The effects of progesterone, prostaglandin F2α and oxytocin on the calcium-activation of the uterus

The relationship between “activator-calcium” (A-Ca), progesterone (P), prostaglandin F2α (PGF2α) and oxytocin (Oxy) has been examined in 100 uterine strips of 34 pregnant and 100 strips of 34 post partum rabbits. At the 25th day of gestation, uterine P was 13.9±1.3 ng/g, while within 3–12 hours post partum 3.3±0.3 ng/g tissue (P<0.001). Uterine strips, mounted isometrically in Krebs' solution, sustained maximum excitability in a steady state when exposed every 30 seconds for 4 seconds to an electric field of 12 V/5 cm (a.c.). The maximally contracting muscles were then rinsed at intervals of 6 minutes with Ca-free Krebs.In Ca-free Krebs, the post partum uterus lost 31% of its Ca and 96% of its excitability in a short 25 minutes, while the pregnant uterus lost 30% of its Ca and 93% of its excitability in 50 minutes (P<0.001). Since the extracellular space is 30% in the uterus, this 30% Ca, lost by both muscles, most probably was extracellular Ca and the small A-Ca fraction which is presumably “bound” more strongly at the membrane systems of the P-dominated pregnant, than the non-dominated post partum uterus. The significantly faster and more complete recovery from Ca-deficiency and inexcitability of the pregnant than the post partum uterus (P<0.001), at different levels of external Ca, further substantiates this premise. So does the demonstration that exposure to Ca-free Krebs increases ⁴⁵Ca-efflux 400% in the post partum and only 110% in the pregnant uterus (P<0.001). Exposure to 100 ng/ml PGF2α in normal Krebs has a similar effect on the ⁴⁵Ca-efflux of the post partum uterus, while the response of the pregnant uterus is indistinct (P<0.001).These highly significant differences between the post partum and the pregnant uteri in their Ca-efflux explain the higher threshold (P<0.001) and lower “sensitivity” to PGF2α and Oxy (P<0.001) of the pregnant than the post partum uterus. The already very highly significant differences between the two muscles, in threshold and sensitivity to these two most potent oxytocics, were increased still further by rendering the uterine strips Ca-deficient. All together, these findings substantiate the early contention (1–7,18,19) that uterine function at the cellular level is regulated by opposing actions of the suppressor P and the intrinsic stimulant PG or other oxytocic agents on threshold, excitability and the Ca-activation of the contractile process.     

The “activator-Ca” of the pregnant and post partum rabbit uterus

From 25 days pregnant and post partum rabbits, a total of 133 uterine strips were excised and studied $\text{in}$$\text{vitro}$ under a variety of experimental conditions, to define functionally the regulatory state of the “activator-Ca” (ACa) which couples excitation with contraction in these two extreme regulatory conditions of the uterus. Using Verapamil and Ruthenium-red (both of which inhibit Ca-influx), MnCl₂ (which, in addition, displaces Ca from binding sites), or EGTA (a chelating agent), excitability and ⁴⁵Ca-efflux, were measured. The studies showed that in the progesterone-dominated pregnant uterus the ACa is more strongly bound than in the progesterone-deficient post partum uterus and that extracellular-Ca plays a greater role in the activation of the latter than in that of the former. The effects on excitability of Ca-deficiency and inhibition of Ca-transport indicate that the site of strong binding of the ACa in the pregnant uterus is in or near the plasma membrane, partly accounting for the physiological character of this membrane under progesterone dominance.     

The effect of prostaglandin F2alpha on the activator calcium of the uterus.

The mechanism through which PGF2_α exerts its oxytocic action was studied in 150 uterine strips, 48 excised from 25 days pregnant and 102 from post partum rabbits. PGF2_α delayed the loss of excitability upon exposure of the uterus to Ca-free Krebs Ringer Bicarbonate (KRB) solution and accelerated recovery when half (1.25 mM) of the normal CaCl₂ was replaced in the KRB. This effect of PGF2_α was more pronounced in the post partum than the pregnant uterus, which resisted Ca-deficiency by high affinity binding in its plasma membrane of the activator-Ca (A-Ca).The Ca-ionophore A23187 simulated the action of PGF2_α but only during stimulation with 12 V/5 cm and not with 60 V/5 cm. This finding suggests that while the effect of PGF2_α is limited to a control of the movement of the extracellular and membrane-bound Ca, A23187 affects the distribution of Ca liberated by the strong (60 V/5 cm) electric field from internal stores of the myometrial cells. In the presence of Ruthenium-red (a Ca-influx inhibitor) and only 1.25 mM CaCl₂, PGF2_α restored excitability slowly, indicating that PGF2_α is an oxytocic agent because it promotes Ca-influx. However, knowing that Ca-efflux is in part dependent upon Ca-influx the most informative present finding was the observation that PGF2_α did not promote ⁴⁵Ca-efflux when ⁴⁰Ca-influx was inhibited by Verapamil. This demonstration provided more direct evidence that PGF2_α promotes the influx of the A-Ca and thus explained the mechanism of action of this key regulator at the molecular level.     

The effect of prostaglandin F2α on the activator calcium of the uterus

The mechanism through which PGF2_α exerts its oxytocic action was studied in 150 uterine strips, 48 excised from 25 days pregnant and 102 from post partum rabbits. PGF2_α delayed the loss of excitability upon exposure of the uterus to Ca-free Krebs Ringer Bicarbonate (KRB) solution and accelerated recovery when half (1.25 mM) of the normal CaCl₂ was replaced in the KRB. This effect of PGF2_α was more pronounced in the post partum than the pregnant uterus, which resisted Ca-deficiency by high affinity binding in its plasma membrane of the activator-Ca (A-Ca).The Ca-ionophore A23187 simulated the action of PGF2_α but only during stimulation with 12 V/5 cm and not with 60 V/5 cm. This finding suggests that while the effect of PGF2_α is limited to a control of the movement of the extracellular and membrane-bound Ca, A23187 affects the distribution of Ca liberated by the strong (60 V/5 cm) electric field from internal stores of the myometrial cells. In the presence of Ruthenium-red (a Ca-influx inhibitor) and only 1.25 mM CaCl₂, PGF2_α restored excitability slowly, indicating that PGF2_α is an oxytocic agent because it promotes Ca-influx. However, knowing that Ca-efflux is in part dependent upon Ca-influx the most informative present finding was the observation that PGF2_α did not promote ⁴⁵Ca-efflux when ⁴⁰Ca-influx was inhibited by Verapamil. This demonstration provided more direct evidence that PGF2_α promotes the influx of the A-Ca and thus explained the mechanism of action of this key regulator at the molecular level.     

Inhibition of prostaglandin synthesis and contractility in the rabbit and rat uterus by ibuprofen

Sixty uterine strips were excised from 8 pregnant and 7 post partum rabbits andstimulated electrically in vitro until they developed maximum isometric tension. The non-steroidal anti-inflammatory agent, Ibuprofen, at concentrations of 125, 250 and 500 μg/ml, signidicantly reduced tension of the 55 experimental uteri (P<0.001) within 7.5 minutes, in comaparison with the pretreatment value. Tension in 15 solvent-treated controls remained stable during the same observation period. The reduction in tension was greater in the post partum than the pregnant uteri (P<0.05). Sixteen additional uterine strips, excised from 4 preganant and 4 post partum rabbits were treated either with 500 μg Ibuprofen or solvent for 7.5 minutes. Radioimmunoassay showed that Ibuprofen significantly reduced the uterine levels of PGE (P<0.001) and PGE (P<0.001 post partum; P<0.05 pregnant) and again the effect was greater in the post partum unteri. These findings suggest that the suppression of uterine function by Ibuprofen is mediated by inhibition of PG-synthesis.In a subsequent study, 36 rats were treated with Ibuprofen on days 20 and 21 of pregnancy, at the ineffective dose level of 4 mg/day and the effective levels of 12, 20 and 30 mg/day, In comparison with the first group. Spontaneous labor was significantly delayed in the other three groups (P<0.05, P<0.01 and P<0.001, respectively). In addition, 7 rats were treated with 30 mg/day Ibuprofen and 7 with solvent on days 19 and 20 of pregnancy. In day 21, the Ibuprofen-treated rats showed a significant (P<0.001) reduction in the uterine PGF and PGE concentrations, indicating that the prolongation of pregnancy is mediated by an inhibition of uterine PG-synthesis.     

The Birth and Survival of Wildebeest Calves

This paper describes social organization, parturition, post partum behavior of wildebeest mothers and offspring, and calf predation during the annual birth peak in Ngorongoro Crater, Tanzania. The wildebeest's “follower-calf” system, unique among the Bovidae, is remarkably effective in protecting neonates. Even during the one-month peak, the major predator on calves, the spotted hyena, is unable to feed to satiation. Calf survival is consistently high, despite large fluctuations in the numbers of wildebeest, with consequent effects on the size of the yearly calf crop.     

水痘-带状疱疹病毒地方分离株在兔脑神经细胞中的形态与形态发生特征

为阐明水痘-带状疱疹病毒济南分离株（VZVJ1）在兔脑神经细胞（RNC）中的形态与形态发生特征,我们利用超薄切片电子显微镜技术对感染VZVJ1的RNC进行了观察研究。结果表明RNC在感染VZVJI6h后核内可见散在的核衣壳,12h后细胞核和细胞质内核衣壳明显增多,24h达高峰,而细胞核和细胞质内的成熟病毒颗粒较少见。病毒大小、形态基本一致,呈圆形或椭圆形,核心直径30～50nm,核衣壳74～96nm,成熟病毒110～180nm。核衣壳内有3种类型的核心,即电子致密核心、部分致密核心和电子透明核心。细胞核和细胞质内均可见核心样电子致密体和布纹样结构。在细胞质内还可见少量“繁殖复合体”,由膜性结构包绕多个囊泡构成。提示VZVJ1在RNC中的形态发生不同于其它性质的细胞。     

Absorption of Escherichia coli endotoxin (lipopolysaccharide) from the uteri of postpartum dairy cows

An experiment was conducted to test the hypothesis that Escherichia coli (E. coli ) endotoxin is readily absorbed from uteri of early postpartum cows and that the absorbed endotoxin provokes systemic relcase of prostaglandins. Eleven postpartum Holstein dairy cows (aged 3 to 7 yr) with normal puerperium were selected and divided into a treatment group (n=7), which received intrauterine infusions of E. coli endotoxin, and a control group (n=4), which received intrauterine infusions of 10 ml of saline on Days 5 and 20 post partum. Blood samples were collected once every 30 min for 6 h starting from the time of infusion. Harvested sera samples were analyzed for concentrations of stable metabolites of prostacyclin (PCM), prostaglandin F(2alpha) (PGFM), and thromboxane A(2) (TXB(2)). Plasma samples were qualitatively tested for the presence of endotoxin. Endotoxin was detected in the plasma samples of cows that received endotoxin on Day 5 post partum 4 h after the infusion. Endotoxin was not detected in any of the samples from control cows on Days 5 and 20 post partum or from treatment group cows on Day 20 post partum. Cows treated on Day 5 post partum showed increases in serum PGFM concentrations from 710 +/-64pg/ml to peak concentrations of 1223 +/- 47 pg/ml within 2 h, followed by a decline to baseline concentrations within 4 h. The amount of PGFM released in treated cows on Day 5 post partum was higher (P < 0.05) than in control cows on Day 5 or in treated and control cows on Day 20 post partum. Serum PCM concentrations increased from 156+/-24 pg/ml to peak concentrations of 1348+/-127 pg/ml within 1 h. The amount of PCM released in treated cows on Day 5 postpartum was higher (P< 0.05) than in control cows on Day 5 or in treated and control cows on Day 20 post partum. The TXB(2) concentrations increased from 315+/-38 pg/ml to peak concentrations of 5043 +/- 242 pg/ml within 1 h and fell to baseline concentrations within 5 h. The amount of TXB(2) concentrations released in treated cows on Day 5 post partum was significant (P < 0.05) compared with those of cows in the other groups. The results support the hypothesis that uteri of early postpartum cows are capable of absorbing endotoxin, and the absorbed endotoxin provokes changes in the serum concentrations of prostanoids.     

Mammary Secretion of IgG in Sows

The IgG-concentration was determined in serum of 3 pregnant sows before and after partus and in colostrum of 7 sows 0–6 days post partum. The IgG-concentration decreased in serum before partus and increased after partus. The lowest value (1.5 g/100 ml) was observed at partus. The results indicate that IgG is transmitted from serum to colostrum. The concentration of IgG in colostrum was found to be 2.1–10.4 g/100 ml at partus. The concentration decreased very fast during the first day post partum. During 3–6 days post partum the IgG concentration was rather constant (0.3–0.5 g/100 ml). The importance of the results for the passive immunization of piglets is discussed.     

Postpartum adrenocortical function in dairy cows with dystocia submitted to cesarean section

The effects of the stress of dystocia on the adrenocortical function post partum in cows (n = 6) requiring a cesarean section were assessed by an adrenocorticotropic hormone (ACTH) stimulation test. Nine cows that calved normally were used as controls. The plasma glucocorticoid levels, before and 60 min after an intramuscular injection of 25 IU ACTH, were 4.4 +/- 0.5 (mean +/- SD) and 21.5 +/- 2.4 ng/ml 1 d post partum, 1.9 +/- 0.3 and 18.4 +/- 2.9 ng/ml 4 d post partum and 2.7 +/- 1.1 and 14.6 +/- 3.3 ng/ml 8 d post partum, respectively. Corresponding values of glucocorticoids in cows with normal calving were 4.5 +/- 3.6 and 18.1 +/- 5.2 ng/ml 1 d post partum, 1.7 +/- 1.3 and 13.2 +/- 5.5 ng/ml 4 d post partum and 1.9 +/- 1.7 and 14.6 +/- 3.3 ng/ml 8 d post partum. There were no statistically significant differences of the values between cows with dystocia requiring a cesarean section and cows with normal calving. The results indicate that dystocia requiring a cesarean section like normal calving does not lead to significant depression of the adrenocortical function post partum.     

Frequency modulation of theta bursts of the septal neurons in the removal of ascending afferent effects in rabbits

Medial septal-diagonal band (MS-DB) units were examined extracellularly in chronic rabbits under two experimental conditions: 1) in an intact septum, under anaesthetic doses of pentobarbital (40 mg/kg, i.v.); 2) in a basally undercut septum of unanaesthetized rabbits. The background rhythmic burst activity was undistinguishable in both states. Low-frequency electric stimulation of afferent inputs (MFB, CA1, LS) led to entrainment of the theta-cycles. The upper limit of following was almost normal in the undercut septum, but was strongly reduced under pentobarbital. In units with the driving "by pause", the duration of the initial silent period under pentobarbital was increased almost twofold but in the basally undercut septum it was the same as in the normal state. Some MS-DB units with weak or absent theta-modulation reacted to stimulation by stimulus-locked single spike discharges which followed up to high frequencies in both conditions.     

Relation between circulating sex steroid concentrations and sexual behaviour during pregnancy and post partum in the domestic rabbit

Sexual behaviour of 16 female and 12 male rabbits was studied during pregnancy and early post partum. The main behavioural events of the male (nuzzling and mounting) did not differ in the presence of receptive or non-receptive females. When introduced into the cage of the male, receptive and non-receptive females flattened to the floor or circled around. Sexual receptivity to males decreased in early pregnancy and increased to a maximum a few days around parturition; on Days 1 and 6 post partum, all experimental rabbits submitted to mating. Two groups of females were distinguished: one group submitting to mating whatever the stage of pregnancy, the second being receptive only during the few days before parturition or post partum. During pregnancy and early post partum there was no relation between the colour of the vulva and the female sexual behaviour. Does remained sexually receptive even when progesterone concentrations were high. Nevertheless, the number of receptive females was higher when progesterone concentrations decreased around parturition and the mean daily progesterone values were consistently higher in non-receptive than in receptive females. Oestrogen concentrations during pregnancy were very low and were not related to receptive behaviour.     

The reactivity of human erythrocyte membrane cholesterol with a cholesterol oxidase

Cholesterol oxidase (EC 1.1.3.6, Brevibacterium sp.), which catalyzes the reaction: cholesterol + O₂ → Δ4-cholestenone + H₂O₂, has no effect on the cholesterol of intact (human) erythrocytes and of “resealed” ghosts, when it is present only outside these ghosts. The cholesterol of “leaky” ghosts, of “resealed” ghosts with enzyme trapped within, and of “inside-out” vesicles, was completely oxidized. This pattern indicates that the inner (cytoplasmic) membrane surface must be exposed to the enzyme for the reaction to occur, and that outer surface cholesterol only becomes reactive after the membrane has been degraded by the oxidation of inner surface cholesterol. The enzymatic oxidations followed monotonic first-order kinetics, and hence gave no evidence to support the two states of cholesterol in the membrane that had been postulated earlier from studies on the plasma lipoprotein extraction of cholesterol from the membrane.     

The role of endogenous estrogens in the maturation process of the bovine placenta

The plasma estrogen and progesterone concentrations of 19 pregnant cows (average duration of pregnancy 266.0 +/- 2.3 d at the start of the study) were determined daily from Day 6 pre partum to Day 1 post partum. Parturition was induced in all cows by administration of 10 mg i.m. flumethasone. Values were centered around the delivery date (Day 0) following either induced normal calving (n = 3) or surgical delivery (n = 16). In animals showing spontaneous expulsion of the fetal membranes (Group 1, n = 6) the average total estrogen concentration increased significantly from Day 6 until Day 1 before parturition (1329.2 +/- 317.9 to 3719.8 +/- 951.2 pg/ml in total estrogens). A marked decrease was observed on Day 1 post partum (459.4 +/- 344.2 pg/ml). In comparison with Group 1, animals showing either a delayed or partial expulsion of the fetal membranes, or in which the placenta could be withdrawn 16 h after calving (Group 2, n = 5), had consistently lower total estrogen concentrations between Day 6 (595.4 +/- 174.8 pg/ml) and Day 1 (1884.3 +/- 565.1 pg/ml) before parturition. The estrogen values of the cows with retained placenta (Group 3, n = 8) from Days 6 to 0 pre partum were significantly lower than those of Group 2. Total estrogen concentrations of the three groups 1 d post partum did not differ significantly. It is generally recognized that estrogens play an important role in the maturation process of the placentomes. Our investigation demonstrates that not only is the magnitude of the prepartum rise in estrogens of great influence of the maturation process but the duration of this rise is likewise important. These two factors are vital for a normal expulsion of the fetal membranes.     

Memory effect in the ignition of a low-pressure glow discharge in nitrogen in a long discharge tube

Results are presented from experimental studies of breakdown and the initial stage of a discharge in a long tube (with an interelectrode distance of 40 cm and a diameter of 2.8 cm) at a pressure of ～1 Torr and pulse discharge current of ～10 mA. Breakdown was produced by positive voltage pulses with a linearly growing leading edge with a steepness of dU/dt ～ 10⁶–10⁸ V/s. The time interval between pulses was varied from τ = 0.5 ms to 1 s, the pulse duration being 10 ms. The work was aimed at studying the memory effect of the discharge gap, namely, the influence of the previous pulse on the breakdown characteristics of the next one. In the experiments, the breakdown voltage was measured at different values of dU/dt and τ. It was found that the memory effect was absent at τ ～ 1 s. At the same time, an increase in the breakdown voltage with increasing dU/dt was observed. In the range of τ ≈ 50–200 ms, the breakdown voltage also did not depend on τ, but the memory effect took place. The memory effect in this case consisted in that the breakdown voltage decreased with increasing dU/dt, so that, at dU/dt ～ 10⁷ V/s, the breakdown voltage was two times lower than in the case of τ ～ 1 s. For τ ～ 1–10 ms, the memory effect manifested itself in that the breakdown voltage depended on τ: it could either decrease (the “normal” effect) or increase (the “anomalous” effect) with increasing τ. Breakdown of the discharge gap was preceded by the propagation of an ionization wave, except for the case of small τ values in the domain of existence of the anomalous effect. Estimates allowing one to qualitatively explain the experimental results are made.     

The effects of cobalt and iodine supplementation of the pregnant ewe diet on immunoglobulin G, vitamin E, T3 and T4 levels in the progeny

Sixty twin-bearing ewes were allocated to one of four dietary treatments investigating the effects of supplementary iodine or cobalt during late pregnancy on lamb serum immunoglobulin G (IgG), triiodothyronine (T3), thyroxine (T4) and vitamin E concentrations, and lamb IgG absorption efficiency. Ewes were offered grass silage ad libitum supplemented with 800 g per ewe per day of a 190 g/kg crude protein (CP) concentrate from day 126 of gestation until parturition plus one of the following supplements (n = 15 per treatment); no supplement (C); 26.6 mg iodine per day for final 3 weeks pre partum (I-3); 26.6 mg iodine/day for final week pre partum (I-1); 20 mg cobalt/day for final 3 weeks pre partum (Co-3). Lambs were blood sampled at 24 and 72 h post partum for serum IgG and vitamin E concentrations. Ten lambs from C and I-3 were blood sampled at 1 h post partum for serum IgG, vitamin E, T3 and T4 concentrations. There were no differences in serum IgG, vitamin E or T4 values (P > 0.05) at 1 h post partum between lambs born to the C and I-3 ewes. T3 levels were lower in I-3 compared with C progeny (P < 0.05). Supplemental iodine reduced colostral IgG absorption efficiency (P < 0.001) and lamb serum IgG concentrations at 24 and 72 h post partum (P < 0.001). Serum vitamin E concentration in I-3 and I-1 lambs was lower than in Co-3 lambs at 24 h post partum, while at 72 h post partum I-3, I-1 and Co-3 lambs had significantly lower concentrations than C lambs (P < 0.001). Supplementing the ewe's diet with 26.6 mg/day of iodine for the final week of pregnancy reduced lamb serum IgG concentration at 24 and 72 h post partum. The lower total and free T3 values in the progeny of I-3-treated ewes suggest interference in the synthesis and metabolism of thyroid hormones when ewes receive excessive dietary iodine for 3 weeks immediately pre partum. Based on these findings, the indications are that the toxicity level for iodine in the diet of the pregnant ewe should be lowered to 20 mg per ewe per day, equivalent to 40% of its current level. The finding that high-level cobalt supplementation during the final 3 weeks of pregnancy will have a negative effect on serum vitamin E concentration at 72 h post partum is a new and significant finding and previously has not been reported in the literature.     

The effects of ovariectomy and strech on the regulatory profile and activity of the uterus

Following ovariectomy of five New Zealand white rabbits at day 25 of pregnancy, the intrauterine pressure (IUP) and uterine progesterone (P) and prostaglandin (PG) levels were measured sequentially at days 25, 26 and 27. At day 25, when the uterine P and PGE and PGF were high, massive intrauterine treatment with 500 μg PGF2α provoked only a sustained contracture on which only low level oscillation in IUP was superimposed. At day 26, when the P levels had decreased significantly (P<0.001) and the PG levels had not changed significantly, 50 μg PGF2α significantly increased cyclic IUP as compared with the day 25 value (P<0.001). At day 27, when the P levels decreased further, as little as 5 μg PGF2α provoked still higher cyclic IUP, in spite of a significant reduction in PG levels (P<0.05).Stretching the uterus of six post partum and six 26 days pregnant rabbits (after removing the uterine contents) significantly increased the uterine PGF levels (P<0.001). However, stretch increased only cyclic IUP of the post partum uterus and was without effect on the pregnant uterus, which still had high P levels. These results indicate that the myometrium activated by exogenous PG or stretch, regardless of whether the uterine PG levels increase, remain unchanged or even moderately decrease, provided that the uterine P levels are reduced to a critical value.     

Effects of birth on energy metabolism in the rat kidney.

The oxygen-consumption rates and the activities of fumarase and beta-hydroxyacyl-CoA dehydrogenase were compared in mitochondria isolated from fetal- and neonatal-rat kidney. Whole-organ ATP, phosphocreatine and creatine contents were determined in parallel. Kidney mitochondrial respiratory rates in the presence of succinate, glutamate/malate and palmitoyl-L-carnitine increased between 21 days post coitum and 1 day post partum, together with activities of oxidative enzymes. However, this postnatal maturation of oxidative metabolism was not yet initiated in mitochondria isolated from kidney 1 h post partum. An increase in ATP and phosphocreatine was observed immediately after delivery; newborn-rat kidney ATP content then remained high, whereas phosphocreatine reserves decreased considerably between 6 h and 1 day post partum. It is concluded that the increase in high-energy phosphate compounds observed at birth is not initially related to an activation of oxidative phosphorylation, and probably involves a transient stimulation of anaerobic glycolysis, while a progressive mitochondrial maturation takes place in the rat kidney during the first day of newborn life.     

Absence of tissue inhibitor of metalloproteinases 3 disrupts alveologenesis in the mouse

Tissue inhibitors of metalloproteinases (TIMPs) regulate extracellular matrix (ECM) degradation by matrix metalloproteinases (MMPs) throughout lung development. We examined lungs from TIMP3 null mice and found significant air space enlargement compared with wild type (WT) animals during a time course spanning early alveologenesis (post‐partum days 1, 5, 9 and 14). Trichrome staining revealed a similar pattern of collagen distribution in the walls of nascent alveoli; however, the alveolar walls of TIMP3 mutant mice appeared to be thinner than controls. Assessment of MMP2 and MMP9 activities by gelatin zymography demonstrated a significant elevation in the active form of MMP2 at post‐partum days 1 and 5. Treatment of null pregnant dams with a broad spectrum synthetic metalloproteinase inhibitor, GM6001, on embryonic day 16.5 enhanced the formation of primitive alveoli during the saccular stage of lung development as evidenced by a partial, but significant, rescue of alveolar size in post‐partum day 1 animals. We propose that increased MMP activity in the absence of TIMP3 enhances ECM proteolysis, upsetting proper formation of primitive alveolar septa during the saccular stage of alveologenesis. Therefore, TIMP3 indirectly regulates alveolar formation in the mouse. To our knowledge, ours is the first study to demonstrate that in utero manipulation of the TIMP/MMP proteolytic axis, to specifically inhibit proteolysis, significantly affects lung development.     

Chronobiological characterization of the first estrous cycle in Brasileiro de Hipismo mares during the postpartum period

This study was conducted on 32 mares during the first 30 d of the postpartum period to characterize the first estrous cycle, assessing ovarian cyclicity by determining plasma progesterone concentration and by transrectal palpation. The total pregnancy rate of the breeding season was 81.25%. The present results show that the incidence of estrus occurring at the beginning of the breeding season were early, long and anovulatory. The mares that did not become pregnant ovulated on average 14.5 d post partum, and those that became pregnant ovulated at 19.6 d post partum (P<0.05). On the basis of clinical and hormonal data, we divided the animals into 4 groups, all presenting signs of estrus: Group 1, animals that did not ovulate (n=7) and that presented basal P(4) levels (0.01-2.34 ng/ml) during the first 30 postpartum days; Group 2, animals that ovulated and did not become pregnant (n=13); Group 3, animals that ovulated and became pregnant (n=8). Maximal P(4) levels ranged from 4.40 to 13.50 ng/ml (Group 2) and from 3.70 to 20.50 ng/ml (Group 3). Group 4 were animals that presented high plasma P(4) levels before any clinical sign of ovulation (n=3). The absence of pregnancy could not be attributed to a failure of the corpus luteum, since the groups of mares that became pregnant exhibited similar plasma P(4) levels as the group of nonpregnant mares. Our findings demonstrated that mares exhibited differences in the timing of the first postpartum estrus, the duration of the first postpartum estrus and the timing of the first postpartum ovulation according to the month of the breeding season in which foaling occurs under tropical conditions. Furthermore, our results indicate that the foal heat may be used since its utilization did not affect the total pregnancy rate of the breeding season.