THE EFFECT OF L-THYROXINE ON THE ANEMIA RESPONSE IN TRYPANOSOMA-CONGOLENSE INFECTED-RABBITS

The development of anaemia is a major pathological manifestation in ch ronic trypanosomosis. The anaemia in African trypanosomosis coincides with a marked decrease in plasma concentration of both thyroxine (T4) and 3,5,3' triiodothyronine (T3). To evaluate the effect of trypanosom e-induced hypothyroidism on the development of anaemia, sexually matur e white New Zealand rabbits were used. Three groups were set up, each of ten rabbits: one group was infected with Trypanosoma congolense; th e second group was infected but given replacement doses of thyroxine ( treated); the third group was not infected. Small volumes of blood wer e collected for the determination of parasitaemia and packed cell volu me (PCV). The concentrations of T3 and T4 were measured in plasma by r adioimmunoassay. The decrease in PCV correlated closely (y = -0.38x 15.2; r = 0.82, P = 0.001) with the intensity and duration of parasita emia. The critical PCV value was 0.15 11-1 with a peak parasitaemia of approximately 5 x 10(6) trypanosomes ml-1 of blood. There was a signi ficant correlation between the plasma T3 and PCV (y = 0.049x + 0.57; r = 0.66, P = 0.020). There was also a good positive correlation betwee n T4 and PCV (y = 14.5 + 3.03; r = 0.95, P < 0.001) in the infected un treated group. The PCV levels were significantly different among the t hree groups of animals (P < 0.05). The infected-treated animals sustai ned longer periods of infection than the infected and untreated ones. The sustained physiological level of bioactive thyroid hormones T3 and T4 significantly arrested the decline in PCV as the disease progresse d. The hormonal treatment thus enhanced the survival of the animals in fected with Trypanosoma congolense.