Search

SUMMARY Hypophysectomized red-spotted newts [Notophthalmus (Triturus, Diemictylus) viridescens viridescens Rafinesque] received autoplastic, homoplastic or xenoplastic grafts of pituitary glands beneath the lower jaw. Autografted animals, in accord with previous observations, survived indefinitely. Homografted animals had a mean survival time several times longer than either that of unimplanted, hypophysectomized animals or that of homografts of skin. No difference between rates of iodine turnover was found between thyroid glands of animals with homografts and animals with autografts but in both groups the rates of iodine turnover were lower than in intact controls. Great variation was found among the mean survival times of animals with xenografts. Newts with pituitary grafts from the frog, Rana pipiens, survived about as long as unimplanted hypophysectomized animals. Pituitary grafts from the salamander, Desmognathus monticola, apparently gave rise to some toxic reaction since their host newts died within short periods of time, yet newts with grafts from the mudpuppy, Necturus maculosus, lived longer than hypophysectomized control animals and some newts grafted with glands from a west coast newt, Taricha torosa, lived indefinitely.

A LTHOUGH the coagulation of blood has been widely studied in avian and mammalian subjects, relatively little attention has been directed toward the phenomenon as it appears in the lower vertebrates. The Amphibia, however, have not been entirely neglected. The various investigations of Tait and his collaborators (cf. Tait and Green, 1926), as well as those of a few earlier workers cited by them, have brought forth certain information concerning the coagulation of blood in the frog. All amphibian blood thus far described has been found to contain delicate structures

Several neurotransmitters and hormones with potential to trigger a simultaneous contraction of the oviducts and the spermathecal myoepithelium were examined. Saline (0.05 ml), or 0.05 ml saline plus acetylcholine (9 mg), norepinephrine (50 micrograms), arginine-vasotocin (25 units), prostaglandin F2 alpha (3 micrograms) were injected into the spermathecal region of female newts (n = 24 per group). The numbers of sperm present in the cloacae of prostaglandin-injected animals (107 +/- 30 SEM) were significantly greater than the numbers detected in saline (27 +/- 5 SEM) and in uninjected (14 +/- 3 SEM) controls. Smaller and less consistent increases in the numbers of sperm were detected in the vasotocin- and norepinephrine-injected groups. Study of sections from ovulating female newts failed to produce evidence that pressure from the passage of ova through the posterior portion of the oviduct forced sperm from the spermatheca. Observations indicate an active role for the spermathecal myoepithelium in the discharge of stored sperm and of a role for prostaglandin F2 alpha in triggering that discharge.

Thyroidal function in the red-spotted newt was assessed both in 125 I tracer studies and in the measurement of glandular and circulating thyroxine (T 4 ) and triiodothyronine (T 3 ) by radioimmunoassay (RIA). Thyroidal uptake of 125 I was low, being 0.6% at 2 days and 3.6% at 14 days following injection of the tracer. A significant fraction of the injected dose continued to circulate as inorganic iodide at 7 and 14 days following injection, indicating a low rate of renal clearance for iodine. [ 125 I]T 4 represented only 6.2% of thyroidal 125 I at 2 days post-injection, but this figure had increased to 14% by 14 days, suggesting a slow but significant synthesis of hormone. By RIA the T 4 content in thyroids of animals freshly collected in the field was 3.42 ± 0.16 ug/mg protein, a level comparable to that found in beef thyroids. In contrast T 3 stores in the thyroid of the newt were only 9.1 ± 1.2 ng/mg protein. Although no [ 125 I]T 4 was detected in the serum of animals for as long as 21 days after injection, circulating thyroid hormones were detected by RIA at levels of 3.0 ± 0.3 ng T4hn1 and 0.28–0.72 ng T 3 /ml in freshly collected animals. The data suggest that T 4 in the serum may arise mainly from peripheral deiodination of T 4 . Large amounts of an iodoprotein with electrophoretic properties of thyroglobulin were found in the serum of newts. This protein contained 5% of the serum 125 I at 2 days postinjection and accounted for 30% of the serum radioactivity at 14 days. In captive newts, serum T 4 levels were three times greater and glandular T 4 levels approximately two times lower than those of freshly collected animals, suggesting that the newt thyroid responds to the stresses of captivity by accelerated release of thyroid hormone.

ALTHOUGH the thyroid gland is of extreme importance in the metamorphosis of amphibians, its function in cold blooded vertebrates in general is still obscure1. Several workers have suggested that thyroid hormones enable poikilotherms to withstand changes in environmental temperature. For example, Evropeitzeva2 reported that larvae of Coregonus lavaretus ludoga withstood exposure to 29° C for 5 min after treatment with 0.033 per cent thiourea, whereas untreated animals died. Suhrmann3 found that immersion in a solution of thiourea increases the upper lethal temperature in the goldfish, Carassius auratus. Dent and Lynn4 also indicated that the thyroid may play a part in tolerance to changes in temperature. But the most striking report in this field comes from the work of Fortune5,6, who has reported that in the minnow, Phoxinus phoxinus L., the thermal death point is raised some 10° C by treatment with thiourea. She states: “Phoxinus already treated with thiourea for 3 days, were subjected to a rise in temperature of 10° C (that is, to 33° C) over 2 days. They survived indefinitely at this temperature and appeared normal, the controls dying under such conditions between 23° C and 24° C”. On the other hand, La Roche and Leblond7 state that the ability of salmon parr to withstand rising temperatures is impaired by radiological thyroidectomy and is restored by the administration of thyroid powder.

The cytology of pigment-bearing cells is followed in the integument of the red-spotted newt, Notophthalmus viridescens viridescens Rafinesque, with observations beginning in the late embryo and continuing through to the adult. Dermal melanophores appear in late tailbud stages, and dermal xanthophores differentiate prior to hatching. In young larvae, both become widely and evenly distributed in the dorsal skin, but in older larvae a pattern develops so that melanophores are absent from certain circumscribed lateral regions designated as melanophore voids. Iridophores differentiate and accumulate among the xanthophores which have remained in the voids. Those xanthophores then are transformed into proerythrophores; that is, their form is altered from stellate to punctate, their nuclei change from fusiform to ovoid, and their pterinosomes are largely replaced by lipid droplets. In some of the voids, the proerythrophores migrate into the epidermis to become the erythrophores of the red spots. The remaining voids cease to exist when their proerythrophores disappear and are replaced by dermal melanophores. At the same time, some dermal melanophores accumulate to form dorsal black spots, and a morphologically different type of melanophore differentiates within the epidermis. In the interspot regions of the eft, xanthophores hypertrophy and pack the dermis, giving an orange color to the skin. In the interspot regions of the adult newt, xanthophores with fewer organelles produce a yellow color on the ventral surface, and, in combination with melanophores and iridophores, produce a greenish color in the dorsum.