A pilot study evaluating ceftriaxone and penicillin G as treatment agents for neurosyphilis in human immunodeficiency virus-infected individuals.

To compare intravenous (iv) ceftriaxone and penicillin G as therapy for neurosyphilis, blood and CSF were collected before and 14-26 weeks after therapy from 30 subjects infected with human immunodeficiency virus (HIV)-1 who had (1) rapid plasma reagin (RPR) test titers >/=1&rcolon;16, (2) reactive serum treponemal tests, and (3) either reactive CSF-Venereal Disease Research Laboratory (VDRL) tests or CSF abnormalities: (a) CSF WBC values >/=20/microL or (b) CSF protein values >/=50 mg/dL. At baseline, more ceftriaxone recipients had skin symptoms and signs (6 [43%] of 14 vs. 1 [6%] of 16; P=.03), and more penicillin recipients had a history of neurosyphilis (7 [44%] of 16 vs. 1 [7%] of 14; P=.04). There was no difference in the proportion of subjects in each group whose CSF measures improved. Significantly more ceftriaxone recipients had a decline in serum RPR titers (8 [80%] of 10 vs. 2 [13%] of 15; P=. 003), even after controlling for baseline RPR titer, skin symptoms and signs, or prior neurosyphilis were controlled for. Differences in the 2 groups limit comparisons between them. However, iv ceftriaxone may be an alternative to penicillin for treatment of HIV-infected patients with neurosyphilis and concomitant early syphilis.

Monoclonal antibodies prepared against Dictyostelium actin: characterization and interactions with actin.

Three mouse monoclonal antibodies, Act I, Act II, and Act IV, against actin from the cellular slime mold Dictyostelium discoideum, have been made and characterized. All three antibodies are IgG1 and share the following properties: They form stable complexes with monomeric Dictyostelium actin, which prevents polymerization of the actin into filaments. On addition to preformed actin filaments, they cause a reduction in filament size and in the viscosity of the actin solution. They cross-react strongly with actins from the lower eucaryotes Physarum and Acanthamoeba, but not with alpha-actins from rabbit and human muscle or beta- and gamma-actins from human erythrocytes and a human B lymphoid cell line. Act II and Act IV recognize a similar antigenic determinant that is topographically distinct from that identified by Act I. In protein immunoblotting, only Act I bound strongly to Dictyostelium actin. Analysis of actin fragments with this technique showed that amino acids 13 to about 50 are required for Act I binding to actin. A comparison of the amino acid sequences of actins from lower eucaryotes and higher vertebrates implicates threonine 41 as a critical residue in the Act I antigenic site. The properties of Act II and Act IV suggest that they recognize antigenic sites involving the NH2-terminal six residues.

Actin and myosin: control of filament assembly.

Actin filaments, assembled from highly purified actin from either skeletal muscle or Dictyostelium amoebae, are very stable under physiological ionic conditions. A small and limited amount of exchange of actin filament subunits for unpolymerized actin or subunits in other filaments has been measured by three techniques: fluorescence energy transfer, incorporation of 35S-labelled actin monomers into unlabelled actin filaments, and exchange of [14C]ATP with filament-bound ADP. A 40 kDa protein purified from amoebae destabilizes these otherwise stable filaments in a Ca2+-dependent manner. Myosin purified from Dictyostelium amoebae is phosphorylated both in the tail region of the heavy chain and in one of the light chains. Phosphorylation appears to regulate myosin thick-filament formation.

Actin filaments undergo limited subunit exchange in physiological salt conditions.

The exchange of actin filament subunits for unpolymerized actin or for subunits in other filaments has been quantitated by three experimental techniques: fluorescence energy transfer, incorporation of 35S-labeled actin monomers into unlabeled actin filaments, and exchange of [14C]ATP with filament-bound ADP. In the fluorescence energy transfer experiments, actin labeled with 5-(iodoacetamidoethyl)aminonaphthalene-1-sulfonic acid (IAENS) served as the fluorescent energy donor, and actin labeled with either fluorescein-5-isothiocyanate (FITC) or fluorescein-5-maleimide (FM) served as the energy acceptor. Fluorescent-labeled actins from Dictyostelium amoebae and rabbit skeletal muscle were very similar to their unlabeled counterparts with respect to critical actin concentration for filament assembly, assembly rate, ATP hydrolysis upon assembly, and steady-state ATPase. As evidenced by two different types of fluorescence energy transfer experiments, less than 5% of the actin filament subunits exchanged under a variety of buffer conditions at actin concentrations greater than 0.5 mg/ml. At all actin concentrations limited exchange to a plateau level occurred with a half-time of about 20 min. Nearly identical results were obtained when exchange was quantitated by incorporation of 35S-labeled Dictyostelium actin monomers into unlabeled muscle actin or Dictyostelium actin filaments. Furthermore, the proportion of filament-bound ADP which exchanged with [14C]-ATP was nearly the same as actin subunit exchange measured by fluorescence energy transfer and 35S-labeled actin incorporation. These experiments demonstrate that under approximately physiologic ionic conditions only a small percentage of subunits in highly purified skeletal muscle or Dictyostelium F-actin participate in exchange.

ATP-driven steady-state exchange of monomeric and filamentous actin from Dictyostelium discoideum.

When [35S]actin monomer from the slime mold Dictyostelium discoideum is added in trace amounts to a population of unlabeled Dictyostelium actin molecules assembled to steady state, it rapidly exchanges with the pool of actin filaments. This exchange between monomeric and filamentous actin is dependent on the presence of ATP. In addition, the exchange appears to occur via filament ends, because cytochalasin D, a drug that interacts specifically with actin filament ends to inhibit filament assenbly, inhibits the exchange reaction.

On the question of body fluid volume or sodium status influencing renin release.

1. The extent to which renin release is affected by simultaneous changes in body Na and body fluid volume was studied in six sheep. 2. The animals' water intake was restricted for 10-17 days after which they were offered solutions containing varying amounts of NaCl. 3. Plasma renin concentration (PRC) of water restricted sheep was 2-3 times normal. 4. The changes in PRC following drinking were inversely related to the amount of sodium consumed, Na excretion and plasma Na concentration. There was no correlation between the changes of PRC and of plasma volume in so far as the latter is reflected by alterations in plasma protein concentration. 5. We conclude that changes in renin release were related to the animals' handling of NA, and not to alterations in body fluid volume. 6. These findings are compatible with the proposition that renin release was mediated by a macula densa mechanism.

Renal responses of Australian lungfish to vasotocin, angiotensin II, and NaCl infusion.

The Australian lungfish (Neoceratodus forsteri) responds to intravenous injections of 0.63 ng/kg or more of arginine vasotocin with increased dorsal aortic blood pressure, inulin clearance, urine flow, and tubular rejection of Na+. Single injections of 1 ng/kg or more of angiotensin II or norepinephrine also increase dorsal aortic pressure but do not cause consistent diuresis and natriuresis, Continuous infusions of angiotensin II or repeated injections of norepinephrine produce sustained hypertension and more modest diuresis and natriuresis than are seen after injections of arginine vasotocin that cause less hypertension. Infusions of isosmolar or hyposmolar NaCl solutions increase blood pressure, inulin clearance, urine flow, and tubular Na+ rejection in a manner resembling the response to argininge vasotocoin injections. These data are consistent with the hypothesis that arginine vasotocin is released in response to volume expansion in lungfishes and that it may act on the kidney as a diuretic and natriuretic hormone. They do not rule out a more direct action of expansion on renal functions.

Renin responses to water restriction and rehydration.

1. The effect of restricted water intake and rapid rehydration was studied in three conscious sheep with respect to plasma renin concentration (PRC), blood corticosteroid levels, plasma protein and electrolyte concentrations, and the renal and faecal excretion of sodium and potassium.2. During water restriction the plasma concentrations of renin, protein and sodium rose while aldosterone levels were low or undetectable. Plasma potassium levels were unchanged. External sodium and potassium balance appeared to be unaffected.3. During rehydration the sheep drank more than their estimated water deficit in 3-4 min with the following effects: PRC rose three- to fourfold during the ensuing 12 hr. Aldosterone levels too rose, while plasma protein, sodium and potassium concentrations fell. Urinary sodium excretion virtually ceased for 24 hr, and urine flow rate increased only little during this period.4. If there was a single stimulus to renin release during water restriction and rehydration, it was not an alteration in vascular or extravascular volume, total body sodium, systemic B.P. or plasma sodium concentration.5. It is concluded that the rise in PRC in these experiments is compatible with the theory that altered sodium transport at the macula densa was the stimulus for renin release.