Effect of hindlimb unweighting on tissue blood flow in the rat.

The purpose of this study was to characterize the distribution of blood flow in the rat during hindlimb unweighting (HU) and post-HU standing and exercise and examine whether the previously reported (Witzmann et al., J. Appl. Physiol. 54: 1242-1248, 1983) elevation in anaerobic metabolism observed with contractile activity in the atrophied soleus muscle was caused by a reduced hindlimb blood flow. After either 15 days of HU or cage control, blood flow was measured with radioactive microspheres during unweighting, normal standing, and running on a treadmill (15 m/min). In another group of control and experimental animals, blood flow was measured during preexercise (PE) treadmill standing and treadmill running (15 m/min). Soleus muscle blood flow was not different between groups during unweighting, PE standing, and running at 15 m/min. Chronic unweighting resulted in the tendency for greater blood flow to muscles composed of predominantly fast-twitch glycolytic fibers. With exercise, blood flow to visceral organs was reduced compared with PE values in the control rats, whereas flow to visceral organs in 15-day HU animals was unaltered by exercise. These higher flows to the viscera and to muscles composed of predominantly fast-twitch glycolytic fibers suggest an apparent reduction in the ability of the sympathetic nervous system to distribute cardiac output after chronic HU. In conclusion, because 15 days of HU did not affect blood flow to the soleus during exercise, the increased dependence of the atrophied soleus on anerobic energy production during contractile activity cannot be explained by a reduced muscle blood flow.     

Fatigability and blood flow in the rat gastrocnemius-plantaris-soleus after hindlimb suspension.

The purpose of this study was to test the hypothesis that hindlimb suspension increases the fatigability of the soleus during intense contractile activity and determine whether the increased fatigue is associated with a reduced muscle blood flow. Cage-control (C) and 15-day hindlimb-suspended (HS) rats were anesthetized, and either the gastrocnemius-plantaris-soleus (G-P-S) muscle group or the soleus was stimulated (100 Hz, 100-ms trains at 120/min) for 10 min in situ. In the G-P-S preparation, blood flow was measured with radiolabeled microspheres before and at 2 and 10 min of contractile activity. The G-P-S fatigued markedly at this stimulation frequency, and the differences between C and HS animals were not significant until the 9th min of contractile activity. In contrast, the stimulation resulted in faster rates and significantly larger amounts of fatigue in the soleus from HS than from C animals. The atrophied soleus showed significant differences by 1 min of stimulation (C = 70 +/- 1% vs. HS = 57 +/- 2% of peak train force) and remained different at 10 min (C = 64 +/- 4% vs. HS = 45 +/- 2% peak train force). Relative blood flow to the soleus was similar between groups before and during contractile activity (rest: C = 20 +/- 3 vs. HS = 12 +/- 3; 2 min: C = 128 +/- 6 vs. HS = 118 +/- 4; 10 min: C = 123 +/- 11 vs. HS = 105 +/- 11 ml.min-1.100 g-1). In conclusion, these results established that 15 days of HS increased the fatigability of the soleus, but the effect was not caused by a reduced muscle blood flow.     

Amniotic fluid lipoxygenase metabolites during spontaneous labor and after RU486 treatment during late pregnancy in rhesus macaques

To determine changes in amniotic fluid (AF) lipoxygenase metabolites prior to spontaneous labor and after RU486 administration, we implanted AF and vascular catheters and myometrial electromyographic (EMG) electrodes in 8 rhesus macaques at 120-130 days of pregnancy (term = 167 days). Four animals had AF samples taken serially until they delivered their infants normally at term. The other four animals received RU486 (20 mg/kg/day) for 3 days. AF samples were collected every 2-3 days and at 12 hour intervals for 72 hours before and after treatment with RU486. Uterine activity was monitored continuously. LTB4, 5-HETE and 15-HETE were measured by radioimmunoassay. In untreated animals, LTB4 and 5-HETE concentrations in AF increased significantly (P less than 0.05) 4 days before delivery with no change in 15-HETE. After RU486, mean levels of LTB4 and 5-HETE were increased although the difference was not statistically significant. No change in 15-HETE levels was observed. In conclusion, LTB4 and 5-HETE increase in AF before the onset of spontaneous labor. Progesterone receptor blockade by RU486 does not reproduce the changes in AF lipoxygenase metabolites observed during normal parturition.     

Oxytocin infusion from day 10 after oestrus extends the luteal phase in non-pregnant cattle

Oestrus was synchronized in 8 cyclic heifers by progesterone treatment (PRID), after which the animals were monitored for one control cycle to measure the inter-oestrous interval. Osmotic minipumps containing saline (controls, N = 3) or oxytocin (N = 5) were implanted subcutaneously on Day 10 of the second cycle, and removed 12 days later. Jugular venous blood samples were collected daily for measurement of progesterone, and every 2 days for oxytocin. In addition, blood samples were taken every 10 min from 1 h before to 3 h after minipump insertion for measurement of plasma 15-keto-13,14-dihydroprostaglandin-F-2 alpha (PGFM) and every 30 min over the same period for measurement of progesterone and oxytocin. The lengths of the first untreated cycle in both groups of heifers were 20.2 +/- 0.56 (mean +/- s.e.m.) days compared with 25.4 +/- 0.81 days after oxytocin treatment (P less than 0.001). Oxytocin plasma concentrations in treated animals rose from less than 10 pg/ml to 70-500 pg/ml by 2 h after the start of oxytocin infusion and remained elevated until treatment was withdrawn. There was no increase in PGFM concentrations immediately after minipump insertion. Plasma progesterone concentrations were similar in treated and control animals but remained at mid-luteal levels for an average of 5 days longer in treated heifers. It is concluded that continuous administration of oxytocin can extend the luteal life-span in cattle.     

Role of endogenous nitric oxide in hyperoxia-induced airway hyperreactivity in maturing rats.

We sought to define the effects of maturation and hyperoxic stress on nitric oxide (NO)-induced modulation of bronchopulmonary responses to stimulation of vagal preganglionic nerve fibers. Experiments were performed on decerebrate, paralyzed, and ventilated rat pups at 6-7 days (n = 21) and 13-15 days of age (n = 23) breathing room air and on rat pups 13-15 days of age (n = 19) after exposure to hyperoxia (>/=95% inspired O(2) fraction for 4-6 days). Total lung resistance (RL) and lung elastance (EL) were measured by body plethysmograph. Vagal stimulation and release of acetylcholine caused a frequency-dependent increase in RL and EL in all animals. The RL response was significantly potentiated in normoxic animals by prior blockade of nitric oxide synthase (NOS) (P < 0.05). Hyperoxic exposure increased responses of RL to vagal stimulation (P < 0.05); however, after hyperoxic exposure, the potentiation of contractile responses by NOS blockade was abolished. The response of EL was potentiated by NOS blockade in the 13- to 15-day-old animals after both normoxic and hyperoxic exposure (P < 0.01). Morphometry revealed no effect of hyperoxic exposure on airway smooth muscle thickness. We conclude that NO released by stimulation of vagal preganglionic fibers modulates bronchopulmonary contractile responses to endogenously released acetylcholine in rat pups. Loss of this modulatory effect of NO could contribute to airway hyperreactivity after prolonged hyperoxic exposure, as may occur in bronchopulmonary dysplasia.     

CORRELATION OF DNA ACCUMULATION RATE WITH THYMIDYLATE SYNTHETASE AND THYMIDINE KINASE ACTIVITIES IN DEVELOPING RAT CEREBELLUM: EFFECT OF THYROXINE1

Abstract— Using the method of least squares, a logistic curve was fitted to the data points for DNA content in neonatal rat cerebellum versus postnatal age (day 0 is the day of birth). The resultant equation was differentiated to give an expression for the rate of cerebellar DNA accumulation in units of ng/h per mg wet cerebellum. The DNA accumulation rate in control rats increased from 77.0 at 2 days of age to a maximum of 108 at 7 days of age and declined thereafter to a minimum of 16.3 on day 15. Thyroxine treatment significantly (P < 0.05) increased the rate to 89.8 (117% of control) at 2 days of age, and a significant elevation was maintained to 6 days of age at which time a maximum rate of 115 (114% of control) was attained. The rate was significantly decreased below control at 9 and 12 days of age, and reached a minimum of 9.22 on day 15. The developmental pattern for the activity of cerebellar thymidylate synthetase (EC 2.1.1.6), in units of pmol/h per mg wet cerebellum, closely paralleled the pattern for DNA accumulation rate in both control and thyroxine-treated animals. In controls, thymidylate synthetase activity increased from 98.6 at 2 days of age to a maximum of 125 at 7 days of age and declined thereafter to a minimum of 30.0 at 15 days of age. In thyroxine-treated animals, the activity was significantly increased to 118 (122% of control) at 4 days of age and remained significantly elevated through 6 days of age at which time a maximum activity of 154 (115% of control) was attained; thereafter, the activity was significantly decreased below control and reached a minimum of 16.9 (56.3% of control) on day 15. The developmental pattern for the activity of cerebellar thymidine kinase (EC 2.7.1.21) did not parallel the DNA accumulation rate quite so closely, in neither treated nor control animals, as did the pattern for thymidylate synthetase activity. These data suggest that thymidylate synthetase activity in the developing rat cerebellum may be more important for maintenance of replicative DNA synthesis than is thymidine kinase activity. In addition, the thyroxine-induced acceleration of the increase and subsequent decline in rate of DNA accumulation and in the activities of thymidylate synthetase and thymidine kinase in developing rat cerebella is probably the result of alterations in the number of external granular cells undergoing replicative DNA synthesis.     

Differential inhibition of regional gastrointestinal tissue to progesterone in the rat

The influence of progesterone on contractile activity of three gastrointestinal regional tissues was evaluated. Up to six dose levels of progesterone were administered subcutaneously to male rats daily for four days. Progesterone blood levels measured with radioimmunoassay on the fourth day revealed that the range of progesterone exposure to the male animals did not exceed the progesterone blood level peak reported during the normal hormonal cycle of female rats. Log-dose response curves indicate that esophageal, antral, and colonic tissues from progesterone treated animals showed a significant reduction in contractile activity compared to the corresponding tissue from non-progesterone treated control animals. Esophageal and colonic tissues were two and 12-fold, respectively, more sensitive to the inhibitory progesterone influence compared to antral tissue. This study supports the concept that normal circulating levels of progesterone may have an influence on specific gastrointestinal regional function in addition to the effects of progesterone blood levels during pregnancy.     

Intracranial self-stimulation motivates weight-lifting exercise in rats.

The purpose of this study was to determine the feasibility of using a positive reinforcement protocol to motivate weight-lifting exercise in rats. Intracranial self-stimulation was used to induce weight-lifting exercise. Bipolar electrodes were implanted in the ventral tegmental area of rats, and the animals were trained to bar press on a continuous reinforcement schedule for electrical brain stimulation. Animals with response rates of 1,200-1,500 presses/h were then trained with a discriminative light stimulus to alternate between a normally positioned bar and an elevated bar that could be reached only by standing on the hindlimbs. The animals were fitted with a weighted jacket at a starting resistance of 5-10% of their body weight. Weight-training sessions were conducted 5 days/wk for 10 wk. Training consisted of 600 presses/session, alternating every 15 presses between the low and high bars. At the beginning of each subsequent week, the resistance was progressively increased, with some animals eventually training at resistances greater than 50% of their body weight. At the end of the training period, the rats were lifting over 550% of the starting weight. Gastrocnemius size and mean fiber diameter were increased in the weight-lifting animals. This model combines exercise with positive incentive and has the advantages of being relatively easy to implement and not producing any apparent physical or mental trauma in the animal.     

Calcium requirements of cardiac myofibril ATPase activity following exhaustive exercise

Myocardial contractility is reduced in rats following strenuous activity. Thus, the purpose of this study was to determine some of the cellular mechanisms that may contribute to the depressed contractile function. Myofibril ATPase activity was determined with varying free calcium and monomeric vanadate (Vi) concentrations. The Mg2+ stimulated myofibril ATPase activities were significantly reduced in the activity group (E). Myofibril ATPase activity from control animals increased from 0.056 +/- 0.021 to 0.216 +/- 0.030 mumol X Pi X mg-1 X min-1 with 0.1-10.0 microM Ca2+. The addition of 15.0 microM Vi resulted in a 37% decrease in ATPase activity of C animals. With regard to the experimental group, the myofibril ATPase activity at 0.1 and 1.0 microM Ca2+ were depressed (P less than 0.05) with the values at 5.0 and 10.0 microM Ca2+ being similar to the control group (P greater than 0.05). Incubations with Vi resulted in an enhanced myofibril ATPase activity for E compared to C animals. The ATPase activities were increased by 17, 10, 10 and 15% at 3.0, 5.0, 10.0 and 15.0 microM Vi. The results suggest that the exhaustive exercise raises the CA2+ requirement for half-maximal activation of cardiac myofibril ATPase activity and that the contracto-regulatory mechanism of cardiac muscle is similarly altered.     

Histomorphochemical effects of shortwave diathermy on healing of experimental muscular injury in dogs

The biceps femoris muscle was surgically incised and sutured in 10 clinically healthy mongrel dogs, aged 1-2 yr and weighing 10-15 kg. The surgical wounds of 5 dogs were exposed to shortwave diathermy for 5 min daily for 7 days, starting a day after the creation of trauma. The remaining 5 dogs served as control. After 15 days of healing, the tissues from biceps femoris muscle were collected and subjected to histomorphological and histochemical examination. Mature collagen bundles were seen at healing site in diathermy treated animals while there were immature collagen fibres and more number of fibroblasts in control animals. Normal muscle fibres could be seen on either side of the healing tissue in treated animals whereas in control animals, atrophied and necrosed muscle fibres were encountered. The neutral and acid mucopolysaccharides, lipid droplets in the intermyofibrillar area and the activity of alkaline phosphatase, adenosine triphosphatase and lactate dehydrogenase at the healing site was better in treated as compared to controls.     

Recovery of skeletal muscle mass after extensive injury: positive effects of increased contractile activity

The present study was designed to test the hypothesis that increasing physical activity by running exercise could favor the recovery of muscle mass after extensive injury and to determine the main molecular mechanisms involved. Left soleus muscles of female Wistar rats were degenerated by notexin injection before animals were assigned to either a sedentary group or an exercised group. Both regenerating and contralateral intact muscles from active and sedentary rats were removed 5, 7, 14, 21, 28 and 42 days after injury (n = 8 rats/group). Increasing contractile activity through running exercise during muscle regeneration ensured the full recovery of muscle mass and muscle cross-sectional area as soon as 21 days after injury, whereas muscle weight remained lower even 42 days postinjury in sedentary rats. Proliferator cell nuclear antigen and MyoD protein expression went on longer in active rats than in sedentary rats. Myogenin protein expression was higher in active animals than in sedentary animals 21 days postinjury. The Akt-mammalian target of rapamycin (mTOR) pathway was activated early during the regeneration process, with further increases of mTOR phosphorylation and its downstream effectors, eukaryotic initiation factor-4E-binding protein-1 and p70(s6k), in active rats compared with sedentary rats (days 7-14). The exercise-induced increase in mTOR phosphorylation, independently of Akt, was associated with decreased levels of phosphorylated AMP-activated protein kinase. Taken together, these results provided evidence that increasing contractile activity during muscle regeneration ensured early and full recovery of muscle mass and suggested that these beneficial effects may be due to a longer proliferative step of myogenic cells and activation of mTOR signaling, independently of Akt, during the maturation step of muscle regeneration.     

The effect of head-down hypokinesia on functional state of diaphragm in rats

The effects of long-term (21 days) head-down (-30 degrees) hypokinesia (HDH) on respiratory system and a functional state of diaphragm were investigated in rats. Minute ventilation, oesophageal and abdominal pressure, integrated electrical activity of diaphragm were measured in control and experimental group (after 21 days of HDH) of animals. The measurements were made in several body positions atresting and in occlusion breathing. The results indicate that HDH causes reduction in minute ventilation of lungs, decrease in orthostatic stability and functional reserve of the respiratory system capacity. It was established that the basic mechanism of HDH respiratory effects is contractile failure of diaphragm related to damage in excitation-contraction coupling in its muscular fibres.     

The effect of intestinal anaphylaxis on postprandial motility in the rat

We have previously utilized a rat animal model to demonstrate that challenge of fasted sensitized animals with antigenic food protein is associated with diarrhea and altered intestinal myoelectric and motor activities. In this paper we examine the effect of intestinal anaphylaxis on postprandial motility in the same animal model. Hooded Lister rats were sensitized (S) by intraperitoneal injection of 10 micrograms egg albumin (i.e., antigen (Ag) and compared with sham-sensitized controls (C). Seven days later, three bipolar jejunal electrodes and a jejunostomy tube, for motility recording and Ag administration, were implanted. On day 14, intestinal myoelectric and motor activities were measured in fed animals before and after intraluminal challenge with Ag (100 mg egg albumin/0.5 mL saline) or placebo (P; 0.5 mL saline). Specific immunoglobulin E serum titres were greater than or equal to 1:64 in S animals, while C animals showed no response. None of the C animals challenged with P or Ag and none of the S animals challenged with P defecated after challenge, but all the S animals challenged with Ag developed diarrhea (p less than 0.001). There was no disruption or alteration of the fed motility pattern in C animals challenged with P or Ag, or S animals challenged with P. In fed S animals challenged with Ag the fed motility pattern persisted, but there was a significant (p less than 0.05) increase in the number of high-amplitude aborally propagating clustered contractions, where the phasic contractile activity was superimposed on a sustained tonic elevation of intraluminal pressure lasting 5-10 s.(ABSTRACT TRUNCATED AT 250 WORDS)     

Short-term exercise improves myocardial tolerance to in vivo ischemia-reperfusion in the rat.

These experiments examined the independent effects of short-term exercise and heat stress on myocardial responses during in vivo ischemia-reperfusion (I/R). Female Sprague-Dawley rats (4 mo old) were randomly assigned to one of four experimental groups: 1) control, 2) 3 consecutive days of treadmill exercise [60 min/day at 60-70% maximal O2 uptake (VO2 max)], 3) 5 consecutive days of treadmill exercise (60 min/day at 60-70% VO2 max), and 4) whole body heat stress (15 min at 42 degrees C). Twenty-four hours after heat stress or exercise, animals were anesthetized and mechanically ventilated, and the chest was opened by thoracotomy. Coronary occlusion was maintained for 30-min followed by a 30-min period of reperfusion. Compared with control, both heat-stressed animals and exercised animals (3 and 5 days) maintained higher (P < 0.05) left ventricular developed pressure (LVDP), maximum rate of left ventricular pressure development (+dP/dt), and maximum rate of left ventricular pressure decline (-dP/dt) at all measurement periods during both ischemia and reperfusion. No differences existed between heat-stressed and exercise groups in LVDP, +dP/dt, and -dP/dt at any time during ischemia or reperfusion. Both heat stress and exercise resulted in an increase (P < 0.05) in the relative levels of left ventricular heat shock protein 72 (HSP72). Furthermore, exercise (3 and 5 days) increased (P < 0.05) myocardial glutathione levels and manganese superoxide dismutase activity. These data indicate that 3-5 consecutive days of exercise improves myocardial contractile performance during in vivo I/R and that this exercise-induced myocardial protection is associated with an increase in both myocardial HSP72 and cardiac antioxidant defenses.     

Effects of melatonin supplementation prior to Ovsynch protocol on ovarian activity and conception rates in anestrous Murrah buffalo heifers during out of breeding season

Buffalo heifers have tendency to show anestrus during summer season. Melatonin has been used for correcting summer dependent anestrous via inducing resumption of ovarian activity. Therefore, the investigation was conducted to compare efficacy of melatonin for induction of estrus and conception rate with Ovsynch protocol in summer anestrous Murrah buffalo heifers. Thirty, summer anestrous Murrah buffalo heifers were selected and divided into two groups- treatment (n?=?20; 12 melatonin implants) and control (n?=?10; no treatment). On day 28 post-implant insertion, animals of both the groups were subjected to Ovsynch protocol. Blood sampling and ovarian ultrasonography were conducted to measure plasma melatonin, progesterone concentration and ovarian dynamics, respectively. No animal in either group showed estrus during first 28?days post-implant insertion. However, estrus induction rate was 100% after Ovsynch protocol in both groups. As compared to controls, treatment group exhibited higher (p?<?0.05) plasma melatonin on days 1, 4, 8, 15, 22 and 28 post-melatonin, with highest concentration on day 4. The progesterone concentration increased (p?<?0.05) on days 15 and 22 post-melatonin treatment. The treatment group had larger (p?<?0.05) preovulatory follicle on day of AI, subsequently developed larger (p?<?0.05) corpus luteum and higher plasma progesterone concentrations by day 12 post-AI as compared to the control group. The overall conception rate was 50 and 20% in treatment and control groups, respectively. In conclusion, melatonin treatment along with Ovsynch protocol improved the luteal profiles as well as the conception rate in buffalo heifers when compared with animals treated with Ovsynch protocol alone during summer season.     

Heat shock does not attenuate low-frequency fatigue.

Whole-body hyperthermia or heat shock confers protection to myocardial contractility against reperfusion-induced injury. The purpose of this study was to determine whether heat shock could provide similar protection to skeletal muscle contractility against low-frequency fatigue. Male Sprague-Dawley rats (6 rats/group) were heat shocked at 41.5 degrees C for 15 min either 24 h or 4 days prior to fatiguing stimulation to compare the contractile responses of the plantaris muscle with those of a nonheated group. Both 24 h and 4 days after heat shock, the 72-kDa heat shock protein (HSP72) was elevated above control levels. There were no differences between the heat-shocked and non-heat-shocked animals in measures of contractility prior to fatiguing contractions or in resistance to fatigue. Heat-shock preconditioning did not lead to improved postfatigue force recovery above control responses and, in fact, delayed the recovery of force. This study does not support the use of heat-shock therapy to improve skeletal muscle contractile performance under fatiguing conditions.     

Effect of vitamin A deficiency on cardiovascular function in the rat

Selected parameters of cardiovascular function were evaluated in vitamin A-deficient rats at 70 days of age. Resting heart rate was increased by an average of 100 bpm (21.4+/-2.7%), whereas resting systolic blood pressure was normal in vitamin A-deficient animals. The maximal contractile force developed per milligram weight of tissue by aortic rings excised from vitamin A-deficient animals was reduced in response to high potassium (-25.0+/-8.7%) and phorbol 12,13-dibutyrate (-36.8+/-8.4%) but was only slightly reduced in response to norepinephrine (-17.8+/-11.1%). Intimal rubbing to remove the endothelium had no effect on the loss in contractile responsiveness, and the relaxant response to acetylcholine was similar between control and vitamin A-deficient tissue groups. This suggests that the decrease in contractility of vascular smooth muscle from the vitamin A-deficient rats did not involve altered release of endothelium-derived vasoactive factors. Western blot analysis suggested a reduction in the protein levels of several differentiation markers including alpha-actin (-22%), calponin (-37%), desmin (-37%), and vinculin (-40%), whereas the level of PKCalpha was unchanged from control values. Our findings indicate a significant decrease in contractile responsiveness of aortic smooth muscle of the vitamin A-deficient rat that may be associated with a down regulation in the expression of contractile-related proteins.     

Effect of exogenous progesterone and eCG treatment on ovarian follicular dynamics in vicunas (Vicugna vicugna)

The aim of the present study was two-fold. First, to evaluate the effect of exogenous progesterone on ovarian follicular dynamics in order to assess its ability to synchronize ovarian activity in the vicuna. Secondly, to evaluate the ovarian response to the treatment with eCG through the observation of the structures developed in the ovaries. Follicular dynamics was monitored daily by transrectal ultrasonography in 12 adult, non-pregnant vicunas. Plasma progesterone and estradiol-17beta concentrations were measured in blood samples collected daily. In experiment 1, intravaginal devices containing 0.33g of progesterone were inserted into the vagina and kept in place for 5 days (treatment group, n = 8). After progesterone withdrawal, five animals were further monitored in order to evaluate the efficacy of the CIDR to synchronize the emergence of a dominant follicle. In experiment 2, four females received 750IU of eCG IM. Two were previously monitored ultrasonographically to confirm the absence of a dominant follicle at the beginning of the superstimulatory treatment (group A). The other two animals had a CIDR inserted into the vagina for 5 days and the superstimulatory treatment was applied 24h after device withdrawal (group B). Females from both groups were surgically explored 96 h after eCG injection; the ovaries were exposed and the number of newly formed structures produced by each ovary was counted. Peak progesterone concentrations (25.9 +/- 5.29 nmol l(-1), mean +/- S.E.M.) were attained on day 1 after device insertion, remained high until the day of device withdrawal (9.7 +/- 1.98 nmol l(-1)) and decreased to 5.5 +/- 1.13 nmol l(-1) the day after. There was no follicle development to the state of dominance after device insertion. Moreover, mean follicle diameter steadily decreased after insertion of the device until the minimum mean value (1.85 +/- 0.17 mm) was recorded on day 5 (P = 0.006). Similarly, plasma concentrations of estradiol-17beta remained below 35 pmol l(-1) during the period of progesterone treatment in all animals and the mean estradiol-17beta declined with the lowest value (22.1 +/- 2.19 pmol l(-1)) being recorded on day 4 after device insertion. After superstimulation of follicular development with eCG, the total number of follicles that developed was 33 in group A and 58 in group B and the mean number of newly developed ovarian structures per female was 22.75 +/- 4.26. In conclusion, progesterone released by the CIDR exerts a negative effect on ovarian follicular development and function suggesting intravaginal devices could be used to synchronize the beginning of follicular waves during a superstimulatory treatment. There was also a tendency for greater ovarian follicular development when the animals were previously treated with progesterone.     

Oxidation-reduction potentials in the cecal contents of rats and mice.

The oxidation-reduction potential (ORP) in the cecal contents of conventional rats, germ-free mice, and mice with a Colonization Resistance Factor flora (CRF-mice) was investigated. By using animals that were anaesthetized for a longer period of time, we attempted to eliminate the disturbing influence of oxygen. In addition, measurements were made under anaerobic conditions. For the rats, the ORP values reached a more or less constant level after about 30 min following the insertion of the electrodes. The mean ORP at that time was -458 mV (SD = 45 mV). The mean ORP values for the mice showed a more gradual reduction than was found in the rats. The curves leveled off at about 100 min following the insertion of the electrodes. The mean ORP values 100 min after electrode insertion were: germ-free mice, + 3 mV (SD = 39 mV); CRF-mice, -554 mV (SD = 29 mV). In rats, the ORP value decreased after death; no decrease was observed in mice. No difference was found in the values obtained when measuring under anaerobic or aerobic conditions after death.