228 METABOLIC HORMONES 



normally show a maximal urine flow, comparable to that of rats 

 with "diabetes insipidus", which follows inactivation, or removal, 

 of the neurohypophysis and therefore of the store of the anti- 

 diuretic hormone (§ 5.322). When adrenalectomized, the water- 

 loaded rats, with or without their neurohypophyses, show less 

 than 1/lOth of the urine flow of either unoperated or merely 

 neurohypophysectomized controls (Chester Jones, 1957^; cf. 

 Table 27). 



The decrease in diuresis in adrenalectomized rats (Fig. 5-16, 

 p. 216) is greater than could be accounted for by the decrease of 

 the blood pressure to a half, or even the correlated drop to l/6th 

 in G.F.R., the glomerular filtration rate. It may be assumed to be 

 due to the lack of adrenocortical hormones. 



If rats are loaded with hypertonic saline, instead of water, the 

 urine flow in the controls is halved, as compared with that in the 

 rats with diabetes insipidus. This is mainly because the anti- 

 diuretic hormone, ADH, is secreted in response to increased 

 tissue salinity and higher osmotic pressure of the blood (§ 5.322). 

 Adrenalectomy, by removing the source of the diuretic hormone, 

 reduces urine flow still further, though not so greatly as in the 

 case of water-loading. This is because the higher level of salts in 

 the glomerular filtrate reduces the volume of obligatory endos- 

 mosis. The action appears to be independent of the presence or 

 absence of the neurohypophysis (see Chester Jones, 1957«, for 

 further details). 



The secretion of hydrocortisone, that causes relative tubule 

 impermeability, is stimulated by adrenocorticotrophin, ACTH 

 (§ 4.231). 



5.322 Increase in cell permeability and antidiiiresis leading to 

 dilution of the blood-salts 



Dehydration can occur both on land and in any hypertonic 

 aquatic environment. The animals' response to this usually 

 includes waterproofing some parts of the body surface to restrict 

 water loss and increasing the permeability of other parts to allow 

 of water uptake or reabsorption. 



Invertebrates. No example of a hormone that increases tissue 

 permeability to water has so far been found in the reports on 



