Radioimmunoassay of plasma relaxin levels throughout pregnancy and at parturition in the pig

Relaxin concentrations in peripheral plasma have been measured throughout pregnancy and immediately following parturition in the pig by radioimmunoassay. Gestation ranged from 114-117 days. Relaxin concentrations remained below 2 ng/ml during the first 100 days of pregnancy and then rose gradually to a mean of 11.9 ng/ml by 3 days before parturition. At this time, relaxin levels began to rise more rapidly and over the next 2 days increased to a mean concentration of 44.0 ng/ml by 30 h before parturition. Relaxin concentrations then increased sharply to a mean of 145.6 ng/ml by 14 h before parturition. This maximum was followed be a rapid decrease to a mean of 42.4 ng/ml by 2 h before parturition. At one day following parturition, relaxin levels were less than 1 ng/ml.

Further evidence that extrinsic acetylcholine acts preferentially on extrajunctional receptors in the chick biventer cervicis muscle

The specificity of action of extrinsic acetylcholine on extrajunctional and junctional receptors in the chick biventer cervicis muscle was studied by determining its ability to protect the responses evoked by acetylcholine and by tetanic nerve stimulation from the blockade by alpha-bungarotoxin, an irreversible binding agent of acetylcholine receptors. At concentrations of 50-100 mug/ml, acetylcholine caused a desensitization to extrinsic acetylcholine but not to nerve stimulation and protected only the contractile response to extrinsic acetylcholine from the toxin blockade whereas neither the response to tetanic nerve stimulation nor the endplate potentials were protected. For the protection of the latter, higher concentrations of acetylcholine were needed. In the presence of physostigmine, a concentration of acetylcholine as low as 10 mug/ml protected the endplate potentials from the toxin blockade. By contrast, d-tubocurarine protected the tetanic contraction and the endplate potentials induced by nerve stimulation at a concentration which produced the same protection of acetylcholine-induced contraction as that produced by 50-100 mug/ml acetylcholine. These results indicate that in contrast to d-tubocurarine, extrinsic acetylcholine at low concentrations acts preferentially on the extrajunctional receptors in the absence of an anticholinesterase.

Effects of chronic treatment with various neuromuscular blocking agents on the number and distribution of acetylcholine receptors in the rat diaphragm

1. Acetylcholine receptors in the end-plate and non-end-plate areas of the rat diaphragm, after treating the animal with hemicholinium-3, alpha- or beta-bungarotoxin in vivo, were studied by their specific binding of labelled alpha-bungarotoxin. 2. Subcutaneous injection of maximum tolerable doses of hemicholinium-3 (50 mug/kg) twice daily for 7 days increased the number of extrajunctional receptors along the whole length of muscle fibre, the approximate density of receptor on muscle membrane being increased from 6/mum2 in normal diaphragm to 38/mum2. Junctional receptors were also increased in number from 2-2 x 10(7) to 2-8 x 10(7) per end-plate. 3. Five days after denervation, there were approximately 153/mum2 extrajunctional receptors and the number of receptors on the end-plate was increased by 220%. 4. Intrathoracic injection of beta-bungarotoxin (50 mug/kg) also increased the density of extrajunctional receptors to approximately 104/mum2, and the number of end-plate receptors by 140% in 5 days. The neuromuscular block was extensive and prolonged. 5. [3H]Diacetyl alpha-bungarotoxin (150 mug/kg) injected into thoracic cavity caused complete neuromuscular blockade for 12 hr. At 24 hr, the synaptic transmission was restored in 80% of the junctions with less than 10% end-plate receptors freed, whereas the safety factor for transmission in normal diaphragm was 3-5. Extrajunctional receptors appeared to increase within 24 hr. This increase continued despite the restoration of neuromuscular transmission, and the receptor density at 5 days was approximately 5l/mum2. The number of junctional receptors, however, was not increased. Repeated injection of the toxin gave the same result. 6. It is concluded that the numbers of junctional and extrajunctional acetylcholine receptors are regulated in different ways, and the possible role of acetylcholine is discussed.

Stability of aflatoxin B-1 and ochratoxin A in brewing

The stability of aflatoxin B-1 and ochratoxin A in brewing was investigated by adding the purified toxins to the raw materials at 1 and 10 mug/g levels during mashing in a conventional micro-brewing process. The results indicate that both toxins are stable to heat and are insensitive to cooker mash treatment. Both mycotoxins were partially removed in the mashing and brewing processes. About 14 to 18% and 27 to 28% of the added toxins were found in the final beers brewed from starting materials containing 1 and 10 mug, respectively, of either toxin per g. The possible route of transmission of mycotoxins into beer is discussed.

Mutant hamster cells exhibiting a pleiotropic effect on carbohydrate metabolism

Sixty-seven galactose negative (Gal minus) clones were established from survivors after treatment of Chinese hamster lung (V79) cells with 5-bromodeoxyuridine and black light. The mutational origin of these clonal isolates was inferred on the basis of the previously demonstrated mutagenic action of the combined treatment, persistence of the Gal minus phenotype in cell progeny in the absence of selection, conditional lethality of three isolates, interallelic complementation, and assignment of a homologous human gene to chromosome A2. In contrast to the parental cells, Gal minus mutants could not utilize exogenous galactose, mannose, fructose, galactose 1-phosphate, glucose 1-phosphate, or glucose 6-phosphate. Permeation of galactose into mutant cells appeared unimpaired. In intra- and interspecific cell hybrids, the mutation causing the Gal minus phenotype behaved like a recessive character. The pleiotropic nutritional response was due not to deficiency of any one specific enzyme in the Leloir pathway but to significant reduction in activities of phosphoglucomutase, NADP-dependent isocitrate dehydrogenase, and perhaps other enzymes. In temperature-sensitive Gal minus mutants grown at permissive temperature or in complementing intra- and interspecific cell hybrids, the activities of these enzymes were restored to normal levels, accompanied by a regained ability to use the particular hexoses or hexose monophosphates. We postulate that the change from Gal + to Gal minus phenotype in hamster cells could be due to mutations at a regulatory gene locus, or at a yet unknown locus with enzymic defect that causes secondary metabolic imbalances.

THE INTERACTION OF KNOBS AND B CHROMOSOMES OF MAIZE IN DETERMINING THE LEVEL OF RECOMBINATION

Enhancement of recombination by B chromosomes is influenced by the kind of heterochromatic knob present in or near the tested region of the A chramosomes. In homomorphic chromosome 9 bivalents of KS/KS constitution, double exchanges were increased at the expense of singles, but in the K*/Ks heteromorphs there was a gain in both single and double exchanges at the expense of no-exchange tetrads. Modification of the B chromosome enhancement in different knob compounds was observed only in the megasporocytes.—Different frequencies of recombination are found in plants with odd and even numbers of B Chromosomes; this effect is especially striking in the megasporocytes. The modification in recombination produced by an odd or even number of B chromosomes is a function of the interaction of a particular region and the knob constitution. Odd numbers of B chromosomes were more effective than even numbers in causing increased recombination.—It is concluded that heterochromatic knobs and the essentially heterochromatic supernumeraries may interact in the process of crossing over, with the level of recombination determined in part by knob constitution.

Chromosome assignment of the human gene for galactose-1-phosphate uridyltransferase

Somatic cell hybrids formed between galactose-negative mutant Chinese hamster cells and human lymphocytes were selected in galactose medium and analyzed for the concurrent presence of specific human chromosome(s) and human galactose-1-phosphate uridyltransferase. In one of the hybrid clones only a single human chromosome, A2, was consistently present when the hybrid cells were maintained in the selective medium, suggesting that the location of the structural gene for galactose-1-phosphate uridyltransferase is on this chromosome. Among subclones derived from this cell hybrid in the absence of selection, a complete concordance was demonstrated between the ability or inability to utilize galactose and the concomitant presence or absence of the human transferase and the A2 chromosome.

Influence of chronic neostigmine treatment on the number of acetylcholine receptors and the release of acetylcholine from the rat diaphragm

1. Rats were treated twice daily for 7 days with neostigmine and the diaphragm was isolated for study of its acetylcholine content, release upon nerve stimulation and the number of receptors in the end-plate.2. While the content of total acetylcholine was unchanged, the release of acetylcholine on stimulation with trains of 500 pulses at 100 Hz every 20 sec was reduced by about 50%. Five days after the end of neostigmine treatment the release of acetylcholine recovered to normal.3. The total number of acetylcholine receptors in the end-plate as measured from the binding of N, O-di[(3)H]acetyl alpha-bungarotoxin was reduced from 2.1 x 10(7) to 1.2 x 10(7) per end-plate.4. The above-mentioned changes are not due to acute pharmacological effects of neostigmine, nor to an immediate effect of cholinesterase inhibition but presumably due to chronic accumulation of acetylcholine at the neuromuscular junction.

N,O-di and N,N,O-tri ( 3 H) acetyl -bungarotoxins as specific labelling agents of cholinergic receptors

1. alpha-Bungarotoxin isolated from the venom of Bungarus multicinctus was acetylated with [(3)H] acetic anhydride and N-[(3)H] acetyl imidazole. Tri-N-acetyl and hexa-N-acetyl derivatives were obtained from the former, and N,O-di, N,N,O-tri and N,N,N,O-tetraacetyl derivatives from the latter reaction, respectively.2. There were parallel decreases in both neuromuscular blocking action in the phrenic nerve-diaphragm preparation of rats and depression of acetylcholine response of the rectus abdominis muscle of frogs with increased acetylation. Also, a parallel but greater decrease of toxicity in mice was found.3. N,O-Di and N,N,O-triacetyl toxins were localized mostly in the motor endplate region of the rat diaphragm, whereas a slight nonspecific binding along the whole muscle fibre in addition to the peak in the endplate region was observed with N,N,N,O-tetraacetyl and tri-N-acetyl toxins. In contrast, there was a marked nonspecific binding with hexa-N-acetyl toxin and no peak was observed at the endplate zone.4. The specific binding was saturable and irreversible. The number of toxin-receptive sites in one endplate was 1.9-2.2 x 10(7) for all of the labelled toxins irrespective of their potency.5. (+)-Tubocurarine protected effectively against the binding as well as the irreversible neuromuscular blocking effect of the toxins.6. Denervation of the rat diaphragm caused an increase of toxin-receptive sites beginning from the endplate zone at 1-2 days and then along the whole muscle fibre, reaching the maximum at about 18 days. The total receptive sites increased by about 30-fold.7. The significance of the findings is discussed and it is concluded that N,O-di and N,N,O-tri-[(3)H] acetyl alpha-bungarotoxins are specific and irreversible labelling agents for the cholinergic receptors of skeletal muscle.

Induction of auxotrophic mutations by treatment of Chinese hamster cells with 5-bromodeoxyuridine and black light

Treatment of an aneuploid Chinese hamster cell line (V79) in tissue culture with 5-bromodeoxyuridine and black light, with or without prior exposure of cells to another mutagen, led to the isolation of auxotrophic mutants, each of which exhibits a specific nutritional requirement for glycine, uridine, purine, or for a combination of glycine, hypoxanthine, and thymidine. 61 mutants that could not use exogenous galactose were also isolated. Thus, this treatment functions as an inductive, but not as a selective, procedure for mutations in mammalian cells.

Role of cardiotoxin and phospholipase A in the blockade of nerve conduction and depolarization of skeletal muscle induced by cobra venom

1. The effects of phospholipase A (PhA), cardiotoxin (CTX) and neurotoxin (cobrotoxin) isolated from Formosan cobra (Naja naja atra) venom on conduction of the rat phrenic nerve and membrane potential of the rat diaphragm were studied.2. Phospholipase A, lysolecithin and cobrotoxin were without effect on the axonal conduction. Cardiotoxin was the only active agent in cobra venom, but it was less potent than the crude venom.3. The blocking action of cardiotoxin was markedly accelerated by the simultaneous administration of phospholipase A. However, the minimum effective concentration of cardiotoxin (100 mug/ml), was not decreased by phospholipase A. Pretreatment of the nerve with phospholipase A, followed by washout, did not alter the activity of cardiotoxin.4. Cardiotoxin (3 mug/ml) completely depolarized the membrane of superficial muscle fibres within 60 min, being 3 times more potent than the crude venom. Phospholipase A, on the other hand, needed a dose 30 times higher and a prolonged period of incubation to induce depolarization of similar extent. Cobrotoxin was without effect on membrane potentials.5. CaCl(2) (10 mM) effectively antagonized the nerve blocking as well as the depolarizing effect of the crude venom, cardiotoxin or cardiotoxin plus phospholipase A. By contrast, the slow depolarizing effect of phospholipase A was enhanced by high concentrations of calcium.6. Cardiotoxic fractions of Indian cobra venom affected both nerve conduction and diaphragm membrane potential in exactly the same way as cardiotoxin. Toxin A of the same venom was without effect.7. It is concluded that the active agent in cobra venoms either on axonal conduction or on muscle membrane is cardiotoxin. The synergistic effect of phospholipase A on cardiotoxin appears to be due to acceleration rather than potentiation of its action. The mechanism of action of cardiotoxin and its synergism by phospholipase A are discussed.

Promotion of crown-gall tumor growth by lysopine, octopine, nopaline, and carnosine

The growth of crown-gall tumors on primary bean leaves (Phaseolus vulgaris L. cv. "Pinto") was promoted by the addition of d-lysopine, d-octopine, l-carnosine, or nopaline. Assayed on tumors induced by Agrobacterium tumefaciens strain B6, the relative activity was octopine = carnosine > lysopine >> nopaline; assayed on tumors induced by A. tumefaciens strain T-37, which induces tumors which form nopaline, the relative activity was nopaline = octopine = carnosine > lysopine. From one to three applications of carnosine or octopine gave equal additive increments in tumor growth, showing that a continual supply of these substances is required to maintain an increased rate of growth. At concentrations above 0.1 mm, pairs of these growth-promoting substances were less active than when applied singly. Inhibition of octopine-induced growth was obtained by applying 0.01 mm carnosine with 1 mm octopine and partial inhibition was obtained when carnosine was added 10 hr after octopine. Equimolar mixtures of lysopine, octopine, and carnosine, however, were at least as active in promoting tumor growth as any of the compounds added singly at equivalent concentrations. The activity of 0.1 to 0.5 mm lysopine, octopine, and carnosine was inhibited, respectively, by 1 mml-lysine, l-arginine, and l-histidine and this inhibition was limited in each case to the basic amino acid corresponding to that of the growth factor. Arginine fully inhibited octopine-induced tumor growth when applied as much as 6 hr after octopine, indicating that this inhibition was not due to prevention of octopine uptake. Although four separate substances were found which promoted tumor growth, the molecular specificity required for activity of each compound was high. Evidence is presented which suggests that a tumor growth-promoting substance extracted from tumorous leaves is a carnosine-like derivative of l-histidine.

Studies on the status of free amino and carboxyl groups in cobrotoxin

The status of free amino groups in cobrotoxin was studied by stepwise modification with trinitrobenzene sulfonate. Lys-27 was selectively modified without altering the activity of cobrotoxin. However, complete loss of activity was observed when Lys-27 and Lys-47 were trinitrophenylated, suggesting that the epsilon-amino group of Lys-47 is essential for the activity of cobrotoxin. The alpha-amino group of N-terminal leucine had no correlation with activity, demonstrated by the guanidination of the lysine residues with O-methylisourea followed by trinitrophenylation of the alpha-amino group. The carboxyl groups in cobrotoxin were modified with glycine methyl ester after activation with water-soluble carbodiimide. Six out of seven free carboxyls reacted in the absence of guanidine.HCl without altering the biological activity. When the remaining carboxyl was modified in the presence of 5 M guanidine.HCl, the resulting toxin was devoid of activity. This "buried" carboxyl is essential for activity and was identified as the gamma-carboxyl group of Glu-21.

Antagonism by propranolol of the inhibitory effect of phenoxybenzamine on noradrenaline uptake in vivo

The reduction of noradrenaline stores and [3H]noradrenaline concentration in the heart of mice and rats induced by phenoxybenzamine-treatment, alone or in combination with cold-stress, was prevented by propranolol. Propranolol also antagonized a similar effect induced by phentolamine but not that induced by other noradrenaline uptake inhibitors, such as desipramine, cocaine, guanethidine and reserpine. Analysis of the time-course of antagonism by propranolol indicates that it was evident only when the β-adrenoceptor blocking agent remained in the body. The inhibitory effect of phenoxybenzamine on noradrenaline stores reappeared when propranolol was excreted. Propranolol alone did not change cardiac noradrenaline stores or [3H]noradrenaline. It is concluded that the restoration of reflexly increased adrenergic discharge to normal, because of unmasking of spare α-adrenoceptors resulting from β-adrenoceptor blockade by propranolol rather than competition for binding at the active site of phenoxybenzamine, is responsible for the observed antagonism.