Effect of thyroidectomy, i-thyroxine and temperature on hemopoiesis in the chequered water snake, Natrix piscator

Proliferative thyroid lesions in three diplodactylid geckos: Nephrurus amyae, Nephrurus levis, and Oedura marmorata

Over a 5-mo period, three diplodactylid geckos housed at the National Aquarium were diagnosed with proliferative thyroid lesions: a rough knob-tail gecko (Nephrurus amyae), a smooth knob-tail gecko (Nephrurus levis), and a marbled velvet gecko (Oedura marmorata). Clinical signs included an intraoral mass or ventral throat swelling (or both), oral bleeding, and weight loss. Both of the knob-tail geckos died. The histologic diagnosis for the rough knob-tail gecko was thyroid carcinoma with metastases to the liver and lungs, and thyroid carcinoma with no metastases was reported in the smooth knob-tail gecko. A thyroidectomy was performed on the marbled velvet gecko with a histologic diagnosis of adenomatous hyperplasia. Postoperative weight loss and bradycardia resolved following oral supplementation with levothyroxine. The animal is in normal health 10 mo post-surgery. Five other diplodactylid geckos in the collection remain unaffected, giving a 38% prevalence of proliferative thyroid lesions (3/8). The etiology remains undetermined. This is the first report of a cluster of proliferative thyroid lesions in geckos.

Circadian time dependence of erythropoietic and respiratory responses of Indian garden lizard, Calotes versicolor, to mammalian urinary erythropoietin and thyroxine

The circadian stage-dependent effects of mammalian urinary erythropoietin (Ep) and thyroxine (T4) on tissue energy metabolism (in vivo and in vitro) and erythropoiesis were examined in the Indian garden lizard. Both T4 and Ep increased erythropoiesis and also affected hepatic and muscle energy metabolism. Although both treatments increased circulating RBC count, irrespective of the timing of the treatment, the maximum erythropoietic stimulation was achieved only in the late photophase (9 hr after light onset, HALO). Hepatic oxygen uptake was significantly elevated at 3 and 9 HALO following in vivo Ep administration and 3, 9, and 15 HALO following in vivo T4 injection. In contrast, in vitro addition of either Ep or T4 to hepatic homogenates of untreated lizards significantly elevated respiratory rate, irrespective of the time of tissue collection. The rate of muscle tissue respiration was statistically elevated when Ep was administered in vivo at 9 and 15 HALO. The oxygen uptake was stimulated by T4 only at 15 HALO. While in vitro addition of Ep to tissue homogenates significantly depressed the respiratory rate of muscle collected at 3 HALO, addition of T4 stimulated oxygen uptake by the muscle tissue collected at 9 and 15 HALO. It is concluded that the effectiveness of Ep or T4 largely depends upon the phase of the organism's circadian system(s).

Nuclear receptors for L-triiodothyronine in trout erythrocytes

We have developed an in vitro assay to evaluate saturable specific binding of triiodothyronine (T3) by erythrocyte (RBC) nuclei isolated from rainbow trout. Our results indicate that the nuclei contain a T3-saturable protein which binds T3 with temperature, and pH dependency, high T3 affinity (Ka = 1.6 X 10(9) M-1), and relative thyroid hormone (TH) analog affinities (TRIAC greater than T3 greater than T4 greater than rT3 greater than T2) which are characteristic of TH receptors in other vertebrates. Our estimate of the maximal T3 binding capacity (MBC) of nuclei isolated from heterogeneous populations of RBCs at different maturational stages (MBC = 3.6 fM/mg DNA; 13 sites/nucleus) was 10-100 times lower than would be expected of a TH-responsive tissue. Differential cell counts revealed that 1% of the RBCs in our trout were immature (pro-RBCs). Pro-RBCs, in contrast to mature RBCs, contain abundant heterochromatin, mitochondria, and polyribosomes, and synthesize hemoglobin. Evaluation of binding data for RBC nuclei taken from trout in which erythropoiesis was stimulated by prior bleeding indicated that MBC was directly proportional to the absolute number of pro-RBC nuclei in the incubation. Our maximum estimate of MBC for pro-RBC nuclei (458 fmol/mg DNA; 1781 sites/nucleus) falls within the range of MBC values reported for other vertebrate TH-responsive tissues. These data indicate that RBCs of rainbow trout contain a nuclear protein (putative receptor) which binds T3 with characteristics similar to the TH receptor of higher vertebrates, and that nuclear T3 binding may be diminished during RBC maturation.

Erythropoietin, testosterone, and thyroxine in the erythropoietic response of the snake, Xenochrophis piscator

The erythropoietic response of snakes was examined after injecting human urinary erythropoietin (Ep), testosterone propionate (TP), and L-thyroxine (T4), separately and in combinations, into starved ophids. The effect of starvation was reflected by a decrease in the number of erythrocytes, a fall in hemoglobin concentration, and a decline in hematocrit. Statistically significant elevation of erythrocyte number, hemoglobin concentration, and hematocrit was observed at 24 hr following the administration of Ep + T4, and Ep + TP + T4 into starved ophids. The erythrocyte number was also increased by T4 treatment at 24 hr. Furthermore, while T4 and Ep individually increased the red blood cell number at 168 hr, T4, TP + T4, and Ep + TP + T4 elevated the hemoglobin concentration and Ep + T4 and Ep + TP + T4 increased the hematocrit value. It is suggested that the influence of any one of the hormones utilized in the present study on blood morphology of fasted snakes depends to a greater extent on the presence or absence of the other hormone(s).

Thyroid and skin-shedding in the rat snake (Ptyas korros)

Epidermal-thyroid relationships were studied in thyroidectomized (Tx) Ptyas korros kept at 23 degrees C by observing changes in shedding frequency (SF), body weight, oxygen consumption rate (OCR), and postsurgical survival. Tx animals showed increased SFs but lost weight and eventually died, as did Tx animals receiving 3-mono-iodotyrosine injections. However, injections of 3, 5-diiodothyronine inhibited shedding and the animals survived longer. OCRs were similar in all control and experimental groups. It is concluded that among thyroid secretions, only iodothyronines inhibit shedding. Snake shedding is concluded not to reflect general metabolic status as it does in lizards.