This paper describes some new characteristics of the phosphoenolpyruvate carboxykinase CO(2)-oxaloacetate exchange reaction in purified preparations of Rhodospirillum rubrum. The enzymatic activity has been purified 169-fold. Nucleotide diphosphates substitute for nucleotide triphosphates in the exchange reaction. Nucleotide diphosphates will not support the synthesis of phosphoenolpyruvate from oxaloacetate. This reaction differs significantly from the CO(2)-oxaloacetate exchange reaction in higher plants and animals.

Pyruvate Kinase↗

PubMed1966

The participation of acetyl-CoA in pyruvate carboxylase.

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Adenosine Triphosphate↗

PubMed1966

The visual cells of the chicken as revealed by phase contrast microscopy.

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Animals↗

PubMedDate not supplied

Epididymal markers in human infertility.

Alpha-glucosidase, glycerophosphocholine, and L-carnitine were measured in sperm-free seminal plasma to determine whether these markers reflected the epididymal function of men attending an infertility clinic. The putative markers correlated well with each other (r = 0.66 to 0.70) and in 92% of 283 cases were accurate in categorizing semen as containing normal or subnormal amounts of markers. Glucosidase was considered the best index of epididymal function and was used for a further 306 samples. The ejaculate content of epididymal markers was correlated with testicular volume and serum testosterone below values of 30 ml and 30 nmol/l, respectively. Markers were also correlated with the concentration and motility of spermatozoa in semen. Seventy-one of 425 patients (17%) displayed subnormal epididymal secretions, mainly in association with hypogonadism (Klinefelter syndrome, Kallman syndrome, idiopathic hypogonadotropic hypogonadism) but also in cases of obstructed ducts, maldescended testicles, and local irradiation following hemicastration. Because azoospermic patients had reduced epididymal markers with both high and low FSH levels and a large proportion of men with reduced glucosidase and normal FSH suffered from testicular failure, it is suggested that other indices of testicular function are required for correct interpretation of reduced epididymal markers. Thirteen patients (3%) had low markers for which no cause was apparent; these may be cases of infertility due to isolated epididymal dysfunction.

Adult↗

PubMedDate not supplied

Transport of inositol into the distal cauda epididymidis of the rat.

The transport of [3H]myo-inositol into the lumen of the rat distal cauda epididymidis was studied by luminal perfusion in vitro. Entry was time and tubule length-dependent and saturable transport could be demonstrated with Vmax of 237 pmol/(30 min. cm) and K+ of 1 mM. Secretion of unlabeled inositol into the epididymal lumen was maintained for 5 hours at a concentration 6 times greater than that of the bathing solution. The turnover time of the epithelial pool of inositol was 4.5 hours, from which the intracellular concentration was estimated to be 26.6 mM. Transport was not reduced by metabolic inhibitors, and it was demonstrated that exchange diffusion across the basolateral membranes could drive the uptake in this region.

Animals↗

PubMedDate not supplied

Effect of joint position and ligament tension on the MR signal intensity of the cruciate ligaments of the knee.

Six cadaveric lower extremities were imaged with T1-weighted spin-echo pulse sequences with the knees extended and flexed to 90 degrees. Magnetic resonance signal intensities of the anterior cruciate ligament (ACL) and posterior cruciate ligament (PCL) were compared. Changing from extension to flexion resulted in decreased signal intensity in six of six ACLs and five of six PCLs. Two of the knees were then imaged with and without tension applied to the ACL. Both specimens showed a decrease in signal intensity with tension, followed by an increase in signal intensity with release of the tension. Finally, in three of the limbs the ACL was surgically reconstructed and then imaged with and without tension applied to the tendon graft. Signal intensity decreased with tension and increased with release of the tension in all three specimens. Thus, joint position and changes in ligament tension affect the signal intensity of the ACL and PCL, generally resulting in a signal intensity decrease with tension.

Aged↗

PubMedDate not supplied

GABA transport in Saccharomyces cerevisiae.

Gamma-aminobutyrate (GABA) accumulation in growing cultures of Saccharomyces cerevisiae was shown to occur by means of an active transport system that is inhibited by proton ionophores, azide, fluoride and arsenate ions. Transport occurred maximally at pH 5.0 and exhibited apparent Km values of 12 microM and 0.1 mM. Accumulated GABA did not efflux upon treatment with proton ionophores and exchanged with extracellular material only very slowly. However, release was complete upon treatment with nystatin. These observations raise the possibility that a major portion of intracellular GABA is sequestered in the vacuole. The response of GABA uptake to growth on various nitrogen sources suggested that uptake may be subject to several types of regulation.

Biological Transport, Active↗

PubMedDate not supplied

Maturation of human spermatozoa (from selected epididymides of prostatic carcinoma patients) with respect to their morphology and ability to undergo the acrosome reaction.

Spermatozoa were recovered from three regions of the epididymis of six prostatic carcinoma patients. After washing and incubating for 3 h in Ham's F-10 medium, with or without 5 microM A23187 for the last 30 min, spermatozoa were tested for vitality by hypotonic swelling and permeated with methanol to detect the acrosome with peanut agglutinin. Whereas the extent of spontaneous acrosome reactions was similar for spermatozoa from all regions of the duct, 17 and 28% of spermatozoa from the corpus and cauda epididymidis respectively, responded to stimulation by A23187 with acrosome reactions but there was no stimulation by A23187 of spermatozoa from the efferent ducts. The percentage of morphologically normal spermatozoa increased stepwise towards the distal regions, with abnormalities being mostly enlarged heads in more proximal regions; they were largely absent from the cauda epididymidis. Sperm head swelling was similarly observed in cynomolgus monkey spermatozoa from the caput epididymidis but not the more distal regions. These forms were not observed when spermatozoa were fixed before smearing, indicating that they were artefacts of sperm preparation. The changes in the susceptibility of non-fixed epididymal spermatozoa to produce morphological artefacts and the gain in their acrosomal response to ionophore demonstrate maturational changes of spermatozoa in the human epididymis.

Acrosome↗

PubMedDate not supplied

Recent biochemical approaches to post-testicular, epididymal contraception.

Results from recent animal models with implications for putative human male contraceptives acting on the epididymis are reviewed. Inducing sterility by enhancing sperm transport through the epididymis has not been achieved. The induction of infertility in males of several species is easier to achieve by direct actions of drugs on sperm function (e.g. inhibition of sperm-specific isoenzymes of the glycolytic pathway by chloro-compounds) than by indirectly reducing amounts of epididymal secretions normally present in high concentration (e.g. alpha-glucosidase, L-carnitine). The former show promise for the clinic since human spermatozoa are susceptible to inhibition. On the other hand, the infertile male mice of the c-ros knock-out model demonstrate the influence of even a small region of the epididymis on fertility, so that targeting the as yet unknown epididymal factors presumably secreted in limiting amounts by this epididymal segment, is a new lead for a contraceptive. Targeting a specific sperm protein acquired in the testis, but depleted in the epididymis by toxicants that induce rapid infertility, may also lead to the discovery of new contraceptives, but these will require developing new means of organ-specific delivery of contraceptive drugs.

Animals↗

PubMedDate not supplied

Effect of acute androgen withdrawal by GnRH antagonist on epididymal sperm motility and morphology in the cynomolgus monkey.

Hormonal male contraception requires an induction phase before azoospermia and contraceptive safety are achieved. The nature of spermatozoa that may be ejaculated during this induction phase was studied in a nonhuman primate. The GnRH antagonist Cetrorelix was administered daily to five cynomolgus monkeys to induce testicular regression, and the vehicle was given to five control animals. Within 16 days, the antagonist reduced androgens by 80% in the serum and by 50% in the epididymis. Sperm were obtained by mincing different epididymal regions and were examined for morphology (subjectively) and motility (objectively) after removal of the organs 16 and 25 days after continuous treatment. Spermatozoa entering the epididymis of monkeys undergoing regression differed from those of vehicle-treated controls in their greater susceptibility to disruption during preparation for morphological staining. The acquisition of motility by sperm in the epididymides attached to regressing testes occurred in the same epididymal region as controls but did not achieve the median velocities attained by sperm in controls during epididymal passage. Values for most sperm motion parameters developed as in the controls, and, during epididymal passage, sperm developed resistance to stresses encountered during preparation for morphological analysis. These observations suggest that spermatozoa ejaculated before spermatogenesis ceases may be potentially fertilizing because epididymal maturation continues in an androgen-deprived organ. From these preclinical studies, it can be concluded that in men, applying hormonal contraception precautions against pregnancy must be recommended before azoospermia is induced, since the epididymis can partially compensate for poor-quality sperm produced by a regressing testis even when levels of circulating androgens and tissue androgens are low.

Androgen Antagonists↗