Heart cyclic nucleotide responses to sustained aortic constriction in neonatal and adult rats.

The present studies examined adenosine and guanosine 3',5'-cyclic monophosphate (cAMP and cGMP) levels in left ventricular tissue of neonatal and adult rats subjected to 3-10 days of abdominal aortic constriction. Left ventricular cAMP levels were elevated after 3 days of pressure overloading in neonatal rats (2,274 +/- 430 pmol/g; mean +/- SE) compared with composite control values (1,280 +/- 124) obtained from sham-operated neonates, sham-operated adults, and aortic-constricted adult groups. cAMP levels declined progressively until, at 10 days after aortic constriction, values were lower (681 +/- 25 pmol/g) than control (1,621 +/- 107). Left ventricular cGMP level was higher in sham-operated neonatal (38 +/- 3 pmol/g) than in sham-operated adult rats (17 +/- 1) at 3 and 10 days postsurgery, but pressure overloading exerted no effect on cGMP measurements. Adenylate cyclase activity in left ventricular tissue homogenate was higher in 3-day sham-operated neonatal (58 +/- 3 pmol X mg protein-1 X min-1) compared with sham-operated adult (10 +/- 1) rats as the result of augmented nonmuscle cell activity. Elevated cAMP values in 3-day, pressure-overloaded neonates occurred despite lower adenylate cyclase activity (44 +/- 2), via degradative modulation (cAMP phosphodiesterase). Guanylate cyclase activity in left ventricular tissue was consistent with prevailing cGMP levels and was not influenced by aortic constriction. The present experiments show that neonatal cardiac enlargement is associated with biphasic alterations in cAMP level which are modulated, at least in part, via degradative reactions.

Serotypes and antibiotic susceptibilities of Pseudomonas aeruginosa isolates from single sputa of cystic fibrosis patients.

A phenotypic characterization of Pseudomonas aeruginosa from single sputum samples of 21 typical cystic fibrosis patients indicated a high frequency of heterogeneity among isolates on the basis of differences in antibiotic resistance, colony morphology, pigmentation, and serotype. Two or more isolates with different but stable susceptibilities to carbenicillin, gentamycin, streptomycin, tetracycline, chloramphenicol, and sulfamethoxazole plus trimethoprim were detected in 38% of the sputa. Differences generally were independent of the mucoid state of the strain. O-antigen group determination with the Difco typing set showed that two or more serologically distinct strains were present in 10/21 sputum specimens. Nonmucoid derivatives of mucoid isolates almost always retained both the antibiotic susceptibilities and serotype of their parent strain. These data suggest that cystic fibrosis patients may be cocolonized/coinfected by different strains of P. aeruginosa more frequently than generally believed. Alternatively, phenotypically distinct strains from a single patient might arise as phenotypic dissociants from a single infecting strain. Because of the frequency and multiplicity of phenotypically distinct P. aeruginosa isolates which we obtained from our cystic fibrosis patients, it is important to select multiple isolates from sputum cultures for antimicrobial susceptibility testing so as to assess adequately the susceptibility of this organism to antibiotic therapy in cystic fibrosis. We recommend that several colonies of each distinguishable colony type of P. aeruginosa be pooled for the antibiogram.