Search Results

You are looking at 1 - 10 of 12 items for

  • Author: W. D. Currie x
Clear All Modify Search
Free access

W. B. CURRIE and G. D. THORBURN

C.S.I.R.O., Division of Animal Physiology, Ian Clunies Ross Animal Research Laboratory, P.O. Box 239, Blacktown, N.S.W. 2148, Australia

(Received 20th June 1974)

There is an obligatory requirement for continued secretory activity of the goat CL throughout pregnancy because the placenta does not secrete progesterone in this species (Linzell & Heap, 1968; van Rensburg, 1971; Thorburn & Schneider, 1972; Irving, Jones & Knifton, 1972a). Ovariectomy or ablation of the CL during pregnancy inevitably causes abortion, the effects being due solely to the withdrawal of progesterone (Meites, Webster, Young, Thorp & Hatch, 1951; Irving et al., 1972a). Regression of the CL, as indicated by an abrupt decline in circulating progesterone concentrations, occurs on the day before parturition at term (gestation length 150±3 days) and also before pathological abortion (van Rensburg, 1971). Van Rensburg (1971) has suggested that the decrease in progesterone may reflect a withdrawal of maternal pituitary luteotrophin as a result

Free access

W. D. Currie and N. C. Rawlings

Summary. In ewes in the mid-luteal phase, LH pulse frequency (P < 0·01) and amplitude (P < 0·05) increased during a 24 h infusion of naloxone (0·5 mg/kg/h) compared to a 24 h infusion of vehicle (mean ± s.e.m.; 0·25 ± 0·03 vs 0·14 ± 0·01 pulses/h and 0·84 ± 0·08 vs 0·55 ± 0·08 ng/ml serum, respectively). The increase in pulse amplitude was immediate, but was less (P < 0·05) during the second 12h, compared to the first 12 h, of naloxone infusion (0·52 ± 0·14 vs 0·98 ± 0·08 ng/ml serum). Oestradiol concentrations were higher (P < 0·01) during naloxone than during control infusion (5·63 ± 0·26 vs 4·13 ± 0·15 pg/ml serum). In ovariectomized ewes in the breeding season, LH pulse frequency was lower (P < 0·01) during a 24 h infusion of morphine (0·5 mg/kg/h) than during a 24 h infusion of vehicle (mean ± s.e.m.; 1·17 ± 0·08 vs 1·71 ± 0·06 pulses/h). We conclude that long-term infusion of naloxone results in a sustained increase in LH pulse frequency but only a transient elevation in pulse amplitude. No effects on FSH secretion were noted. LH secretion was sensitive to morphine in the absence of ovarian steroids, suggesting that ovarian steroids are not required for the presence of functional opioid receptors capable of modulating LH release.

Keywords: LH; FSH; ewe; morphine; naloxone

Free access

A. C. O. Evans, W. D. Currie and N. C. Rawlings

Summary. The pattern and opioidergic control of the secretion of gonadotrophins in prepubertal heifer calves were examined. Ten age-matched Hereford heifer calves were weighed and a blood sample was taken every 2 weeks from 2 to 25 weeks of age and then weekly until 60 weeks of age. At 60 weeks, a fertile bull was introduced and at 75 weeks of age pregnancy diagnosis was performed by transrectal ultrasonography. At 4, 12, 18, 24 and 32 weeks of age, the opioid antagonist naloxone was injected (i.v., n = 5; 1 mg kg−1 body weight) each hour for 12 h. Control heifers received sterile saline at the same ages. Blood samples were collected every 12 min for the 12 h treatment and serum samples were analysed for luteinizing hormone (LH) and follicle-stimulating hormone (FSH). Samples taken once every 2 weeks from 2 to 60 weeks were analysed for LH, FSH and oestradiol, and weekly samples were taken for progesterone determination. There was no effect of naloxone on the age at puberty, which was 56·2 ± 0·7 weeks at a body weight of 388·5 ± 8·0 kg. The mean age at conception was 63·4 ± 0·5 weeks. On the basis of samples taken every other week, serum concentrations of LH were high at 10 weeks and between 40 and 60 weeks of age. From the periods of intensive blood collection, the early rise in mean serum concentrations of LH appeared later at 12 and 18 weeks of age and was caused by a rise in LH pulse amplitude. Serum FSH concentrations were increased between 20 and 22 weeks and oestradiol concentrations at 22, 56 and 58 weeks of age. At 4 weeks, naloxone increased mean LH concentrations, pulse amplitude and pulse frequency (P < 0·01) and thereafter only decreased LH pulse amplitude at 18 weeks (P < 0·05) and increased LH pulse frequency at 24 weeks (P < 0·05). The FSH secretion was pulsatile at all ages and naloxone only increased FSH pulse amplitude at 4 weeks.

From these data we conclude that (i) there is an early transient increase in gonadotrophin secretion in prepubertal heifers, (ii) significant opioidergic inhibition of gonadotrophin secretion occurs only in very young heifers and (iii) a decrease in endogenous opioid inhibition of LH secretion, particularly LH pulse amplitude, allows for the early rise in LH secretion.

Keywords: puberty; gonadotrophins; naloxone; heifer

Free access

W. J. LONGLEY, D. L. BLACK and G. N. CURRIE

Summary.

The influence of various autonomic drugs on the circular muscle of the oviduct was studied. The changes in oviduct motility patterns were measured in anaesthetized Dutch Belted rabbits with a perfusion apparatus and pressure transducer. Intravenous noradrenaline (1 to 4 μg/kg) and adrenaline (2·5 to 7·5 μg/kg) resulted in a sustained contraction of the oviduct followed by contraction at a higher tone. Isoprenaline (1 to 4 μg/kg) caused a relaxation of the oviduct musculature. Phenoxybenzamine (3 mg/kg subcutaneously) blocked the action of adrenaline for at least 4 hr. Propranolol blocked the action of isoprenaline for 1 to 2 hr. The results of administering acetylcholine and scopolamine were inconclusive.

Free access

W. J. LONGLEY, D. L. BLACK and G. N. CURRIE

Passage of ova through the oviduct of the rabbit normally requires about 3 days, and is quite uniform for most mammalian species. The influence of oestrogen on the rate of ovum movement through the oviduct appears to be dose-dependent; high doses retard, while relatively low doses increase, the rate of movement (see Chang & Harper, 1966, for a detailed discussion). Progesterone has been reported to have no effect on transport rate (Black & Asdell, 1959; Greenwald, 1961) while other work indicates that it may block movement (Austin, 1949) or increase rate of movement (Wislocki & Snyder, 1933; Harper, 1964). The influence of autonomic drugs on the oviduct musculature was discussed in an earlier paper (Longley, Black & Currie, 1968).

In this experiment the influence of various autonomic drugs on

Free access

A. C. O. Evans, W. D. Currie and N. C. Rawlings

The control of gonadotrophin secretion during the early developmental period in the bull is poorly understood; opioidergic regulation may be involved. The opioid antagonist naloxone was administered to bull calves (i.v. n = 5; 1 mg kg−1 body weight h−1) for 12 h at 4, 12, 18, 24 and 32 weeks of age. Control animals (n = 5) received sterile saline solution. During the treatment period, 4 ml blood samples were collected every 12 min. The calves were also weighed and blood samples collected every two weeks from 2 to 48 weeks of age. Scrotal circumference was measured from 20 to 48 weeks of age to determine age at puberty. Serum samples were assayed for concentrations of LH, FSH, testosterone and oestradiol. On the basis of blood samples taken every two weeks, serum concentrations of LH increased to a peak at six weeks of age and then decreased; serum concentrations of FSH reached a peak at 20 weeks of age. Serum concentrations of testosterone and oestradiol increased with scrotal circumference from 20 to 48 weeks of age. On the basis of blood samples taken every 12 min for 12 h, we concluded that the early rise in serum LH concentrations was due to an increase in LH pulse frequency. LH pulse amplitude decreased from 4 to 18 weeks of age and FSH pulse amplitude from 4 to 32 weeks of age. Naloxone treatment increased LH pulse frequency at 4 and 24 weeks of age but not at 12, 18 or 32 weeks of age. LH pulse amplitude was depressed and mean serum concentrations of LH were increased by naloxone at 4 weeks of age. At 12 weeks of age, LH pulse amplitude and mean and basal serum LH concentrations were increased by naloxone. At 18 weeks, only mean concentrations of LH were increased by naloxone. The only effect of naloxone on FSH secretion was to increase FSH pulse amplitude at 24 weeks of age. We conclude that there is opioidergic inhibition of LH secretion in the young bull calf, but that between 12 and 18 weeks of age a decrease in opioidergic inhibition on LH pulse frequency contributes to the overall increase in mean circulating concentrations of LH at this time.

Free access

P. W. Concannon, L. Isaman, D. A. Frank, F. J. Michel and W. B. Currie

Summary. Concentrations of progesterone and of 13,14-dihydro-15-keto-prostaglandin F-2α (PGFM) were measured in plasma collected from 6 bitches every 3 h starting 2·8–4·6 days before parturition (birth of first pup) and continuing until 0·4–0·8 days post partum, and in additional samples collected less frequently. Progesterone concentrations at 48, 24, 12 and 3 h pre partum averaged 2·8 ± 0·3, 2·2 ± 0·4, 1·0 ± 0·3 and 0·7 ± 0·2 ng/ml. At those times PGFM values averaged 380 ± 80, 800 ± 220, 1450 + 450 and 1930 ± 580 pg/ml, respectively. Mean concentrations of PGFM increased about 2·5-fold between 48 and 15 h pre partum in association with the onset of luteolysis, and then increased another 2·5 times before parturition as progesterone fell to nadir values. Peak levels of PGFM ranged from 1060 to 7150 pg/ml (2100 ± 600 pg/ml) and occurred within 1–9 h after the birth of the first pup and before the birth of the last pup. These results suggest that prepartum luteolysis in dogs is initiated by increases in maternal concentrations of PGF, and that progesterone withdrawal causes a further increase in PGF which completes luteolysis and provides a major portion of the uterotonic activity causing expulsion of pups.

Keywords: pregnancy; parturition; luteolysis; prostaglandin; dog

Free access

W. D. Currie, J. Ravindra, D. L. Kingsbury and N. C. Rawlings

Summary. Fifteen ovariectomized ewes were treated with implants (s.c.) creating circulating luteal progesterone concentrations of 1·6 ± 0·1 ng ml−1 serum. Ten days later, progesterone implants were removed from five ewes which were then infused with saline for 64 h (0·154 mol Nacl 1−1, 20 ml h−1, i.v.). Ewes with progesterone implants remaining were infused with saline (n = 5) or naloxone (0·5 mg kg−1 h−1, n = 5) in saline for 64 h. At 36 h of infusion, all ewes were injected with oestradiol (20 μg in 1 ml groundnut oil, i.m.). During the first 36 h of infusion, serum luteinizing hormone (LH) concentrations were similar in ewes infused with saline after progesterone withdrawal and ewes infused with naloxone, but with progesterone implants remaining (1·23 ± 0·11 and 1·28 ± 0·23 ng ml−1 serum, respectively, mean ± sem, P > 0·05). These values exceeded circulating LH concentrations during the first 36 h of saline infusion of ewes with progesterone implants remaining (0·59 ± 0·09 ng ml−1 serum, P < 0·05). The data suggested that progesterone suppression of tonic LH secretion, before oestradiol injection, was completely antagonized by naloxone. After oestradiol injection, circulating LH concentrations decreased for about 10 h in ewes of all groups. A surge in circulating LH concentrations peaked 24 h after oestradiol injection in ewes infused with saline after progesterone withdrawal (8·16 ± 3·18 ng LH ml−1 serum). At the same time, circulating LH concentrations in ewes infused with saline or naloxone, but with progesterone implants remaining, were similar to concentrations observed before injection (0·91 ± 0·27 and 1·35 ± 0·28 ng LH ml−1 serum, respectively). The results suggested that naloxone antagonism of opioid-dependent progesterone suppression of LH secretion was not equivalent to progesterone withdrawal. It was concluded that progesterone blockade of oestradiol positive feedback on LH secretion in ewes does not depend upon endogenous opioid peptide activity at naloxone-sensitive receptors.

Keywords: opioids; luteinizing hormone surge; oestradiol; progesterone; naloxone; sheep

Free access

W. D. Currie, R. J. Medhamurthy, S. J. Cook and N. C. Rawlings

Diurnal and seasonal fluctuations were detected in luteinizing hormone (LH) interpulse interval, but not amplitude, in ewes examined during the mid-luteal phase of an oestrous cycle at five stages of the breeding season. Daytime and night-time LH interpulse intervals were greater in the early and late than in the mid-breeding season (P < 0.05). During the early and late breeding season, LH interpulse interval was less during daylight than during darkness (P < 0.05). Toward the mid-breeding season, interpulse interval decreased during daytime earlier in the season than the night-time decrease. It was concluded that the diurnal fluctuations observed are a component of a circannual rhythm in LH secretion resulting from gradual seasonal transitions in photoperiodic drive to, or an endogenous rhythm in, the hypothalamic–pituitary axis in ewes.

Free access

I. B. J. K. Joseph, W. D. Currie and N. C. Rawlings

Summary. During the breeding season, five groups of three ewes were implanted at ovariectomy with 0·36, 0·5, 1·0 and 6·0cm oestradiol implants or implants containing no steroid. Eleven days after receiving implants, blood samples were taken every 10 min for 6 h; implants were then removed. Treatments were repeated three times during each of two consecutive breeding seasons and four times during the intervening anoestrus. In ovariectomized ewes without steroid treatment, luteinizing hormone (LH) pulse frequency increased from early to mid-breeding season, decreased to a minimum at mid-anoestrus and increased to reach a maximum at the mid-point of the second breeding season, subsequently declining. LH pulse amplitude was inversely related to frequency. Basal serum LH concentrations decreased gradually from the first breeding season to reach a minimum at mid-anoestrus and gradually increased to reach a maximum at the end of the second breeding season. Mean serum LH and folliclestimulating hormone (FSH) concentrations were higher at the end of the second breeding season compared with the beginning of the first breeding season.

All parameters of gonadotrophin secretion were decreased much more by oestradiol during the anoestrus than during the breeding season. LH pulse frequency was decreased during anoestrum and at high oestradiol concentrations during the first breeding season. Apart from LH pulse amplitude, the decreases in all parameters of gonadotrophin secretion were less during the second compared with the first breeding season. The minimum effective dose of oestradiol required to decrease mean and basal serum concentrations of LH during anoestrus was lower than in the breeding season. The minimum effective dose of oestradiol required to decrease mean serum concentrations of FSH was lower in the first compared with the second breeding season. Oestradiol depression of LH pulse amplitude and mean serum concentrations of LH and FSH showed a dose dependency during the breeding season. During anoestrus dose dependency was seen for basal concentrations of LH and mean serum concentrations of LH and FSH. We conclude that significant chronic changes in gonadotrophin secretion occur in the ewe with time after ovariectomy. Sensitivity to oestradiol also changes, and the effects of oestradiol are not always dose dependent. We suggest that the circannual pattern of LH pulse frequency and basal LH secretion are directly linked to the circannual cycle of photoperiod. Enhanced negative feedback depression of tonic gonadotrophin secretion by oestradiol during anoestrus may be symptomatic or result from the LH pulse generating systems being depressed below a certain threshold by a steroid independent mechanism, directly linked to the circannual cycle of photoperiod.