Given an abstract, generate a keyword (a noun phrase) that best describes the focus or contribution of the paper. Such keywords can be directly from the given abstract or outside it.

[EX Q]: Abstract: Sequential development of Leishmania braziliensis promastigotes from a noninfective to an infective stage was demonstrated. The generation of infective forms was related to their growth cycle and restricted to stationary stage organisms. Using immunofluorescence techniques, we have noticed that the binding of a monoclonal antibody (mAb) against L. braziliensis (VD5/25) increased progressively as the promastigotes developed in culture and was maximal with the infective forms. This antigenic differentiation was not detected with an anti-L. braziliensis polyclonal rabbit antiserum, suggesting that only a few epitopes, including that recognized by VD5/25, have their expression effectively increased on the surface of infective promastigotes. Immunoprecipitation of lysates of surface-iodinated L. braziliensis promastigotes with this mAb revealed two proteins of apparent 65,000 and 50,000 Mr, the 50,000 Mr protein probably representing the unreduced form of the major surface glycoprotein described in several species of Leishmania (GP65). The increasing expression of this epitope was not found with L. chagasi promastigotes, but seems to occur with the parasites from the L. mexicana complex. Intracellular survival of L. braziliensis was completely inhibited when the infective promastigotes were treated with VD5/25. It appears, therefore, that the increasing expression of GP65 on the promastigote surface represents an essential mechanism of leishmania survival in the macrophage.
[EX A]: Animal

[EX Q]: Abstract: The influence of serotonin (5-hydroxytryptamine) on human detrusor and on pig detrusor, trigone, bladder neck and urethral smooth muscle was explored in a series of in vitro experiments. Serotonin evoked a dose-dependent and reversible contraction of the detrusor. The reverse response was triggered in trigone, bladder neck and urethral smooth muscle--a dose-dependent and reversible relaxation. The maximum amplitude of this relaxation was 85 +/- 15% of the relaxation produced by electrical nerve stimulation. The effect of serotonin was unaltered by blockade of ganglia, alpha- and beta-adrenergic receptors, cholinergic receptors and prostaglandin synthesis. The serotonin antagonists ketanserin, methysergide and cyproheptadine partly inhibited the effect of serotonin. The antagonism differed in potency on strips of different origin. The antagonists were ineffective or minimally effective in blocking responses to nerve stimulation. The effect of serotonin was probably mediated by specific serotonin receptors different from the serotonin-S2-receptors predominating in vascular smooth muscle. Serotonin is a potential neurotransmitter in lower urinary tract smooth muscle, but its importance in micturition physiology and pathophysiology is unknown.
[EX A]: Animal

[EX Q]: Abstract: The influence of the peptide chain length of partial enzymic hydrolysates of protein on nitrogen and amino acid absorption was studied in 12 subjects using a jejunal perfusion technique. Three hydrolysates of egg white and an equivalent amino acid mixture were perfused at 30 mmol/L and 100 mmol/L in two separate experiments. Two hydrolysates (OH1 and OH2) contained mainly dipeptides and tripeptides, whereas the third (OH3) comprised tripeptide to pentapeptides as judged chromatographically. Nitrogen absorption was significantly slower from the higher chain length mixture, OH3, than from the short chain mixtures, OH1 and OH2, at both concentrations. Similarly, several amino acid residues were absorbed less well from OH3 than from OH1 and OH2. These data demonstrate that the chain length of heterogeneous mixtures of peptides affects absorption of nitrogen and individual amino acid residues, and suggest that brush border hydrolysis of tetrapeptides and pentapeptides limits absorption from enzymic hydrolysates of protein which simulate the composition of the postprandial luminal contents.
[EX A]:
Amino Acids