Search

This study has investigated the effect of continuous intrafetal infusion of PGE2 or saline on hormone concentrations and the length of gestation in sheep. Fetal and maternal vascular catheters were surgically implanted at 112.3 +/- 1.3 days (n = 10), and the infusions were started at 121 +/- 1.2 days of gestation (term = 147). Fetuses were infused with either PGE2 (n = 5; 2 micrograms/min for 48 h and then increased to 4 micrograms/min for the remainder of the experiment) or the vehicle solution (n = 5; sterile isotonic saline) via the fetal carotid artery. In the PGE2-infused group, fetal and maternal plasma PGE2 concentrations increased (P < 0.001) after the change to the higher dose rate (4 micrograms/min) and remained elevated, fetal plasma immunoreactive ACTH (ir-ACTH) concentrations dramatically increased after the start of the infusion being maximal at 11 h before decreasing to match concentrations exhibited by the saline-infused group. Fetal plasma cortisol concentrations increased after the start of the PGE2 infusion (P = 0.05) and increased further after the change to the higher dose rate of 4 micrograms/min (P < 0.001). Concentrations of PGE2, ir-ACTH, and cortisol in the saline-infused group did not change until labor. Plasma concentrations of PGE2 (P < 0.001) and ir-ACTH (P < 0.005) increased on the day of labor in both treatment groups, and fetal cortisol concentrations increased (P < 0.001) in both groups in the last few days before labor. The proportion of low molecular weight ir-ACTH in the plasma of PGE2-infused fetuses was significantly higher than that of saline-infused fetuses (P < 0.001) during the first 15 days of infusion. In the saline-infused group, the proportion of low molecular weight ir-ACTH increased in the last few days before labour (P = 0.001), whereas no change was seen in PGE2-infused fetuses at this time. Maternal plasma progesterone concentrations decreased in both groups in the last few days before labor (P < 0.001). Fetuses infused with PGE2 delivered at 138.4 +/- 2.1 days, whereas control fetuses infused with saline delivered at 148.2 +/- 0.5 days (P < 0.001). The spontaneous increase in PGE2 preceding normal labor may thus play an important role in activation and maturation of the hypothalamic-pituitary-adrenal axis in fetal sheep.

Prostaglandin (PG) F(2alpha) secreted from the uterus is the luteolysin of the estrous cycle and is also believed to be responsible for luteolysis in the pregnant doe at term. We have reported that basal progesterone concentrations decrease before basal PGF(2alpha) concentrations increase, which is inconsistent with this view. In this study we investigated whether luteolysis is associated with increased frequency or amplitude of pulsatile PGF(2alpha) secretion in does over the last 2 wk of gestation. Progesterone concentrations decreased approximately 1 wk before parturition. There was no accompanying increase in PGF(2alpha) concentrations or pulse frequency, and those pulses that were observed were of lesser amplitude and duration than those that have been associated with luteolysis in cycling ewes. A small increase in PGF(2alpha) pulse frequency was identified during the 3 days before parturition, but this was not associated with any change in progesterone concentrations. The biological significance of these small changes in PGF(2alpha) pulse frequency is obscure, although the high concentration of this eicosanoid at labor may have been related to the final, precipitous decline in plasma progesterone concentrations. These findings do not support the notion that PGF(2alpha) is the principal luteolysin in the pregnant doe at term.

We investigated the temporal relationship of fetal cortisol secretion to circulating concentrations of fetal ACTH1-39 and its high-molecular weight precursors in goats. We also measured the concentrations of progesterone, estradiol-17beta estrone sulfate, prostaglandin (PG) E, PGF2alpha, and PGF2alpha metabolite (PGFM) in maternal arterial plasma over the last month of gestation. Prostaglandin concentrations were also measured in utero-ovarian venous plasma. There was a positive association between ACTH1-39 in fetal plasma and the prepartum surge in fetal cortisol that commenced 8 days before labor. The fetal cortisol surge was followed by a simultaneous decrease in maternal progesterone and an increase in plasma estrogens commencing 3-4 days before labor. No change in basal prostaglandin concentration occurred before this time. There was a positive veno-arterial difference of PGE and PGF2alpha across the uterine vascular bed, confirming the uteroplacental unit as a major source of these eicosanoids in the plasma of the pregnant doe. We conclude that the fetal signal for parturition precedes luteolysis by some 5 days and find no evidence of changes in the basal concentrations of PGE and PGF2alpha in maternal plasma at the time of luteolysis.

The factors involved in the control of steroid secretion from the ovine placenta and in fetal growth are as yet unclear. We hypothesized that factors derived from the fetal pituitary may play a role in the production and release of placental steroids and in growth of the fetus, and have investigated the effects of fetal hypophysectomy performed between day 70 and day 79 of gestation (term = 147 days) on systemic concentrations of hormones derived from the placenta, and on fetal growth. Maternal peripheral progesterone, placental lactogen and uterine vein progesterone increased significantly from day 90 in all ewes. Peripheral concentrations of prostaglandin E2 and peripheral and uterine vein oestrone sulfate increased significantly in the control group but not in the fetal hypophysectomy group. Uterine vein prostaglandin E2 increased significantly after day 95 in the control group and after day 105 in the fetal hypophysectomy group. Early fetal hypophysectomy caused marked growth retardation. The weights of the brain, kidneys and liver of hypophysectomized fetuses were the same as those of controls suggesting that their growth is not under pituitary control. In contrast, the weights of heart and lungs were reduced in proportion to body weight, suggesting that heart, lung and carcass growth were under pituitary control. Our data indicate that the fetal pituitary influences the control of placental steroid and prostaglandin E2 biosynthesis after day 90 of gestation in sheep, but that output of other hormones such as placental lactogen is independent of pituitary control, and may determine organ-specific growth parameters that are unaffected by removal of the fetal pituitary.

The effects of exogenous oxytocin (OT) and estradiol-17 beta (E2) on plasma concentrations of prostaglandin (PG) E2 and 13, 14-dihydro-15-keto-PGF2 alpha (PGFM) were investigated on Day 14-15 (NP) of the estrous cycle and Days 14-16 (PI) and 21-25 (EP) of pregnancy in the ewe. Basal concentrations of PGFM were significantly elevated in utero-ovarian venous (UOV) plasma on Day 14 of pregnancy (4.05 +/- 0.81 nM, mean +/- SEM) compared to that observed on Day 14 of the cycle or Days 21-25 of pregnancy (2.29 +/- 1.3 nM and 1.06 +/- 0.56 nM, respectively). PGFM release increased significantly following intera-arterial bolus injections of 50, 500, and 5000 mU OT at 2-h intervals in all experimental groups. There was no significant difference in area and peak height of the PGFM response between the 3 groups studied. The time to peak PGFM response was, however, significantly longer in the PI group. No significant changes in concentration of PGFM were observed in any experimental group following 1-h infusions of E2 at 5, 50, and 500 pmol/min. Long-term (15-18 h) infusion of E2 at 83 pmol/min increased the peak height of the OT-induced PGFM response at both stages of gestation studied. PGE2 concentrations in UOV plasma were less than 0.05 nM in all samples studied. These results demonstrate that PG release can be induced in response to OT during the period in which ovine trophoblastic protein-1 (oTP-1) is released by the conceptus. During pregnancy, oTP-1 does not appear to inhibit the E2 induction of uterine OT receptors.

Ultrastructural features of the regressing corpus luteum have been studied in the ewe at the end of the estrous cycle. Luteal cells secrete densely-staining granules which have been reported to contain progesterone. This process appears to be maximal at Day 10 of the cycle and begins to taper off noticeably at Day 12. The secretory activity declines gradually till Day 14, but up to this time the fine structure of other cytoplasmic organdIes in the luteal cell shows no remarkable change, save for a gradual increase in the number of autophagocytic bodies which first begin to appear at Day 12. In contrast, on Day 15 there is evidence of marked degeneration; the luteal cells are shrunken, granule secretion has ceased, autophagocytic bodies are numerous and lipid droplets, rarely seen in the fully functional cell, are present in abundance, Lysosomes are observed at all stages of the cycle and there is no dramatic increase in their number towards the end, In some cells at Day 15 the process of degeneration has advanced to the stage where the fine structure of organelles is no longer recognizable and within autophagocytic bodies there are large sites associated with acid phosphatase activity.

The ultrastructure of the corpus luteum of the sheep has been examined throughout the estrous cycle. Small, densely staining granules 0.2 im in diameter, are observed within the luteal cell at Day 2 of the cycle; they increase in number as the cycle progresses and at Day 6 the first signs of secretion are noticed. Maximum secretion of granules takes place at Days 10 and 11, and this is followed by a progressive decline in secretory activity from Day 12 to Day 15 of the cycle. These clear-cut changes in granule formation and secretion therefore reflect the established pattern of progesterone secretion by the ovary during the estrous cycle in the sheep. Fractions were obtained from corpora lutea of sheep by homogenization and differential centrifugation. A correlation was obtained between the presence of densely staining granules (approx 0.2 um diam) and the progesterone content of each fraction. Many types of nonsteroidogenic endocrine cells are known to have a secretory pathway whereby hormones are packaged in the Colgi region and then discharged from the cells via granules; the present work provides the first indication of a steroid hormone, viz, progesterone, being secreted in a similar way.

THE pituitary hormone adrenocorticotrophin (ACTH) belongs to a ‘family’ of peptides derived from a common ‘stem hormone’ (Fig. 1). Depending on the way in which the stem hormone is cleaved, the various peptides are expressed and it is possible that qualitative changes in the expression of the peptide ‘family tree’ may be responsible for the alteration in fetal adrenal function which precedes birth1. We now report evidence for such changes in the rhesus monkey, which has a fetal adrenal comparable with that of man.

It is uncertain whether ovarian bloodflow in ewes remains constant or varies with the stage ofthe oestrous cycle. In an experiment in whichminimal estimates' of the ovarian steroid secretion rates were obtained, Short, McDonald & Rowson (1963) cannulated the "major vein draining the corpus luteum or ripe Graafian follicle". The bloodflow rates obtained were lower in oestrous than in di-oestrous ewes. Moore, Brown & Smythe (1965) using a similar technique did not find that the rates varied cyclically. In the present study, seventeen Merino and five Corriedale ewes were used. They were 5 to 7 years old and had regularly exhibited oestrus at intervals of 17 days. Anaesthesia was induced and maintained with sodium pentobarbitone except on nine occasions when anaesthesia was maintained with fluothane. The abdomen was opened by a mid-ventral incision and 12,500 i.u. of heparin were given intravenously. A polyvinyl catheter was passed into each utero- ovarian vein through an incision in a branch of the corresponding middle uterine vein. Each utero-ovarian vein was ligated below the end of the catheter. Tributaries of this vein, other than the ovarian veins, were also ligated so that only ovarian blood entered the catheter. Each catheter (length 9 cm, internal diameter 2\m=.\0mm) was connected with 3\m=.\2-mminternal diameter tubing to form a low-resistance collection system. Timed collections of blood, approxi- mately 80 ml from each ovary, were made simultaneously. The ligatures and catheters were then removed and the incised veins tied off. The abdomen was closed and the animal allowed to recover. Collections were made on 2 successive days in twenty of the ewes. In twelve of these, the ovaries were removed and weighed after the second collection period. In individual ewes during the luteal phase, similar bloodflow rates were obtained at the two collections. Ovarian bloodflow during consecutive periods of sodium pentobarbitone-maintained and fluothane-maintained anaesthesia was similar in each of three ewes examined. Consequently the results from all animals were pooled. For Days 0, 1, 2, 15 and 16 of the oestrous cycle (Text-fig. 1), the mean bloodflow ( + S.E.) was 2-91+0-25 ml/min in ovaries with pre-ovulatory follicles or recent ovulation points and 3-05 + 0-32 ml/min in the contralateral 'inactive' ovaries. The rates during Days 3 to 14, inclusive, of 7-80 + 0-48 ml/min in ovaries with corpora lutea and 6-59 + 0-42 ml/min in those without corpora

The mechanisms involved in the control of oxytocin and progesterone secretion by the ovine corpus luteum have been investigated in vitro using luteal slice incubations. Oxytocin and progesterone were secreted at constant rates from luteal slices for 2 h of incubation (366 +/- 60 pg X mg X h and 18.9 +/- 0.18 ng X mg X h, respectively). Secretion of progesterone, but not of oxytocin, was significantly (p less than 0.02) stimulated in the presence of ovine luteinizing hormone. Incubation of luteal slices in medium containing 100 mM potassium, however, resulted in increased secretion of oxytocin and, to a lesser extent, of progesterone (294 +/- 59% and 142 +/- 15%, respectively, p less than 0.05). Basal oxytocin secretion was reduced during incubation in calcium-free medium, compared to secretion in the presence of calcium (70 +/- 15 and 175 +/- 25 pg X mg X 20 min, respectively, p less than 0.01), whereas progesterone secretion was not altered in the absence of calcium. Secretion of both hormones by luteal slices was stimulated by the addition of the calcium ionophore A23187 (p less than 0.05). Addition of prostaglandin F2 alpha (2.8 microM) had no effect on secretion of either oxytocin or progesterone. We have demonstrated that oxytocin and progesterone can be stimulated, independently, from corpus luteum slices incubated in vitro. The pattern of release is consistent with the proposal that oxytocin, but not progesterone, is associated with and actively released from luteal secretory granules. Our results also indicated that prostaglandin F2 alpha does not directly stimulate release of oxytocin or progesterone from luteal cells in vitro.

The concentration of progesterone in maternal plasma of the bandicoot increased from 3.9 to 12.6 ng/ml between 11 and 4 days before parturition and remained at this level for at least 7 days. Concentrations of 13,14-dihydro-15-keto-prostaglandin F-2 alpha increased from basal levels of 288 pg/ml (4 days before birth) to maximal levels of 2534 pg/ml immediately after parturition, then decreased progressively. It is suggested that PGF-2 alplha, but not progesterone, influences the initiation of parturition in this species.

The secretory lifespan and functional activity of corpus luteum in hysterectomized goats was studied. 6 goats were hysterectomized 30-49 days after fertile mating. 15 mg progesterone was injected prior to surgery and venous blood was collected daily for 7 days postsurgery then every 2-5 days for 70 days and daily thereafter. 1 goat (30 days after mating) contained a dead embryo with autolyzed membranes and a regressing corpus luteum. The other 5 had normal corpora lutea and each had 1 or 2 live fetuses with normal membranes. Plasma progesterone decreased postsurgery over a period of 5-10 days remained somewhat constant for a variable length of time and then decreased to anestrus levels ( less than .05 ng/ml). This depression in luteal function suggested that the maintenance of full functional activity of corpus luteum in goats may be dependent on placental luteotrophin. In 3 of the goats the luteal lifespan exceeded that in intact pregnant animals suggesting that cessation of progesterone production is unlikely to be determined solely by a maternal hypothalamic factor.

Oxytocin, oxytocin-associated neurophysin (neurophysin), prostaglandin F2 alpha (PGF2 alpha), and progesterone concentrations were measured in the utero-ovarian vein (UOV) of sheep during the estrous cycle and early pregnancy. On days 13-16 of the cycle, large pulses of PGF2 alpha, oxytocin, and neurophysin were measured in samples collected at hourly intervals from the UOV draining a corpus luteum (UOV/CL). Most of the PGF2 alpha pulses (96.5%) coincided with a pulse of both oxytocin and neurophysin, whereas only 55.6% of oxytocin pulses coincided with a pulse of PGF2 alpha. Therefore, during luteolysis in sheep, uterine PGF2 alpha release is closely associated with ovarian oxytocin release, and oxytocin release is unlikely to be dependent upon a uterine PGF2 alpha stimulus. During frequent sampling, coincident oxytocin pulses were measured in 1) both UOVs when a CL was present in both ovaries and 2) the jugular vein, carotid artery, and UOV/CL, with a significantly higher oxytocin pulse concentration occurring in jugular venous compared with carotid arterial plasma. Pituitary and luteal release of oxytocin may, therefore, occur simultaneously and be controlled by a circulating factor in sheep. Compared to days 13-16 of the cycle, significantly (P less than 0.001) fewer pulses of PGF2 alpha, which were significantly (P less than 0.001) smaller in amplitude, were measured in UOV samples collected frequently during early pregnancy. The frequency of oxytocin pulses observed in the UOV/CL of pregnant sheep was not significantly (P greater than 0.1) different from that observed in cyclic ewes, although most (86.4%) oxytocin pulses occurred in the absence of a PGF2 alpha pulse. In contrast, when a pulse of PGF2 alpha was observed in the UOV/CL of pregnant ewes, it usually coincided with a pulse of oxytocin. The suppression of uterine PGF2 alpha release during early pregnancy is not considered to result from a lack of stimulation by oxytocin.

THE phospholipids of pulmonary surfactant1 cover the respiratory epithelium and because of their unique properties of lowering surface tension, spreading rapidly and sustaining high surface pressures, allow the lungs to expand easily and prevent their collapse. Deficiency of lung surfactant is the major cause of respiratory distress syndrome in premature babies and also contributes to the respiratory problems of paraquat poisoning and cardiac bypass surgery. It has generally been assumed that surfactant, whether in the lamellar bodies or alveoli, is in an aqueous environment and must, therefore, be hydrated. We show here, however, that fully hydrated surfactant is apparently inactive and that surfactant can only be effective as a surface monolayer if the source of the material is ‘dry’.

Renal clearances of inulin and chromium-51 ethylenediaminetetraacetate were compared in sheep. In 41 clearance periods from five animals the mean clearance ratio of the chelate to inulin was 0.95 ± 0.03 (S.D.). Part of the difference between the two sets of results may have been due to binding of the metal chelate by plasma protein since 1.5 to 2 percent of chromium-51 ethylenediaminetetraacetate in plasma could not be removed by dialysis.

Low birthweight in sheep is associated with increased perinatal mortality. The sheep uterus contains folds of endometrium (caruncles) which form the maternal cotyledon in pregnancy. Alexander (1964) removed caruncles & in a subsequent pregnancy observed a reduction of placental & fetal weight, increased incidence of premature labour & stillbirths. 4 small fetuses have been produced using this technique. Catheters were implanted into the ewe & the fetus between 105 & 110 d. Serial measurements of blood gases, pH, metabolites, cortisol & ACTH were made. The mean fetal carotid PaO2 & haematocrit were 15.9 ± 1.3 mm Hg & 37.4 ± 2.2% compared to 21.6 ± 1.0 mm Hg & 30.3 ± 0.6% in 7 control fetuses (P < 0.01). There were no significant changes in PaCO2 or pH. Plasma glucose (0.66 ± 0.03 μmol/ml), lactate (0.9 ± 0.02 μmol/ml) and a amino nitrogen (aNH2, 6.11 ± 0.25 μmol/ml) were lower than in control fetuses (glucose 1.19 ± 0.02 μmol/ml, lactate 1.47 ± 0.02 μmol/ml and a NH2 7.64 ± 0.02 μmol/ml)suggesting a limitation of placental transfer. We have previously observed increased ACTH with hypoxaemia or hypoglycaemia. However, the concentration of ACTH (69.2 ± 29.7 pg/ml) and cortisol (21 ± 8.2 ng/ml) in the small fetuses was not significantly different from controls.