Search Results

You are looking at 1 - 9 of 9 items for

  • Author: D. E. Walters x
Clear All Modify Search
Free access

D. L. Walters and E. Schallenberger

Summary. An injection of 500 μg prostaglandin (PG) analogue was given on Day 12 (mid-luteal phase) of the oestrous cycle to 8 cows. An LH surge occurred 59 ± 2 h later. LH, FSH, prolactin, oestradiol-17β, progesterone and oxytocin concentrations were determined in blood samples collected from the caudal vena cava and/or the jugular vein at 20-min (5 cows) or 5-min (3 cows; only LH and FSH concentrations were determined) intervals for 24 h, beginning 48 h after the PG injection. Oxytocin concentrations were low and similar in the vena cava and the jugular vein. In blood samples collected every 5 min the interpulse interval for LH and FSH during the period before the LH surge was 38–40 min. In the 20-min samples the interpulse interval for oestradiol was similar to that for LH and FSH, but pulse amplitude and basal concentrations steadily increased to reach maximum concentrations 6–8 h before and again during the LH surge. A decrease in oestradiol concentrations, lasting at least 60 min, occurred just before the start of the LH surge. Progesterone concentrations also increased at the same time as the LH surge. The magnitude of the LH surges varied from 7 to 32 ng/ml, but all cows ovulated and had oestrous cycles of normal length. Distinct pulses of LH and FSH were observed throughout the LH and FSH surges. Pulsatile secretion of LH was not detected for a period of up to 6–12 h following the LH surge, but then low-amplitude pulses occurred. In contrast, the pulsatile secretion of FSH remained at a frequency similar to that observed during the descending phase of the FSH surge. Furthermore, a second increase in FSH concentrations occurred, beginning 4–12 h after the LH-surge.

It is concluded that: (1) the frequent, high-amplitude pulses of oestradiol that occur before and during the LH surge are probably due to stimulation by pulses of LH; (2) the LH surge is the result of an increase in frequency and amplitude of the LH pulses; (3) the second increase in FSH that follows the LH and FSH surges appears to be the result of an increase in the amplitude (not frequency) of the FSH pulses; and (4) very little, if any, oxytocin is secreted from the ovary during the periovulatory phase of the oestrous cycle.

Free access

D. L. Walters, D. Schams and E. Schallenberger

Summary. All hormones were determined in blood samples collected simultaneously from the caudal vena cava and jugular vein at 20-min intervals for 12 h during the early (Day 4) and mid- (~Day 11) luteal phases of the oestrous cycle in 7 cows. Mean concentrations of oestradiol, progesterone and oxytocin were greater (P < 0·01) in the vena cava than in the jugular vein. Pulses of these hormones were also more easily identifiable in the vena cava. The frequency of LH pulses was higher (P < 0·01) during the early luteal than during the mid-luteal phase (8·0 versus 3·6 pulses/12 h). During both phases, 90–96% of all LH pulses were followed within 60 min by a pulse of oestradiol. Basal concentration and amplitude of oestradiol pulses were greater (P < 0·05) during the early than during the mid-luteal phase. The frequency of FSH pulses was similar to that of LH during the early luteal phase (8·5 and 8·0 pulses/12 h) but was greater (P < 0·01) than that of LH during the mid-luteal phase (6·3 versus 3·6 pulses/12 h). Thus, 41% more (P < 0·01) FSH pulses than LH pulses were observed during the mid-luteal phase. However, the separate FSH pulses were associated with low-amplitude short-duration pulses of LH as clarified by an additional study (in 3 cows) using 5-min sampling intervals: 90–100% of all LH/FSH pulses and separate FSH pulses were secreted either concomitantly with or followed by a pulse of progesterone. However, no separate FSH pulses were associated with a pulse of oestradiol. Basal concentration and amplitude of progesterone were greater (P < 0·01) during the mid-luteal than during the early luteal phase. The frequency of oxytocin pulses was similar to that of progesterone during the mid-luteal but not during the early luteal phase. During the mid-luteal phase 97% of all oxytocin pulses were associated with a pulse of progesterone. It is concluded that (1) separate FSH pulses are secreted in addition to parallel LH and FSH pulses during the mid-luteal phase; therefore, the frequency of secretion of LH may be modulated to a greater extent by ovarian steroids than is FSH pulse frequency; (2) pulses of progesterone are probably a result of stimulation by pulses of FSH and/or LH whereas pulses of oestradiol are caused by LH pulses; (3) ovarian oxytocin and progesterone are secreted concomitantly during the mid-luteal phase of the oestrous cycle.

Free access

E. Schallenberger, D. Schams, B. Bullermann and D. L. Walters

Summary. A luteolytic dose (500 μg) of cloprostenol was given on Day 12 of the oestrous cycle to 5 heifers. Blood samples were collected simultaneously from the caudal vena cava and jugular vein at 5–20-min intervals from – 6 to 0 (control period), 0 to 12 and 24 to 36 h after PG injection. Pulses of LH were secreted concomitantly with pulses of FSH during all sampling periods. However, during the control period separate FSH pulses were detected resulting in a shorter (P < 0·01) interpulse interval for FSH than LH (93 versus 248 min). LH and FSH pulse frequencies increased (P < 0·01) beginning 1–3 h after PG to interpulse intervals of 59 and 63 min, respectively, and continued to be maintained 24–36 h after PG. Concomitantly there was a 2–3-fold increase (P < 0·01) in basal concentrations and pulse amplitude for LH (but not FSH). FSH basal concentrations and pulse amplitudes decreased (P < 0·05) in 3 heifers 24–36 h after PG. Pulsatile secretion of oestradiol was observed at frequencies similar to LH during the periods 4–12 h (3 heifers) and 24–36 h (2 heifers) after PG, respectively, resulting in higher (P < 0·05) mean oestradiol concentrations. Progesterone concentrations in the vena cava increased (P < 0·01) 5–10 min after PG but decreased (P < 0·01) 67% by 20 min after PG. This decrease was followed by a rise (P < 0·05) beginning 2–3 h after PG and lasting for an average of 3·3 h. After a steady decline, basal concentrations of 1·0 ng/ml were reached 24–36 h after PG. Basal oxytocin concentrations in the vena cava and jugular vein (8·2 and 4·2 pg/ml) increased (P < 0·01) to reach maximum concentrations (2029 and 701 pg/ml) 5–10 min after PG and then decreased over a 3–5 h period and were lowest (4–3 and 3–2 pg/ml) 24–36 h after PG. Maximum prolactin concentrations were higher and appeared 5–10 min earlier in the jugular vein compared to the vena cava.

It is concluded that: (1) progesterone and oxytocin secretion from the corpus luteum is initially increased and then dramatically decreased by a luteolytic dose of PG; (2) the reduction of progesterone concentrations below a certain threshold level in the presence of low oestradiol concentrations probably eliminates the negative feedback effect on gonadotrophin secretion, thereby allowing the frequency and amplitude of LH pulses, and to a lesser extent the frequency of FSH pulses, to increase; and (3) the increase in FSH and LH pulse frequencies probably stimulates, after a variable period of time, the development of a large follicle that secretes increasing concentrations of oestradiol.

Free access

D. E. Walters, R. G. Edwards and M. L. Meistrich

Summary. All the available data relating to pregnancy and multiple implantations from Bourn Hall Clinic are used to assess the accuracy of two statistical models of implantation. The simple binomial model was found to be incapable of describing both the pregnancy rates and the incidence of multiple implantations, whereas a two-parameter model, incorporating both patient and embryo variability, provided a good fit to the data. The estimates obtained for the two parameters in the second model suggested that 36% of the embryos could implant, and that 43% of patients were capable of sustaining implantation. The Maximum Likelihood method of constructing 95% confidence limits on the estimates of the parameter values is demonstrated.

Free access

R. Newcomb, W. B. Christie, L. E. A. Rowson, D. E. Walters and W. E. D. Bousfield

Summary. The effect of two dose levels (1000 and 2000 i.u.) of three different commercially available batches of PMSG on the ovarian response (ovulations and follicles > 10 mm) of 42 heifers was examined in a randomized incomplete block experiment. Each animal was subjected to two consecutive but different treatments.

A significant effect of dose was observed and there were fewer ovulations, but no reduction in the number of follicles, after the second PMSG treatment. There was no evidence that the ovarian response was affected by the PMSG batch used.

Free access

Ruth E. Fowler, M. H. Johnson, D. E. Walters and Deborah D. Eager

Summary. A detailed study has been made of the progesterone content of uterine flushings taken from rabbits of different endocrine states. A high content of progesterone was recovered from the uterine lumen of pregnant and pseudopregnant rabbits. The amount of progesterone recovered in the flushings was not simply dependent on the concentration in the plasma, because plasma progesterone concentrations rose before detection of progesterone in the flushings and remained high after uterine progesterone content had fallen. Progesterone did not appear in the uterine fluid unless uterine protein was present. This was particularly evident in rabbits treated with progesterone in which, despite abnormally high plasma concentrations, little progesterone was found in uterine fluid until the protein content increased. After treatment of rabbits with oestrogen at the time of ovulation, uterine progesterone was present in higher amounts concomitant with an elevation of protein content although the peak values of progesterone and protein were delayed by 2–3 days. Plasma progesterone concentrations of about 5 ng/ml were necessary before progesterone appeared in the uterine lumen.

Free access

Ruth E. Fowler, M. H. Johnson, D. E. Walters and Hester P. M. Pratt

Department of Physiology, Department of Anatomy, andtDepartment of Applied Biology, Downing Street, Cambridge, U.K.

Free access

P. J. Wright, G. Jenkin, R. B. Heap and D. E. Walters

Summary. Pituitary responsiveness to 200 μg synthetic LH-RH and to 10 μg TRH was determined in anoestrous sheep before and after treatment for 3 weeks with progesterone (100 mg/day), or oestradiol (250 μg/day) plus progesterone (100 mg/day). There was a marked decrease in pituitary responsiveness to LH-RH after progesterone (P < 0·01 ), or oestradiol + progesterone (P < 0·01) treatments, and an increase in response to TRH after oestradiol + progesterone (P < 0·01) treatment. The results demonstrate selective and simultaneous feedback effects of oestradiol and progesterone on pituitary responsiveness to two hypothalamic releasing hormones.

Free access

J. K. Findlay, Nicola Ackland, R. D. Burton, A. J. Davis, Felicity M. Maule Walker, D. E. Walters and R. B. Heap

Summary. The effect of the presence of a preimplantation embryo on protein concentration, rate of protein synthesis, β-glucuronidase and acid phosphatase activities, steroid metabolism and prostaglandin F production in caruncular and intercaruncular tissue have been studied for sheep at Day 15 of pregnancy. The rate of protein synthesis in both tissues was greater in pregnant than in non-pregnant animals, although the difference was only significant in caruncular endometrium. The effect in caruncular tissue was mimicked in ovariectomized animals treated with oestradiol. Localized changes in the caruncular tissue were observed in respect of PGF with an increased tissue concentration, an enhanced basal release when the tissue was incubated in the presence of indomethacin, and a decreased net production. Maximum production of PGF in the 2 tissues was unaffected by the presence of an embryo but it was enhanced by oestradiol or progesterone treatment in intercaruncular tissue of ovariectomized ewes. β-Glucuronidase and acid phosphatase activities and steroid metabolism were unaffected by pregnancy. However, in ovariectomized animals oestradiol treatment stimulated β-glucuronidase activity in endometrium and myometrium. Progesterone treatment stimulated acid phosphatase activity in the intercaruncular endometrium.

The results show that amongst several endometrial constituents investigated relatively few changes were detected by Day 15 post coitum, one day before definitive attachment. Those changes that did occur were associated with the dynamics of PGF production and the rate of protein synthesis, and were consistent with the production of a PGF binding component in caruncular endometrium which may be concerned with the protection of luteal function by redirection of uterine PGF production.

Canonical variate analysis revealed that changes on Day 15 of pregnancy were mimicked most closely in caruncular tissue by treatment of ovariectomized ewes with oestradiol and progesterone, and in intercaruncular tissue by oestradiol treatment only.