Identification of a protein-tyrosine phosphatase (SHP1) different from that associated with acid phosphatase in rat prostate.

Using [32P]poly(Glu,Tyr) as substrate, we have identified, for the first time, in the rat prostatic gland a protein-tyrosine phosphatase activity different from that associated with prostatic acid phosphatase. Concanavalin A-Sepharose 4B was used to separate the two protein-tyrosyl phosphatases activities. The activity retained by the lectin had characteristics of the prostatic acid phosphatase. It was sensitive to inhibition by PNPP and the optimum pH shifted towards physiological values when [32P]poly(Glu,Tyr) was used as substrate. However, the major protein-tyrosine phosphatase activity was not retained by the lectin, and corresponded, at least in part, to SHP1 as probed by the presence of the protein, its mRNA and the loss of PTPase activity after immunodepletion of SHP1. This enzyme is localized within the epithelial cells. Thus, the coexistence of two protein-tyrosine phosphatase activities in rat prostate, one associated with the acid phosphatase and the other related to SHP1, makes it necessary to analyze the importance of both activities in vivo and their possible function regarding prostatic cell growth and its regulation.

Somatostatin binding capacity, guanylate cyclase and tyrosine phosphatase activities during pancreatic proliferation in the rat induced by gastrectomy.

Gastrectomy increased pancreatic growth and this effect was associated with an increase in the number of somatostatin-14 (SS) receptors (146% of control) without altering their affinity. SS increased guanylate cyclase activity twofold in pancreatic acinar membranes from gastrectomized rats. The gastrectomy decreased pancreatic SS-like immunoreactivity (SS-LI) content (55% of control levels) and tyrosine phosphatase activity (74% of control levels). Administration of proglumide (20 mg/kg, IP), a gastrin/cholecystokinin (CCK) receptor antagonist, suppressed the inhibitory effect of gastrectomy on basal tyrosine phosphatase activity and SS-LI content, which returned to control levels. Furthermore, proglumide suppressed the increase of the number of SS receptors and of SS-stimulated guanylate cyclase activity induced by gastrectomy. All this suggests that pancreatic acinar cell growth is associated with upregulation of SS receptors, which could represent a mechanism promoted by the cell to negatively regulate the mitogenic activity of pancreatic growth factors such as CCK. In addition, the results also suggest that the negative regulation of tyrosine phosphatase activity may be important in the events involved in the pancreatic hyperplasia observed after gastrectomy.

Coronary arteries in transposition of the great arteries.

The topic of coronary arteries in transposition of the great arteries (TGA) is complex and confusing despite having been the subject of several recently published reports. One hundred thirty-three autopsy specimens of uncomplicated TGA were studied, with special attention to methodologic issues in anatomic description and classification. Uncomplicated TGA was defined as congenital anomaly involving origin of the aorta from the right ventricle and of the pulmonary artery from the left ventricle. Three types of transposition were recognized ("anterior aorta," "side-by-side," and "posterior aorta") depending on the aortopulmonary relations, which were intrinsically defined by the relation of the valvular orifices of the great arteries with respect to the atrioventricular orifices. The frequency of distribution of individual coronary patterns differs substantially in the first 2 types of TGA. As in normal hearts, coronary arteries in TGA tend to originate from the facing sinuses (adjacent to the pulmonary valve); in TGA, however, variations in further distal anatomy are much more frequent. It is suggested that individual coronary patterns be described in terms of number of ostia, exact ostial location within or outside the aortic sinuses, and proximal course and distribution. The use of strict, simplified classifications of coronary patterns is discouraging because of the relevance of each individual anatomic parameter to clinical aims. Because of the aortopulmonary switch repair for TGA, this study emphasizes the surgical implications of the different coronary features.

Somatostatin binding and modulation of adenylate cyclase in ovine retina membranes.

Somatostatin (SS) receptors in membranes from ovine retinas were examined using 125I-Tyr11-SS as a ligand. Receptor binding was rapid, specific, saturable, reversible and dependent on temperature and membrane concentration. Conditions of apparent equilibrium were obtained at 25 degrees C after a 45 min incubation in the presence of about 0.25 mg membrane protein/ml. Native SS competitively inhibited the binding of 125I-Tyr11-SS in the range of 0.01-10 nM, and half-maximal inhibition was observed at 0.2 nM SS. Scatchard analysis of these data suggested the existence of a single population of SS receptors with a dissociation constant of 0.23 +/- 0.03 nM and a maximum binding capacity of 84 +/- 6 fmol/mg protein. The binding of 125I-Tyr11-SS was inhibited by various synthetic SS analogs in a dose-dependent manner whereas peptides unrelated to SS did not show practically any effect even at concentrations as high as 10(-6) M. SS receptor occupancy appears to be coupled to inhibition of adenylate cyclase activity by a guanine nucleotide-binding regulatory protein, as suggested by the facts that: (a) SS noncompetitively inhibited the stimulatory effect of vasoactive intestinal peptide (VIP) (3 x 10(-7) M) on membrane adenylate cyclase activity but it did not alter basal enzyme activity; and (b) the addition of guanosine 5'-triphosphate (GTP) (10(-5) M) decreased the specific binding of 125I-Tyr11-SS to 26.6% of the control value due to a decrease in SS receptor affinity. The present results support the hypothesis that SS may contribute to the physiological regulation of the functions of the retina.

Selection of resistant mutants of Citrobacter freundii by second and third-generation cephalosporins and imipenem.

Using a single-step selection procedure, resistant mutants could be obtained from three clinical isolates of Citrobacter freundii with two second-generation and four third-generation cephalosporins but not with imipenem. All mutants showed a drastically increased beta-lactamase activity and were cross-resistant to all the cephalosporins examined. Combinations of cloxacillin with the cephalosporins were markedly synergistic, suggesting the principal role of the cephalosporinase in the resistance of these mutants.