally, two groups were injected with a luteolytic dose of prostaglandin F2 alpha (PGF2 alpha) on Day 13 preceded with or without a Buserelin injection (10 micrograms) on Day 12. A control group did not receive a Buserelin injection. Ovaries were recovered and weighed after animals were slaughtered on Day 15. Follicle diameters were measured with calipers. Follicles for all experiments were classified as small (class 1: 3-5 mm diameter), medium (class 2: 6-9 mm), or large (class 3: greater than 9 mm). Heifers receiving only Buserelin had an increased number of medium-sized follicles compared to controls. Buserelin injection administered 24 h before PGF2 alpha reduced the decline in the average weight of the ovaries containing the corpus luteum (7.8 g for Buserelin before PGF2 alpha vs. 6.7 g for no Buserelin before PGF2 alpha). Buserelin pretreatment appeared to delay or prevent complete luteolysis by the injected PGF2 alpha. In experiment 2, 0, or 10 micrograms Buserelin was injected on Day 12 and follicle development was monitored by ultrasonography in situ from Day 12 to estrus. Follicles also were classified as clear or cloudy; cloudy was associated with flocculent material in the follicular fluid or with an indistinct follicular wall.(ABSTRACT TRUNCATED AT 250 WORDS)

Thymosin Gene Expression Is Modulated by Pregnant Mare’s Serum Gonadotropin, Human Chorionic Gonadotropin, and Prostaglandin F2αin the Immature Rat Ovary*

We have investigated thymosin beta 10 mRNA levels in the PMSG/hCG-treated immature rat ovary. Thymosin beta 10 mRNA was constitutively expressed as a single (greater than 600-nucleotide) abundant transcript in the immature rat ovary. Administration of a single dose (50 IU/rat) of PMSG to immature rats resulted in a gradual increase in steady state ovarian thymosin beta 10 mRNA content detectable as early as 12 h and maximal (2-to 3-fold stimulation above preinjection levels) 48 h after PMSG treatment. Ovarian thymosin beta 10 mRNA levels declined thereafter. In separate experiments treatment of PMSG (50 IU)-primed rats with hCG (25 IU) precipitated a dramatic (80%) inhibition of ambient ovarian thymosin beta 10 protein and thymosin beta 10 mRNA; both parameters remained suppressed for the duration of the hormone-induced pseudopregnancy (15 days). HPLC analysis also indicated the presence in the ovary of thymosin beta 4, a variant member of the same protein family; in general, ovarian thymosin beta 4 levels fluctuated in a manner reciprocal to that exhibited by thymosin beta 10. A luteolytic dose of prostaglandin F2 alpha (500 micrograms/rat) had little impact on ovarian thymosin beta 10 gene expression. These findings show that 1) PMSG stimulation of ovarian thymosin beta 10 biosynthesis involves increased expression of the thymosin beta 10 gene; 2) decreased expression of thymosin beta 10 is associated with luteinization, while increased thymosin beta 4 levels characterize this process; and that 3) thymosin beta 4 and beta 10 are coexpressed in this tissue and may play a significant but, as of yet, undefined role(s) in the ovary.

Ontogeny of adenosine response in guinea pig heart and aorta

Effects of maturation on the responses of isolated perfused hearts and aortic rings to adenosine were examined. Dose-response relationships for adenosine were obtained in aortic rings and hearts isolated from immature (5 days) and mature (1-2 mo) guinea pigs. Immature and mature hearts were perfused at constant flows of 9.9 +/- 0.3 and 9.5 +/- 0.4 ml.min-1.g-1, respectively, and displayed basal resistances of 4.8 +/- 0.1 and 6.7 +/- 0.2 mmHg.ml-1.min.g. Immature hearts were more sensitive to exogenous adenosine, displaying a significantly lower 50% effective concentration (EC50, 2.5 x 10(-8) M) than mature hearts (1.1 x 10(-7) M, P less than 0.05). Adenosine induced dilation at a lower threshold dose in immature hearts (3 x 10(-9) M, 6.0 +/- 0.3% relaxation) than in mature hearts (10(-8) M, 3.1 +/- 1.3% relaxation). The time required to elicit 50% of the observed dilation was similar in immature and mature hearts, yet the time required for basal tone to recover by 50% was approximately 100% greater in immature hearts (P less than 0.05). Immature aortic rings, stretched to their optimal resting tensions and contracted with EC85 doses of prostaglandin F2 alpha, displayed a significantly lower EC50 (7.7 x 10(-5) M) than mature rings (1.1 x 10(-4) M, P less than 0.05). The maximum percent response to adenosine was greater in immature vessels (64 +/- 1 vs. 54 +/- 0.4%, P less than 0.05).(ABSTRACT TRUNCATED AT 250 WORDS)

Alterations in Phospholipase A2 Activity during Luteal Regression in Pseudopregnant and Pregnant Rats*

The activity of phospholipase A2 was measured in microsomes prepared from ovaries of superovulated pseudopregnant rats during spontaneous and prostaglandin F2 alpha-induced regression and during regression in pregnant rats. Microsome samples were incubated at 40 C for 90 min in Tris buffer (pH 8.3) with 1.0 mM CaCl2 added. The substrate, radiolabeled phosphatidylcholine, was incorporated into liposomes. During spontaneous regression, there was a significant 2- to 4-fold increase in phospholipase A2 activity, when compared with levels at mid-pseudopregnancy (days 8-9). This elevation was correlated with a significant decrease in plasma progesterone concentration. On day 6 or 7 of pseudopregnancy, treatment of rats with luteolytic doses of prostaglandin F2 alpha also caused a significant increase in phospholipase A2 activity, which remained elevated throughout the 72-h sampling period. In pregnant rats there was a small but significant rise in phospholipase A2 activity after parturition. These results indicate that the activity of phospholipase A2 increases during luteal regression in pregnant and pseudopregnant rats and that it could be involved in the mechanism that causes the loss in progesterone secretion.

Hormone studies in Myxine glutinosa: effects of the eicosanoids arachidonic acid, prostaglandin E1, E2, A2, F2 alpha, thromboxane B2 and of indomethacin on plasma cortisol, blood pressure, urine flow and electrolyte balance.

Hagfish, Myxine glutinosa, were used in an investigation of the possible effects of various eicosanoids and the prostaglandin synthetase inhibitor indomethacin, on cortisol production, blood pressure control, urine flow and electrolyte balance. Cortisol levels in plasma of untreated control animals and plasma from animals 1 h following injection of 50 micrograms kg-1 prostaglandin E1, E2, A2, F2 alpha TXB2 and indomethacin were not detectable. However, plasma cortisol levels rose to between 10 and 26 pg ml-1 1 h following injection of either 50 micrograms kg-1 arachidonic acid or prostaglandin E2. This rise was similar in magnitude to that produced 1 h following administration of 50 micrograms kg-1 porcine ACTH. The resting dorsal aortic blood pressure of between 3.50 and 3.75 mmHg was reduced on average by 50% for 12-15 min when animals received 10 micrograms kg-1 arachidonic acid, prostaglandin E1, E2, A2, and TXB2 and was effectively reduced to zero for 20 min or more following 50 micrograms kg-1 of these eicosanoids. Similar doses of prostaglandin F2 alpha, however, evoked an increase in blood pressure (19-33%) whilst indomethacin was without effect. Control measurements of urine flow in Myxine were estimated to be between 540 and 660 microliters h-1 kg-1. There was a marked reduction in urine output following the arterial vasodepression induced by arachidonic acid, prostaglandin E1, E2, A2 and TXB2 in doses of 10 micrograms kg-1, an effect which became even more pronounced following injection of 50 micrograms kg-1 quantities, leading in some cases to complete anuria.(ABSTRACT TRUNCATED AT 250 WORDS)