Carbohydrates of the Surface of the Normal Human Spermatozoon

ABSTRACT: Autoproteolysis of human spermatozoa produces oligopeptides with oligosaccharide chains of the N-glycosidic-linked type that are released from the “surface exposed” parts of glycoproteins. The products eluted in the previous washing of the spermatozoa have the same composition and solubility characteristics as the oligopeptides from the digestion. This suggests that autoproteolysis is a constant process that normally occurs on the spermatozoa membrane. The cytochemical characterization and localization of the N-glycosidic-linked oligosaccharide receptors on the human spermatozoa membrane after digestion, in the presence or absence of seminal plasma, indicates that only part of the oligosaccharides are cleaved. Their distribution on the different zones of the spermatozoon changed as the probability of detecting these receptors in the intermediate segment increased after proteolysis; this indicates that in this zone the receptors are cryptic ones that become exposed by the action of the proteolytic enzymes. In the presence of seminal plasma most receptors on the acrosome are eliminated.     

INVERSE EXPRESSION OF mdr 1 AND c-myc GENES IN A RHABDOMYOSARCOMA CELL LINE RESISTANT TO ACTINOMYCIN D

Cytotoxic agents used in cancer therapy may induce differentiation in tumour cells with no proliferative potential. However, chemotherapy can also induce multidrug resistance, a formidable obstacle to the successful treatment of tumours. Both events were recently shown to occur in a rhabdomyosarcoma cell line (RD-DAC) resistant to actinomycin D, a drug of choice in the treatment of these tumours. To analyse this connection, cell line RD cultures were investigated with progressive concentrations of actinomycin D and it was shown that a minimum dose (1·2×10⁻⁶ mm) of the drug was necessary to increase mdr 1 mRNA in RD-DAC. The mechanism of mdr 1 overexpression was an increase in the number of copies of the mdr 1 gene, although the mRNA levels were not correlated with mdr 1 amplification. Drug resistance mediated by mdr 1 overexpression coincided with the development of myogenic differentiation in RD-DAC and with a decrease in c- myc mRNA levels, whereas levels of N- myc mRNA showed no modulation. These findings suggest that factors implicated in cell proliferation and differentiation, such as c- myc , may be responsible for the control of genes related to the development of multidrug resistance in rhabdomyosarcomas. Modulation of these factors may determine the sensitivity of rhabdomyosarcoma cells to drugs and may play an important role in triggering the differentiation programme found in these resistant rhabdomyosarcoma cells.     

Infected Myxomas:Report of a Case and Review of the Literature

Myxomas, the most common primary cardiac tumors, rarely become infected. This report describes a patient with a right atrial myxoma and a very unusual and life-threatening complication: infection with resultant bacteremia. The few cases reported in the literature are reviewed. The relevance of transesophageal echocardiography (TEE) in the diagnosis and assessment of atrial masses is emphasized.     

α-Adrenoceptor subtypes and Ca2+ mobilization the rabbit ear artery†

The mobilization of cellular and extracellular Ca²⁺ pools by selective α₁-adrenoceptor (phenylephrine) and α₂-adrenoceptor (xylazine) agonists as well as noradrenaline was evaluated in rabbit ear artery. Noradrenaline and phenylephrine possess full instrinsic activity for both types of Ca²⁺ mobilization whereas xylazine up to 1 mM had only a limited contractile effect, being more effective in inducing extracellular Ca²⁺-dependent response. However, extracellular Ca²⁺ was mobilized by xylazine in a concentration 20 times higher than that required to stimulate pre-junctional α₂-adrenoceptors. Noradrenaline (5 μM) and xylazine (1 mM) induced cellular and extracellular Ca²⁺-dependent contractions which were prazosin-sensitive and yohimbine-resistant. Xylazine-induced contractile activity, particularly that dependent upon the extracellular Ca²⁺ pool, was markedly reduced by selective adrenergic denervation with 6-hydroxydopamine, but the actions of noradrenaline were unaffected. These results suggest that: (1) rabbit ear artery contain post-junctional α¹-adrenoceptor but not α₂-adrenoceptors; (2) stimulation of these α₁-adrenoceptors can account for the overall contractile activity of exogenously added noradrenaline and (3) stimulation of α₁-adrenoceptors results in mobilization of cellular as well as extracellular Ca²⁺ pools.     

Suppression of a Demand Pacemaker in the Presence of Redundant Transvenous Right Ventricular Leads

A ventricular inhibited demand cardiac pacemaker was inhibited in the presence of intimate contact between the active temporary bipolar electrode ring and a retained inactive permanent bipolar electrode tip. Electromagnetic interference effects, lack of insulation, lead breaks, and loose connections were all ruled out as the cause of pacemaker suppression.