Schistosoma mansoni : biological and biochemical studies on adult worms in vitro
The maintenance of adult schistosomes in vitro is characterised by transient production of eggs, limited survival and a visible deterioration in worms during prolonged maintenance. Empirical, or trial and error attempts at improving media for the in vitro maintenance of adult S. mansoni have proved largely unsuccessful. The present study employed a more logical, biochemical approach to in vitro maintenance by quantifying the deleterious changes occurring in. vitro, in an attempt to identify the causes of the rapid cessation of egg production and the concomitant worm deterioration. C2) In Medium 199 supplemented with 10% newborn calf serum, adult mansoni produced a total of 400 eggs per pair during the first 10 days in vitro. Egg deposition was rarely observed beyond this period even though worms survived for up to 60 days. (3) There was a decrease in schistosome biomass during maintenance in vitro. Over 10 days the dry weight of males decreased by 30% while the dry weight of females fell to 50% of its level at isolation from the host. C4) During 5 days vitro the protein content of male schistosomes fell by 30%. There was a corresponding decrease in the protein content of females of 60%. The loss of schistosome gut contents in vitro would account for some but not all of this decline. (5) At least 50% of the glycogen of male S. mansoni was depleted during the first 6 h in vitro. Female glycogen content was less affected by vitro maintenance. The glycogen content of both male and female worms decreased during prolonged in vitro maintenance. The level of glycogen depletion during the initial 24 h in vitro was apparently unaffected by the glucose concentration in the incubation medium. (6) Studies of the uptake and incorporation of glucose, adenine, and the amino acids leucine and alanine from the incubation medium were used to examine the metabolic differences between worms incubated as pairs and worms incubated following separation. (7) Male S. mansoni were capable of fulfilling their biosynthetic amino acid and adenine requirements in copula through trans-integumental uptake whereas paired females were not. (8) Allowing for the obscuring of the tegumental surfaces in copula and for the loss of gut contents, the amino acid uptake and incorporation rates of male and female S. mansoni in vitro reflected the changing somatic requirements of the worms. (9) Amino acid uptake rate and the rate of incorporation of amino acids into schistosome protein were not related to reproductive activity in vitro. CIO) The rates of uptake and incorporation of adenine also reflected somatic rather than germinal requirements, and were not related to reproductive activity in vitro. (11) Adult paired S. mansoni removed the equivalent of twice their combined body dry weight of glucose from the medium during each day of the initial 3 days in vitro. (12) The rapid depletion of male glycogen in vitro appeared to be caused by a decrease in the rate of incorporation of glucose into glycogen by the male worms during the first hour jin vitro. A concomitant decrease was not observed in female schistosomes. (13) Increases in both the rate of uptake of glucose and the rate of its incorporation into glycogen were effected by increasing the glucose concentration in the medium and by the incubation of separated male and female worms. (14) It is proposed that the cessation of egg production and the observed decrease in worm biomass in vitro are due to the failure of adult schistosomes to feed on red blood cells in vitro and that the rates of uptake and incorporation of metabolic precursors in vitro merely reflect the decreasing worm biomass and have little significance to reproductive function in vitro.