246 METABOLIC HORMONES 



its presence can then be detected by its secretion of the melano- 

 phore concentrating hormone (§ 3.223), and the increase in blood 

 calcium. Moreover, in completely hypophysectomized toads 

 injection of mammalian ''Antuitrin" (containing TSH, among 

 other hormones) from the anterior lobe causes a rise in blood 

 calcium, while injection of "Pituitrin" from the posterior lobe 

 causes a decrease (Table 29). There appears to be no exact parallel 

 for the latter effect in other vertebrates; but dilution of calcium 

 ions in the blood, as a result of the action of an antidiuretic fraction 

 in the Pituitrin, causing increased water retention (§ 5.32), does 

 not seem to have been considered. 



AvES. Diffusible serum calcium in some birds has been found to 

 rise to double its normal value just before ovulation, and to fall 

 again afterwards. The calcium is thus made available for eggshell 

 formation, and its release into the blood is believed to be due to 

 secretion of hormone from the parathyroid glands, which show 

 correlated histological signs of secretory activity but have not been 

 fully tested physiologically. Parathyroidectomy resulted in lowered 

 Ca in the blood and premature laying of eggs with less Ca in the 

 shell. This was only achieved if the birds did not die from the 

 lowering of Ca in the blood, which normally stimulates parat- 

 hormone secretion (Polin and Sturkie, 1957). As in the fish, dark- 

 ness also stimulates parathyroid activity; but its damaging effect 

 on the skeleton can be ameliorated by treatment with either 

 vitamin D or ultra-violet light. 



Mammalia. ''The most striking and conspicuous result of the 

 subcutaneous injection of a potent parathyroid extract in a 

 normal dog is the rise in the serum calcium. The amount of this rise 

 is in general proportional to the dose, except that rises above 18 

 mg per cent are seldom observed ; the rise attains its maximum in 

 12 to 18 hours." 



"Extirpation of the parathyroid glands of the dog leads usually 

 within 2 or 3 days to characteristic . . . tetany. There is a 

 prompt and rapid fall in the concentration of calcium in the 

 serum . . . [and] death finally results from exhaustion or from 

 asphyxia due to respiratory spasm" (Thomson and Collip, 1932; 

 Fig. 5-27). This effect can be reversed in the early stages by 

 injecting parathormone. After parathyroidectomy, the bodies of 



