Comparison of different cryoprotectants for freezing donkey (Equus asinus) semen.

The aim of this study was to evaluate two cryoprotectants, dimethylformamide (DMF) and methylformamide (MF) in two concentrations (5 and 7 %) in vitro in donkey semen using a rapid freezing technique and the effect on pregnancy rates in mares. Twenty-four ejaculates from 8 jacks (n = 8; r = 3) were divided into 4 extenders: BotuSemen Gold with 5 % or 7 % MF and 5 % or 7 % DMF, all containing 11 % lactose, 20 % egg-yolk and 0.5 % Equex. Post-thaw evaluations included: sperm motility, membrane function and acrosome status. A linear mixed effect model was used to test the effect of different freezing media on semen parameters. No differences were observed between the 4 freezing media used, for any of the seminal parameters (P > 0.05). However, samples with 5 % DMF showed the highest percentages of sperm with acrosomes and functional membranes (DMF: 5 %: 53.67 ± 22.01; 7 %: 33.92 ± 23.4; MF: 5 %: 44.5 ± 20.46; 7 %: 38.75 ± 27.4) (Data: mean ± SD; P > 0.05). Hence, thirty mares were inseminated: 15 with 5 % DMF and 15 with 7 % DMF. The pregnancy rate was 46 % (7/15) and 0 % (0/15) using the extender with 5 % or 7 % DMF, respectively (P = 0.003). To conclude, the use of 5 % or 7 % of MF or DMF did not affect the in vitro parameters. Despite the lack of differences in vitro with the two DMF concentrations, in vivo results only showed pregnancies when using 5 % DMF. Thus, the results of this study demonstrate the importance of accompanying in vitro semen evaluations with studies that evaluate post-insemination pregnancy rates.

Haematology and biochemistry in healthy llamas at sea level.

In the last years, there has been an increasing interest in llamas, not only as part of a productive system, but mostly as companion animals. Most reports regarding clinical biochemistry and haematology include few llamas and details about their health status are not available. The present study aims to provide haematological and biochemical parameters for llamas of known health status. Twenty-three non-pregnant females and seven males that live in Buenos Aires, Argentina (34°36'S, 58°22'W, at sea level) were studied. Llamas were clinically healthy, in good nutritional status. Animals were kept at grass and were fed hay bale or pellets and water ad libitum. Blood samples were collected by jugular venipuncture in spring. Packed cell volume, leucocyte count, differential white cell count, platelets count, urea, creatinine, total proteins, albumin, alkaline phosphatase, aspartate aminotransferase, alanine aminotransferase, glucose, calcium and phosphate were assessed. No significant differences were observed between males and females, except for platelet count and calcium, which was greater in males (P˂0.01). Values obtained for the different parameters were similar to those previously reported, except for monocytes, alkaline phosphatase, glucose and calcium, that were lower and lymphocytes and platelets count, that were higher in this study. In conclusion, different ambient and methodological conditions might affect some parameters. The parameters hereby presented are representative of llama's population living at sea level in South America.

Expression of Arginine Vasopressin Type 2 Receptor in Canine Mammary Tumours: Preliminary Results.

The aims of this study were to investigate the potential association of arginine vasopressin type 2 receptor (AVPR2) in canine mammary tumours with expression of oestrogen receptors α (ORα) and ß (ORß) and clinicopathological features of the neoplasms. Twenty-six canine mammary tumour samples (11 benign, 15 malignant) were immunolabelled for AVPR2, ORα and ORß antigens. Moderate to intense immunolabelling of AVPR2 antigen, found in all neoplasms, was not significantly associated with expression of ORα or ORß antigens or with clinicopathological features. These findings indicate a potential role for AVPR2 in the development of canine mammary tumours and the use of AVPR2-selective vasopressin analogues as therapeutic options.

Expression of Oxytocin Receptors in Canine Mammary Tumours.

The aims of the present study were: (1) to investigate the presence of oxytocin receptors in benign and malignant canine mammary tumours (CMTs) and to evaluate the possible association between oxytocin receptor (OTR) expression and the expression of oestrogen receptor (OR) α and ORß, and (2) to examine associations between receptor expression and tumour size, clinical stage, histological subtype, tumour grading and lymph node status. Forty-three canine mammary tumour samples (19 benign, 24 malignant) were examined by immunohistochemistry to detect OTR, ORα and ORß expression. Results were expressed as total score for each receptor, calculated as the sum of the percentage of positive cells and the intensity of immunolabelling. In all of the evaluated mammary tumour samples, OTRs were identified and their expression tended to be higher in benign tumours than malignant tumours. Among the malignant tumours, the expression of OTR was significantly higher in grade I and II lesions than in grade III lesions. ORα-positive tumours had a tendency towards a higher OTR total score than ORα-negative tumours. These results report for the first time that CMTs express OTRs and their expression is associated with the presence of ORα. An interaction between oxytocin and the OTR might play a role in the development and progression of this type of neoplasia.

Synchronization of time of ovarian follicular development in llamas (Lama glama) using a protocol based on GnRH and PGF2α.

The aim of this study was to evaluate the effectiveness of a protocol based on GnRH and PGF2α to synchronize the emergence of a new wave of ovarian follicular development in llamas and, therefore, when a new dominant follicle develops. Llamas (n = 18) were assigned to growing, mature or regressing follicle groups according to the phase of the follicular wave at the beginning of treatment. The protocol was initiated with a GnRH analogue (GnRHa) injection on Day 0 followed 7 days later with a d-cloprostenol injection and a second GnRHa injection on Day 10. Ovulation rate after the first GnRHa treatment, day of new follicle emergence, mean plasma progesterone concentration and percentage of animals with a newly developed dominant follicle ≥ 7 mm on Day 10 were evaluated. Ovulation rate after the first GnRHa was less in the regressing than mature and growing follicle groups and new follicular wave emergence occurred earlier in the regressing follicle group than in the other two groups. Mean plasma progesterone concentration in females that had ovulations after the first GnRHa injection was similar. The percentage of animals that had a new follicle ≥ 7 mm on Day 10 was not different among groups and the overall percentage was 66.6%. The total synchronization rate for development of a new wave of follicular development on Day 10 was greater in females having ovulations after the first GnRHa injection than in those that did not have ovulations. In conclusion, the protocol used in the present study was useful for synchronizing ovarian follicular development in 66% of the llamas regardless of the phase of the follicular wave development at the beginning of treatment.

Hormonal changes and follicular activity after treatment with intravaginal progesterone-releasing devices in llamas.

Plasma progesterone (P4 ) concentrations and follicular activity after administration of different P4 doses were evaluated in 33 adult female llamas treated with intravaginal devices. In Study 1, a group of llamas (n = 10) was treated with an intravaginal device (IVD) containing 160 (n = 5) or 780 mg of P4 (n = 5). Based on the results from the first study, in Study 2, females with follicles at different stages of development were treated with the IVD containing 780 mg of P4 (n = 21) or remain untreated (control; n = 12) to evaluate the effect of P4 on follicular activity. In Study 1, the IVD containing 160 mg of P4 induced follicular turnover in 60% of females while the remaining 40% of llamas developed persistent follicles. Thus, this device controlled follicular activity in llamas, although it promotes the persistence of follicles present at start of treatment. Conversely, in both studies, the IVD containing 780 mg of P4 suppressed follicular development and hasten the emergence of a new follicular wave in all females regardless of the follicular phase at insertion. Additionally, in Study 2, this device effectively concentrated the appearance of follicles with ovulatory diameter at a definite time after treatment in comparison with control animals. In conclusion, treatment with an IVD containing 780 mg of P4 would be considered for the control of follicular activity in llamas as it ensures the presence of a young follicle with ovulatory diameter by day 6 after the end of treatment in all females.

Oestrogen and Progesterone Receptors and COX-2 Expression in Endometrial Biopsy Samples During Maternal Recognition of Pregnancy in Llamas (Lama glama).

Endometrial expression of oestrogen receptor-α (ERα), progesterone receptor (PR) and cyclooxigenase-2 (COX-2) was evaluated in non-pregnant and pregnant llamas during the period when luteolysis/maternal recognition of pregnancy is expected to occur. Females (n = 28) were divided into two groups: non-pregnant llamas were induced to ovulate with a Buserelin injection, and endometrial biopsies were obtained on day 8 (n = 5) or 12 (n = 5) post-induction of ovulation. Animals of the pregnant group (n = 18) were mated with a fertile male. Pregnancy was confirmed by the visualization of the embryo collected by transcervical flushing in 5 of 9 animals on day 8 post-mating and by progesterone profile on day 12 post-mating in 4 of 9 animals, when endometrial biopsies were obtained. An immunohistochemical technique was used to evaluate receptors population and COX-2 expression. Pregnant llamas showed a higher percentage of positive cells and stronger intensity for ERα than for non-pregnant llamas in stroma on day 8 and in the luminal epithelium on day 12 post-induction of ovulation, while a deep decrease in endometrial PR population was reported in pregnant llamas on that day in luminal and glandular epithelia and stroma. In the luminal epithelium, COX-2 expression was lower in pregnant than in non-pregnant animals. Briefly, the increase of ERα in pregnant llamas gives further support to the hypothesis that oestrogens are involved in the mechanism of maternal recognition of pregnancy. Endometrial PR decrease in pregnant llamas might be a necessary event to allow the expression of proteins involved in conceptus attachment, a mechanism widely accepted in other species. Moreover, embryo seems to attenuate maternal PGF(2α) secretion during early pregnancy by decreasing the endometrial expression of COX-2 in the luminal epithelium of pregnant llamas.

Ultrasonographic and endocrine characterization of follicular waves in llamas with a special reference to the overlapping phenomenon during successive waves.

Ovarian follicular growth in non-mated llamas occurs in successive waves that generally superimpose their origin on the regression of the preceding wave (overlapping), originating prolonged sexual receptivity in the species. The aim of this study was to perform an ultrasonographic and endocrine characterization of individual and successive waves in non-mated llamas with a special interest on the overlapping phenomenon. Twelve llamas were examined daily by transrectal ultrasonography for at least two consecutive waves. In six females, blood samples were collected daily at the end of each examination. The development of the largest follicle (F) showed a wavelike pattern with a mean duration of 25 days. All waves evaluated were partially overlapped on the preceding wave and emerged at a mean interval of 15.8 ± 0.5 days. This interwave interval determines a mean overlapping degree of 32% of the wave length. Similarly, mean plasma oestradiol-17ß (E2 ) concentrations followed a wavelike pattern. However, E2 concentrations started to decline before the structural regression of the F was observed. Mean basal E2 concentrations remain higher than 10.9 ± 0.6 pmol/l. In conclusion, follicular activity in non-mated llamas is characterized by continuous emergence of successive waves that always overlap the preceding wave with variable degrees. E2 production during the follicular wave is shorter in duration than the morphological development of the F. Finally, the overlapping phenomenon maintains increased plasma E2 concentrations persistently and this could explain the prolonged periods of sexual receptivity registered in llamas.

Oestrogen, progesterone and oxytocin receptors and COX-2 expression in endometrial biopsy samples from the induction of ovulation to luteolysis in llamas (Lama glama).

Endometrial expression of oestrogen (ERα), progesterone (PR) and oxytocin receptor (OR) and cyclooxygenase-2 (COX-2) was evaluated from the induction of ovulation to luteolysis in llamas. Ovarian activity was daily assessed by ultrasonography in five females. Ovulation was induced immediately after the detection of an ovulatory follicle by a GnRH injection (Day 0). Endometrial samples were obtained by transcervical biopsies from the left and right horns on day 0 and days 4, 8, 10 and 12 post-GnRH. Blood samples were collected daily for progesterone and estradiol-17ß determinations by RIA. An immunohistochemical technique was used to study receptors population and COX-2 expression which were then evaluated by two independent observers. The expression of ERα and PR was highest on day 0 in the luminal epithelium and stroma in association with high plasma estradiol-17ß concentrations. Thereafter, a decrease in ERα population was registered on day 4 and a new increase of its expression was observed between days 8 and 12 in those cell types. Conversely, PR population was gradually down-regulated until its lowest expression was reached on day 10 post-GnRH in the luminal epithelium. Content of OR was similar throughout the study in all cell types. The expression of COX-2 was highest from day 8 to 12 post-GnRH in the luminal epithelium, in relation to the time of maximal PGF2α release. Both steroid receptors populations and COX-2 expression were similar between horns. Meanwhile, OR expression was higher in the right than in the left uterine horn. In summary, this study showed that the loss of endometrium sensitivity to progesterone by days 8-10 post-induction of ovulation and the concomitant increase of COX-2 expression could play a key role in the mechanism of luteolysis and somehow be related to the short corpus luteum lifespan of llamas.

Development of corpus luteum susceptibility to an analog of prostaglandin F2α, throughout the luteal phase in llamas (Lama glama).

The aim of the present study was to evaluate the susceptibility of the corpus luteum to d-cloprostenol (synthetic analog of PGF(2α)) throughout the luteal phase in llamas. Female llamas (n=43) were induced to ovulate by GnRH injection in the presence of an ovulatory follicle and randomly assigned into one of six groups: control and treated with an injection of d-cloprostenol on Day 3, 4, 5, 6 or 8 post GnRH. Blood samples were collected to determine plasma progesterone concentrations. There was no effect of treatment on animals injected on Day 3 or 4 post-GnRH. In animals treated on Day 5, different responses were observed. No effect of treatment was recorded in 27% of the animals whereas 55% of the llamas showed a transitory decrease followed by a recovery in plasma progesterone concentrations after d-cloprostenol injection, indicative of a resurgence of the corpus luteum, extending the luteal phase a day more than in control animals. In the remaining 18% of the animals injected on Day 5, (corresponding to those exhibiting the greatest plasma progesterone concentrations at the day of injection), complete luteolysis was observed. Plasma progesterone concentrations decreased to below 1 ng ml(-1) 24 h after d-cloprostenol in llamas injected on Day 6 or 8 post-GnRH. In conclusion, the corpus luteum of llamas is completely refractory to PGF(2α) until Day 4 after induction of ovulation, being partially sensitive by Day 5 and fully responsive to PGF(2α), by Day 6 after induction of ovulation.

p53 immunostaining is correlated with reduced survival and is not correlated with gene mutations in resected pulmonary large cell carcinomas.

Malignancy of pulmonary large cell carcinomas (LCC) increases from classic LCC through LCC with neuroendocrine morphology (LCCNM) to large cell neuroendocrine carcinomas (LCNEC). However, the histological classification has sometimes proved to be difficult. Because the malignancy of LCC is highly dependent on proteins with functions in the cell cycle, DNA repair, and apoptosis, p53 has been targeted as a potentially useful biological marker. p53 mutations in lung cancers have been shown to result in expression and protein expression also occurs in the absence of mutations. To validate the importance of both p53 protein expression (by immunostaining) and p53 gene mutations in lung LCC (by PCR-single strand conformational polymorphism analysis of exons 5, 6, 7, and 8) and to study their relationships with clinical factors and sub-classification we investigated the correlation of p53 abnormalities in 15 patients with LCC (5 classic LCC, 5 LCNEC, and 5 LCCNM) who had undergone resection with curative intent. Of these patients, 5/15 expressed p53 and none had mutant p53 sequences. There was a negative survival correlation with positive p53 immunostaining (P = 0.05). After adjustment for stage, age, gender, chemotherapy, radiotherapy, and histological subtypes by multivariate analysis, p53 expression had an independent impact on survival. The present study indicates that p53 assessment may provide an objective marker for the prognosis of LCC irrespective of morphological variants and suggests that p53 expression is important for outcome prediction in patients with the early stages of LCC. The results reported here should be considered to be initial results because tumors from only 15 patients were studied: 5 each from LCC, LCNEC and LCCNM. This was due to the rarity of these specific diseases.

p53 immunostaining is correlated with reduced survival and is not correlated with gene mutations in resected pulmonary large cell carcinomas

Malignancy of pulmonary large cell carcinomas (LCC) increases from classic LCC through LCC with neuroendocrine morphology (LCCNM) to large cell neuroendocrine carcinomas (LCNEC). However, the histological classification has sometimes proved to be difficult. Because the malignancy of LCC is highly dependent on proteins with functions in the cell cycle, DNA repair, and apoptosis, p53 has been targeted as a potentially useful biological marker. p53 mutations in lung cancers have been shown to result in expression and protein expression also occurs in the absence of mutations. To validate the importance of both p53 protein expression (by immunostaining) and p53 gene mutations in lung LCC (by PCR-single strand conformational polymorphism analysis of exons 5, 6, 7, and 8) and to study their relationships with clinical factors and sub-classification we investigated the correlation of p53 abnormalities in 15 patients with LCC (5 classic LCC, 5 LCNEC, and 5 LCCNM) who had undergone resection with curative intent. Of these patients, 5/15 expressed p53 and none had mutant p53 sequences. There was a negative survival correlation with positive p53 immunostaining (P = 0.05). After adjustment for stage, age, gender, chemotherapy, radiotherapy, and histological subtypes by multivariate analysis, p53 expression had an independent impact on survival. The present study indicates that p53 assessment may provide an objective marker for the prognosis of LCC irrespective of morphological variants and suggests that p53 expression is important for outcome prediction in patients with the early stages of LCC. The results reported here should be considered to be initial results because tumors from only 15 patients were studied: 5 each from LCC, LCNEC and LCCNM. This was due to the rarity of these specific diseases.

Uterine estrogen receptor alpha and progesterone receptor during the follicular and luteal phase in llamas.

Estrogen receptor-alpha (ERalpha) and progesterone receptor (PR) were characterized in different endometrial cell types as luminal and glandular epithelium and stroma during the follicular (FP) and the luteal phase (LP) in llamas. Animals were examined daily by transrectal ultrasonography for the determination of the presence of an ovulatory follicle and ovulation was immediately induced by a GnRH injection (Day 0). Endometrial samples were obtained by transcervical biopsies from the left uterine horn on Day 0 (FP) and 9 days after the GnRH injection (Day 9, LP). Blood samples were collected on these days for estradiol 17beta and progesterone determination by RIA. An immunohistochemical technique was used to visualize ERalpha and PR immunostaining which was then analyzed by two independent observers. Total positive area and average staining for ERalpha were affected by the phase of the ovarian activity: in the three cell types there was more positive area and intense staining during the FP than during the LP. Similar findings were observed for PR, more positive stained areas were found during the FP than during the LP in the epithelia. In addition, the three cell types had more intense staining during the FP than during the LP. An effect of the cell type for ERalpha and PR was observed; epithelia (luminal and glandular) had more positive stained areas and greater intensity than stromal cells. In conclusion, the results of the present study suggest that in llamas, like in other ruminants, estradiol has a stimulatory effect while progesterone downregulates the ERalpha and PR and that the receptor is cell type specific.

Conformation state of the ryanodine receptor and functional effects of ryanodine on skeletal muscle.

The ryanodine receptor (RyR) and the dihydropyridine (DHP) receptor (L-channels) comprise the main elements of the functional feet of the triadic element in skeletal muscle. These two main elements have conformational states that are regulated by the membrane potential and the consequent electrical field. The pharmacological action of ryanodine on skeletal muscle depends upon the physiological functional state of the RyR. At a resting potential of -90 m V, ryanodine at very low concentrations, 10(-11) M, causes the RyR to have a low conductance state which allows calcium to leak from the terminal cisternae of the sarcoplasmic reticulum and to be recycled with ATP utilization, leading to a marked increase in oxygen consumption and aerobic metabolism. At concentrations greater than 10(-6) M, ryanodine can cause a slowly developing contracture of resting muscle, inhibit the muscle twitch when the RyR complex is formed during stimulation, and, if formed before stimulation, accelerate the development of contracture. Biochemical studies have revealed that the RyR has four binding sites in which the conductance state depends upon the number of sites occupied by ryanodine. Our present understanding of the RyR-operated calcium channel is the result of an interdisciplinary approach in which each discipline (anatomy, physiology, biophysics, and biochemistry) contributes to our knowledge of the pharmacological action of ryanodine.

Cisplatinum enhancement of myocardial Mg2+ transport.

Cisplatinum in a concentration (4.3 x 10(-6) M) corresponding to the therapeutic plasma concentration for cancer patients was found to cause a marked enhancement of magnesium efflux and uptake in perfused frog myocardium. The magnesium content of the perfused frog ventricle is increased from 6.66 +/- 0.34 mumol/g wet wgt to 8.03 +/- 0.38 mu mol/g wet wgt. Cisplatinum had a negative inotropic action reducing contractile force to 46 +/- 8% of initial force after 40 min of perfusion. The corresponding control contractile force was reduced to 74 +/- 7%. Removal of calcium and magnesium from the perfusion solution containing 0.5 mM EDTA for 10 minutes caused contractile force to be reduced to 0 after 6 beats at 24 min-1. After ten minutes of perfusion with EDTA, 1.87 mu mol/g wet wgt of magnesium was lost from control ventricles. Cisplatinum increased the loss to 4.08 +/- 0.34 mu mol/g wet wgt. The magnesium lost during EDTA perfusion was completely recovered after 5 minutes of perfusion in Ringer or Tyrode solution by both control and cisplatinum treated frog ventricles. The contractile force also recovered to the level prior to perfusion with EDTA Ringer. The rate of Mg2+ efflux in EDTA Ringer is largest during the first 3 minutes and was 0.170 +/- 0.051 p mol cm-2 sec-1 for controls and 0.798 p mol cm-2 sec-1 for the cisplatinum treated ventricles. During the last 7 min of perfusion in EDTA Ringer the Mg2+ efflux was reduced to 0.057 +/- 0.005 p mol cm-2 sec-1 for control ventricles and 0.170 p mol cm-2 sec-1 for the cisplatinum treated ventricles. Cisplatinum increased both magnesium efflux and influx and influx in the frog myocardium, increased magnesium content to a higher level and reduced contractile force. The effect of cisplatinum on magnesium transport is attributed to an increase in the charged form of cisplatinum that accumulates inside the cell where chloride content is low and the chloride of cisplatinum is displaced to form a positively charged cisplatinum.

Myocardial magnesium transport: effect of gramicidin S and epinephrine.

Initial magnesium transport in low magnesium Ringer in the frog myocardium consists of at least two systems, a fast system with high capacity with a time constant of 30 seconds and a slow transport system that operates with a time constant of 165 seconds. Both transport systems appear to be electroneutral and can operate either against an electrochemical gradient or with an electrochemical gradient. The fast transport system can transport Mg2+ in an outward direction at 1.84 p mol cm-2 sec-1; the slow system causes Mg2+ to be transported outward at 0.05 p mol cm-2 sec-1. Gramicidin S (5 microM) decreases the slow outward transport system to 0.01 p mol cm-2 sec-1 and at concentrations greater than 1 microM inhibits not only slow magnesium outflux in low calcium Ringer but also inhibits magnesium influx during recovery of Mg2+ in Ringer. Gramicidin S at 5 microM decreases Mg2+ influx from .04 p mol cm-2 sec-1 to 0.01 p mol cm2 sec-1 indicating that influx and efflux may take place on the same transport system. In the presence of 10 mM Mg2+ Gramicidin S increases magnesium content. Epinephrine increases magnesium efflux and overcomes the inhibition of Mg2+ efflux by Gramicidin S.

Calcium dependent magnesium uptake in myocardium.

The frog myocardium maintains magnesium content at a steady state level when stimulated at 0.4Hz while being perfused with Ringer's solution containing 1 x 10(-3) M Ca2+ and 5 x 10(-7) M magnesium. When calcium is removed 43% of tissue magnesium is lost within 30 seconds or 12 beats. Restoration of calcium to the perfusion solution causes reaccumulation of magnesium from a solution containing 5 x 10(-7) M magnesium. The reaccumulation of magnesium indicates a highly selective transport system for magnesium which is dependent upon the presence of calcium. Calcium appears to reduce the leak of magnesium from the myocardium and enhances the transport of magnesium into the myocardial cell. Intracellular magnesium is a necessary cofactor for hundreds of enzymes, and is essential for protein synthesis and as an extracellular divalent cation helps to stabilize excitable membranes in conjunction with calcium. The concentration of ionized magnesium in the sarcoplasm of myocardial muscle has an average value of 1.45 mM +/- 1.37 (standard deviation), N = 19) with a range of 0.5 to 3.6 mM (1). The heart with its numerous mitochondria and high enzymatic activity is vulnerable to myocardial damage due to magnesium loss. The isolated frog ventricle conserves intracellular magnesium when perfused with Ringer's solution containing no added magnesium and maintains function for hours. The ability to conserve magnesium suggests a low permeability of the sarcolemma to magnesium and an extremely efficient inward transport system. Removal of calcium as well as magnesium from the perfusion solution causes a rapid loss of tension in the electrically driven frog ventricle (0.4) Hz.(ABSTRACT TRUNCATED AT 250 WORDS)

Stimulation-enhanced 3-O-methylglucose efflux from the frog sartorius: kinetics and properties of the system.

The characteristics of the process by which contraction enhances glucose transport in the frog sartorius were studied. Electrical stimulation increased the permeability of muscles to 3-O-methylglucose (3-O-MeGlc), a nonmetabolizable glucose analogue, increasing efflux as well as uptake. Enhanced efflux was due to an increase in Vmax of the efflux process. A lactacidosis had no effect on basal 3-O-MeGlc efflux, and replacement of media Na+ with Li+ did not affect stimulation-induced uptake. Also, basal and stimulated uptake was not affected by 1 microM 12-O-tetradecanoylphorbol-13-acetate (TPA), a protein kinase C activator. Lastly, N-carbobenzoxy-glycyl-L-phenylalaninamide, which inhibits insulin-enhanced, but not basal, glucose uptake in adipocytes, inhibited both basal and stimulated 3-O-MeGlc fluxes in the frog sartorius. From these findings, we conclude: (1) contraction and exercise enhance glucose transport in muscle by increasing the number of transporters in the plasma membrane, or their turnover, by an unknown process; and (2) basal glucose transport of muscle, unlike that of adipocytes, can not be distinguished from stimulated transport on the basis of its insensitivity to N-carbobenzoxyglycyl-L-phenylalaninamide.