Effect of bromocriptine on prostacyclin release and cyclic nucleotides on rat aortic and uterine tissues

The effect of bromocriptine mesylate on cyclic nucleotides and PGI₂ release by rat aortic and uterine tissues was investigated. Treatment of rats with bromocriptine (10 mg kg⁻¹ I.P. daily for 14 days) increased PGI₂ release by the thoracic aorta from 0.67 ± 0.02 to 1.4 ± 0.03 ng/mg wet tissue (P < 0.001; n = 6). This increase was antagonized by treatment with sulpiride (15 mg kg⁻¹). Incubation of the arterial tissue with bromocriptive (50 ug ml⁻) in vitro also stimulated PGI₂ release. Mepacrine (160 μg ml⁻) significantly decreased both basal and stimulated PGI₂ release. Incubation of myometrial tissue from pregnant rats with bromocriptine (50 μg ml⁻¹) in vitro significantly decreased PGI₂ release from 1.25 ± 0.07 to 0.60 ± 0.08 ng/mg wet tissue (P < 0.05, n = 6).It also elevated uterine cAMP from 40 ± 2 to 64 ± 3 pmoles/100 mg wet tissue. Both effects were antagonized by sulpiride. Bromocriptine did not affect uterine cGMP or the cyclic nucleotides in the aorta. It is concluded that the increase in aortic PGI₂ was mediated via activation of dopamine D-2 receptors that stimulate phospholipase A₂ enzyme. The decrease in myometrial PGI₂ release may be related to the increase in uterine cAMP resulting from activation of dopamine D-1 receptors. Previous studies suggested a role for PGI₂ in implantation in the rat. The results suggest that the inhibitory effèct on uterine PGI₂ may underlie the reported inhibition of bromocriptine on implantation. On broad basis, the decrease in uterine PGI₂ together with the reported luteolytic effect of bromocriptine point to a potential role for the compound in postcoital contraception.     

Thiostrepton resistance mutations in the gene for 23S ribosomal RNA of halobacteria

Mutants of Halobacterium (H.) halobium and H. cutirubrum were isolated which are resistant to the 70S ribosome inhibitor thiostrepton. Using primer extension analysis, resistance was shown to correlate with base changes at position 1159, which corresponds to position 1067 of the E. coli 23S rRNA. In four mutants, A1159 was replaced by U, in one mutant by G. The results show that not only methylation (Cundliffe & Thompson (1979) Nature 278, 859-861) of A1067 (E. coli nomenclature), but also base changes at this position cause high-level resistance to thiostrepton.     

Modulation of ornithine decarboxylase activity in the normal and regenerating rat liver by different doses of hydra peptide morphogen

The authors studied the anabolic effect of peptide morphogen of the hydra undecapeptide on normal and regenerating rat liver. Ornithine decarboxylase (EC 4.1.1.17) activity served as a marker. Intraperitoneal injection of the peptide into intact animals stimulated ornithine decarboxylase activity in a dose-dependent manner. In partially hepatectomized rats the peptide stimulated ornithine decarboxylase activity in the dose of 20 micrograms/kg body weight while greater doses inhibited the enzyme activity.     

Application of halophilic nuclease H of Micrococcus varians subsp. halophilus to commercial production of flavoring agent 5'-GMP

RNA was degraded at 60 degrees C for 24 h by halophilic nuclease H in supernatants from broth cultures of Micrococcus varians subsp. halophilus containing 12% NaCl. Since contaminating 5'-nucleotidase exhibited almost no activity under these conditions, the 5'-GMP formed could be recovered from the reaction mixture, and the yield was 805 mg from 5 g of RNA.     

Spatially resolved cytosolic calcium response to angiotensin II and potassium in rat glomerulosa cells measured by digital imaging techniques

The response of cytosolic calcium [Ca2+]i to angiotensin II (AII) and potassium (K+) in individual rat glomerulosa cells was determined using the calcium-sensitive fluorescent dye, fura-2 and digital imaging. Control (4 mM K+) cytosolic calcium levels were generally in the 80-120 nM range and increased monotonically as [K+] was increased from 4 to 12 mM. There was no delay in the onset of the response. In most cells the [Ca2+]i decreased from its peak after 3-4 min, even in the presence of superfusate containing elevated K+. The time course of the change in [Ca2+]i in response to AII stimulation, on the other hand, was more variable. It was most often characterized by an early decrease followed by a large delayed increase. The response also was observed to decline during sustained AII stimulation. The majority of the cells showed some response to one or the other secretagogue with a sizeable minority (25%) having an increase in [Ca2+]i in excess of 200%. While the majority showed a response, the cell to cell variation was substantial. Finally, the pattern of cytosolic calcium increase sometimes showed a marked dependence on the secretagogue used, with different regions of the same cell being more strongly affected by one agent or the other. A few cells (10%) responded to AII only at one pole, establishing a large concentration gradient of calcium across the cell. Because of differences in time course, pattern, and degree of responsiveness, it is likely that the mechanisms underlying the Ca2+ elevation with K+ and AII are different.     

Structure of the spectrin-actin binding site of erythrocyte protein 4.1

The complete primary structure of the functional site of erythrocyte protein 4.1 involved in spectrin-actin associations has been determined. The sequence of this domain, which contains 67 amino acids and has a molecular mass of 8045 daltons, has been obtained by NH2-terminal sequence analysis of an 8-kDa chymotryptic peptide, three endoproteinase lysine C-cleaved peptides and two peptides obtained by Staphylococcus aureus protease V8 cleavage. All peptides including the 8-kDa domain peptide were purified by reverse-phase high performance liquid chromatography. Antibodies against two different synthetic peptides of the 8-kDa domain are able to inhibit the association between protein 4.1, spectrin, and F-actin, corroborating that the 8-kDa domain is responsible for the formation of a ternary complex. A computer search of the 8-kDa sequence with the National Biomedical Research Foundation database did not detect any significant homologies to known sequences. Protein 4.1 is not related to any known proteins and may represent a new protein superfamily.