SOME EFFECTS OF MAMMALIAN THYROID STIMULATING HORMONE, ELASMOBRANCH PITUITARY GLAND EXTRACTS AND TEMPERATURE ON THYROIDAL ACTIVITY IN NEWLY HATCHED DOGFISH (SCYLIORHINUS CANICULUS)

Abstract

SUMMARY: 1. Groups of recently hatched dogfish (Scyliorhinus caniculus) were given a series of injections of mammalian thyroid stimulating hormone (TSH) at three dose levels, or of aqueous extracts of each of the three lobes of the adult elasmobranch pituitary gland. Control animals received injections of distilled water or extract of adult brain. The uptake of ¹³¹I by the thyroid was measured subsequent to the injections and the histology of the thyroid was studied. The experiments were conducted over a range of temperatures, thus producing data on the effect of temperature variation on thyroidal activity. 2. The uptake of ¹³¹I by the thyroid gland is very markedly enhanced by a high dose of mammalian TSH (1·00 i.u.) and is significantly increased by an intermediate dose (0·10 i.u. TSH). Enhancement by a very low dose (0·01 i.u. TSH) is doubtful, the observed increase in uptake of ¹³¹I being significant only at the 10% level. The highest dose also accelerated folliculogenesis and induced hyperplastic changes in the thyroid. 3. There were indications that the extract of the ventral lobe of the adult elasmobranch pituitary contains a thyroid-stimulating principle. 4. The rate of iodine metabolism increases directly with the temperature over the range 8·6–13·6° C.