REGIONAL DISTRIBUTION OF THYROID STIMULATING HORMONE 



ACTIVITY IN THE PITUITARY GLAND OF THE 



ATLANTIC STINGRAY, DASYATIS SABINA 



Rodney G. Jackson and Martin Sage' 



ABSTRACT 



The possibility that the elasmobranch pituitary contains thyroid stimulating hormone 

 (TSH) activity was investigated by measuring the increase in the release of thyroxine 

 from thyroid glands of the Atlantic stingray, Dasyatis sabina, incubated with homogenates 

 of various pituitary regions. The ventral lobe of the pars distalis contained most of 

 the TSH activity, with lesser amounts in the neurointermediate lobe. Histological tech- 

 niques were not sensitive enough to detect changes in the thyroid associated with the 

 increase in thyroxine release. It is concluded that the elasmobranch pituitary contains 

 TSH activity but its functional significance remains to be determined. 



Few studies have been conducted to examine 

 the functional relationship between the pituitary 

 and the thyroid gland of elasmobranchs. Dodd 

 and Goddard (unpublished but cited by Dent 

 and Dodd, 1961) hypophysectomized adult dog- 

 fish, Scyliorhinus caniculus, but found no his- 

 tological changes in the thyroid after 2 years, 

 whereas Vivien (1964) found that after decapi- 

 tation of Scyliorhimis embryos the thyroid failed 

 to complete its differentiation. The latter result 

 is, of course, open to several interpretations 

 since decapitation removes more than the pitu- 

 itary . Injection of homoplastic pituitary homo- 

 genates into Scyliorhinus resulted in histological 

 signs of stimulation of the thyroid gland (Vivien, 

 1941; Olivereau, 1954). Unfortunately, histo- 

 logical methods of assessing thyroid activity are 

 frequently both insensitive (Sage and Robins, 

 1970) and unreliable (Swift, 1960). 



Ferguson, Dodd, Hunter, and Dodd (unpub- 

 lished data summarized by Dodd et al. (1963)) 

 using the McKenzie mouse assay found thyroid 

 stimulating hormone (TSH) activity in all parts 

 of the S. caniculus pituitary, most of it being 



' The University of Texas, Marine Science Institute, 

 Port Aransas, TX 78373. 



Manuscript accepted May 1972. 



■"ISHERY BULLETIN: VOL. 71, NO. 1, 1973. 



in the ventral lobe. However, the highest ac- 

 tivity found was much less than that found in 

 the posterior lobe of the mouse pituitary, which 

 presumably does not contain TSH. Their re- 

 sults could be interpreted as suggesting that the 

 small amount of TSH activity found in the dog- 

 fish pituitary was of no significance. The inter- 

 pretation of assays of lower vertebrate TSH on 

 mammalian assay systems is further complicat- 

 ed by the probability of phylogenetic specificitj'' 

 of hormone action. It is known that teleost TSH 

 is relatively inactive on the mammalian thyroid 

 (Fontaine, 1969); similarly it is possible that 

 if there is an elasmobranch TSH it may have low 

 activity on mammalian tissues. In a recent re- 

 view Gorbman (1969) states that "definite proof 

 of a TSH-like principle in elasmobranch pitui- 

 taries remains to be provided." In an attempt 

 to elucidate this problem we investigated the 

 stimulatory eflFects of homogenates of the dif- 

 ferent regions of the pituitary of Dasyatis sabina 

 on thyroxine release from the animal's own thy- 

 roid gland in vitro. This technique eliminates 

 the problem of phylogenetic specificity, and, by 

 measuring thyroxine release, avoids the problems 

 of interpretation associated with histological 

 assessment of thyroid activity. 



93 



