George H. Stabenfeldt

Effects of endotoxin infusion on circulating levels of eicosanoids, progesterone, cortisol, glucose and lactic acid, and abortion in pregnant cows

The effects of Escherichia coli endotoxin infusions (1.0 or 2.5 micrograms kg-1 over 6 h) on pregnancy were investigated in cows in the first, second and third trimester of gestation. Endotoxin increased the plasma levels of prostaglandins (PGs), thromboxane B2 and cortisol, and decreased progesterone. The severity of the clinical signs and the magnitude of the increases in plasma PGs, thromboxane B2 and cortisol tended to depend on the dose of endotoxin, but were independent of the gestation period. There was hyperglycemia followed by hypoglycemia and lactic acidemia. Hyperglycemia and lactic acidemia were significant only at the high dose of endotoxin. Endotoxin infusion at both doses caused a preferential mobilization of oleic acid from adipose tissue, and also had some effects on the mobilization of palmitic and stearic acids during the post-infusion period. The cows in the first trimester of gestation were more sensitive to the abortifacient effect of endotoxin than cows in the second and third trimester of gestation. The results of this study indicate that the mechanism of endotoxin-induced abortion in cows initially involves a prolonged release of PGF2 alpha and its subsequent stimulant effect on uterine smooth muscle contraction and luteolytic effect leading to a gradual decline in the plasma levels of progesterone. It was concluded that pregnancy terminates in the absence of an adequate level of progesterone, especially during the first trimester of gestation, when progesterone of extraluteal origin is not yet available, coupled with the PGF2 alpha-induced propulsive contraction of the uterus. In addition, the metabolic and circulatory failures in severe cases of endotoxemia, especially at the high dose of endotoxin, resulting either directly or indirectly via the release of various autacoids, catecholamines and cortisol, may also contribute to the termination of pregnancy at any stage of gestation.

Persistence of luteal activity in the non-pregnant ewe

Abstract Four cases of spontaneous persistence of the corpus luteum (CL) in the ewe are presented along with data concerning normal luteolysis in two ewes. The persistence of the CL in the four ewes resulted in oestrous cycle lengths of 26, 56, 139 and 145 days. Daily plasma levels of progesterone, 15-keto-13,14-dihydro-PGF2α and 11-ketotetranor PGF compounds are reported. In addition, blood samples were taken at two h intervals during the initial prolongation of the CL in two of the ewes. In these ewes, pulsatile release of PGF2α occurred at the expected time, and the release of PGF2α during each pulse, as well as total release from the first to the last pulse, were similar to those of ewes undergoing normal luteolysis. However, the interval between individual pulses was greatly increased in ewes with persistence of the CL, having means of 18.0 h and 18.5 h for two of the ewes sampled intensively. In contrast, two ewes undergoing normal luteolysis had interpulse intervals of 6.8 and 7.2 h, respectively. The results suggest that spontaneous persistence of the CL in the ewe is not due to a primary inability of the uterus to produce PGF2α. A disturbance of the system which acutely controls individual pulses of PGF2α (and thus their frequency) seems to be a more likely cause for the malfunction. In all four cases, the prolonged luteal phase was finally terminated by active release of PGF2α.

Endocrine responses in the llama to copulation.

Nine adult female llamas were used to determine the time course for secretion of luteinizing hormone (LH) and estradiol-17beta (E(2)) following a single copulation (average 18 min), and progesterone (P(4)) during the development of the subsequent luteal phase. Heparinized blood samples were obtained through an indwelling jugular cannula at 15-min intervals for up to 24 h following copulation and then once daily for up to 10 d. Luteinizing hormone, assayed by radioimmunoassay (RIA) using a monoclonal antibody 518B7 against the beta subunit of bovine LH, was determined at 15 min intervals for 24 h following copulation. Estradiol-17beta was determined by RIA at 4-h intervals following copulation, then daily, while P(4) values were determined daily by enzyme immunoassay. A significant increase in LH concentration was observed by 15 min after the onset of copulation, with the peak of the preovulatory surge of LH occurring at 2 h; values were basal by 7 h after copulation. Estradiol-17beta values, unchanged through 18 h after copulation, tended to decline at 22 h (24 h, P<0.10) and were significantly lower than 18 h values by 48 h (P<0.05) after copulation. The first significant P(4) increase occurred at 3 d after copulation, with values increasing through 10 d. The LH surge observed subsequent to copulation is consonant with the llama being an induced ovulator.

Urinary and plasma estrogen conjugates, estradiol and estrone concentrations in nonpregnant and early pregnant mares

A direct radioimmunoassay for estrogen conjugates (EC) was applied to paired blood and urine samples collected from 20 mares and compared against estrone (E(1)) and estradiol-17beta (E(2)) to monitor changes in estrogen production during ovulatory cycles and early pregnancy. Blood samples were taken daily from five mares through two consecutive ovulations and from six mares at 6-h intervals starting 48 hours prior to ovulation and continuing after ovulation had occurred. Blood samples were also collected daily or three times per week from conception until Day 60 of pregnancy in nine pregnant mares. The mean urinary EC, plasma EC and plasma E(2) dynamics were parallel in nonpregnant mares, with a 3-fold increase in mean urinary EC concentrations from baseline to the ovulatory peak, a 1.8-fold increase in mean plasma EC concentrations and a 1.4-fold increase in mean plasma E(2) concentrations. In early pregnancy, a two-fold increase in mean plasma E(1) and EC concentrations occurred in concert with a five-fold rise in mean urinary EC concentrations, whereas plasma E(2) did not change. Following hydrolysis and chromatographic separation, E(1) and E(2) were identified as the hydrolytic products in the urine of nonpregnant and pregnant mares; however, an unidentified estrogen was the major hydrolytic product in nonpregnant mares and pregnant mares prior to Day 38 of pregnancy. The increased resolution of the EC profiles compared with the profiles of other estrogen components indicates that the determination of EC in urine or plasma provides a useful alternative method for monitoring reproductive events in mares.

The effect of a potent GnRH agonist on gonadal and sexual activity in the horse

Abstract A potent agonist of gonadotropin releasing hormone (GnRHa) was administered to stallions (n=3) and mares (n=4) during the physiologic breeding season in order to downregulate gonadal activity. Stallions received an increasing regimen of 12.5 mg (5 d), 25 mg (10 d), and 50 mg (15 d) GnRHa per day, for a total of 30 d. Libido and semen quality were not affected by the treatment. The only treatment effect observed was an initial rise in luteinizing hormone (LH) concentration and a slight decline in testosterone concentration during treatment in two of three stallions. These data suggest that daily GnRHa therapy is not a practical method for the suppression of sexual behavior in the stallion at the dosage and interval utilized. Mares received 25 mg i.m. GnRHa per day, for a total of 35 d (n=2), or 40 d (n=2). While estrus and ovulation occurred in two mares during the first half of treatment, follicular development was suppressed in all mares by the end of treatment. Following treatment, ovulation occurred in all mares between 12 and 16 d after treatment. While gonadal activity and estrous behavior can be suppressed in mares with GnRHa therapy, animals require up to 30 d of treatment before suppression of ovarian activity is achieved.

Urinary steroids in the periparturient and postpartum periods through early pregnancy in llamas

Urinary steroids were determined daily in the periparturient and postpartum periods, including early pregnancy, in the female llama. Estrone sulfate (E(1)S) and pregnanediol glucuronide (PdG) concentrations were determined by enzyme immunoassay with values corrected for variations in urine concentration by creatinine. Estrone sulfate concentrations, elevated during the last 20 days of gestation through 12 hours before parturition, were declining at the time of delivery. Pregnanediol glucuronide concentrations followed a pattern similar to that of estrone sulfate except that values began to decrease 5 days before parturition. Values for both E(1)S and PdG were basal by 24 hours after delivery. The first significant elevation of estrone sulfate, indicative of initial follicle development, was observed 5 days after parturition. Pregnanediol glucuronide concentrations were low during the postpartum period until 4 to 5 days after breeding. The PdG values rose steadily following copulatory-induced ovulation, which was initiated at about 2 weeks postpartum; values continued to increase through the first 15 days of pregnancy.

Serum LH, FSH, estradiol-17β and progesterone profiles of native and crossbred goats in a tropical semiarid zone of Venezuela during the estrous cycle

Abstract The patterns of serum luteinizing hormone (LH), follicle stimulating hormone (FSH), progesterone and estradiol-17β during the estrous cycle of six crossbred (Alpine × Nubian × Native) and six native goats showing a 21 day estrous cycle in a semiarid zone of Venezuela are presented. In the crossbred goats, FSH had two significant peaks on Days 19 and 0 (33 ± 8.6 ng ml −1 and 25 ± 6 ng ml −1 , respectively); in contrast, native goats only had one significant peak on the day of estrus (22 ± 2 ng ml −1 ), with the increase beginning on Day 17. During the follicular phase of crossbred goats, estradiol-17β and LH increased to 28 ± 6 pg ml −1 and 23 ± 6.9 ng ml −1 , respectively, on Day 0. Prior to Day 0, LH increased to 10.0 ± 4.9 ng ml −1 on Day 18, decreasing to 1.5 ng ml −1 on Day 19, while estradiol-17β was increasing. This relationship between estradiol-17β and LH was not found to exist in native does, which presented a LH peak on Day 0 (30 ± 8 ng ml −1 and 35 ± 10 ng ml −1 in first and second estrus, respectively). LH basal levels were notably higher in native does. The highest concentrations of progesterone (10 and 12 ng ml −1 ) were detected on Days 12 and 15 in crossbred and native females, respectively. In conclusion, the relationship between estradiol-17β and gonadotropins during the follicular phase in crossbred goats suggests negative and positive feedback effects on both LH and FSH. Serum concentrations of LH were higher in native than in crossbred goats, whereas concentrations of FSH were higher in crossbred does. Thus, genetic factors need to be taken into account when comparing blood levels of gonadotropins in goats raised in tropical semiarid zones.

Year and season effects on oestrus and ovarian activity in ewes of different breeds and crosses

Abstract The dates of onset and cessation of ovulation and oestrus and the duration of the ovulatory, oestrous, anovulatory and anoestrous seasons were determined for Suffolk, Rambouillet, Dorset, Finnish Landrace and reciprocal F 1 crosses between the last three breeds in a study which extended over 3 years. Ovulation rate, duration of oestrus and cycle length were also examined. Among the purebreds the major source of variation in these traits could be attributed to differences between the Rambouillet and the remaining breeds. Rambouillet ewes commenced and ceased ovarian and oestrous activity earlier than the Finn; first ovulation also occurred earlier in the Rambouillet than in the Suffolk and the duration of ovarian activity was longer for the Rambouillet than for either of these breeds. The oestrous season was 27 days shorter for the Rambouillet than for the Dorset, due to a higher incidence of ovulation without oestrus in the Rambouillet. The anoestrum was between 27 and 65 days longer for the Rambouillet than for any of the other purebreds. The period of anovulation was longest for the Suffolk breed. There was little evidence for heterosis in the duration of the breeding and non-breeding seasons. The repeatability of components of the breeding season was generally low. Ovulation rate increased slightly from early to mid-season and then declined significantly as the breeding season advanced, in all breeds.

Effects of paraquat on plasma glucose, cortisol, catecholamines, and insulin in the beagle.

Paraquat is known to produce hyperglycemia in rodents, although the mechanisms responsible for the hyperglycemic effect of paraquat are not clearly understood. In this study we report the effects of paraquat (25 mg/kg iv) on plasma glucose, cortisol, catecholamines, and insulin in dogs. Paraquat caused a significant increase in plasma glucose level at all times of measurement except at 0.5 hr following paraquat administration. The cortisol levels after paraquat treatment were increased to 133, 305, 279, 418, 517, 672, and 567% above zero time control at 0.5, 1.5, 3, 6, 12, and 24 hr, and at death time respectively. The catecholamines at these times were increased to 42, 17, 72, 118, 138, 226, and 435% above the control. In contrast to cortisol and catecholamines, the plasma insulin levels after paraquat treatment were significantly decreased at 3, 6, 12, and 24 hr. These hormonal observations can explain, at least in part, the observed hyperglycemia, since all promote hyperglycemic states. For example, cortisol is gluconeogenic, catecholamines are glycogenolytic, and lower insulin levels result in depressed peripheral glucose utilization.

Associations among prostaglandin F2alpha, plasma zinc, copper and iron concentrations and fetal loss in cows and mares

The objective of this study was to test the hypothesis that PGF2alpha is associated with abortion and changes in plasma Zn, Cu, and Fe concentrations in cows and mares in their first trimester of pregnancy. Eleven pregnant cows were infused with endotoxin (n = 5) or endotoxin plus an inhibitor of cycloxygenase, flunixin meglumine (n = 6). Blood was collected over a 5-d period. Additionally, 4 mares were treated every 24 h with cloprostenol sodium and blood was collected hourly until abortion. Plasma Zn, Cu, and Fe were determined. Three of five cows treated with endotoxin aborted, but none of the six cows treated with endotoxin and flunixin meglumine aborted. Aborting cows had lower plasma Zn (P = 0.048) over the 5-d study period compared with the nonaborting cows. The changes in Zn corresponded to release of PGF2alpha. All 4 mares aborted and plasma Zn concentrations were lower (P = 0.008) and Cu/Zn was higher (P = 0.02) 12 h after cloprostenol treatment. Plasma Zn may be a useful biomarker for risk of spontaneous abortion, and the decline in plasma Zn may be caused by PGF2alpha.