Summary. In 4 Clun Forest ewes maternal peripheral plasma concentrations of progesterone were still elevated at the onset of parturient uterine activity. Fetal and maternal plasma concentrations of oestrogen started to rise before parturition and concentrations in maternal plasma were positively correlated with parturient uterine activity (P < 0·05; r = +0·42). Fetal plasma concentrations of corticosteroids were positively correlated with fetal plasma concentrations of oestrogen (P < 0·01; r = +0·65), but negatively correlated with maternal peripheral plasma progesterone concentrations (P < 0·05; r = −0·50). Before parturition plasma concentrations of PGF rose but stayed high only in maternal peripheral plasma. Maternal peripheral plasma concentrations of PGF were positively correlated with uterine activity (P < 0·05; r = +0·79) and plasma concentrations of oestrogen (P < 0·05; r = +0· 79), but negatively correlated with plasma concentrations of progesterone (P < 0·01; r = −0·54).
N. C. Rawlings and W. R. Ward
N. C. Rawlings and W. R. Ward
Summary. In 7 ewes during late pregnancy, peripheral plasma concentrations of oestrogens were correlated with uterine activity (P < 0·01; r=+0·47).
In myometrial tissue, the concentration of progesterone was similar to that in plasma; it rose to a plateau from Days 115 to 130 of pregnancy and then fell, but was still detectable during parturition. Myometrial oestrogen concentration was much higher than in plasma; from a peak at Days 100–115 it decreased, but rose sharply just before parturition.
N. C. Rawlings and W. R. Ward
Summary. Fetal hypophysectomy performed between 97 and 130 days of gestation caused a significant (P < 0·005) prolongation of pregnancy in 5 goats in which every fetus was treated. Three of these goats gave birth spontaneously. Sham surgery or hypophysectomy of one fetus of twins had no effect on gestation length. Hypophysectomized kids, delivered after prolonged pregnancy, were significantly heavier than normal term kids (P < 0·005) and had lighter adrenals (P < 0·025). Measurements of maternal peripheral plasma concentrations of progesterone and total unconjugated oestrogens showed that the changes in goats carrying hypophysectomized fetuses were similar to those of normal pregnancy except that the prepartum oestrogen peak was absent, whether or not parturition occurred spontaneously.
A. M. Shareha, W. R. Ward and Kathleen Birchall
Gn-RH (3 μg/hr for 8 hr) evoked a surge of LH in ewes during the anoestrous season which was of similar peak height to that found at oestrus but of shorter duration. When Gn-RH was given on 3 consecutive days, the response was considerably reduced on the 2nd and 3rd day. Follicles grew as a result of Gn-RH infusion but peripheral plasma oestrogen concentration did not increase. During the anoestrous season 9/18 ewes ovulated but only 1/6 did so at mid-anoestrus, Mature follicles or a CL were found in 15/18 ewes that had increased peripheral plasma progesterone concentrations for 1-5 days (11 ewes) or 9-14 days (4 ewes). The concentrations of progesterone found were always lower than those observed during the normal cycle. In the breeding season 10/11 ewes ovulated but there was no evidence that the induced CL were maintained.
A. S. Nanda, W. R. Ward and H. Dobson
Summary. Four control cows released a normal LH surge in response to 1 mg oestradiol benzoate i.m. Compared to controls, 30 min transport of 5 cows 16–18 h after oestradiol significantly delayed the onset (P < 0·05), suppressed the amplitude (P < 0·01) and reduced the total LH release (P < 0·001) in 4 cows and totally blocked the surge in the 5th cow. Just before the onset of transport, 5 cows were given 250 mg naloxone i.v. In 3 cows, the LH surge was delayed and reduced in amplitude and duration and was totally blocked in the other two, i.e. naloxone did not avert the detrimental effects of transport.
Transport stimulated cortisol release in cows. Cows given naloxone + transport released significantly more (P < 0·001) cortisol than did those subjected to transport alone. In conclusion, naloxone appeared to have further stimulated the hypothalamo– pituitary–adrenal axis of cows under stress.
Keywords: transport; LH; cortisol; naloxone; opioids; cows
KAREN M. NUTI, W. F. WARD and R. K. MEYER
Unilateral ovariectomy on the 3rd day of pregnancy in the rat resulted in arrested embryonic development and decreased implantation in the ipsilateral uterine horn. These degenerative changes were apparent 48 hr, but not 24 hr, after operation. A single subcutaneous injection of either oestrone (1·0 μg) or progesterone (2·0 mg) at 08.00 hours on the 5th day of pregnancy induced implantation and foetal maintenance in the ipsilateral horn. Treatment with progesterone was consistently more effective than oestrogen.
These observations suggest that unilateral ovariectomy induces a hormonal deficiency in the adjacent uterine horn which is incompatible with optimum preimplantation embryonic development.
A. S. Nanda, W. R. Ward and Hilary Dobson
Summary. Four cows released an LH surge after 1·0 mg oestradiol benzoate administered i.m. during the post-partum anoestrous period with continuing low plasma progesterone. A similar response occurred in the early follicular phase when plasma progesterone concentration at the time of injection was < 0·5 ng/ml. Cows treated with a progesterone-releasing intravaginal device (PRID) for 8 days were injected with cloprostenol on the 5th day to remove any endogenous source of progesterone. Oestradiol was injected on the 7th day when the plasma progesterone concentration from the PRID was between 0·7 and 1·5 ng/ml. No LH surge occurred. Similarly, oestradiol benzoate injected in the luteal phase of 3 cows 0·9–2·1 ng progesterone/ml plasma) did not provoke an LH surge. An oestradiol challenge given to 3 cows 6 days after ovariectomy induced a normal LH surge in each cow. However, when oestradiol treatment was repeated on the 7th day of PRID treatment, none released LH.
It is concluded that ovaries are not necessary for progesterone to inhibit the release of LH, and cows with plasma progesterone concentrations > 0·5 ng/ml, whether endogenous or exogenous, did not release LH in response to oestradiol.
Keywords: oestradiol; progesterone; LH; cows
H. C. Pant, Hilary Dobson and W. R. Ward
Summary. Immunization against oestrogen resulted in elevated LH concentrations, in the form of a pulsatile release, which rose from 3 to as much as 41 ng/ml approximately every 1·5 h, even in the presence of high plasma progesterone concentrations. Elevated FSH concentrations showed only minor oscillations without consistent synchrony to the LH pulses. Injection of 250 μg stilboestrol did not abolish the LH pulses but in 2 out of 8 ewes FSH was initially lowered. Injection of 1 mg stilboestrol abolished the LH pulses within 11 h and decreased FSH values in 2 out of 4 ewes. Between 16 and 35 h after injection there was a large increase in LH and FSH concentrations. Thus, in the ewe, the tonic secretion of LH and FSH is controlled by a negative feedback action of oestrogen, and diethylstilboestrol will exert both positive and negative feedback effects on both gonadotrophins, depending upon dose. Infusion of LH was unable to alter the frequency or height of the LH pulses, thereby excluding regulation of the LH pulses by a short feedback mechansim.
N. C. Rawlings, H. C. Pant and W. R. Ward
Summary. Six ewes were treated twice daily with intravenous injections of antiserum to oestrogens and 3 ewes received normal sheep serum from Day 140 of gestation until parturition. All 9 ewes experienced normal parturitions and produced healthy active lambs after similar gestation lengths. Progesterone and prostaglandin F concentrations in maternal jugular venous plasma were similar in the immunized and control ewes, but total unconjugated oestrogen concentrations were significantly higher in the immunized ewes (P < 0·005). It is concluded that immunization of the ewe against total unconjugated oestrogens did not affect the normal occurrence of parturition.
R. G. Cooke, A. Knifton, R. J. Fitzpatrick and W. R. Ward
In goats the corpus luteum (CL) is essential for the maintenance of pregnancy (Meites, Webster, Young, Thorp & Hatch, 1951). Cooke, Knifton & Ward (1975) showed that removal of the CL caused a sudden decline in uterine venous plasma concentrations of progesterone and abortion occurred after a consistent interval of 30 h; there was an abrupt increase in the concentration of uterine venous plasma prostaglandin (PG) F about 24 h after removal of the CL, before or coincident with cervical softening and dilatation. The present experiments were designed to examine, on this simplified 'model', any effects of intra-arterial infusions of PGF-2α on uterine motility, cervical dilatation and the interval to abortion.