JACKSON and SAGE: TSH IN AN ELASMOBRANCH 



RESULTS 



A preliminary study was carried out to deter- 

 mine responsiveness of the thyroid to homoge- 

 nates of the various regions of pituitary and to 

 control material. The results (Table 1) indi- 

 cated that the addition of large amounts of pro- 

 tein or protein hydrolysate resulted in a stim- 

 ulation of the gland, thus suggesting an inade- 

 quate culture medium. The medium was there- 

 fore modified by the addition of 0.5 mg lactal- 

 bumin hydrolysate/ml, and the response to var- 

 ious regions of the pituitary reexamined (Table 

 2). TSH activity was greatest in the ventral 

 lobe of the proximal pars distalis, but significant 

 activity was also found in the neurointermediate 

 lobe. The latter is not due to the presence of 

 thyroxine in this pituitary lobe since the thy- 

 roxine content of the homogenates was unde- 

 tectable. In this respect the elasmobranch is 

 unlike the mammal where the neural lobe does 

 concentrate thyroxine (see review by Pitt-Rivers 

 and Tata, 1959). 



Histological methods have previously been 

 used to assay the state of thyroid activity. In 



Table 1. — Percentage increase in release of thyroxine 

 from Dasyatis thyroid tissue produced by adding homo- 

 genates of various regions of the Dasystis pituitary or 

 lactalbumin hydrolysate to a medium containing salts, 

 urea, and glucose. 



* Significantly differs from zero, P<0.01. 



Table 2. — Percentage increase in the release of thy- 

 roxine from Dasyatis thyroid tissue produced by adding 

 homogenates of various regions of the Dasyatis pituitary 

 to a medium containing salts, urea, glucose plus lactal- 

 bumin hydrolysate. 



Item 



N 



Mean 



SE 



order to determine whether such techniques 

 would detect stimulation resulting from incuba- 

 tion of thyroids with whole pituitary homoge- 

 nates, interferometric measurements on the col- 

 loid were made together with a determination 

 of the percentage of the follicular area occupied 

 by epithelium. Neither technique was sensitive 

 enough to detect the stimulation observed by 

 measuring changes in the release of thyroxine 

 (Table 3). 



Table 3. — A comparison of the effectiveness of various 

 techniques for determining the response of Dasyatis thy- 

 roid glands to 3-day stimulation in vitro by homogenates 

 of whole Dasyatis pituitaries (1 pituitary/thyroid). 



Mean percentage 

 Item N of control 



values ± SE 



Increase in release of thyroxine 

 Increase in area of follicles occupied by 



epithelium 

 Decrease in interferometric measure of 



dry wt/unit area of colloid 



12 ♦51±16 



7 4.4 ±5.1 



12 63 ±38 



Significantly differs from zero, /'<0.01. 



DISCUSSION 



Significantly differs from zero, P-CO.OS. 

 Significantly differs from zero, /'<0.02. 



The present work confirms the unpublished 

 but frequently quoted work of Ferguson et al. 

 (Dodd et al., 1963) in that there is TSH activity 

 in the elasmobranch pituitary and that the great- 

 est concentration is found in the ventral lobe 

 where gonadotropic activity has also been found 

 (Dodd, Evennett, and Goddard, 1960) . The find- 

 ing of lesser amounts of TSH activity in the 

 neurointermediate lobe is in agreement with the 

 finding of Goddard and Dodd (unpublished but 

 quoted by Dodd et al, 1960). However, their 

 suggestion that the activity is due to a thyro- 

 tropin releasing factor cannot explain the pre- 

 sent results obtained in vitro with thyroid tis- 

 sue. The nature of the neurointermediate thy- 

 roid stimulating substance is unknown. Dodd 

 et al. (1963) reported that it is heat stable, 

 whereas the activity of the dogfish ventral lobe 

 is not. However, it is not possible to argue that 

 the activity in the neurointermediate lobe is non- 

 protein since all the activity present in the frog 

 {Rana tempor^aria) pituitary is heat stable and 

 some at least of this is presumed to be the protein 

 TSH. 



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