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W. F. Pope and F. Stormshak

Summary. Pregnant and non-pregnant ewes were utilized to determine whether the presence of the embryo affected the binding of prostaglandin (PG) F-2α to a uterine luminal protein. The uterine horn adjacent to the corpus luteum was flushed on Day 13 of gestation or the oestrous cycle. Flushings were incubated with [3H]PGF-2α and subsequently eluted through a Sephadex column. Uterine luminal proteins of pregnant and non-pregnant ewes eluted with the void volume and failed to bind PGF-2α.

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L. V. SWANSON and F. STORMSHAK

Summary.

Norepinephrine, dopamine, and serotonin concentrations in the hypothalamus and stalk-median eminence were estimated in nine Hereford heifers at the onset of oestrus or 48 hr later. Significant differences in levels of monoamines at these stages of the oestrous cycle were not evident. Norepinephrine levels were similar in the hypothalamus and the stalk-median eminence, but dopamine and serotonin concentrations were significantly higher in the stalk-median eminence.

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HELEN E. KELLEY and F. STORMSHAK

Summary.

Rabbits were injected intravenously with luteinizing hormone (lh) or saline solution on Day 9 of pseudopregnancy and killed ½, 24 or 48 hr later. Corpora lutea of lh-treated animals had decreased significantly in size and progesterone content at 24 and 48 hr compared to corpora lutea of control rabbits. Luteal content and concentration of 20α-hydroxypregn-4-en-3-one were increased at ½ hr but decreased over the next 48 hr.

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P. K. Chakraborty and F. Stormshak

A single injection or two consecutive daily injections of oestradiol into intact ewes from Days 9 to 13 of the oestrous cycle induce premature luteal regression (Stormshak, Kelley & Hawk, 1969; Hawk & Bolt, 1970; Howland, Akbar & Stormshak, 1971). If the ewes are hysterectomized on Days 5 or 9 of the cycle, oestradiol administered between Days 9 and 13 does not cause regression of the CL, suggesting an involvement of the uterus in the effect of oestradiol on the CL (Stormshak et al., 1969; Bolt & Hawk, 1975). It has been proposed that the uterine luteolysin in the ewe is prostaglandin F-2α (McCracken et al., 1972), and oestradiol injection on Days 9 and 10 of the cycle results in an increased concentration of prostaglandin F-2α in uterine venous plasma 18 hr after the last injection (Ford et al., 1975).

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R. J. GERRITS, H. W. HAWK and F. STORMSHAK

Summary.

Polyethylene spirals (IUDs) were inserted by laparotomy on the 1st day of oestrus into one or both uterine horns of cyclic gilts; sham-operated gilts served as controls. Immediate post-operative oestrous cycles averaged 20·0 days for twenty-seven gilts with IUDs and 19·8 days for fourteen controls. Eleven gilts with IUDs were mated at nineteen later oestrous periods; all returned to oestrus after mating, with cycles averaging 21·2 days.

Gilts were autopsied at 3, 8 to 10 or 14 days after mating. Ova were fertilized in IUD gilts and most embryos were still alive 8 to 10 days after mating. A high rate of embryonic mortality occurred between 8 and 14 days. Leucocytes were present in the uterine lumen of IUD gilts at 8 to 10 and 14 days after mating.

In twenty gilts killed 9 or 14 days after mating, weights of corpora lutea were significantly less in IUD gilts than in controls; luteal progesterone levels, however, did not differ significantly. In the IUD gilts there was no evidence that corpora lutea were smaller on the side of the IUD than on the contralateral side.

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R. Friedman, T. Lais, D. W. Weber and F. Stormshak

An experiment was conducted to investigate the responses of the bovine infundibulum to noradrenaline in vitro. Twelve beef heifers were killed and examined in equal numbers during pro-oestrus and dioestrus (day 12 of the oestrous cycle). A jugular blood sample was collected from each heifer immediately before killing, and the sera were subsequently analysed by radioimmunoassay for progesterone and oestradiol. A strip of each infundibulum (ipsilateral and contralateral to the ovary bearing the largest follicle or functional corpus luteum) was placed into a tissue bath and sequentially exposed to increasing concentrations of noradrenaline (0.4, 0.8 and 1.6 μg ml−1). Changes in frequency and amplitude of isometric contractions and tissue tone were recorded. Infundibula ipsilateral to ovaries bearing the largest follicle in pro-oestrous heifers responded to all concentrations of noradrenaline with greater frequency of contractions than did either contralateral infundibula or both ipsilateral and contralateral infundibula of dioestrous animals (stage of cycle × tissue location interaction, P< 0.01). Changes in the amplitude of contractions induced by noradrenaline did not differ between stages of the cycle studied or the location of the infundibulum within the animal. Mean tone of ipsilateral and contralateral infundibula of pro-oestrous and dioestrous animals increased linearly with exposure to all concentrations of noradrenaline tested (P< 0.05). However, the response of infundibula of dioestrous animals was greater than that of infundibula of pro-oestrous heifers (P ≤ 0.06). These data demonstrate that the bovine infundibulum is responsive to noradrenaline, and suggest that responses to this neurotransmitter may be governed by concentrations of oestrogen and progesterone to which the infundibulum is exposed.

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F. STORMSHAK, R. P. LEHMANN and H. W. HAWK

Summary.

Plastic spirals were surgically inserted into one uterine horn of thirty-two ewes and into both uterine horns of four salpingectomized ewes on Days 4 and 6 of the oestrous cycle, respectively (1st day of oestrus = Day 1). Sham operations were performed on controls. Ewes were autopsied on Day 8 of a subsequent oestrous cycle.

The presence of a plastic spiral either in the anterior or posterior portion of the uterine horn interfered with development of the corpus luteum (cl) in the adjacent but not of that in the opposite ovary. The administration of 1600 i.u. of hcg/day from Days 3 to 6 of the oestrous cycle counteracted the inhibitory effect of the spiral on cl development. Intra-uterine spirals interfered with cl development in salpingectomized ewes, thus eliminating the oviduct as a major pathway through which the inhibitory effect of the spiral on the cl is mediated.

The oestrous cycle during which spirals were inserted was not consistently shortened when the cl were present only in the ovary adjacent to the operated uterine horn.

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EM Paslay, Jaeger JR, U Salli and F Stormshak

The aim of this study was to determine whether endogenous progesterone regulates synthesis and secretion of luteal oxytocin. In Expt 1, mature ewes (n = 5 per group) were assigned randomly to control or mifepristone (RU486) treatment groups. Ewes were injected s.c. twice a day with vehicle or 10 mg RU486 on days 5-7 of the oestrous cycle (oestrus = day 0). On day 8, after an i.v. injection with prostaglandin F(2alpha) (250 microg cloprostenol), venous blood samples were collected at frequent intervals to determine plasma oxytocin concentrations. Plasma oxytocin concentrations of RU486-treated ewes were not significantly different from those of control ewes. In Expt 2, ewes were injected s.c. each day with vehicle or 175 mg RU486 on days 2-5 of the oestrous cycle followed by administration of prostaglandin F(2alpha) on day 6. Four of five RU486-treated ewes showed 'split-oestrus' (oestrous behaviour for 36 h and then again at 84-108 h after the onset of initial oestrus). There was no significant difference in mean plasma oxytocin or progesterone concentrations between treatment groups. The mean masses of mature corpora lutea from control and RU486-treated ewes on day 6 of the oestrous cycle did not differ significantly (394.8 +/- 28.8 versus 319.5 +/- 48.3 mg). RU486-treated ewes contained mature corpora lutea, new corpora lutea (two of four ewes) and preovulatory follicles (>or= 10 mm, two of four ewes). The average interoestrous interval for RU486-treated ewes was 9 days more than that for control animals (26.2 +/- 2.9 versus 17 +/- 0.5 days; P < 0.025).

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F Stormshak, C T Estill, J A Resko and C E Roselli

Two experiments were conducted to determine whether an estradiol challenge could cause a female-type LH surge in castrated male- and female-oriented rams (MORs and FORs). Administration of 17β-estradiol to castrated MORs and FORs and ovariectomized ewes caused an initial reduction in LH secretion followed for 12–20 h by a surge release of LH in the ewes. No surge release of LH occurred in the MORs and FORs. The pattern of changes in LH secretion within rams and ewes did not differ between the breeding and nonbreeding seasons. Treatment failed to elicit female-typical receptive sexual behaviors in the rams but did stimulate increased sexual receptivity in the ewes as determined by the measures of responsiveness to the teaser ram. Overall, no differences were found in hypothalamic–hypophyseal function in response to exogenous estradiol between MORs and FORs. These data are interpreted to suggest that in contrast to sexual attraction, the neural mechanisms controlling the LH surge and female receptivity are defeminized in MORs.